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TRANSCRIPT
MATERIALS SCIENCE AND TECHNOLOGIESES
FUNCTIONALLY GRADED
MATERIALS
NATHAN J REYNOLDS
EDITOR
Nova Science Publishers Inc New York
Copyright copy 2012 by Nova Science Publishers Inc
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DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS
Additional color graphics may be available in the e-book version of this book
Library of Congress Cataloging-in-Publication Data
Functionally graded materials editor Nathan J Reynolds p cm Includes index ISBN 97S-1-6 I 209-616-2 (hardcover) I Functionally gradient materials 1 Reynolds Nathan 1 TA4IS9FS5FS42011 620 J IS--dc23 2011027544
Published by Nova Science Publishers Inc t New York
L Llicignono A Gug lielllloli olld F QII _ltjrill i
319
CONTENTS
vii
A Linear Multi-Layered Model and Its Applications in Fracture and Contact Mechanics of Elastic Functionally G-aded Materials Liao-Liang Ke and Yue-Sheng Wang
Functionally Graded Materials Obtained by Combustion Synthesis Techniques A Review 93 Roberlo Rosa and Paolo Veronesi
The Method of Fundamental Solutions fOl- Thennoelastic Analysis of Functionally Graded Materials 123 Hili Wang and Qing-Hua Qin
Three-Dimensional The-mal Buckling Analysis of Functionally Graded Arbitrary Straight-Sided Quadrilateral Plates 157 p Malekzadeh
The Mechanical Response of Metal-Ceramic Functionally Graded Materials Models and Experiences 181 Gahriella Bolzon
Simulation of Quasi-Static Crack Propagation in Functionally Graded Materials 193 Marlin Sl eigemann
Cylind rically- or Spherically-Symmetric Problems of Functionally Graded Materials 249 Xian-Fang Li and Xu-Long Peng
Functionally Graded Foams for Filter Fabrication 305
tm or mical
~sed or - No out of
ial ~ of or
~ Icated
~~d in anlage
- nise
ni 10 the
F THE
Preface
Chapter 1
Chapter 2
Chapter 3
Chaptemiddot 4
Chapter 5
bapter 6
C pteI 7
pt ) 8
In Functionally Graded Materials ISBN 978-1-61209-616-2
Editor Nathan J Reynolds copy 2012 Nova Science Publishers Inc
Chapter 3
THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS OF FUNCTIONALLY
GRADED MATERIALS
Hui Wang12
and Qing-Hua Qin3
1Institute of Scientific and Engineering Computation
Henan University of Technology
Zhengzhou 450052 China 2State Key Laboratory of Structural Analysis for
Industrial Equipment Dalian University of Technology
Dalian 116024 PRChina 3Research School of Engineering Australian National University
Canberra ACT 0200 Australia
ABSTRACT
Thermoelastic simulation of functionally graded materials is practically important for
engineers Here the extension and assembly of our two previous papers (Computational
Mechanics 2006 38 p51-60 Engineering Analysis with Boundary Elements 2008 32
p704-712) is presented to evaluate the transient temperature and stress distributions in
two-dimensional functionally graded solids In this chapter the analog equation method
is used to obtain an equivalent homogeneous system to the original nonhomogeneous
governing equation after which radial basis functions and fundamental solutions are used
to construct the related approximated solutions of particular part and complementary part
respectively Finally all unknowns are determined by satisfying the governing equations
at interior points and boundary conditions at boundary points Numerical experiments are
performed for different 2D functionally graded material problems and the meshless
method described in this chapter is validated by comparing available analytical and
numerical results
Corresponding author Email qinghuaqinanueduau Fax +61 2 61250506
Hui Wang and Qing-Hua Qin 124
Keywords Functionally graded materials Thermoelasticity Method of fundamental
solutions Radial basis functions Analog equation method
1 INTRODUCTION
Functionally graded materials (FGMs) can usually be viewed as special inhomogeneous
materials whose properties are dependent on spatial coordinates In FGMs due to the
continuous change of material properties in space the absence of interfaces between different
constituents or phases largely reduces the degree of material property mismatch and brings
appealing physical behaviors superior to homogeneous and conventional materials For
example for the classic ceramicmetal FGMs the ceramic phase offers thermal barrier effects
and protects the metal from corrosion and oxidation and the FGM is toughened and
strengthened by the metallic constituent A smooth transition between a pure metal and a pure
ceramic may result in a multifunctional material that combines the desirable high temperature
properties and thermal resistance of the ceramic with the fracture toughness and strength of
the metal Thus FGMs can be applied to many engineering structures subjected to severe
thermal loadings such as high temperature and thermal shocks to reduce thermal stresses and
suffer less thermal damage [1]
So far two models have been used to characterize the material gradation One is the so-
called continuum model in which analytical functions such as exponent and power-law
functions are commonly used to describe the continuously varying material properties
Although the continuum model may not be physical in practice this model is convenient for
conducting mathematical analysis The other is the micromechanics model which takes into
account interactions between constituent phases and uses a certain representative volume
element (RVE) to estimate the average local stress and strain fields of the composite after
which the local average fields are used to evaluate the effective material properties The
Mori-Tanaka method [2] and the self-consistent method [3] are two representatives of these
models In this paper attention is focused on the continuum model only
From the view point of mathematics the thermoelastic analysis in FGMs is described by
partial differential equations with variable coefficients to which a closed-form analytical
solution is difficult to obtain and is available for limited problems with simple geometries
certain types of gradation of material properties specific types of boundary conditions and
special loading cases Therefore numerical methods have been developed for investigating
static or dynamic problems mainly involving the evaluation of temperature field and stress
fields to reduce dependency on costly and time consuming experimental analysis Among the
established numerical methods the finite element method (FEM) [4-6] or the graded finite
element method [7 8] the boundary element method (BEM) or boundary integral equation
method (BIEM) [9-11] are most versatile to deal with thermoelastic analysis More recently
as alternatives to the FEM and BEM meshless methods have been used for thermal analysis
of FGMs The method employs a set of scattered points instead of elements to approximate
solutions and exhibits advantages of avoiding mesh generation simple data preparation and
easy post-processing The corresponding developments in thermal and stress computation in
FGMs include Rao and Rahman [12] used element-free Galerkin method (EFGM) to
simulate stress fields near the crack tip in FGMs The same method was used by Dai et al
The Method of Functional Solutions hellip 125
[13] to study thermomechanical behavior of FGM plates Ching and Yen [14 15] analyzed
the static and transient responses of FGMs under mechanical and thermal loads by means of
the meshless local PetrovndashGalerkin (MLPG) method [16 17] Moreover Sladek et al solved
dynamic anti-plane shear crack problem and transient heat conduction in FGMs by a meshless
local boundary integral equation (LBIE) method [18 19]
As a Greenrsquos function-based meshless method the method of fundamental solution
(MFS) has been well established to determine the steady-state temperature distribution in
linear or nonlinear FGM with temperature-dependent thermal conductivity [20 21] by means
of the corresponding fundamental solutions or Greenrsquos functions [22] There are other similar
methods such as the virtual boundary collocation method [23] and charge simulation method
[24] F-Trefftz method [25] and the singularity method [26] These methods use essentially
fictitious source points outside the solution domain of interest and the corresponding
fundamental solutions to approximate the target function The unknown coefficients of the
fundamental solutions and the coordinates of the fictitious sources are found by forcing the
approximation to satisfy the boundary conditions Advantages of MFS include pure boundary
collocations good adaptivity and little data preparation This is because the Greenrsquos
functions used satisfy a priori the governing partial differential equation (PDE) for the
problem Moreover no any singular evaluations of fundamental solutions are encountered in
the MFS due to the distinctive locations of source points Although the conventional MFS
has been successfully applied to FGMs the application is yet very limited due to the fact that
the corresponding fundamental solutions or Greenrsquos functions for general FGMs are either not
available or mathematically too complex [22 27] The nonhomogeneous nature of FGMs
prohibits a simple construction and implementation of fundamental solutions for general
FGMs with various gradations Moreover when dealing with nonzero body forces or transient
problems the conventional MFS seems to be very inefficient
The objective of the chapter is to present a mixed meshless algorithm based on the MFS
and radial basis function (RBF) for analyzing two-dimensional thermomechanical problems
of FGMs with various graded behaviors In the present algorithm the analog equation method
(AEM) [28] or dual reciprocity method (DRM) [29] is used to obtain the equivalent
homogeneous system to the original nonhomogeneous equation and then RBF and MFS are
used to approximate the related particular part and complementary part respectively Finally
the enforcing satisfaction of governing equations at interpolation points and boundary
conditions at boundary nodes is used to determine all unknowns
The structure of the chapter is organized as follows Section 2 provides a full description
of the 2D thermomechanical system in FGMs In Section 3 the material properties of FGMs
used in this chapter are reviewed and the detailed solution procedure is presented in Sections
4 and 5 for transient thermal response and thermoelastic analysis respectively Some
conclusions are presented in Section 6
2 MATHEMATICAL FORMULATION
In this section basic formulations of thermoelasticity in FGMs are reviewed so that the
chapter is self-contained For the convenience of presentation the Cartesian tensor notation is
adopted The subscript comma in the following equations indicates a space derivative and
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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The Method of Functional Solutions hellip 155
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Hui Wang and Qing-Hua Qin 156
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Additional color graphics may be available in the e-book version of this book
Library of Congress Cataloging-in-Publication Data
Functionally graded materials editor Nathan J Reynolds p cm Includes index ISBN 97S-1-6 I 209-616-2 (hardcover) I Functionally gradient materials 1 Reynolds Nathan 1 TA4IS9FS5FS42011 620 J IS--dc23 2011027544
Published by Nova Science Publishers Inc t New York
L Llicignono A Gug lielllloli olld F QII _ltjrill i
319
CONTENTS
vii
A Linear Multi-Layered Model and Its Applications in Fracture and Contact Mechanics of Elastic Functionally G-aded Materials Liao-Liang Ke and Yue-Sheng Wang
Functionally Graded Materials Obtained by Combustion Synthesis Techniques A Review 93 Roberlo Rosa and Paolo Veronesi
The Method of Fundamental Solutions fOl- Thennoelastic Analysis of Functionally Graded Materials 123 Hili Wang and Qing-Hua Qin
Three-Dimensional The-mal Buckling Analysis of Functionally Graded Arbitrary Straight-Sided Quadrilateral Plates 157 p Malekzadeh
The Mechanical Response of Metal-Ceramic Functionally Graded Materials Models and Experiences 181 Gahriella Bolzon
Simulation of Quasi-Static Crack Propagation in Functionally Graded Materials 193 Marlin Sl eigemann
Cylind rically- or Spherically-Symmetric Problems of Functionally Graded Materials 249 Xian-Fang Li and Xu-Long Peng
Functionally Graded Foams for Filter Fabrication 305
tm or mical
~sed or - No out of
ial ~ of or
~ Icated
~~d in anlage
- nise
ni 10 the
F THE
Preface
Chapter 1
Chapter 2
Chapter 3
Chaptemiddot 4
Chapter 5
bapter 6
C pteI 7
pt ) 8
In Functionally Graded Materials ISBN 978-1-61209-616-2
Editor Nathan J Reynolds copy 2012 Nova Science Publishers Inc
Chapter 3
THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS OF FUNCTIONALLY
GRADED MATERIALS
Hui Wang12
and Qing-Hua Qin3
1Institute of Scientific and Engineering Computation
Henan University of Technology
Zhengzhou 450052 China 2State Key Laboratory of Structural Analysis for
