Download - EFFECTS OF COMPOSITE LAYER PLATE ON MODAL
EFFECTS OF COMPOSITE LAYER PLATE ON MODAL EXPERIMENTAL
ANALYSIS
NUR AZLEEN BINTI ABDOL MULOK
Report submitted in partial fulfilment of the requirement for the award of
Bachelor of Mechanical Engineering
Faculty of Mechanical Engineering
UNIVERSITY MALAYSIA PAHANG
JUNE 2013
vi
ABSTRACT
The composite plates are basic structural components in aerospace, mechanical and civil
industries. This project presents the experimental modal analysis of dynamical behavior
of plates made up of woven glass fiber and epoxy matrix in free-free boundary
conditions. Two composite plates with different number of layers were analysed. The
dynamic characteristics observed are natural frequency and mode shape. The result
obtained by experimental modal analysis technique for each structure is then compared
with the result obtained by using finite element method (FEM). From the results, the
influence of number of layers on flexural natural frequencies is investigated. It shows
that as the number of layers increase, the natural frequencies also increases.
Comparative study is done between the experimental and the finite element result
obtained from ALGOR. From the ODS result, it shows that the dominant mode shape
for both four and eight layers composite plates are mode 1. The prediction of dynamical
behavior plays an important role for their future design applications.
vii
ABSTRAK
Plat komposit merupakan struktur komponen asas dalam industri aeroangkasa,
mekanikal dan juga awam. Projek ini membentangkan tentang eksperimen modal
analisis bagi mengenal pasti tingkah laku dinamik plat yang diperbuat daripada gentian
kaca tenunan dan digabungkan bersama matriks epoksi dalam keadaan sempadan bebas.
Dua plat komposit yang mempunyai jumlah lapisan gentian kaca yang berbeza telah
dianalisis. Keputusan yang diperolehi daripada eksperimen menggunakan teknik modal
analisis bagi mendapatkan kekerapan semula jadi dan bentuk mod bagi setiap struktur
kemudiannya dibandingkan dengan keputusan yang diperolehi dengan menggunakan
kaedah analisis unsure finite (FEM). Daripada keputusan yang diperolehi, pengaruh
jumlah lapisan yang terdapat pada plat komposit memberikan kesan kepada frekuensi
semulajadi telah disiasat. Keputusan menunjukkan bahawa semakin banyak lapisan pada
plat komposit, semakin tinggi nilai frekuensi yang diperolehi. Selain itu, hasil
eksperimen itu disahkan oleh unsur perisian ALGOR. Daripada eksperimen ODS yang
dilakukan, keputusan menunjukkan bahawa bentuk mod yang utama bagi empat dan
lapan lapisan plat ialah mod 1. Ramalan tingkah laku dinamik memainkan peranan yang
penting untuk mengetahui keupayaan plat komposit sebagai struktur dalam sebuah
sistem.
TABLE OF CONTENTS
Page
APPROVAL SHEET i
SUPERVISOR’S DECLARATION
ii
STUDENT’S DECLARATION
DEDICATION
iii
iv
ACKNOWLEDGEMENTS
v
ABSTRACT
vi
ABSTRAK
vii
TABLE OF CONTENTS
viii
LIST OF TABLE
xi
LIST OF FIGURES
xii
LIST OF ABBREVIATIONS
xv
CHAPTER 1 INTRODUCTION
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction
5
2.2 Composite Materials
6
2.2.1 Introduction to Composite Materials
6
1.1 Introduction
1
1.2 Project Background
3
1.3 Problem Statement
3
1.4 Project Objective
4
1.5 Scope of The Project
4
1.6 Gantt Chart 4
2.2.2 History of Composite Materials
7
2.3 Classification of Composite
8
2.3.1 Continuous Fiber
8
2.3.2 Discontinuous Fiber
9
2.4 Composite Fabrication Process
10
2.4.1 Basic Hand Lay-up Technique
10
2.5 Finite Element Method
12
2.5.1 Introduction
12
2.5.2 Application of FEM
13
2.5.3 Advantages of Using FEM
14
2.6 Modal Analysis
15
2.6.1 Frequency Response Function (FRF)
16
2.6.2 Advantages of Modal Analysis
16
2.7 Natural Frequency
17
2.8 Operating Deflection Shapes 17
CHAPTER 3 METHODOLOGY
3.1 Introduction
19
3.2 Flow Chart
20
3.3 Material Selection
21
3.4 Fabrication of Fiberglass Composite Plate
22
3.4.1 Hand Lay-up Technique
22
3.5 Finite Element Analysis
23
3.5.1 Solidwork Design
26
3.5.2 Simulation Method Using ALGOR 29
3.6 Modal Analysis
31
