developments in weld fatigue-j wong
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1
Recent developments in fatigue of
welds
Professor Greg Glinka - University of Waterloo
Dr. Mohamad El-zein – John Deere
Jim Wong - John Deere
SAE FD&E - 15 Oct 2008
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Speaker Contact Info:
•� Jim Wong
–� WongJamesD@JohnDeere.com
–� 309-765-3891
John Deere - MTIC
One John Deere Place
Moline IL 61265
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Where are they now?
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Deere Weld Modeling History
•� 2000 - Investigation into using Shell FE Models
for use obtain local peak stresses for e-N fatigue
calculations
–� Evaluated both Nominal and Hot Spot Stress Methods
–� Kt’s were based on traditional definition of Nominal
stress
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Deere Weld Modeling History
•� 2003 - Investigation to determine Through-the-
Thickness stress distributions using Shell FE
–� Established method to calculate actual stress field
–� Kt library for various weld types created
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Deere Weld Modeling History
•� 2005 – Establishment of GY2 FE Shell Model
Technique
–� Correlation to 3D-FE fine mesh solutions
–� Residual Stress Effects Included
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Weld Life Check List
��Global Loads ��Material Properties
��Local Loads, Stresses or Strains ��Stress concentration Factors
��Peak stress at weld toe/critical points ��Through thickness stress distribution ��Residual Stresses
��Calculate Weld Life
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8 © 2008 Grzegorz Glinka. All rights reserved.
�n
Load
F
�peak
9 © 2008 Grzegorz Glinka. All rights reserved.
�peak �nom
�nom
10 © 2008 Grzegorz Glinka. All rights reserved.
A) remote (nominal) through thickness stress, B) the actual through-
thickness stress distribution in the weld toe cross section, C) linearized through-thickness stress distribution in the weld toe cross
section, D) the actual stress distribution in the plate surface, E) extrapolated (linearly) stress distribution in the plate surface
r
t
tp
D
B
A
�peak
�n
�hs
C
P
M
�
E
h h p
11 © 2008 Grzegorz Glinka. All rights reserved.
�peak
r
t
tp
C
�n �
V
H
�n
V
t C
�n �n
H
12 © 2008 Grzegorz Glinka. All rights reserved.
Shown are: the experimental definition and determination
of the hot spot stress, the actual through thickness stress
distribution and the hot spot stress resulting from the
linearization of the actual stress fields t
�hs
0.4t
1.0t
x
y
0
�peak The stress �xx in the plate
surface is believed to be linear in this region !
�xx(x)
Strain
gauges Courtesy: E. Niemi
13 © 2008 Grzegorz Glinka. All rights reserved.
a) A body with an angular notch subjected to multiple loading modes
and resulting through-the-thickness stress distribution, b) decomposition of the nominal (linear) stress distribution in the notch
cross section into the membrane and bending contribution
b
) �n1
T
�n2
�peak r
The stress concentration
factors, , and
are not constant and not
the same!
They depend on the
geometry and on the
stress ratio: �mn/ �b
n!
14 © 2008 Grzegorz Glinka. All rights reserved.
x
2) y
�b2 =�n
2
t
�b2
�2pe
ak
1) y
�a1= �n
1
t
�b1
x
�1peak
15 © 2008 Grzegorz Glinka. All rights reserved.
Stress concentration factors Kmt,hs and Kb
t,hs
DO NOT DEPEND on the stress ratio �mhs/ �
bhs
and they are constant for given geometry!!
a) Pure axial
load
b) Pure bending
load
y
�hsm
t x
�mpeak
F
M
x
b) y
�hsb
t
�bpeak
16 © 2008 Grzegorz Glinka. All rights reserved.
a) T-butt weldment and resulting through-the-thickness stress distribution,
b) decomposition of the nominal (linear) stress distribution in the weld toe plate cross section, c) the hot spot stress as a sum of the hot spot membrane
and bending stress, d) the actual peak stress as a sum of the stress concentration on the hot spot membrane and bending stress
c) d
)
The stress concentration factors and
depend only on the geometry and they
can be used for any stress ratio !!
a) y
�a
T
�b
x
�pe
ak b
)
17 © 2008 Grzegorz Glinka. All rights reserved.
a) Stress distribution in the critical cross section near the cover plate ending and the nominal or the hot spot stress �n (independent of length L ) and �hs
(independent of length L), b) Stress distribution in the critical plane near the ending of a vertical attachment (gusset) and the nominal or the hot spot stress �n (dependent on length L ) or �hs
(independent of length L)
- depends on L and is constant along the weld toe line
Independent of L but it changes along the weld toe
line
y
x
PP
�(x,y)
a)
L
t�peak
�h
s
y
x
PP�(x,
y)
b)
L
t
18 © 2008 Grzegorz Glinka. All rights reserved.