Industrial Equipment Dalian University of Technology
Dalian 116024 PRChina 3Research School of Engineering Australian National University
Canberra ACT 0200 Australia
ABSTRACT
Thermoelastic simulation of functionally graded materials is practically important for
engineers Here the extension and assembly of our two previous papers (Computational
Mechanics 2006 38 p51-60 Engineering Analysis with Boundary Elements 2008 32
p704-712) is presented to evaluate the transient temperature and stress distributions in
two-dimensional functionally graded solids In this chapter the analog equation method
is used to obtain an equivalent homogeneous system to the original nonhomogeneous
governing equation after which radial basis functions and fundamental solutions are used
to construct the related approximated solutions of particular part and complementary part
respectively Finally all unknowns are determined by satisfying the governing equations
at interior points and boundary conditions at boundary points Numerical experiments are
performed for different 2D functionally graded material problems and the meshless
method described in this chapter is validated by comparing available analytical and
numerical results
Corresponding author Email qinghuaqinanueduau Fax +61 2 61250506
Hui Wang and Qing-Hua Qin 124
Keywords Functionally graded materials Thermoelasticity Method of fundamental
solutions Radial basis functions Analog equation method
1 INTRODUCTION
Functionally graded materials (FGMs) can usually be viewed as special inhomogeneous
materials whose properties are dependent on spatial coordinates In FGMs due to the
continuous change of material properties in space the absence of interfaces between different
constituents or phases largely reduces the degree of material property mismatch and brings
appealing physical behaviors superior to homogeneous and conventional materials For
example for the classic ceramicmetal FGMs the ceramic phase offers thermal barrier effects
and protects the metal from corrosion and oxidation and the FGM is toughened and
strengthened by the metallic constituent A smooth transition between a pure metal and a pure
ceramic may result in a multifunctional material that combines the desirable high temperature
properties and thermal resistance of the ceramic with the fracture toughness and strength of
the metal Thus FGMs can be applied to many engineering structures subjected to severe
thermal loadings such as high temperature and thermal shocks to reduce thermal stresses and
suffer less thermal damage [1]
So far two models have been used to characterize the material gradation One is the so-
called continuum model in which analytical functions such as exponent and power-law
functions are commonly used to describe the continuously varying material properties
Although the continuum model may not be physical in practice this model is convenient for
conducting mathematical analysis The other is the micromechanics model which takes into
account interactions between constituent phases and uses a certain representative volume
element (RVE) to estimate the average local stress and strain fields of the composite after
which the local average fields are used to evaluate the effective material properties The
Mori-Tanaka method [2] and the self-consistent method [3] are two representatives of these
models In this paper attention is focused on the continuum model only
From the view point of mathematics the thermoelastic analysis in FGMs is described by
partial differential equations with variable coefficients to which a closed-form analytical
solution is difficult to obtain and is available for limited problems with simple geometries
certain types of gradation of material properties specific types of boundary conditions and
special loading cases Therefore numerical methods have been developed for investigating
static or dynamic problems mainly involving the evaluation of temperature field and stress
fields to reduce dependency on costly and time consuming experimental analysis Among the
established numerical methods the finite element method (FEM) [4-6] or the graded finite
element method [7 8] the boundary element method (BEM) or boundary integral equation
method (BIEM) [9-11] are most versatile to deal with thermoelastic analysis More recently
as alternatives to the FEM and BEM meshless methods have been used for thermal analysis
of FGMs The method employs a set of scattered points instead of elements to approximate
solutions and exhibits advantages of avoiding mesh generation simple data preparation and
easy post-processing The corresponding developments in thermal and stress computation in
FGMs include Rao and Rahman [12] used element-free Galerkin method (EFGM) to
simulate stress fields near the crack tip in FGMs The same method was used by Dai et al
The Method of Functional Solutions hellip 125
[13] to study thermomechanical behavior of FGM plates Ching and Yen [14 15] analyzed
the static and transient responses of FGMs under mechanical and thermal loads by means of
the meshless local PetrovndashGalerkin (MLPG) method [16 17] Moreover Sladek et al solved
dynamic anti-plane shear crack problem and transient heat conduction in FGMs by a meshless
local boundary integral equation (LBIE) method [18 19]
As a Greenrsquos function-based meshless method the method of fundamental solution
(MFS) has been well established to determine the steady-state temperature distribution in
linear or nonlinear FGM with temperature-dependent thermal conductivity [20 21] by means
of the corresponding fundamental solutions or Greenrsquos functions [22] There are other similar
methods such as the virtual boundary collocation method [23] and charge simulation method
[24] F-Trefftz method [25] and the singularity method [26] These methods use essentially
fictitious source points outside the solution domain of interest and the corresponding
fundamental solutions to approximate the target function The unknown coefficients of the
fundamental solutions and the coordinates of the fictitious sources are found by forcing the
approximation to satisfy the boundary conditions Advantages of MFS include pure boundary
collocations good adaptivity and little data preparation This is because the Greenrsquos
functions used satisfy a priori the governing partial differential equation (PDE) for the
problem Moreover no any singular evaluations of fundamental solutions are encountered in
the MFS due to the distinctive locations of source points Although the conventional MFS
has been successfully applied to FGMs the application is yet very limited due to the fact that
the corresponding fundamental solutions or Greenrsquos functions for general FGMs are either not
available or mathematically too complex [22 27] The nonhomogeneous nature of FGMs
prohibits a simple construction and implementation of fundamental solutions for general
FGMs with various gradations Moreover when dealing with nonzero body forces or transient
problems the conventional MFS seems to be very inefficient
The objective of the chapter is to present a mixed meshless algorithm based on the MFS
and radial basis function (RBF) for analyzing two-dimensional thermomechanical problems
of FGMs with various graded behaviors In the present algorithm the analog equation method
(AEM) [28] or dual reciprocity method (DRM) [29] is used to obtain the equivalent
homogeneous system to the original nonhomogeneous equation and then RBF and MFS are
used to approximate the related particular part and complementary part respectively Finally
the enforcing satisfaction of governing equations at interpolation points and boundary
conditions at boundary nodes is used to determine all unknowns
The structure of the chapter is organized as follows Section 2 provides a full description
of the 2D thermomechanical system in FGMs In Section 3 the material properties of FGMs
used in this chapter are reviewed and the detailed solution procedure is presented in Sections
4 and 5 for transient thermal response and thermoelastic analysis respectively Some
conclusions are presented in Section 6
2 MATHEMATICAL FORMULATION
In this section basic formulations of thermoelasticity in FGMs are reviewed so that the
chapter is self-contained For the convenience of presentation the Cartesian tensor notation is
adopted The subscript comma in the following equations indicates a space derivative and
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
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[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
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[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
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[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
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[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
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[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
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Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
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and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
L Llicignono A Gug lielllloli olld F QII _ltjrill i
319
CONTENTS
vii
A Linear Multi-Layered Model and Its Applications in Fracture and Contact Mechanics of Elastic Functionally G-aded Materials Liao-Liang Ke and Yue-Sheng Wang
Functionally Graded Materials Obtained by Combustion Synthesis Techniques A Review 93 Roberlo Rosa and Paolo Veronesi
The Method of Fundamental Solutions fOl- Thennoelastic Analysis of Functionally Graded Materials 123 Hili Wang and Qing-Hua Qin
Three-Dimensional The-mal Buckling Analysis of Functionally Graded Arbitrary Straight-Sided Quadrilateral Plates 157 p Malekzadeh
The Mechanical Response of Metal-Ceramic Functionally Graded Materials Models and Experiences 181 Gahriella Bolzon
Simulation of Quasi-Static Crack Propagation in Functionally Graded Materials 193 Marlin Sl eigemann
Cylind rically- or Spherically-Symmetric Problems of Functionally Graded Materials 249 Xian-Fang Li and Xu-Long Peng
Functionally Graded Foams for Filter Fabrication 305
tm or mical
~sed or - No out of
ial ~ of or
~ Icated
~~d in anlage
- nise
ni 10 the
F THE
Preface
Chapter 1
Chapter 2
Chapter 3
Chaptemiddot 4
Chapter 5
bapter 6
C pteI 7
pt ) 8
In Functionally Graded Materials ISBN 978-1-61209-616-2
Editor Nathan J Reynolds copy 2012 Nova Science Publishers Inc
Chapter 3
THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS OF FUNCTIONALLY
GRADED MATERIALS
Hui Wang12
and Qing-Hua Qin3
1Institute of Scientific and Engineering Computation
Henan University of Technology
Zhengzhou 450052 China 2State Key Laboratory of Structural Analysis for
Industrial Equipment Dalian University of Technology
Dalian 116024 PRChina 3Research School of Engineering Australian National University
Canberra ACT 0200 Australia
ABSTRACT
Thermoelastic simulation of functionally graded materials is practically important for
engineers Here the extension and assembly of our two previous papers (Computational
Mechanics 2006 38 p51-60 Engineering Analysis with Boundary Elements 2008 32
p704-712) is presented to evaluate the transient temperature and stress distributions in
two-dimensional functionally graded solids In this chapter the analog equation method
is used to obtain an equivalent homogeneous system to the original nonhomogeneous
governing equation after which radial basis functions and fundamental solutions are used
to construct the related approximated solutions of particular part and complementary part
respectively Finally all unknowns are determined by satisfying the governing equations
at interior points and boundary conditions at boundary points Numerical experiments are
performed for different 2D functionally graded material problems and the meshless
method described in this chapter is validated by comparing available analytical and
numerical results
Corresponding author Email qinghuaqinanueduau Fax +61 2 61250506
Hui Wang and Qing-Hua Qin 124
Keywords Functionally graded materials Thermoelasticity Method of fundamental
solutions Radial basis functions Analog equation method
1 INTRODUCTION
Functionally graded materials (FGMs) can usually be viewed as special inhomogeneous
materials whose properties are dependent on spatial coordinates In FGMs due to the
continuous change of material properties in space the absence of interfaces between different
constituents or phases largely reduces the degree of material property mismatch and brings
appealing physical behaviors superior to homogeneous and conventional materials For
example for the classic ceramicmetal FGMs the ceramic phase offers thermal barrier effects
and protects the metal from corrosion and oxidation and the FGM is toughened and
strengthened by the metallic constituent A smooth transition between a pure metal and a pure