3.6.1 Impact Hammer Testing
31
3.6.2 Modal Analysis Procedure
33
3.7 Operating Deflection Shapes (ODS) 36
CHAPTER 4 RESULT & DISCUSSIONS
4.1 Introduction
39
4.2 Result of Fabrication of Composite Plate
39
4.3 Result of Natural Frequencies
42
4.3.1 Natural Frequency by Finite Element Analysis
(FEA)
42
4.3.2 Natural Frequency By Experimental Modal
Analysis
43
4.3.3 Comparison between Natural Frequency of FEA
and Modal Analysis
44
4.4 Result of Mode Shapes for Modal Analysis
46
4.4.1 Mode Shapes by ALGOR (FEM)
47
4.4.2 Mode Shapes by Experimental Modal Analysis
47
4.5 Comparison Between Result Obtained by FEA and
Modal Analysis
47
4.5.1 Result of 4 Layers Composite Plate
48
4.5.2 Result of 8 Layers Composite Plate
51
4.6 Result for ODS
53
4.6.1 Result by Calculation (Theoretical)
54
4.6.2 Result by Experimental ODS
54
4.7 Comparing the Displacement of the Calculated Mode
Shapes
55
4.8 Comparing Mode Shapes Obtain from Calculation and 57
Experimental ODS
4.8.1 Result of 4 Layers Composite Plate by ODS
57
4.8.2 Result of 8 Layers Composite Plate by ODS
61
4.9 Discussion of The Comparison
64
4.9.1 Discussion on Result of FEA and Modal
Analysis
65
4.9.2 Discussion on Result of Calculation and
Experimental ODS
66
CHAPTER 5 CONCLUSION & RECOMMENDATIONS
5.1 Introduction
69
5.2 Conclusion
69
5.3 Recommendations 70
REFERENCES 71
APPENDICES
APPENDIX A
73
APPENDIX B
74
APPENDIX C
75
APPENDIX D
76
APPENDIX E
77
APPENDIX F
78
APPENDIX G
79
APPENDIX H
80
APPENDIX I 81
LIST OF TABLES
Table No. Title Page
2.1 Machining composites – Trade to be considered 12
3.1 Properties of the composite reinforcing fibers. 21
4.1 The frequency and displacement of composite plate with 4 layers
by using FEA
43
4.2 The frequency and displacement of composite plate with 8 layers
by using FEA
43
4.3 The frequency and displacement of composite plate with 4 layers
by using modal analysis
44
4.4 The frequency and displacement of composite plate with 8 layers
by using modal analysis
44
4.5 Comparison of natural frequency between FEA and experimental
modal analysis of 4 layers plate
44
4.6
Comparison of natural frequency between FEA and experimental
modal analysis of 8 layers plate
45
4.7 The frequency and displacement of composite plate with 4 layers
by using calculation
54
4.8 The frequency and displacement of composite plate with 8 layers
by using calculation
54
4.9 The frequency and displacement of composite plate with 4 layers
by using ODS
55
4.10
The frequency and displacement of composite plate with 8 layers
by using ODS
55
LIST OF FIGURES
Figure No. Title Page
2.1 A unidirectionally reinforced layers crossplied FRP laminate,
shows the microcracking and nonuniform fiber packing
6
2.2 Typical reinforcement type 8
2.3 Example of composites: a) particulate, random; b) discontinuous
fibres, unidirectional; c) discontinuous fibres, random; d)
continuous fibres, unidirectional
9
2.4 The basic concept in using the hand lay-up technique 11
2.5 Schematic overviewing the response problem 15
2.6 The simple plate Frequency Response Function 16
2.7 Frequency Domain ODS from a set of FRF’s 18
3.1 Methodology Flow Chart 20
3.2 Dimension of the glass fiber 22
3.3 Cutting of the glass fiber by using scissors 23
3.4 Mixing epoxy resin with the catalyst 24
3.5 A thin coat is applied on the platform before the first glass fiber is
layed out
24
3.6 Gel coat is applied to the first layer
25
3.7 Scraper used to remove all entrapped air 25
3.8 Material selection for the composite plate (E-Glass) 26
3.9 The SOLIDWORKS drawing of the 4 layers composite plate 27
3.10 The SOLIDWORKS design for the 8 layers composite plate 28
3.11 Exploded view of the four layers composite plate 28
3.12 Exploded view of eight layers composite plate 29
3.13 The analysis type of the simulation is chosen to be Natural
Frequency (modal)
30
3.14 Meshing of the composite plate 31
3.15 Example of the setup for modal testing 32
3.16 Experiment setup for modal testing, impact hammer test 33
3.17 Sensitivity setting of the hammer and accelerometer 34
