Consideration of the Residual Stress Relief in Fatigue ... · Fatigue testing of welded specimens...

Consideration of the Residual Stress Relief in Fatigue Assessment of Welded Components

I. Varfolomeev, D. Siegele, S. Moroz, M. Brand

Fraunhofer IWM, Freiburg, Germany

J. Baumgartner

Systemzuverlässigkeitund Maschinenakustik

Fraunhofer LBF, Darmstadt, Germany

ESIS TC1 Workshop „Structural Integrity of Weldments“, December 5-6, 2012, Freiburg

� Motivation

� Material, mechanical testing

Outline

� Fatigue testing of welded specimens

� Numerical weld simulation

� Modelling residual stress relief

� Test evaluation

� Conclusions

© Fraunhofer-Institut für Werkstoffmechanik IWM

2


� Straightforward, easy-to-apply procedure

� Approval in engineering community

� Basis – uniaxial S-N curves

IIW recommended practice

� Basis – uniaxial S-N curves

� Assessment in terms of nominal (normal or shear) stress,

structural hot spot stress, effective notch stress

� Simplified fatigue analysis approach for classified structural components

(FAT classes)


3


IIW based assessment

S-N curves for steels, normal stress, constant amplitude loading


4


IIW recommended practice

Open issues, limitations

� Validation � availability of experimental data for different types of joints

� Treatment of joints which are not described by available models

� Consideration of

� specific notch geometry

� welding distortion

� multiaxial stress state

� redistribution of residual stress due to external loading

� Transferability of test results to other geometries


5


� Transferability of test results to other geometries

Topics partly addressed in this study

Material S460NL (fine grained steel) – static tests

True stress-strain curves

1200

400

600

800

1000

wah

re S

pa

nn

un

g [

MPa] TT2Z01 RT

TT2Z02 RTTT2Z03 RTTT2Z04 RTTT2Z06 100°CTT2Z07 100°CTT2Z09 200°CTT2Z10 200°CTT2Z12 300°CTT2Z13 300°CTT2Z14 350°CTT2Z15 400°CTT2Z16 400°CTT2Z30 450°C

Tru

e s

tre

ss [M

Pa

]


6


0

200

0.0 0.2 0.4 0.6 0.8 1.0

wahre Dehnung [mm/mm]

TT2Z30 450°CTT2Z19 500°CTT2Z18 500°CTT2Z17 560°C

True strain [mm/mm]

Material S460NL – cyclic tests, RT

LCF tests on base metal

R = -1 R = 0 R = 0,5Rε = -1 Rε = 0 Rε = 0,5

Str

ess, M

Pa

Str

ess, M

Pa

Str

ess, M

Pa


7


Time, sTime, s Time, s

Cyclic plasticity model – parameter fit

Chaboche (1)

0

200

400

600

Span

nun

g [

MPa]

0.2% Versuch

0.4% Versuch

0

200

400

600

Spannung [

MPa]

0.2% Versuch

0.4% Versuch

0

200

400

600

Spannung [

MPa]

0.2% Versuch

0.4% Versuch

R = -1 R = 0 R = 0,5

-600

-400

-200

-1.0 -0.5 0.0 0.5 1.0 1.5

Dehnung [%]

Span

nun

g

0.4% Versuch

0.6% Versuch

1.0% Versuch

0.2% Anpassung

0.4% Anpassung

0.6% Anpassung

1.0% Anpassung

-600

-400

-200

0.0 0.5 1.0 1.5 2.0 2.5

Dehnung [%]

Spannung

0.4% Versuch

0.6% Versuch

1.0% Versuch

0.2% Anpassung

0.4% Anpassung

0.6% Anpassung

1.0% Anpassung

-600

-400

-200

0.0 1.0 2.0 3.0 4.0 5.0

Dehnung [%]

Spannung

0.4% Versuch

0.6% Versuch

1.0% Versuch

0.2% Anpassung

0.4% Anpassung

0.6% Anpassung

1.0% Anpassung


8


Specimen geometry and test setup

Plastic pre-stressing under compressive loading


9


Load vs. displacement records

Plastic pre-stressing

24

8

12

16

20

24

Kra

ft, F

[kN

]

Probe TT4KU01

Probe TT4KU02

Probe TT4KU03

Probe TT4KU05

Probe TT4KU13

Probe TT4KU25

Probe TT4KU30

Probe TT4KU33

Probe TT4KU36

Probe TT4KU38

Lo

ad

, kN


10


0

4

0.00 0.02 0.04 0.06 0.08 0.10 0.12

Schrumpf, ∆L0 [mm]

Probe TT4KU38

Probe TT4KU39

Probe TT4KU20

Probe TT4KU29L0 = 10 mm

Length reduction, mm

Test vs. FEA results

Material model after Chaboche (1)


24

8

12

16

20

24

Kra

ft, F

[kN

]