ceramic may result in a multifunctional material that combines the desirable high temperature
properties and thermal resistance of the ceramic with the fracture toughness and strength of
the metal Thus FGMs can be applied to many engineering structures subjected to severe
thermal loadings such as high temperature and thermal shocks to reduce thermal stresses and
suffer less thermal damage [1]
So far two models have been used to characterize the material gradation One is the so-
called continuum model in which analytical functions such as exponent and power-law
functions are commonly used to describe the continuously varying material properties
Although the continuum model may not be physical in practice this model is convenient for
conducting mathematical analysis The other is the micromechanics model which takes into
account interactions between constituent phases and uses a certain representative volume
element (RVE) to estimate the average local stress and strain fields of the composite after
which the local average fields are used to evaluate the effective material properties The
Mori-Tanaka method [2] and the self-consistent method [3] are two representatives of these
models In this paper attention is focused on the continuum model only
From the view point of mathematics the thermoelastic analysis in FGMs is described by
partial differential equations with variable coefficients to which a closed-form analytical
solution is difficult to obtain and is available for limited problems with simple geometries
certain types of gradation of material properties specific types of boundary conditions and
special loading cases Therefore numerical methods have been developed for investigating
static or dynamic problems mainly involving the evaluation of temperature field and stress
fields to reduce dependency on costly and time consuming experimental analysis Among the
established numerical methods the finite element method (FEM) [4-6] or the graded finite
element method [7 8] the boundary element method (BEM) or boundary integral equation
method (BIEM) [9-11] are most versatile to deal with thermoelastic analysis More recently
as alternatives to the FEM and BEM meshless methods have been used for thermal analysis
of FGMs The method employs a set of scattered points instead of elements to approximate
solutions and exhibits advantages of avoiding mesh generation simple data preparation and
easy post-processing The corresponding developments in thermal and stress computation in
FGMs include Rao and Rahman [12] used element-free Galerkin method (EFGM) to
simulate stress fields near the crack tip in FGMs The same method was used by Dai et al
The Method of Functional Solutions hellip 125
[13] to study thermomechanical behavior of FGM plates Ching and Yen [14 15] analyzed
the static and transient responses of FGMs under mechanical and thermal loads by means of
the meshless local PetrovndashGalerkin (MLPG) method [16 17] Moreover Sladek et al solved
dynamic anti-plane shear crack problem and transient heat conduction in FGMs by a meshless
local boundary integral equation (LBIE) method [18 19]
As a Greenrsquos function-based meshless method the method of fundamental solution
(MFS) has been well established to determine the steady-state temperature distribution in
linear or nonlinear FGM with temperature-dependent thermal conductivity [20 21] by means
of the corresponding fundamental solutions or Greenrsquos functions [22] There are other similar
methods such as the virtual boundary collocation method [23] and charge simulation method
[24] F-Trefftz method [25] and the singularity method [26] These methods use essentially
fictitious source points outside the solution domain of interest and the corresponding
fundamental solutions to approximate the target function The unknown coefficients of the
fundamental solutions and the coordinates of the fictitious sources are found by forcing the
approximation to satisfy the boundary conditions Advantages of MFS include pure boundary
collocations good adaptivity and little data preparation This is because the Greenrsquos
functions used satisfy a priori the governing partial differential equation (PDE) for the
problem Moreover no any singular evaluations of fundamental solutions are encountered in
the MFS due to the distinctive locations of source points Although the conventional MFS
has been successfully applied to FGMs the application is yet very limited due to the fact that
the corresponding fundamental solutions or Greenrsquos functions for general FGMs are either not
available or mathematically too complex [22 27] The nonhomogeneous nature of FGMs
prohibits a simple construction and implementation of fundamental solutions for general
FGMs with various gradations Moreover when dealing with nonzero body forces or transient
problems the conventional MFS seems to be very inefficient
The objective of the chapter is to present a mixed meshless algorithm based on the MFS
and radial basis function (RBF) for analyzing two-dimensional thermomechanical problems
of FGMs with various graded behaviors In the present algorithm the analog equation method
(AEM) [28] or dual reciprocity method (DRM) [29] is used to obtain the equivalent
homogeneous system to the original nonhomogeneous equation and then RBF and MFS are
used to approximate the related particular part and complementary part respectively Finally
the enforcing satisfaction of governing equations at interpolation points and boundary
conditions at boundary nodes is used to determine all unknowns
The structure of the chapter is organized as follows Section 2 provides a full description
of the 2D thermomechanical system in FGMs In Section 3 the material properties of FGMs
used in this chapter are reviewed and the detailed solution procedure is presented in Sections
4 and 5 for transient thermal response and thermoelastic analysis respectively Some
conclusions are presented in Section 6
2 MATHEMATICAL FORMULATION
In this section basic formulations of thermoelasticity in FGMs are reviewed so that the
chapter is self-contained For the convenience of presentation the Cartesian tensor notation is
adopted The subscript comma in the following equations indicates a space derivative and
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
In Functionally Graded Materials ISBN 978-1-61209-616-2
Editor Nathan J Reynolds copy 2012 Nova Science Publishers Inc
Chapter 3
THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS OF FUNCTIONALLY
GRADED MATERIALS
Hui Wang12
and Qing-Hua Qin3
1Institute of Scientific and Engineering Computation
Henan University of Technology
Zhengzhou 450052 China 2State Key Laboratory of Structural Analysis for
Industrial Equipment Dalian University of Technology
Dalian 116024 PRChina 3Research School of Engineering Australian National University
Canberra ACT 0200 Australia
ABSTRACT
Thermoelastic simulation of functionally graded materials is practically important for
engineers Here the extension and assembly of our two previous papers (Computational
Mechanics 2006 38 p51-60 Engineering Analysis with Boundary Elements 2008 32
p704-712) is presented to evaluate the transient temperature and stress distributions in
two-dimensional functionally graded solids In this chapter the analog equation method
is used to obtain an equivalent homogeneous system to the original nonhomogeneous
governing equation after which radial basis functions and fundamental solutions are used
to construct the related approximated solutions of particular part and complementary part
respectively Finally all unknowns are determined by satisfying the governing equations
at interior points and boundary conditions at boundary points Numerical experiments are
performed for different 2D functionally graded material problems and the meshless
method described in this chapter is validated by comparing available analytical and
numerical results
Corresponding author Email qinghuaqinanueduau Fax +61 2 61250506
Hui Wang and Qing-Hua Qin 124
Keywords Functionally graded materials Thermoelasticity Method of fundamental
solutions Radial basis functions Analog equation method
1 INTRODUCTION
Functionally graded materials (FGMs) can usually be viewed as special inhomogeneous
materials whose properties are dependent on spatial coordinates In FGMs due to the
continuous change of material properties in space the absence of interfaces between different
constituents or phases largely reduces the degree of material property mismatch and brings
appealing physical behaviors superior to homogeneous and conventional materials For
example for the classic ceramicmetal FGMs the ceramic phase offers thermal barrier effects
and protects the metal from corrosion and oxidation and the FGM is toughened and
strengthened by the metallic constituent A smooth transition between a pure metal and a pure
ceramic may result in a multifunctional material that combines the desirable high temperature
properties and thermal resistance of the ceramic with the fracture toughness and strength of
the metal Thus FGMs can be applied to many engineering structures subjected to severe
thermal loadings such as high temperature and thermal shocks to reduce thermal stresses and
suffer less thermal damage [1]
So far two models have been used to characterize the material gradation One is the so-
called continuum model in which analytical functions such as exponent and power-law
functions are commonly used to describe the continuously varying material properties
Although the continuum model may not be physical in practice this model is convenient for
conducting mathematical analysis The other is the micromechanics model which takes into
account interactions between constituent phases and uses a certain representative volume
element (RVE) to estimate the average local stress and strain fields of the composite after
which the local average fields are used to evaluate the effective material properties The
Mori-Tanaka method [2] and the self-consistent method [3] are two representatives of these
models In this paper attention is focused on the continuum model only
From the view point of mathematics the thermoelastic analysis in FGMs is described by
partial differential equations with variable coefficients to which a closed-form analytical
solution is difficult to obtain and is available for limited problems with simple geometries
certain types of gradation of material properties specific types of boundary conditions and
special loading cases Therefore numerical methods have been developed for investigating
static or dynamic problems mainly involving the evaluation of temperature field and stress
fields to reduce dependency on costly and time consuming experimental analysis Among the
established numerical methods the finite element method (FEM) [4-6] or the graded finite
element method [7 8] the boundary element method (BEM) or boundary integral equation
method (BIEM) [9-11] are most versatile to deal with thermoelastic analysis More recently
as alternatives to the FEM and BEM meshless methods have been used for thermal analysis
of FGMs The method employs a set of scattered points instead of elements to approximate
solutions and exhibits advantages of avoiding mesh generation simple data preparation and
easy post-processing The corresponding developments in thermal and stress computation in
FGMs include Rao and Rahman [12] used element-free Galerkin method (EFGM) to
simulate stress fields near the crack tip in FGMs The same method was used by Dai et al
The Method of Functional Solutions hellip 125
[13] to study thermomechanical behavior of FGM plates Ching and Yen [14 15] analyzed
the static and transient responses of FGMs under mechanical and thermal loads by means of
the meshless local PetrovndashGalerkin (MLPG) method [16 17] Moreover Sladek et al solved
dynamic anti-plane shear crack problem and transient heat conduction in FGMs by a meshless
local boundary integral equation (LBIE) method [18 19]
As a Greenrsquos function-based meshless method the method of fundamental solution
(MFS) has been well established to determine the steady-state temperature distribution in
linear or nonlinear FGM with temperature-dependent thermal conductivity [20 21] by means
of the corresponding fundamental solutions or Greenrsquos functions [22] There are other similar
methods such as the virtual boundary collocation method [23] and charge simulation method
[24] F-Trefftz method [25] and the singularity method [26] These methods use essentially
fictitious source points outside the solution domain of interest and the corresponding
fundamental solutions to approximate the target function The unknown coefficients of the
fundamental solutions and the coordinates of the fictitious sources are found by forcing the
approximation to satisfy the boundary conditions Advantages of MFS include pure boundary
