developments in weld fatigue-j wong

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

Run Smart, Run Fast, Run Lean

2

Speaker Contact Info:

•� Jim Wong

–� [email protected]

–� 309-765-3891

John Deere - MTIC

One John Deere Place

Moline IL 61265


3

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


5


•� 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


6


•� 2005 – Establishment of GY2 FE Shell Model

Technique

–� Correlation to 3D-FE fine mesh solutions

–� Residual Stress Effects Included


7

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


8 © 2008 Grzegorz Glinka. All rights reserved.

�n

Load

F

�peak


�peak �nom

�nom


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


�peak

r

t

tp

C

�n �

V

H

�n

V

t C

�n �n

H


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


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!


x

2) y

�b2 =�n

2

t

�b2

�2pe

ak

1) y

�a1= �n

1

t

�b1

x

�1peak


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


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

)


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


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

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GY2 Approach for Fatigue Life

Prediction Using Shell Finite

Element Results



•� 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


c)

The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

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


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




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


Shell FE model

A -

A

B -

B

t

t y

x

Welded joint

h

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•� 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



6 m

m

28


��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




Range of application - reasonably designed weldments, (K.Iida and T. Uemura, ref. 11)

g =

h

�

r

t

l = hp

P P


Range of application - reasonably well designed weldments, (K.Iida and T. Uemura, ref. 11)

g =

h

�

r

t

l = hp

M M


Validated for : 0.02 � r/t �0.16 and 30o � � � 60o

, source [11]

t

r

t1= tp

�

hp

h

P P

y

x


where:

Validated for : 0.02 � r/t �0.16 and 30o � � � 60o, source [11]

t

r

t1= tp

�

hp

h

y

x

M M


r �

r


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 �


r �

f (r

)

r


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


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:


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


��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




Where:

Derived

for:


Derived for:

Where:

44







45

Residual stresses


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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.


47

Residual stress effect on mean stress


48







49

EXAMPLES


50

The T-Joint Weldment


51

Weld Geometry (all locations)

=tp hp

t

x

y


52

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)


53

�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


54

Solid Element Model Details

885,069 nodes

613,891 elements

2,700,000 dof


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



Comparison GY2 shell vs. 3D fine mesh FEA


57

T-joint


58

T-joint


59

Fatigue Analysis Results (�-N Method)


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







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.


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


70

Thank You


developments in weld fatigue-j wong

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