3.18 DASYlab 10.0 modules for modal analysis 34
3.19 Construction of plate in ME’scopeVES 35
3.20 Numbering of points for the plate 35
3.21 Curve fitting to select the peaks from the graph 36
3.22 Example of the experiment setup for ODS 37
4.1 Four layers plate: (a) Top view; (b) side view 40
4.2 Eight layers plate: (a) Top view; (b) side view 41
4.4 The surface smoothness of the plate. (a) The unsmooth surface of
the plate (b) The smooth surface of the plate
42
4.5 Graph of comparison of natural frequency between FEA and
modal analysis for 4 layers plate
45
4.6 Graph of comparison of natural frequency between FEA and
modal analysis for 8 layers plate
46
4.7 First mode shape of 4 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
48
4.8 Second mode shape of 4 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
49
4.9 Third mode shape of 4 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
50
4.10 Fourth mode shape of 4 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
50
4.11 Fifth mode shape of 4 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
51
4.12 First mode shape of 8 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
51
4.13 Second mode shape of 8 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
52
4.14 Third mode shape of 8 layers composite plate, (a) Finite element
analysis, (b) Experimental modal analysis
53
4.15 Comparison between displacement in each modes of 4 layers
composite plate
56
4.16 Comparison between displacement in each modes of 8 layers
composite plate
56
4.17 First mode shape of 4 layers composite plate, (a) Calculation,
(b) Experimental ODS
57
4.18 Second mode shape of 4 layers composite plate, (a) Calculation,
(b) Experimental ODS
58
4.19 Third mode shape of 4 layers composite plate, (a) Calculation,
(b) Experimental ODS
59
4.20 Fourth mode shape of 4 layers composite plate, (a) Calculation,
(b) Experimental ODS
60
4.21 Fifth mode shape of 4 layers composite plate, (a) Calculation,
(b) Experimental ODS
60
4.22 First mode shape of 8 layers composite plate, (a) Calculation,
(b) Experimental ODS
61
4.23 Second mode shape of 8 layers composite plate, (a) Calculation,
(b) Experimental ODS
62
4.24 Third mode shape of 8 layers composite plate, (a) Calculation,
(b) Experimental ODS
63
4.25 Fourth mode shape of 8 layers composite plate, (a) Calculation,
(b) Experimental ODS
63
4.26 Fifth mode shape of 8 layers composite plate, (a) Calculation,
(b) Experimental ODS
64
4.27 Dominant mode for 4 layers composite plate 67
4.28 Dominant mode for 8 layers composite plate 67
LIST OF ABBREVIATIONS
FEA Finite Element Analysis
FEM Finite Element Method
DOF Degree Of Freedom
SDOF Single Degree Of Freedom
MDOF Multi Degree Of Freedom
FRF Frequency Response Function
DAQ Data Acquisition System
CAD Computer Aided Diagram
IGES Initial Graphics Exchange Specification
FFT Fast Fourier Transform
2D Two Dimensional
3D Three Dimensional
SI International System of Units
UMM Unit Modal Mass
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
Recently, there has been a lot of discussion and review about the role of
composite materials as the one of the most common material used in a lot of the
growing industries that exists today. Some of the most common use of composite
materials in everyday life would be sports equipments, ship building, automobile,
and aircraft.
There are many types of composite materials used in the industries. Fiber
reinforced composite materials includes glass, carbon, aramid, boron and also
ceramics (Tsipas et al, 2012). The fibreglass is one of the types of composite. There
are divided further by the types of fibreglass. In this study, the woven fabric
composites will be used during the experiments. The application of this woven fabric
composites are wide especially in the engineering application. The benefit of using
woven fabrics as the reinforcement is that it provides conformability and also
excellent integrity for any advanced structural composite application (Mishra et al,
2012).