collocations good adaptivity and little data preparation This is because the Greenrsquos
functions used satisfy a priori the governing partial differential equation (PDE) for the
problem Moreover no any singular evaluations of fundamental solutions are encountered in
the MFS due to the distinctive locations of source points Although the conventional MFS
has been successfully applied to FGMs the application is yet very limited due to the fact that
the corresponding fundamental solutions or Greenrsquos functions for general FGMs are either not
available or mathematically too complex [22 27] The nonhomogeneous nature of FGMs
prohibits a simple construction and implementation of fundamental solutions for general
FGMs with various gradations Moreover when dealing with nonzero body forces or transient
problems the conventional MFS seems to be very inefficient
The objective of the chapter is to present a mixed meshless algorithm based on the MFS
and radial basis function (RBF) for analyzing two-dimensional thermomechanical problems
of FGMs with various graded behaviors In the present algorithm the analog equation method
(AEM) [28] or dual reciprocity method (DRM) [29] is used to obtain the equivalent
homogeneous system to the original nonhomogeneous equation and then RBF and MFS are
used to approximate the related particular part and complementary part respectively Finally
the enforcing satisfaction of governing equations at interpolation points and boundary
conditions at boundary nodes is used to determine all unknowns
The structure of the chapter is organized as follows Section 2 provides a full description
of the 2D thermomechanical system in FGMs In Section 3 the material properties of FGMs
used in this chapter are reviewed and the detailed solution procedure is presented in Sections
4 and 5 for transient thermal response and thermoelastic analysis respectively Some
conclusions are presented in Section 6
2 MATHEMATICAL FORMULATION
In this section basic formulations of thermoelasticity in FGMs are reviewed so that the
chapter is self-contained For the convenience of presentation the Cartesian tensor notation is
adopted The subscript comma in the following equations indicates a space derivative and
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
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[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
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69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
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Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 124
Keywords Functionally graded materials Thermoelasticity Method of fundamental
solutions Radial basis functions Analog equation method
1 INTRODUCTION
Functionally graded materials (FGMs) can usually be viewed as special inhomogeneous
materials whose properties are dependent on spatial coordinates In FGMs due to the
continuous change of material properties in space the absence of interfaces between different
constituents or phases largely reduces the degree of material property mismatch and brings
appealing physical behaviors superior to homogeneous and conventional materials For
example for the classic ceramicmetal FGMs the ceramic phase offers thermal barrier effects
and protects the metal from corrosion and oxidation and the FGM is toughened and
strengthened by the metallic constituent A smooth transition between a pure metal and a pure
ceramic may result in a multifunctional material that combines the desirable high temperature
properties and thermal resistance of the ceramic with the fracture toughness and strength of
the metal Thus FGMs can be applied to many engineering structures subjected to severe
thermal loadings such as high temperature and thermal shocks to reduce thermal stresses and
suffer less thermal damage [1]
So far two models have been used to characterize the material gradation One is the so-
called continuum model in which analytical functions such as exponent and power-law
functions are commonly used to describe the continuously varying material properties
Although the continuum model may not be physical in practice this model is convenient for
conducting mathematical analysis The other is the micromechanics model which takes into
account interactions between constituent phases and uses a certain representative volume
element (RVE) to estimate the average local stress and strain fields of the composite after
which the local average fields are used to evaluate the effective material properties The
Mori-Tanaka method [2] and the self-consistent method [3] are two representatives of these
models In this paper attention is focused on the continuum model only
From the view point of mathematics the thermoelastic analysis in FGMs is described by
partial differential equations with variable coefficients to which a closed-form analytical
solution is difficult to obtain and is available for limited problems with simple geometries
certain types of gradation of material properties specific types of boundary conditions and
special loading cases Therefore numerical methods have been developed for investigating
static or dynamic problems mainly involving the evaluation of temperature field and stress
fields to reduce dependency on costly and time consuming experimental analysis Among the
established numerical methods the finite element method (FEM) [4-6] or the graded finite
element method [7 8] the boundary element method (BEM) or boundary integral equation
method (BIEM) [9-11] are most versatile to deal with thermoelastic analysis More recently
as alternatives to the FEM and BEM meshless methods have been used for thermal analysis
of FGMs The method employs a set of scattered points instead of elements to approximate
solutions and exhibits advantages of avoiding mesh generation simple data preparation and
easy post-processing The corresponding developments in thermal and stress computation in
FGMs include Rao and Rahman [12] used element-free Galerkin method (EFGM) to
simulate stress fields near the crack tip in FGMs The same method was used by Dai et al
The Method of Functional Solutions hellip 125
[13] to study thermomechanical behavior of FGM plates Ching and Yen [14 15] analyzed
the static and transient responses of FGMs under mechanical and thermal loads by means of
the meshless local PetrovndashGalerkin (MLPG) method [16 17] Moreover Sladek et al solved
dynamic anti-plane shear crack problem and transient heat conduction in FGMs by a meshless
local boundary integral equation (LBIE) method [18 19]
As a Greenrsquos function-based meshless method the method of fundamental solution
(MFS) has been well established to determine the steady-state temperature distribution in
linear or nonlinear FGM with temperature-dependent thermal conductivity [20 21] by means
of the corresponding fundamental solutions or Greenrsquos functions [22] There are other similar
methods such as the virtual boundary collocation method [23] and charge simulation method
[24] F-Trefftz method [25] and the singularity method [26] These methods use essentially
fictitious source points outside the solution domain of interest and the corresponding
fundamental solutions to approximate the target function The unknown coefficients of the
fundamental solutions and the coordinates of the fictitious sources are found by forcing the
approximation to satisfy the boundary conditions Advantages of MFS include pure boundary
collocations good adaptivity and little data preparation This is because the Greenrsquos
functions used satisfy a priori the governing partial differential equation (PDE) for the
problem Moreover no any singular evaluations of fundamental solutions are encountered in
the MFS due to the distinctive locations of source points Although the conventional MFS
has been successfully applied to FGMs the application is yet very limited due to the fact that
the corresponding fundamental solutions or Greenrsquos functions for general FGMs are either not
available or mathematically too complex [22 27] The nonhomogeneous nature of FGMs
prohibits a simple construction and implementation of fundamental solutions for general
FGMs with various gradations Moreover when dealing with nonzero body forces or transient
problems the conventional MFS seems to be very inefficient
The objective of the chapter is to present a mixed meshless algorithm based on the MFS
and radial basis function (RBF) for analyzing two-dimensional thermomechanical problems
of FGMs with various graded behaviors In the present algorithm the analog equation method
(AEM) [28] or dual reciprocity method (DRM) [29] is used to obtain the equivalent
homogeneous system to the original nonhomogeneous equation and then RBF and MFS are
used to approximate the related particular part and complementary part respectively Finally
the enforcing satisfaction of governing equations at interpolation points and boundary
conditions at boundary nodes is used to determine all unknowns
The structure of the chapter is organized as follows Section 2 provides a full description
of the 2D thermomechanical system in FGMs In Section 3 the material properties of FGMs
used in this chapter are reviewed and the detailed solution procedure is presented in Sections
4 and 5 for transient thermal response and thermoelastic analysis respectively Some
conclusions are presented in Section 6
2 MATHEMATICAL FORMULATION
In this section basic formulations of thermoelasticity in FGMs are reviewed so that the
chapter is self-contained For the convenience of presentation the Cartesian tensor notation is
adopted The subscript comma in the following equations indicates a space derivative and
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
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[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
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[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
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[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
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69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
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Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 125
[13] to study thermomechanical behavior of FGM plates Ching and Yen [14 15] analyzed
the static and transient responses of FGMs under mechanical and thermal loads by means of
the meshless local PetrovndashGalerkin (MLPG) method [16 17] Moreover Sladek et al solved
dynamic anti-plane shear crack problem and transient heat conduction in FGMs by a meshless
local boundary integral equation (LBIE) method [18 19]
As a Greenrsquos function-based meshless method the method of fundamental solution
(MFS) has been well established to determine the steady-state temperature distribution in
linear or nonlinear FGM with temperature-dependent thermal conductivity [20 21] by means
of the corresponding fundamental solutions or Greenrsquos functions [22] There are other similar
methods such as the virtual boundary collocation method [23] and charge simulation method
[24] F-Trefftz method [25] and the singularity method [26] These methods use essentially
fictitious source points outside the solution domain of interest and the corresponding
fundamental solutions to approximate the target function The unknown coefficients of the
fundamental solutions and the coordinates of the fictitious sources are found by forcing the
approximation to satisfy the boundary conditions Advantages of MFS include pure boundary
collocations good adaptivity and little data preparation This is because the Greenrsquos
functions used satisfy a priori the governing partial differential equation (PDE) for the
problem Moreover no any singular evaluations of fundamental solutions are encountered in
the MFS due to the distinctive locations of source points Although the conventional MFS
has been successfully applied to FGMs the application is yet very limited due to the fact that
the corresponding fundamental solutions or Greenrsquos functions for general FGMs are either not
available or mathematically too complex [22 27] The nonhomogeneous nature of FGMs
prohibits a simple construction and implementation of fundamental solutions for general
FGMs with various gradations Moreover when dealing with nonzero body forces or transient
problems the conventional MFS seems to be very inefficient
The objective of the chapter is to present a mixed meshless algorithm based on the MFS
and radial basis function (RBF) for analyzing two-dimensional thermomechanical problems
of FGMs with various graded behaviors In the present algorithm the analog equation method
(AEM) [28] or dual reciprocity method (DRM) [29] is used to obtain the equivalent
homogeneous system to the original nonhomogeneous equation and then RBF and MFS are
used to approximate the related particular part and complementary part respectively Finally