Probe TT4KU01

Probe TT4KU02

Probe TT4KU03

Probe TT4KU05

Probe TT4KU13

Probe TT4KU25

Probe TT4KU30

Probe TT4KU33

Probe TT4KU36

Probe TT4KU38

Probe TT4KU39

Lo

ad

, kN


11


0

4

0.00 0.02 0.04 0.06 0.08 0.10 0.12


Probe TT4KU39

Probe TT4KU20

Probe TT4KU29

Chaboche (1)


Further cyclic plasticity models

0

200

400

600

Spannung [M

Pa]

0.2% Versuch

0

200

400

600

Span

nung [

MPa]

0

200

400

600

Spannung [M

Pa]

R = -1

Chaboche (2)

-600

-400

-200

-1.0 -0.5 0.0 0.5 1.0 1.5

Dehnung [%]

Spannung

0.2% Versuch

0.4% Versuch

0.6% Versuch

1.0% Versuch

0.2% Abaqus

0.4% Abaqus

0.6% Abaqus

1.0% Abaqus

-600

-400

-200

0.0 0.5 1.0 1.5 2.0 2.5

Dehnung [%]

Span

nung

-600

-400

-200

0.0 1.0 2.0 3.0 4.0 5.0

Dehnung [%]

Spannung

200

400

600

[M

Pa] 200

400

600

[M

Pa]200

400

600

[M

Pa]

R = -1

R = 0 R = 0,5

Ellyin-Xia


12


-600

-400

-200

0

200

0.0 0.5 1.0 1.5 2.0 2.5

Dehnung [%]

Spannung [M

Pa]

-600

-400

-200

0

0.0 1.0 2.0 3.0 4.0 5.0

Dehnung [%]

Spannung [M

Pa]

-600

-400

-200

0

-1.0 -0.5 0.0 0.5 1.0 1.5

Dehnung [%]

Spannung [M

Pa]

0.2% Versuch

0.4% Versuch

0.6% Versuch

1.0% Versuch

0.2% Anpassung

0.4% Anpassung

0.6% Anpassung

1.0% Anpassung R = 0 R = 0,5

Test vs. FEA results

Material model after Chaboche (2) and Ellyin-Xia (EXM)


24

8

12

16

20

24

Kra

ft, F

[kN

]

Probe TT4KU01

Probe TT4KU02

Probe TT4KU03

Probe TT4KU05

Probe TT4KU13

Probe TT4KU25

Probe TT4KU30

Probe TT4KU33

Probe TT4KU36

Probe TT4KU38

Probe TT4KU39

Probe TT4KU20

Lo

ad

, kN


13


0

4

0.00 0.02 0.04 0.06 0.08 0.10 0.12


Probe TT4KU20

Probe TT4KU29

Chaboche (2)

Ellyin-Xia


4PB specimen for S-N curve testing

Objectives

� Perform tests in resonant testing machine

� Variable stress ratio (R)

� Specimens with and without plastic pre-straining


14


Crack patterns in bend specimens

Cracks initiate at the specimen surface, both in the middle and at the edges


15


the edges

Moderate data scatter

Exceptions: non-metallic inclusions and fretting

S-N curve, R = -1

410

430

Str

ess

am

pli

tud

e [

MPa]

no pre-st ressing, R = -1

irregular tests

350

370

390

Str

ess

am

pli

tud

e [

MPa]

f ret t ing

non-metallic inclusions


16


330

1.E+04 1.E+05 1.E+06 1.E+07

Nf [LW]

f ret t ing

Nf, cycles

S-N data for bend specimens

420

430

380

390

400

410

420

Str

ess

am

pli

tud

e [

MPa

]

no pre-st ressing, R = -1

no pre-st ressing, R = -0,76



plast ic pre-st ressing, R = -1

plast ic pre-st ressing, R = -0,76

plast ic pre-st ressing, R = -0,61


17


360

370

1.E+04 1.E+05 1.E+06

Str

ess

am

pli

tud

e [

MPa

]

Nf [LW]Nf, cycles

Damage parameters

Smith, Watson, Topper

� Take into account effects due to mean stress and stress triaxiality

� Allow for comparison of fatigue curves for different specimen geometries and/or loading conditions

( ) ( )NNcbbf

222

2

1 εσσε

σ ′′+′

=∆ +

Smith, Watson, Topper

Fatemi, Socie ( ) ( ) γγ γτ

σ

σγ c

ff

b

f

fnNN

Gk 221

2 0

max, ′+′

=

+

∆

( ) ( )

EP

NNE

nSWT

cb

fff

b

f

f

n

2

222

1max,

21max,

εσ

εσσε

σ

∆=

′′+′

=∆ +


18


Further parameters: Findly; Brown and Miller; Liu; Chu, Conle und Bonnen; …

DP-N data for bend specimens (DP = Damage

Parameter)

0.0028

0.003

keine Vorbelastung, R = -1

keine Vorbelastung, R = -0.76



stat . Vorbelastung, R = -1

stat . Vorbelastung, R = -0.76


[-]

375

400

425

450Chaboche; Element 8





stat . Vorbelastung, R = -1



[M

Pa]

105

106

0.0024

0.0026

PFS

[-]

Schwingspielzahl

105

106

300

325

350

PSW

T [

MPa]