Since the application of the composite materials are more onto the structures
of the automotive, aircraft, shipbuilding and mass transit bodies, subjected widely to
dynamic loading that can cause excessive vibration (Velmurugan et al, 2011). To
determine the different modes of vibration, the dynamic response of the composite
structures need to be understood and studied.
2
Due to the advancement on the computer aided data acquisition system and
instrumentation, it has become more important for the experimentalist to do
experimental modal analysis (Sahu et al, 2012). There are many researchers that did
the research on the laminated composite laminates, but the research on the dynamic
characteristics of the woven fabric composite laminates are still limited.
The method that will be used to test the woven fabric composite would be by
modal analysis using the FFT (Fast Fourier Transform) analyzer. This study will
involve the experiment on the woven fiber Glass/Epoxy composites plate. The
specimen will be in free-free boundary condition form.
The woven fabric composite specimens are fabricated by using the hand-
layup technique. The material required for the fabrication of the composite plates are
E-glass woven roving which act as the reinforcement (Owens Corning) , Epoxy as
the resin and hardener as catalyst.
The composite will have different number of layers. The effect of layers in
the composite will be determined by using the modal analysis experiment. The result
from the FFT analyzer will then be compared with the Finite Element Method (FEM)
tool ALGOR. The results will lead to the natural frequency of each of the different
layer composite and the modal shape can be obtained by the ANSYS (Stanciu et al,
2011).
The prediction that the FEM tool ALGOR produce is important when
comparing with the FFT result. There should not be much difference in the natural
frequency data during the comparison. The study of this dynamic behaviour and
characteristics of woven composite plates plays an important role for the future
application of this material.
3
1.2 PROJECT BACKGROUND
Since there are not that many studies directed on the composite materials, the
dynamic characteristic of the composite material itself are hard to find.
Composite materials are widely used in a lot of the developing industries
today. Some of the industrial sectors that use composite materials are aerospace,
automobile, boats, chemicals, domestic, electrical and leisure. In aerospace only will
consist of a lot of composite materials such as wings, helicopter blade, landing gears,
seats, floors, interior panels, fuel tanks and nose cones (Rawlings et al, 2006).
As stated above, the application of the composite materials is important in
many industries. So, in order to gain the valuable information about the dynamic
characteristics this study need to be done. The effect that the different geometrical
parameters especially the number of layers in the free-free boundary condition of the
woven fabric composite plates can be known (Mishra et al, 2012).
1.3 PROBLEM STATEMENT
In recent years, the study about dynamic behaviour of the composite
materials has become significant due to the increasing demand in the industries. The
natural frequency of the material should be known to prevent any disastrous impact
for any engineering structure. Fiberglass material is considered as a safe material to
be used, but the damages in the material itself are rather hard to be detected. So, it is
really important to know the factors that contribute to the danger that can be
catastrophic (Chang et al, 1992). The main reason this study is made is to produce a
better understanding of the dynamic behaviour that are made from the woven fiber
composite materials especially for the plates. The effects of different number of layer
in the composite plates in free-free boundary condition are studied in detail.
4
1.4 PROJECT OBJECTIVE
The objective of conducting this project is to study the dynamic properties
and behaviour of composite layer by using modal analysis and finite element
analysis.
1.5 SCOPE OF THE PROJECT
The scope of carrying out this project includes:
i. The analysis of fibreglass composite will be carried out by using Finite
element analysis tool ALGOR.
ii. The type of composite use would be fibreglass as the reinforcement and
epoxy as the resin.
iii. The experimental result will be obtained by model testing by using impact
hammer.
iv. The experimental result and the computational result will be compared.
v. It is the analysis of the natural frequency by using model analysis and FEM
on the composite plate to find out the mode shape and natural frequency.
vi. Experimental Operational Deflection Shape (ODS) by motor of 53Hz.
vii. Validation of experimental ODS is done by using calculation and the result is
compared.