the enforcing satisfaction of governing equations at interpolation points and boundary
conditions at boundary nodes is used to determine all unknowns
The structure of the chapter is organized as follows Section 2 provides a full description
of the 2D thermomechanical system in FGMs In Section 3 the material properties of FGMs
used in this chapter are reviewed and the detailed solution procedure is presented in Sections
4 and 5 for transient thermal response and thermoelastic analysis respectively Some
conclusions are presented in Section 6
2 MATHEMATICAL FORMULATION
In this section basic formulations of thermoelasticity in FGMs are reviewed so that the
chapter is self-contained For the convenience of presentation the Cartesian tensor notation is
adopted The subscript comma in the following equations indicates a space derivative and
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Hui Wang and Qing-Hua Qin 154
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The Method of Functional Solutions hellip 155
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Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 126
repeated subscripts in a variable represent summation Because FGMs can be viewed without
loss of generality as isotropic nonhomogeneous materials the following formulations and
processes are provided for general thermomechanical problems in 2D elastic solids
Furthermore it is well known that for a fully coupled thermomechanical problem such as
forging and casting it is not only the thermal field that influences the displacement and stress
fields but also the deformation itself that induces change in temperature distribution Here
for the sake of simplicity the thermomechanical deformation is considered to be sequentially
coupled in that sense that the temperature change influences the stress distributions only
21 Basic Equations of Heat Conduction in FGMs
(1) Heat Conduction Equation
Let us consider an isotropic and linear elastic domain bounded by the boundary
The Cartesian coordinates T
1 2( )x xx are used to describe temperature distribution and
infinitesimal static deformations The transient heat conduction in isotropic heterogeneous
media is then governed by the following relation
(1)
or
(2)
where T is the desired temperature field in the domain under consideration 1 2 i j
and represents the plane gradient and Laplace operators respectively
0t stands for spatial variable Parameters k c are the thermal conductivity density
and specific heat respectively which are assumed to depend on the space coordinate in our
analysis f denotes the internal heat source generated per unit volume
(2) Thermal boundary and initial conditions
To keep the system complete Eq (1) or (2) should be supplemented with the following
thermal boundary conditions
(3)
and the initial condition
(4)
0T t
k T t f t c tt
xx x x x x x
2
T tk T t k T t f t c
t
xx x x x x x x
2
11 22
1
2
3
T t T t
Tq t k q t
n
q t h T T
x x x
x x x
x x
00T Tx x
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 127
In Eq (3) T and q are specified values on the boundary 1 and
2 respectively h
and T stand for the coefficient of convection and the temperature of ambient fluid
respectively is the unit outward normal to the boundary 1
2 and 3 are
complementary parts of the boundary ie 1 2
2 3 1 3 and
1 2 3
22 Basic Equations of Thermoelasticity in FGMs
(1) Governing Equations
The governing equations for thermoelasticity involve the equilibrium equation
constitutive equation and strain-displacement relation For 2D continuously
nonhomogeneous isotropic and linear elastic FGMs the mechanical equilibrium requires
(5)
where ij denotes the components of Cauchy stress tensor and
ib the components of body
force per unit volume
The stress tensor ij and strain tensor
are related by the constitutive equation or the
generalized Hookersquos law which is given in the form
(6)
with
where E have different values for plane stress and plane strain states such that
and parameters ( ) ( )E x x and ( ) x are functions of space coordinates and represent
elastic modulus Poisson ratio and linear coefficient of thermal expansion respectively T
denotes the temperature change the material experiences with respect to the stress-free
reference configuration which can be determined by solving the heat conduction system If
the change in temperature is positive we have thermal expansion and if negative thermal
contraction
n
0 Ωij j ib x
ij
2ij ij kk ij ijm T
2
1 2
2 1
E
1 2
Em
2
for plane strain
1 2 1 for plane stress
1 1 21
E E
E E
x
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
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[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
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[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
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[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
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[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
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Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
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Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
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[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
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[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
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[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
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[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
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Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
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Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
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[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
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[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
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Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 128
If the displacement components are small enough that the square and product of its
derivatives are negligible then the relation of strain component and displacement
components iu can be written as
(7)
Substituting Eqs (6) and (7) into the equilibrium equation (5) yields the second-order
partial differential equation (PDE) in terms of displacement components as
(8)
(2) Mechanical Boundary Conditions
The boundary value problem (BVP) defined by Eqs (5) (6) and (7) is completed by
adding the following displacement and surface traction boundary conditions
(9)
where iu is the prescribed displacements on
u and it the given tractions on
t For a well-
posed problem we have nullu t and u t
3 MATERIAL PROPERTIES OF FGMS
Material properties of FGMs such as thermal conductivity density elastic modulus and
so on usually vary in space For illustrate this variation we take the ceramicmetal FGM as
an example The metalceramic FGM is often a mixture of two kinds of materials one is the
metal and the other is ceramic Without losing generality we assume that the left surface of
the FGM plate is ceramic rich and right is metal rich The region between the two surface
consists of material blended with both of them For convenience the x-axis is set along the
horizontal direction as illustrated in Figure 1 At any position x in the ceramicmetal FGM
the local volume fraction of metal is assumed to be ( )V x which can be used to characterize
the gradation Generally speaking ( )V x can be any non-singular non-negative function of x
To gain insight into the effect of material gradation on the thermoelastic behavior of the
FGM it is assumed that 1P and
2P are material parameters of ceramic and metal phases
respectively
ij
1( )
2ij i j j iu u
0k ki i kk i k k k i k k i i i iu u u u u mT m T b
i i u
i ij j i t
u u
t n t
x
x
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 129
Figure 1 Illustration of FGM structure
(1) Power-Law Type FGM (P-FGM)[30]
In this case the local volume fraction of metal ( )V x is assumed in the form of a simple
power-law distribution
(10)
where the power is the volume fraction exponent and L is the thickness of the FGM
layer It can be seen that the gradation given in Eq (10) implies that the FGM layer always
has 100 metal when ( ) 1V h and pure ceramic when (0) 0V which is of course
desirable
As a first order approximation the effective properties of a functionally graded material
can be obtained using the rule of mixtures for example
(11)
Figure 2 shows the variation of the effective material property versus non-dimensional
length with different power
(2) Exponential Type FGM (E-FGM)[31]
In this case the local volume fraction of metal ( )V x is assumed as
(12)
from which the effective properties of a functionally graded material can be given by
(13)
The gradient parameter in Eq (13) in fact can be determined by means of specified
material properties of the ceramic and metal phases
( ) V x x L
1 2( ) 1 ( ) ( )P x V x P V x P
( )x
LV x e
1 1( ) ( )x
LP x V x P Pe
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Hui Wang and Qing-Hua Qin 154
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The Method of Functional Solutions hellip 155
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for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 130
(14)
and then the variation of the effective property along the graded direction is displayed in
Figure 2 for the purpose of comparison
Figure 2 Variation of the effective material property vs the non-dimensional thickness
It can be seen that the variation of graded parameter changes the material property of
FGMs Thus in the present work the effect of graded parameter is investigated to illustrate
the thermal and elastic behaviors of FGMs
4 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR THERMAL
ANALYSIS
The boundary value problem (BVP) consisting of Eqs (1)-(4) can be converted into a
Poisson-type equation using the analog equation method (AEM) For this purpose suppose
2
1
lnP
P
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
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[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
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69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 131
( ) ( )tT T tx x is the sought solution to the BVP under consideration which is a continuously
differentiable function with up to two orders in If the Laplacian operator is applied to this
function namely
2 ( ) ( ) t tT b x x x (15)
then the solution of Eq (1) can be established by solving the linear equation (15) under the
same boundary conditions (3) and initial condition (4) if the fictitious source distribution
( )tb x is known
Itrsquos well known that the solution to the linear equation (15) can be written as a sum of the
complementary solution ( )t
hT x satisfying the following homogeneous equation
2 ( ) 0t
hT x (16)
and the particular solution satisfying the inhomogeneous equation
(17)
Then the total solutions for temperature field and heat flux at time instance t can be given
by
(18)
where ( )t
hq x and ( )t
pq x are the complementary and particular solutions for heat flux
respectively
41 Complementary Solutions
To obtain a weak solution of Laplace equation (16) the method of fundamental solution
is employed here In the MFS the desired solution can be expressed as a linear combination
of fundamental solutions or Greenrsquos functions associated with the governing equation under
consideration to guarantee prior the analytical satisfaction of the governing equation For this
purpose N fictitious source points ( 12 )si i Nx lying on the pseudo boundary the
virtual boundary similar to the physical boundary are selected as shown in Figure 3
Moreover it is assumed that at each source point there exists a virtual load t
i As a result
the potential ( )t
hT x and the boundary heat flux ( )t
hq x at any field point in the domain or on
the physical boundary can be written as [32-38]
( )t
pT x
2 ( ) ( )t t
pT b x x
( ) ( ) ( ) ( ) ( ) ( )t t t t t t
h p h pT T T q q q x x x x x x
x
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
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[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
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[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
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[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
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[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
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69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