The advantage of using expression
lies in the fact that the membrane stress �hsm and the bending
stress �hsb can be determined by simple decomposition of the
linearized through-thickness stress field, �(x=0,y), which can be
directly obtained from the coarse mesh 3-D or shell Finite
Element (GY2) analysis. Thus the equation above provides the
link between the FE stress analysis data, �hsm and �hs
b, and the
peak stress, �peak, at the weld toe, necessary for the fatigue
analysis
19
GY2 Approach for Fatigue Life
Prediction Using Shell Finite
Element Results
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20 © 2008 Grzegorz Glinka. All rights reserved.
•� Multiaxial state of
stress at weld toe
•� One shear and two
normal stresses
•� Due to stress
concentration, �xx
is the largest
component –� Predominantly responsible
for fatigue damage
�zz
�xx
�xx
�zz
�zx �xz
21 © 2008 Grzegorz Glinka. All rights reserved.
c)
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tp
t
hp
h
middle plane
of the main plate
physical common plane
for the attachment and the main plate
Middle plane of the attachment a)
b)
x
z
y
0
(h+
t/2
)
(h+tp/2)
h/2 h/2
h
(h/2+tp/2)
(h/2
+t/
2) h/2 h/2
h/2
h/2
d) x
z
y
0
22
The GY-2 Model
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The image cannot be dis
tp
t
h
h
middle plane of
the main plate physical common
plane for the
attachment and the
main plate
Middle plane of the attachment
(h+
t/2)
(h+tp/2) h/2
h/2
h
(h/2+tp/2)
(h/2
+t/
2)
h/2 h/2 h/2
h/2
Element Nodes
Reference points where
stress is to be determined
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23 © 2008 Grzegorz Glinka. All rights reserved.
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doubler middle plane
main plate middle plane
tp
physical common plane for the doubler and the main plate
h
t
(tp/2
+ t
/2)
h
h/2
�
�
����
������
t/2 t/2
t/2
t/2
24 © 2008 Grzegorz Glinka. All rights reserved.
Shell FE model
A -
A
B -
B
t
t y
x
Welded joint
h
25
•� The FE formulation for shell elements gives top and bottom
stresses, �top, and �bottom
•� The stress distribution through the thickness is considered to
be linear
•� The membrane and bending stresses are obtained from
�top
�bottom
Shell element at midplane
Shell Element Model Details
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26 © 2008 Grzegorz Glinka. All rights reserved.
6 m
m
27 © 2008 Grzegorz Glinka. All rights reserved.
28
Weld Life Check List
��Global loads ��Material Properties
��Local loads, stresses or strains ��Stress concentration factors
��Peak stress at weld toe/critical points ��Through thickness stress distribution ��Residual stresses
��Calculate Weld Life
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29 © 2008 Grzegorz Glinka. All rights reserved.
Range of application - reasonably designed weldments, (K.Iida and T. Uemura, ref. 11)
g =
h
�
r
t
l = hp
P P
30 © 2008 Grzegorz Glinka. All rights reserved.
Range of application - reasonably well designed weldments, (K.Iida and T. Uemura, ref. 11)
g =
h
�
r
t
l = hp
M M
31 © 2008 Grzegorz Glinka. All rights reserved.
Validated for : 0.02 � r/t �0.16 and 30o � � � 60o
, source [11]
t
r
t1= tp
�
hp
h
P P
y
x
32 © 2008 Grzegorz Glinka. All rights reserved.
where:
Validated for : 0.02 � r/t �0.16 and 30o � � � 60o, source [11]
t
r
t1= tp
�
hp
h
y
x
M M
33 © 2008 Grzegorz Glinka. All rights reserved.
r �
r
34 © 2008 Grzegorz Glinka. All rights reserved.
Probability Density Function
Angle, � [deg]
f(�
)
0.0 200.0 40.0 80.0 120.0 160.0 0.0
0.05
0.01
0.02
0.03
0.04
MF-1
MF-2
MF-3 MF-4
MF-5
MF-5: μ=4.0084, �=0.2832
MF-4: μ=3.9669, �=0.4135
MF-3: μ=3.9496, �=0.2665
MF-2: μ=3.7854, �=0.4668
MF-1: μ=4.0789, �=0.1710
r �
35 © 2008 Grzegorz Glinka. All rights reserved.
r �
f (r
)
r
36 © 2008 Grzegorz Glinka. All rights reserved.
Probability Density Function – Log-normal
SCF, (Ktt)
f(K
tt)
0.0 9.0 1.8 3.6 5.4 7.2 0.00
1.20
0.24
0.48
0.72
0.96
MF-1
MF-2
MF-3
MF-4
MF-5
MF-5: MF-4: MF-3: MF-2: MF-1:
μ=0.8481, �=0.1770 μ=0.9602, �=0.1835 μ=0.7998, �=0.1635 μ=1.0180, �=0.2834 μ=0.9224, �=0.1978
37 © 2008 Grzegorz Glinka. All rights reserved.