1.6 GANTT CHART
The Gantt chart is illustrating the project schedule. The starting and finishing
week of the project is stated in the chart. It is divided into two rows for each
progress. The first row will illustrate the planned period for the element while the
second row is the actual period that is done to complete it. The Gantt chart for this
particular project can be referred to Appendix A
CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
In this chapter, the explanation about the project will be stated in detail. It
started off with the introduction to the composite materials. Since the composite
material itself has many types, the classification of the composite material will be
explained further. The main focus would be for the E-glass woven roving which will
be used in the experiment.
Other than the explanation on the composite material, there will also be some
discussion on the modal analysis itself. Since the experimental investigation will be
carried out by using modal analysis technique with the Fast Fourier Transform,
DASYLab, impact hammer and also the triaxial accelerometer, the explanation will
go deeper in order to give a clear view on how the process will flow and also the
connection between all of the elements stated.
Moreover, Finite Element method (FEM) tool ANSYS will also be explain in
detail in order to show the function of using this particular software. This tool is
needed so that the result can be compared with the FFT analyzer.
6
2.2 COMPOSITE MATERIALS
2.2.1 Introduction to Composite Materials
Composite material actually can be define as the combination of two or more
materials that will eventually produce a product with better properties than those
individual components stand alone (Campbell, 2010). It is different than the metallic
alloy. This is because the alloys can actually blend the characteristics and properties
of two or more metals in order to create a hybrid metal that is more stronger, durable
cost-effective than the pure metal. Metal alloys are different from composite
materials because there will be subtle changes in the microstructure which will cause
dramatic variations in their properties (R. Saravanan et al, 2012).
Composite can be define by a lot of different thing if it is taken at the face
value but in the more modern materials engineering, it can be referred to “matrix”
material which is reinforced by fibers. By taking Fiber Reinforce Plastic (FRP) as an
example, the term indicates that thermosetting polyester matrix that contains glass
fibers (Roylance, 2000). Figure 2.1 is showing the laminate fabricated by
unidirectionally crossplying reinforced layers in a 0 ̊-90̊ stacking sequence.
Figure 2.1: A unidirectionally reinforced layers crossplied FRP laminate, shows the
microcracking and nonuniform fiber packing.
7
Source: Harris, B., Engineering Composite Materials, Institute of Metals, 1986.
Composite material is not something that is new to the material engineering.
In fact, the first uses of composite went back to the 1500s B.C. It all started when the
Mesopotamian and Egyptians used the mixture of straw and mud to build stronger
and more durable buildings (Todd Johnson).
2.2.2 History of Composite Materials
The first ever binding materials that were employed to fabricate mortars in
ancient buildings would be mud (Moropoulou et al, 2005). This means that
composite is not really a new technology. This is because even the bricks that are
reinforced with straw and made from mud that were used in ancient civilizations are
also considered as composite (Matthews et al, 2006).
The modern composite industry began in 1930, when it is made almost by
accident. This happened when an engineer became interested by the fiber formed
during the process of applying lettering to a glass milk bottle. Then, in 1937,
salesmen from the Owen Corning Fiberglass Company began selling their fibreglass
in the United States to the interested parties. This company was formed in 1935 by
Owens-Illinois and Corning Glass Works to focus on selling the new fibrous material
(Brent Strong, 1989).
The second generation of the composite starts in 1960s where the composite
is already called the high performance composite. During this era, a new Saint-
Gobain factory in Chambery, France was opened for the production of fibreglass. By
1958, they started to produce composite helicopterblades especially for Alouette II.
At the same time, carbon, boron as well as aramid fiber were also introduced to the
world. Aramid fiber also known as Kevlar is actually discovered after Kwolek tried
to find a solvent to dissolve the nonmelting polymer that she made earlier. This
discovery actually proved that the fiber produced from the aramid solution is actually
five times stronger than steel. It can be applied to bulletproof vests and helmets (Tim
Palucka et al, 2002)
8
2.3 CLASSIFICATION OF COMPOSITE
2.3.1 Continuous Fiber
Continuous fibers have long aspect ratio. Aspect ratio is the length-to-
diameter (l/d ) ratio. However, continuous fibers can have varied aspect ratio
considerably (Rawlings et al, 2006). Continuous fiber composites will usually have
the preferred orientation. The orientation of continuous fiber can be seen from Figure
2.2. Some examples of continuous reinforcements include unidirectional, woven
cloth and helical winding.