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Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
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and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 132
1
1
( ) ( )
( ) ( )
Nt t
h i si si
i
Nt t
h i si si
i
T T
q Q
x x x x x
x x x x x
(19)
in which ( )siT x x and ( )siQ x x are the fundamental solution of the Laplace equation and its
normal derivative respectively
(20)
with
Figure 3 Illustration of the collocation points discretization on the physical and pseudo (virtual)
boundaries
42 Particular Solutions
RBFs are usually expressed in terms of Euclidian distance so they can work well in any
dimensional space Due to these advantages RBFs have been widely used in many practical
problems over the past decades In this section RBF approximation is presented for
evaluating the approximated particular solution at any given time t Firstly the right-hand
term ( )tb x in Eq (17) can be approximated by the standard dual reciprocity procedure
1 1 1 2 2 22
1( ) ln
2
( ) 1( )
2
sj
sisj si si
T r
TQ k k x x n x x n
n r
x x
x xx x
2 2
1 1 2 2si sir x x x x
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Hui Wang and Qing-Hua Qin 154
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The Method of Functional Solutions hellip 155
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[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
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[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
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521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 133
1
( ) ( ) M
t t
j j j
j
b
x x x x x (21)
where M is the number of interpolation points including interior and boundary points for the
domain of interest t
j are coefficients to be determined and are a set of global RBF
with different collocation points
The effectiveness and accuracy of the interpolation depends on the choice of the RBFs
Besides the adhoc function 1+r which is merely a special type of RBF that is used
almost exclusively and uncritically in the engineering literature [33 39 40] the three radial
basis functions polyharmonic splines 2 11 ( 1)nr n thin plate spline (TPS) 2 lnr r and
multiquadrics (MQ) are also commonly used in numerical formulations [36 41-44]
In the RBFs mentioned above the Euclidean distance related to the field and collocation
points is defined as
(22)
Similarly the particular solutions in the domain and defined on the
boundary can also be written as
(23)
with k n if the space interpolation functions are chosen so as to satisfy the
relationship
Table 1 Relation of radial basis function (RBF) and particular solution kernel (PSK)
for the case of Laplace operator
RBF PSK
( )
( )j x x
jx
( )j x x
2 2r c
r
2 2
1 1 2 2j jr x x x x
( )t
pT x ( )t
pq x
1
1
Mt t
p j j
j
Mt t
p j j
j
T
q
x x x
x x x
2 11 nr 1n
2 2 1
24 2 1
nr r
n
2 lnr r4 41 1
ln16 32
r r r
2 2r c 3 2 2 2ln 4
3 9
c c c r c
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
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[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
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[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 134
(24)
In Eq (23) usually refer to the particular solutions kernels (PSK) and the
corresponding expression of PSK for a given RBF is presented in Table 1
43 Complete Solutions
Based on the discussion above the complete solutions at a particular time t can be written
as
(25)
Moreover differentiating Eq (25) with respect to coordinate component yields
(26)
Next in order to obtain the temperature field and heat flux at any time a two-level finite
differencing in time is used For a typical time interval 1[ ] ( 0)k kt t k with time step
1k kt t t the relationship
(27)
leads to by the substitution of Eq (27) into Eq (2)
(28)
2 ( )j j x x x x
( )j x x
1 1
1 1
( ) ( ) s
N Mt t t
i si j j
i j
N Mt t t
i si j j
i j
T T
q Q
x x x x x
x x x x x
1 1
t N Mjsit t
i j
i jk k k
T T
x x x
x xx x x
1
1
1
1
1
k k
k k
k k
T t u u
f t f f
T TT
t t
x x x
x x x
x x
1 1
2 1
2
1
1
1 1
k k
k
k k
k
k k
k T c TT
k k t
k T c TT
k k t
f fk
x x x x xx
x x
x x x x xx
x x
x xx
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 135
In Eq (27) the time-step parameter usually assumes values between 1 (backward
differencing) and 0 (fully explicit scheme) Value 05 yields the Crank-Nicolson scheme
(central differences) known to be the most accurate two-level time stepping strategy
However for the first time step only backward differencing makes sense because other
schemes require that the initial values of the heat fluxes are known As these quantities are
not needed for the analytical solution they should also not arise in the numerical algorithm
On the other hand the backward scheme is unconditionally stable In the present work the
backward time stepping scheme is employed to perform the following analysis for simplicity
Let 1 then Eq (28) reduces to
(29)
At the same time the boundary conditions at 1kt time instance can be written as
(30)
Subsequently N points are chosen on the physical boundary to solve the system
consisting of Eqs (29) and (30) For this purpose substituting Eqs (25) and (26) into Eqs
(29) and (30) yields the following N M equations to determine all unknowns
(31)
where 1 1N
2 2N 3 3N and
1 2 3N N N N The operator L is defined for
convenience as fellows
(32)
1 1 1
2 1
k k k k
kk T c T c T f
Tk k t k t k
x x x x x x x x xx
x x x x
1 1
1
1 1
2
1 1
3
on
on
on
k k
k k
k k
T u t
q q t
h T q h T
x x
x x
x x
1
1
1 1
1 1
1
1
1
k kN Mm mk k
i m si j m j
i j m m
Nk
i n si
i
f c TT
k k t
m M
T
x x x xL x x L x x
x x
x x
1 1
2 2 2
3 3 3 3
1 1
1 1
1
1 1 1
2 2
1 1
1 1
1 1
1
1
Mk k
j n j n
j
N Mk k k
i n si j n j n
i j
N Mk k
i n si n i j n j n j
i j
u n N
Q q n N
h T Q h
x x x
x x x x x
x x x y x x x x
3 3 1
h u
n N
2
k c
k k t
x x xL I
x x
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 136
44 Numerical Examples
In order to demonstrate the efficiency and accuracy of the proposed meshless method and
the selected RBF and virtual boundary transient heat conduction in isotropic materials is first
considered since corresponding analytical results can be used for verification Then the
transient thermal response in FGMs is discussed Though the proposed meshless method has
no restrictions on the spatial variation of the material parameters of FGM the numerical
example presented here is restricted to an exponential variation of the material properties with
Cartesian coordinates for the purpose of comparison
Additionally itrsquos necessary to note that the location of the pseudo boundary is important
to the final numerical stability In the present work the source point is generated by [33-38]
(33)
where the nondimensional parameter 1 is named as similarity ratio and sx
bx and cx
are source point boundary point and central point of the domain respectively
Example 441 Thermal shock problem
To investigate the behavior of the algorithm in the presence of thermal shocks the
benchmark problem in [45] is considered and the solution obtained using the developed
technique is compared with an analytical solution The computing geometry is a unit square
[01]times[01] in which no internal heat source exists Zero initial temperature has been assumed
and homogeneous Neumann boundary conditions (insulation) are prescribed on the sides x =
0 y = 0 and y = 1 respectively The remaining side is subjected to a sudden unit temperature
jump Using the method of variable separation the analytic solution can be obtained as
2
0
4( ) 1 ( 1) cos( )exp( )
(2 1)
i
i i
i
T x t x ti
(34)
with (2 1) 2i i
In the computation thermal diffusivity a = 1 m2s and thermal conductivity of materials k
= 1W(m) is assumed The uniform interpolation scheme is used with the first order
interpolation function 1+r only A total of 20 fictitious source points are selected on the
virtual boundary and 121 uniform interpolation points are used unless there is a special
statement To study the effect of the location of the virtual boundary on the accuracy of the
proposed algorithm Figure 4 presents the relative error of temperature versus similarity ratio
at point (05 05) with time step ∆t= 001 s The results in Figure 4 show that good
computational accuracy and stability is achieved when the similarity ratio is greater than 2
and the optimal value of the similarity ratio is between 25ndash50 Although the virtual
boundary can theoretically be chosen arbitrarily outside of the domain either too small or too
great a distance between the virtual and physical boundaries will reduce accuracy due to the
singularity of the fundamental solution and the restriction of computer precision including
round-off error [46]
( )( 1) ( 1)s b b c b c x x x x x x
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 137
Figure 5 shows the percentage error of temperature for two different time steps It can be
seen that the smaller the time step the higher the accuracy of the results obtained However
more computational time will inevitably be required if a smaller time step is chosen
Additionally further reduction in the time step doesnrsquot reduce the relative error [47]
Figure 4 Effect of similarity ratio on temperature at point (05 05) with ∆t = 001 s
Figure 5 Effect of time step on relative error of temperature with γ = 30
Example 442 Thermal shock problem
Consider a functionally graded square [0 L]times[0 L] with a unidirectional variation of
thermal conductivity [48] In this example zero initial temperature is considered and the same
exponential spatial variation for thermal conductivity and diffusivity is assumed
1 15 2 25 3 35 4 45 5 0
1
2
3
4
5
6
7
Similarity ratio
Re
lative
err
or
in
te
mp
era
ture
t = 05s
t = 10s
0 01 02 03 04 05 06 07 08 09 1 0
1
2
3
4
5
6
7
8
9
x (m)
Re
lative
err
or
in
te
mp
era
ture
t = 05s t = 01s
t = 05s t = 001s
t = 10s t = 01s
t = 10s t = 001s
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 138
(35)
where k0=17W(moC) and a0 = 017 m
2s Two different exponential parameters η = 02 and
05 cm-1
are assumed in numerical calculation On the sides parallel to the y-axis two different
temperatures are prescribed The left side is kept at zero temperature and the right side has the
Heaviside function of time ie u = H(t) On the lateral sides of the square the heat flux
vanishes In the numerical calculation the side length L = 004 m is used The special case
with an exponential parameter η = 0 is considered first In this case the analytical solution is
given as
2 2
21
2 cos( ) sin exp
n
x T n n x an tT x t T
L n L L
(36)
which can be used to verify the accuracy of the present numerical method Numerical results
are obtained using 36 fictitious source points 169 interpolation points γ = 30 and time step
∆t = 1 s Figure 6 shows the temperature field at three points (x = 001 m 002 m and 003 m)
A good agreement between numerical and analytical results is observed from Figure 6
0 10 20 30 40 50 60
-01
0
01
02
03
04
05
06
07
08
Time t (second)
Te
mp
era
ture
(
)
Meshless x=001
x=002
x=003
Analytical x=001
x=002
x=003
Figure 6 Time variation of temperature in a finite square strip at three different positions with η = 0
The discussion above concerns heat conduction in homogeneous materials only since
analytical solutions can be used for verification To illustrate the application of the proposed
algorithm to the FGM consider now the FGM with η = 02 and 05 cm-1
respectively The
variation of temperature with time for three k-values and at position x = 002 m is presented
in Figure 7 As expected it is found from Figure 7 that the temperature increases along with
an increase in η-values (or equivalently in thermal conductivity) and the temperature
approaches a steady state when t gt20 s For final steady state an analytical solution can be
obtained as
0 0( ) ( )x xk x k e a x a e
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 139
(37)
Figure 7 Time variation of temperature at position x = 002m of functionally graded finite square strip
Analytical and numerical results computed at time t =70 s corresponding to stationary or
static loading conditions are presented in Figure 8 The numerical results are in good
agreement with the analytical results for the steady state case Simulateneously it is observed
from Figure 8 that the temperature increases along with an increase in η-values again This is
because the larger thermal conductivity results in smaller resistance to heat transfer from the
right to left
For comparison the results at some particular points obtained by both the proposed
method and the meshless local boundary integral equation method (LBIEM) [42] are listed in
Table 2 It can be seen from Table 2 that the results from the proposed method is slightly
larger than those obtained LBIEM and after t = 50 s the temperature reaches a relatively
steady state It should be mentioned here that the numerical solutions given in reference [42]
probably have certain error to practical computing results produced using LBIEM Moreover