Probability Density Function - Bending
SCF, (Ktb)
f(K
tb)
0.0 2.0 4.0 6.0 8.0 0.00
0.80
0.16
0.32
0.48
0.64
MF-1
MF-2
MF-3
MF-4 MF-5
MF-5:
MF-4:
MF-3:
MF-2:
MF-1:
38 © 2008 Grzegorz Glinka. All rights reserved.
Pro
bab
ilit
y
0.1 0.2 0.4 0.7 1 2 4 7 1
0 Weld toe radius, r
[mm]
0.01
0.02
0.04
0.08
0.10
0.06
0.15
0.20
0.25
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.99
�
Statistical distribution of weld toe radii measured on
similar weldments produced by three manufacturers
MQ2 – production line
MQ1 – R&D workshop MQ5 – University
laboratory
39
Weld Life Check List
��Global loads ��Material properties
��Local loads, stresses or strains ��Stress concentration factors
��Peak stress at weld toe/critical points ��Through thickness stress distribution ��Residual stresses
��Calculate Weld Life
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40 © 2008 Grzegorz Glinka. All rights reserved.
Where:
Derived
for:
41 © 2008 Grzegorz Glinka. All rights reserved.
Derived for:
Where:
42 © 2008 Grzegorz Glinka. All rights reserved.
43 © 2008 Grzegorz Glinka. All rights reserved.
44
Weld Life Check List
��Global Loads ��Material Properties
��Local Loads, Stresses or Strains ��Stress concentration Factors
��Peak stress at weld toe/critical points ��Through thickness stress distribution ��Residual Stresses
��Calculate Weld Life
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45
Residual stresses
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46
The residual stress can not be added linearly to the actual stresses at the
notch tip. However, the residual stress effect can be accounted for by adding it to the pseudo-elastic stress in the Neuber formula.
How to account for RS
In general residual stresses change the
notch tip mean stress rather than the amplitude.
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47
Residual stress effect on mean stress
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48
Weld Life Check List
��Global Loads ��Material Properties
��Local Loads, Stresses or Strains ��Stress concentration Factors
��Peak stress at weld toe/critical points ��Through thickness stress distribution ��Residual Stresses
��Calculate Weld Life
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49
EXAMPLES
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The T-Joint Weldment
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Weld Geometry (all locations)
=tp hp
t
x
y
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GY2 - Shell Element Model Details
19,197 nodes
18,858 elements
114,069 dof
Material:
A22H Steel (ASTM A500 Cold Formed
Steel for Structural Tubing)
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�top (MPa) �bottom
(MPa)
�m (MPa) �b (MPa) �hs (MPa)
Location 1 -7.14 2.19 -2.48 4.67 15.7
Location 2 -7.43 2.04 -2.69 4.74 16.3
Location 3 -5.20 -1.59 -3.39 1.81 10.9
Shell Element Model Summary
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Solid Element Model Details
885,069 nodes
613,891 elements
2,700,000 dof
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0.008” element size at
weld toe
55
�peak via Kt
(GY-2 with 1.5t weld)
�peak from 3-D FEA
Location 1 17.1 MPa 16.9 MPa
Location 2 17.4 MPa 17.4 MPa
Location 3 11.4 MPa 10.6 MPa
Comparison GY2 shell vs. 3D fine mesh FEA
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T-Joint stress distribution
© 2008 Grzegorz Glinka. All rights reserved.
57
T-joint
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58
T-joint
© 2008 Grzegorz Glinka. All rights reserved.
59
Fatigue Analysis Results (�-N Method)
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60
T-Joint experimental vs predicted life
61
T-Joint experimental vs predicted life
62
Gusset Weld
63
Gusset – Out of Plane Loading
64
Gusset –In Plane Loading
65
Square tube on plate
Overview of the experimental set-up
66
Fig. 41. Calculated total fatigue live based on the GY2 hot spot stress approach and the experimental fatigue data
using the JD material data; Welded tube-on-plate specimen (fully reversed lateral load of 21350 N)
Square tube on plate
67
Weld Life Check List
��Global Loads ��Material Properties
��Local Loads, Stresses or Strains ��Stress concentration Factors
��Peak stress at weld toe/critical points ��Through thickness stress distribution ��Residual Stresses
��Calculate Weld Life
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68
Conclusions
•� The GY-2 method provided an accurate
and moderately simple way to obtain the
peak stress for fatigue evaluations
•� The GY-2 method with a single set of
membrane and bending stress
concentration factors provided a good
representation for the through-thickness
stress field.
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69
Manufacturing Process Simulation:
•� Prediction of local mechanical properties and microstructures, residual
stresses and distortions to decrease manufacturing costs and improve
durability calculations.
•� Welding Simulations
•� Heat Treat Simulation
•� Castings
Structural Analysis
•� Consolidation of Fatigue calculations : Initiation and Propagation
Other Areas of Investigation
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70
Thank You
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