Figure 2.2: Typical reinforcement type: a) continuous fiber; b) discontinuous fiber
Source: F.C. Campbell, 2010.
9
2.3.2 Discontinuous Fiber
Discontinuous fiber can also be known by particulate composite. Particulate
reinforcement may have the dimensions that are more or less equal in all direction.
They can come in many shapes including spherical, cubic, platelet, or any irregular
or regular geometry (Rawlings et al, 2006).
Comparing to the continuous fiber, particulate seems to be much weaker and
less stiff, but they are not as expensive as the continuous fiber. Discontinuous fiber
have short aspect ratio and they usually have random orientation (Matthews et al,
2006). Examples of discontinuous fiber are chopped fibers and random mat which
can be seen in Figure 2.3.
Figure 2.3: Example of composites: a) particulate, random; b) discontinuous fibres,
unidirectional; c) discontinuous fibres, random; d) continuous fibres, unidirectional.
Source: Frank L. Matthews, Rees D. Rawlings, 2006.
10
2.4 COMPOSITE FABRICATION PROCESS
2.4.1 Basic Hand Lay-up Technique
It is normally done in a Fibre Reinforced Plastic (FRP) mould that are
polished on the inside part. There is no limit when it comes to the mold. Some may
be as simple as flat surface or some may have infinite edges and curves (Brandon
Lee, 2004). Figure 2.4 shows the basic hand lay-up technique.
Hand lay-up is considered as the simplest and oldest way used to produce
reinforced plastic laminates. The capital investment for using this method is
relatively low comparing to other method. For simplicity, some fabricators may used
brush or simply pour the resin into the molds if spray gun is not available. Spray gun
is the most expensive equipment for hand lay-up process, but it is optional to do so
(American Composite Manufacturers Association, 2004).
Figure 2.4: Basic concept in using the hand lay-up technique.
Source: J.R. Vinson, R.L. Sierakowski, 2008.
11
The very first step to do the hand lay-up is preparing the mold for the
composite to be applied on. The mold should be clean and free from any surface
deformation or particulate because it can affect the final surface condition of the
composite itself. Check the mold from chips and blemishes.
Next step is applying the releasing agent on the surface of the mold so that
the composite can be released easily after curing (Brandon Lee, 2004). Releasing
agent is actually a non-binding polymer or a wax that is first coat to the mold. This
releasing agent can ensure easier release and pop out of the finished cured part from
the mold (Todd Johnson). Some examples of releasing agents are poly vinyl alcohol
(PVA), hard wax and fluorocarbons (Keith Godber, An Overview of Release Agent
Types and Technology).
Resin is another important part in making composite. Resin will hold
everything together while transferring the loads that are applied on the composite
through the fibers to the rest of the structure. Other than the purpose of binding the
structure, resin will also protect it from any kind of corrosion, abrasion, impact and
also environment factors (Fibermax Composites, 2007). Among the most commonly
used resin would be Polyester (orthophthalic and isophthali), epoxy, phenolic and
also vinyl ester. The mixture of resin and the catalyst should be in the correct
quantity which is between 11 2 - 2% when comparing by the weight (Basic Hand
Lay-up Techniques For Reinforced Composites).
Ideally, the lay-up process of the fibreglass reinforcement should start as soon
as the mixture of resin is ready (Basic Hand Lay-up Techniques For Reinforced
Composites). This is because if the time lapse between the lay-up and mixing the
resin is too long, the resin will hardened before it could reached the fiber. This can
produce a low quality composite as a final product. The hand lay-up process can be
done by using brush or even spray gun (American Composite Manufacturers
Association, 2004). From Figure 4, it can be seen that a roller is used to take out all
of the air bubbles from the laminate to ensure even resin deposited and no air bubbles
in the composite.
12
The curing part of the hand lay-up technique is done after the fibreglass
reinforcement and resin finished. The curing time for different composite may varied
according to the size, thickness and type of composite. The curing may be as fast as
two hours or it could even be cured overnight. Upon curing, the composite can be
trimmed according to the desired size and shapes (Beckwith, 2009) as shown in
Table 2.1.
Table 2.1: Machining composites – Trade to be considered
Source: W. Beckwith, 2009.
2.5 FINITE ELEMENT METHOD
2.5.1 Introduction
Finite element method (FEM) is a method that uses numerical to solve
integral or differential equation. A lot of physical problem has applied to this method