different treatments of time domain may also be the main reason causing the discrepancy In
the derivation of LBIEM we noticed that Laplace transformation technology is used instead
of the time stepping scheme However to the steady-state temperature field at x = 001 m the
two methods provided almost same results as shown in Table 2
Table 2 Comparison of LBIEM and the proposed method at η =05cm-1
and x = 001 m
t=10s t=20s t=30s t=40s t=50s t=60s Stable
LBIEM 01871 03281 03800 03986 04019 04053 04581
MFS 03915 04497 04546 04550 04551 04551 04551
Exact 04551
1( ) ( with 0)
1
x
L
e xT x T
e L
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 140
Figure 8 Distribution of temperature along x-axis for a functionally graded finite square strip under
steady-state loading conditions
5 THE METHOD OF FUNDAMENTAL SOLUTIONS FOR
THERMOELASTIC ANALYSIS
For the thermoelastic equation (8) describing displacement responses in general
nonhomogeneous media the fundamental solutions are difficult to obtain in a closed form
However we can circumvent this obstacle by indirect ways From the viewpoint of
mathematics the displacement fields must be in terms of space coordinates regardless of the
particular forms of elastic properties and loading types So we can design an equivalent
elastic system as
(38)
to replace Eq (8) where and are elastic constants of a fictitious isotropic homogeneous
solid and ib the lsquofictitious body forcersquo induced by the sought displacement distributions and
the temperature change
For Eq (38) the solution variables iu can be divided into two parts ie the
complementary solutions h
iu and the particular solutions p
iu that is
(39)
in which the complementary solutions h
iu has to satisfy the homogeneous equation as
(40)
0k ki i kk iu u b
( ) ( ) ( )h p
i i iu u u x x x
0h h
k ki i kku u
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 141
while the particular solutions p
iu are required to satisfy the following inhomogeneous
equation
(41)
Obviously the particular solutions and homogeneous solutions satisfying Eqs (40) and
(41) respectively are not unique without considering the constraints of boundary conditions
51 Complementary Solutions
To obtain an approximate solution of homogeneous equation (40) N fictitious source
points ( 12 )si i Nx locating on the pseudo boundary outside the domain under
consideration are selected Moreover assume that at each source point there is a pair of
fictitious point loads 1i and
2i along 1- and 2- directions respectively According to the
main construction of the MFS the approximate displacement fields at arbitrary points in
the domain or on the boundary can be expressed as a linear combination of fundamental
solutions in terms of assumed sources that is
1
sN
h
i nl li sn
n
u U
x x x (42)
in which the displacement fundamental solution ( )li snU x x denoting the induced displacement
distribution along the i-direction at the field point due to the unit concentrated load acting
in the l-direction at source point snx satisfies the following Navier equation
(43)
Such that is the Dirac delta function concentrated at the source point snx and
lie are the components of the 2 by 2 identity matrix For the case of plane strain the
displacement fundamental solution can be written as [49]
(44)
It is apparent that Eq (42) completely satisfies Eq (40) in the domain based on the
definition of the fundamental solutions and the fact that source point and field point canrsquot
overlap in the MFS
0p p
k ki i kk iu u b
x
x
( ) ( ) lk ki sn li kk sn sn liU U e x x x x x x
sn x x
1 1 (3 4 ) ln
8 (1 )li li l iU v r r
v r
x y
snx x
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 142
52 Particular Solutions
In this section RBFs are used to derive the displacement particular solutions Firstly the
generalized fictitious body forces are approximated as
(45)
where M is the number of interpolating points in the domain m
l are coefficients to be
determined and ( )m x x is a set of RBFs
Similarly the particular solution ( )p
iu x is also approximated by means of the same
coefficient set
(46)
where ( )li m x x is a corresponding kernel of approximate particular solutions Because the
particular solution ( )p
iu x satisfies Eq (41) the precondition to this process is that such
relations
(47)
holds true
Generally the particular solution kernel li can be expressed by the second order
differential of Galerkin-Papkovich function liF as [50]
(48)
Substituting Eq (48) into the left hand term of Eq (47) yields
(49)
where 4 denotes the biharmonic operator As a result we have
(50)
Due to the property of RBFs associated with the Euclidian distance only itrsquos convenient
to write the biharmonic operator in polar coordinate for an assumed function in terms of r
only that is
1 1
( ) ( ) ( )M M
m m
i m i li m l
m m
b
x x x x x
1
( ) ( )M
p m
i li m l
m
u
x x x
( ) ( ) ( )lk ki m li kk m li m x x x x x x
1 1
2li li mm mi mlF F
4
1 = 11 2
kl ki li kk li mmkk liF F
4 1
1li liF
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
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[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
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[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 143
(51)
with Thus integrating Eq (50) yields the expression of liF and then the
required particular solution kernel can be derived using Eq (48)
For the typical conical spline 2 1 ( 1)nr n and thin plate spline (TPS)
2 ln ( 1)nr r n the corresponding set of particular solutions are given as [51]
(1) Conical spline
(52)
with
(2) Thin plate spline
(53)
with
53 Complete Solutions
According to Eq (39) the complete solutions of displacement components are written as
the sum of the particular and homogeneous solutions thus we have
1 1
( ) ( ) ( )N M
n m m
i li n l li l
n m
u U
x x y x (54)
Consequently the stress components can be expressed by substituting Eq (54) into Eqs
(7) and (6) as
4 2 2 1 d d 1 d d
d d d dr r r r
r r r r r r
mr x x
2 1
1 2 2
1 1
2 1 2 1 2 3
n
li li l ir A A r rn n
1
2
4 5 2 2 3
2 1
A n n
A n
2 2
1 2 3 2
1
32 1 1 2
n
li il i l
rA A r r
n n
22
1
2
8 29 27 8 2 2 1 2 4 7 4 2 ln
2 1 2 3 2 1 2 ln
A n n n n n n n r
A n n n n r
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 144
1 1
( ) ( ) ( )N M
n m
ij lij n l lij m l ij
n m
S m T
x x y x x (55)
where
(56)
Finally the satisfaction of Eq (54) to the governing Eq (8) at M interpolation points
and substitution of Eq (54) and (55) into boundary conditions (9) at N boundary nodes
produce a set of linear algebraic equations which can be written in matrix form as
(57)
where the unknown coefficient vector is
54 Numerical Examples
For simplicity the temperature distribution is taken in a close form in the following
computation rather than numerical solution of temperature boundary value problems (BVP)
consisting of heat conduction theory Furthermore in this section three examples of FGM
subjected to mechanical or thermal loads are considered to assess the proposed algorithm In
all three examples except for Poissonrsquos ratio the material properties vary exponentially or
according to a power law This is a reasonable assumption since variation on the Poissonrsquos
ratio is usually small compared with that of other properties
To assess the accuracy and convergence of the approximation the average relative error
( )Arerr defined by
(58)
is introduced where j and j are respectively the analytical and numerical results of
variable at the sample points of interest and L is the total number of these points
lij ij lk k li j lj i
lij ij lk k li j lj i
S U U U
H A B
T
1 1 1 1
1 2 1 2 1 2 1 2
N N M M A
2
1
2
1
L
j j
j
L
j
j
Arerr
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 145
Example 541 Hollow circular plate under radial internal pressure
Consider a hollow circular plate as shown in Figure 9 with inner radius 5 mma and
outer radius 10 mmb under internal radial pressure Suppose that the plate is graded along
the radial direction so that elastic modulus For 0 the Youngrsquos
modulus increases as the radius increases When 0 the problem is reduced to the
analysis of homogeneous media Analytical solutions of stress components for the case of
plane stress state are given in closed form as [52]
(59)
with
Figure 9 Configuration of hollow circular plate under internal pressure
In the practical computation Poissonrsquos ratio and elastic modulus at the internal surface
as well as internal pressure respectively are assumed to be 03 ( ) 200 GPaE a
50 MPaap Figure 10 and Figure 11 display the convergent performance of the proposed
meshless method when the PS basis function 3r is used It is found from Figure 10 and Figure
11 that the accuracy increases with an increase in M or N
In order to investigate the variation of radial and hoop stresses along the radial direction
for various graded parameters 32 boundary nodes and 140 interior interpolation points are
used Comparisons between analytical solutions and numerical results are shown in Figure
12
0( ) ( )E r E r a
r
12 2 2 1
2
12 2 2 1
22 2
2 2
kk
k k
r ak k
kk k k
ak k
a ra b r p
b a
k r k ba ra p
b a k k
2 4 4k
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 146
Figure 10 Convergent performance vs M with 2 and N=32
Figure 11 Convergent performance vs N with 2 and M=140
It is found that regardless of the value of radial stress increases monotonously from
the inner to the outer surface whereas hoop stress does not As increases the value of
radial stress decreases at any point in the cylinder except for the points on the boundary
whereas the maximum hoop stress occurs on the inner surface when 0 and on the outer
surface when 3
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 147
Figure 12 Distribution of radial and hoop stresses with various graded parameter when 32 boundary
nodes and 140 interior interpolation points are used
The variation in the hoop stress looks like rotation around a center when increases It
is also found that the variation in hoop stress in FGMs becomes worse when increases
Therefore to avoid material instability the graded parameter should be smaller than some
critical values
In this example effects of the types and orders of RBF are also tested for the case of the
high graded parameter 4
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 148
Figure 13 Effect of orders of radial basis functions when 32 boundary nodes and 220 interior
interpolation points are used
Figure 13 shows the average relative error distributions It is evident that a higher order
of RBF does not always result in better accuracy The calculation indicates that 3r and
5r in
PS and 2 lnr r and
4 lnr r in TPS seem to be able to produce relatively high accuracy in this
example
Moreover TPS has better accuracy than that of PS Therefore 4 lnr r is used in the
remaining computation
Example 542 Functionally graded elastic beam under sinusoidal transverse load
An elastic beam shown in Figure 14 is considered in this example which is made of two-
phase AlSiC composite The elastic modulus varying exponentially in the z direction is given
by 0( ) zE z E e The left and right end faces of the FG beam are assumed to be simply
supported such that
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 149
(60)
The top surface of the beam is assumed to be free of mechanical force and the bottom
surface is subjected to a distributed load p as shown in Figure 14
(61)
The problem is solved under a plane strain assumption with the length 100 mmL and
thickness 40 mmh The material properties of aluminum and SiC are respectively
70 GPaAlE and 427 GPaSiCE ( [ln( )]SiC AlE E h ) The maximum transverse load
0p is
equal to 10MPa Total 34 boundary nodes and 169 interior interpolation points are selected in
the analysis
Figure 14 Functionally graded beam subjected to symmetric sinusoidal transverse loading
Figure 15 (continued)
(0 ) ( ) 0
(0 ) ( ) 0x x
w z w L z
t z t L z
( 0) ( ) 0
( 0) ( ) 0
x x
z z
t x t x h
t x p t x h
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 150
Figure 15 Transverse displacement and stress components along the line 2z h
Figure 16 Variation of stress components along the cross section 5x L
Figure 15 and Figure 16 respectively show the variation of transverse displacement and
stress components along the line 2z h and 5x L Good agreement can be observed
between the numerical results and analytical solutions [53] Furthermore the shapes of cross-
sections after deformation are provided in Figure 17 from which it can be seen that for
smaller ratios of thickness and length for example 110h L the cross section
approximately maintains plane after deformation This phenomenon demonstrates the validity
of the cross-section assumption in classic thin beam bending theory
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 151
Figure 17 Shape of transverse cross section after deformation with various ratio of thickness and
length
Example 543 Symmetrical thermoelastic problem in a long cylinder
Consider a thick hollow cylinder with same geometries and mechanical boundary
conditions as in Figure 9 The same power-law assumptions are used to define the elastic
modulus and coefficient of thermal expansion that is 0( ) ( )E r E r a and 0( ) ( )r r a
The temperature change in the entire domain is given in a closed form as
(62)
with ( )aT T a and ( )bT T b
The two-phase aluminumceramic FGM is examined here The metal aluminum
constituent is arranged on the inner surface while the ceramic constituent is on the outer
surface The related material properties are 70 GPaAlE 6 o12 10 CAl
151 GPaceramicE 6 o259 10 Cceramic Poissonrsquos ratio is taken to be 03 The inner
and outer boundary temperature changes respectively are o10 CaT and o0 CbT
for 0
ln ln
for 0
ln
a b
a b
T b r T r a
b a
b rT T Tr a
b
a
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 152
Figure 18 Stresses and radial displacement distributions in FGM and homogeneous material with
N=32 M=220
Analytical solutions of displacements and stresses for the case of plane strain state are
provided by Jabbari et al [54] The results in Figure 18 show good agreement between the
analytical solutions and the numerical results in FGM and homogeneous material which
corresponds to 0 Furthermore we again find that after graded treatment the maximum
value of hoop stress decreases from 826MPa to 53MPa Additionally the radial displacement
in FGM also decreases compared to the response in homogeneous media Since the value of
radial displacement is very small radial deformation can be neglected in practical analysis
CONCLUSIONS
The paper presents an efficient meshless method for transient heat transfer and
thermoelastic analysis of FGMs in which the combination of MFS and RBF provides a
powerful numerical procedure Numerical experiments show that a good agreement is
achieved between the results obtained from the proposed meshless method and available
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
The Method of Functional Solutions hellip 153
analytical solutions It is clear that the temperature and stress responses in FGMs differ
substantially from those in their homogeneous counterparts The appropriate graded
parameter can lead to different temperature distribution low stress concentration and little
change in the distribution of stress fields in the domain under consideration
Additionally from the solution procedure we can see that the construction of the full
displacement variables is independent of the type of problem of interest This characteristic
means that the proposed method can be easily extended to other spatial variations of the
material parameters of FGM and other engineering problems instead of restrictions on
exponential variation of the material properties with Cartesian coordinates
On the other hand we must note that the proposed method still has some disadvantages
such as the linear system of equations formed at length being dense and possibly being ill-
conditioned for large and complex domains which are also the inherent disadvantages of
conventional MFS approximation
REFERENCES
[1] Y Miyamoto Functionally graded materials design processing and applications
Chapman and Hall 1999
[2] T Mori and K Tanaka Average stress in matrix and average elastic energy of
materials with misfitting inclusions Acta Metallurgica 21 (1973) 571-574
[3] QH Qin and SW Yu Effective moduli of thermopiezoelectric material with
microcavities International Journal of Solids and Structures 35 (1998) 5085-5095
[4] QH Qin The Trefftz Finite and Boundary Element Method Southampton WIT Press
2000
[5] J Jirousek and QH Qin Application of Hybrid-Trefftz element approach to transient
heat conduction analysis Computers amp Structures 58 (1996) 195-201
[6] W Szymczyk Numerical simulation of composite surface coating as a functionally
graded material Materials Science and Engineering A 412 (2005) 61-65
[7] MH Santare and J Lambros Use of graded finite elements to model the behavior of
nonhomogeneous materials Journal of Applied Mechanics 67 (2000) 819
[8] JH Kim and GH Paulino Isoparametric Graded Finite Elements for
Nonhomogeneous Isotropic and Orthotropic Materials Journal of Applied Mechanics
69 (2002) 502-514
[9] QH Qin Nonlinear analysis of Reissner plates on an elastic foundation by the BEM
International Journal of Solids and Structures 30 (1993) 3101-3111
[10] C Saizonou R Kouitat-Njiwa and J von Stebut Surface engineering with
functionally graded coatings a numerical study based on the boundary element method
Surface and Coatings Technology 153 (2002) 290-297
[11] A Sutradhar and GH Paulino The simple boundary element method for transient heat
conduction in functionally graded materials Computer Methods in Applied Mechanics
and Engineering 193 (2004) 4511-4539
[12] BN Rao and S Rahman Mesh-free analysis of cracks in isotropic functionally graded
materials Engineering Fracture Mechanics 70 (2003) 1-28
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 154
[13] KY Dai GR Liu X Han and KM Lim Thermomechanical analysis of functionally
graded material (FGM) plates using element-free Galerkin method Computers and
Structures 83 (2005) 1487-1502
[14] HK Ching and SC Yen Meshless local Petrov-Galerkin analysis for 2D functionally
graded elastic solids under mechanical and thermal loads Composites Part B
Engineering 36 (2005) 223-240
[15] HK Ching and SC Yen Transient thermoelastic deformations of 2-D functionally
graded beams under nonuniformly convective heat supply Composite Structures 73
(2006) 381-393
[16] J Sladek V Sladek and Ch Zhang Stress analysis in anisotropic functionally graded
materials by the MLPG method Engineering Analysis with Boundary Elements 29
(2005) 597-609
[17] DF Gilhooley JR Xiao RC Batra MA McCarthy and JW Gillespie Jr Two-
dimensional stress analysis of functionally graded solids using the MLPG method with
radial basis functions Computational Materials Science 41 (2008) 467-481
[18] J Sladek V Sladek and Ch Zhang A meshless local boundary integral equation
method for dynamic anti-plane shear crack problem in functionally graded materials
Engineering Analysis with Boundary Elements 29 (2005) 334-342
[19] V Sladek J Sladek M Tanaka and Ch Zhang Transient heat conduction in
anisotropic and functionally graded media by local integral equations Engineering
Analysis with Boundary Elements 29 (2005) 1047-1065
[20] L Marin Numerical solution of the Cauchy problem for steady-state heat transfer in
two-dimensional functionally graded materials International Journal of Solids and
Structures 42 (2005) 4338-4351
[21] L Marin and D Lesnic The method of fundamental solutions for nonlinear
functionally graded materials International Journal of Solids and Structures 44 (2007)
6878-6890
[22] JR Berger PA Martin V Mantiˇc and LJ Gray Fundamental solutions for steady-
state heat transfer in an exponentially graded anisotropic material Zeitschrift fuuml r
Angewandte Mathematik und Physik 56 (2005) 293-303
[23] HC Sun LZ Zhang Q Xu and YM Zhang Nonsingularity Boundary Element
Methods Dalian University of Technology Press (in Chinese) Dalian 1999
[24] MA Golberg CS Chen and JA Fromme Discrete projection methods for integral
equations Computational Mechanics Publications Southampton 1997
[25] K Balakrishnan and PA Ramachandran A particular solution Trefftz method for non-
linear Poisson problems in heat and mass transfer Journal of Computational Physics
150 (1999) 239-267
[26] LC Nitsche and H Brenner Hydrodynamics of particulate motion in sinusoidal pores
via a singularity method AIChE Journal 36 (1990) 1403-1419
[27] YS Chan LJ Gray T Kaplan and GH Paulino Greens function for a two-
dimensional exponentially graded elastic medium Proceedings of the Royal Society A
460 (2004) 1689-1706
[28] JT Katsikadelis The analog equation method- A powerful BEM-based solution
technique for solving linear and nonlinear engineering problems in CA Brebbia
(Ed) Boundary element method XVI CLM Publications Southampton 1994 pp 167-
182
The Method of Functional Solutions hellip 155
[29] D Nardini and CA Brebbia A new approach to free vibration analysis using
boundary elements Applied Mathematical Modelling 7 (1983) 157-162
[30] G Bao and L Wang Multiple cracking in functionally graded ceramicmetal coatings
International Journal of Solids and Structures 32 (1995) 2853-2871
[31] F Delale and F Erdogan The crack problem for a nonhomogeneous plane Journal of
Applied Mechanics 50 (1983) 609
[32] G Fairweather and A Karageorghis The method of fundamental solutions for elliptic
boundary value problems Advances in Computational Mathematics 9 (1998) 69-95
[33] H Wang QH Qin and YL Kang A new meshless method for steady-state heat
conduction problems in anisotropic and inhomogeneous media Archive of Applied
Mechanics 74 (2005) 563-579
[34] WA Yao and H Wang Virtual boundary element integral method for 2-D
piezoelectric media Finite Elements in Analysis and Design 41 (2005) 875-891
[35] H Wang and QH Qin A meshless method for generalized linear or nonlinear
Poisson-type problems Engineering Analysis with Boundary Elements 30 (2006) 515-
521
[36] H Wang and QH Qin Some problems with the method of fundamental solution using
radial basis functions Acta Mechanica Solida Sinica 20 (2007) 21-29
[37] H Wang QH Qin and YL Kang A meshless model for transient heat conduction in
functionally graded materials Computational Mechanics 38 (2006) 51-60
[38] H Wang and QH Qin Meshless approach for thermo-mechanical analysis of
functionally graded materials Engineering Analysis with Boundary Elements 32 (2008)
704-712
[39] MA Golberg CS Chen H Bowman and H Power Some comments on the use of
Radial Basis Functions in the Dual Reciprocity Method Computational Mechanics 21
(1998) 141-148
[40] PW Partridge CA Brebbia and LC Wrobel The dual reciprocity boundary element
method Computational Mechanics Publications Southampton 1992
[41] AHD Cheng Particular solutions of Laplacian Helmholtz-type and polyharmonic
operators involving higher order radial basis functions Engineering Analysis with
Boundary Elements 24 (2000) 531-538
[42] CS Chen and YF Rashed Evaluation of thin plate spline based particular solutions
for Helmholtz-type operators for the DRM Mechanics Research Communications 25
(1998) 195-201
[43] M Golberg Recent developments in the numerical evaluation of particular solutions in
the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
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[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
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interpolation Advances in Computational Mathematics 3 (1995) 251-264
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Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
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and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
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the boundary element method Applied Mathematics and Computation 75 (1996) 91-
101
[44] PA Ramachandran and K Balakrishnan Radial basis functions as approximate
particular solutions review of recent progress Engineering Analysis with Boundary
Elements 24 (2000) 575-582
[45] RA Bialecki P Jurgas and G Kuhn Dual reciprocity BEM without matrix inversion
for transient heat conduction Engineering Analysis with Boundary Elements 26 (2002)
227-236
[46] P Mitic and YF Rashed Convergence and stability of the method of meshless
fundamental solutions using an array of randomly distributed sources Engineering
Analysis with Boundary Elements 28 (2004) 143-153
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497
Hui Wang and Qing-Hua Qin 156
[47] R Schaback Error estimates and condition numbers for radial basis function
interpolation Advances in Computational Mathematics 3 (1995) 251-264
[48] J Sladek V Sladek and Ch Zhang Transient heat conduction analysis in functionally
graded materials by the meshless local boundary integral equation method
Computational Materials Science 28 (2003) 494-504
[49] CA Brebbia and J Dominguez Boundary elements an introductory course
Computational Mechanics Publications Southampton 1992
[50] APS Selvadurai Partial Differential Equations in Mechanics Springer Berlin 2000
[51] AHD Cheng CS Chen MA Golberg and YF Rashed BEM for theomoelasticity
and elasticity with body force--a revisit Engineering Analysis with Boundary Elements
25 (2001) 377-387
[52] CO Horgan and AM Chan The pressurized hollow cylinder or disk problem for
functionally graded isotropic linearly elastic materials Journal of Elasticity 55 (1999)
43-59
[53] BV Sankar An elasticity solution for functionally graded beams Composites Science
and Technology 61 (2001) 689-696
[54] M Jabbari S Sohrabpour and MR Eslami Mechanical and thermal stresses in a
functionally graded hollow cylinder due to radially symmetric loads International
Journal of Pressure Vessels and Piping 79 (2002) 493-497