Schwingspielzahl

260

280

300





stat. Vorbelastung, R = -1

stat. Vorbelastung, R = -0.76


[M

Pa]

0.7

0.8

0.9

1





stat. Vorbelastung, R = -1



[M

Pa]

Fatemi, Socie Smith, Watson, Topper


19


105

106

200

220

240

PFI

N [

MPa]

Schwingspielzahl

105

106

0.5

0.6

0.7

PC

CB [

MPa]

SchwingspielzahlNf, cycles Nf, cycles

Findley Chu, Conle, Bonnen

Welded specimens

Longitudinal stiffenert = 12 mm, 2W = 60 mm, L = 500 mm

D

3

2 2

1


20


W

F

1

2 2

3

Welded specimens – test preparation

Str

ain

due to c

lam

pin

g, µ

m/m


21


Angle deflection, °

Str

ain

due to c

lam

pin

g, µ

m/m

Welded specimens – S-N curves

, M

Pa

, M

Pa

Specimens as-welded

Load a

mplit

ude F

a,

kN

Nom

inal str

ess a

mplit

ude σ

n,a,

MP

a

Load a

mplit

ude F

a,

kN

Nom

inal str

ess a

mplit

ude σ

n,a,

MP

a

crack initiation

failure

crack initiation

failure


22


N, cyclesN, cycles

Crack propagation makes considerable contribution to fatigue life

Welded specimens – S-N curves

Specimens post heat-treated

MP

a

MP

a

Load a

mplit

ude F

a,

kN

Nom

inal str

ess a

mplit

ude σ

n,a,

MP

a

Load a

mplit

ude F

a,

kN

Nom

inal str

ess a

mplit

ude σ

n,a,

MP

a

crack initiation

failure

crack initiation

failure


23


N, cyclesN, cycles

WRS analyses for longitudinal stiffener

� Welding simulation using SYSWELD

� Transfer of results to ABAQUS

� Stresses

� Plastic strains

� Displacements

� Equilibrium iteration in ABAQUS

� Simulation of clamping of the specimen

� Simulation of cyclic loading � relief of residual stresses

� Plasticity model according to Chaboche (2)

200

400

600

[M

Pa]

R = -1


24


-600

-400

-200

0

-1.0 -0.5 0.0 0.5 1.0 1.5

Dehnung [%]

Spannung [M

Pa]

0.2% Versuch

0.4% Versuch

0.6% Versuch

1.0% Versuch

0.2% Abaqus

0.4% Abaqus

0.6% Abaqus

1.0% Abaqus

Axial stresses

a) as welded b) after clamping

c) Fmax = 130 kN d) Fmin = 0


25


Longitudinal stiffener: WRS relief

∆∆∆∆F = 130 kN, R = -1 ∆∆∆∆F = 130 kN, R = 0

500

600Gleichgewicht

Einspannung500

600Gleichgewilcht

Einspannung

as welded

clampingas welded

clamping

0

100

200

300

400

500

Sp

an

nu

ng

, σ

11 [

MP

a]

Einspannung

Fmax=65 kN

Fmin=-65 kN

F=0

0

100

200

300

400

500

Sp

an

nu

ng

, σ

11 [

MP

a]

Einspannung

Fmax=130 kN

Fmin=0

Str

ess σ

11

[MP

a]

Str

ess σ

11

[MP

a]

clamping clamping


26


-100

0

0 10 20 30

Abstand vom Nahtübergang [mm]

-100

0

0 10 20 30

Abstand vom Nahtübergang [mm]Distance to weld toe [mm] Distance to weld toe [mm]

Longitudinal stiffener: WRS relief

400

500

WR

S a

xia

l co

mp

on

en

t, M

Pa

Fmax = 60 kN

-200

-100

0

100

200

300

400

WR

S a

xia

l co

mp

on

en

t, M

Pa R = -1

R = 0 Fmin = -60 kN

F = 0


27


-200

0 100 200 300 400 500

Nominal st ress amplitude, MPa

WRS distribution along the surface

500

700mit Umwandlungen, sigma 11

mit Umwandlungen, sigma 33

mit Umwandlungen, sigma 22

-300

-100

100

300

-50 -40 -30 -20 -10 0 10

Span

nu

ngen

[M

Pa]


28


-500

-300

abgewickelte Länge [mm]

Gurtblech

WRS measurements (X-ray)

300

400

500

nicht geglüht P39 nicht geglüht P48σ11 between 320 and 400 MPa at weld toe (matching with simulation)

-100

0

100

200

300Omega-Mode längs zur Naht

PSI-Mode quer zur Naht

σ11

σ11

σ11

σ11

σ22

σ22

σ22

σ22


29


-300

-200

WEZ 8 mm WEZ 8 mm

σ11 negative in 8 mm distance (surface treatment)

WRS redistribution under cyclic loading


30


Parameter study on butt welded plates

Plate thickness 10 mm, 2 weld passes

Plate thickness 25 mm, 16 weld passes


31


Correlation of FEA results with FAT classes

Analysis approach

� Reference case – longitudinal stiffener

� Calculate fatigue damage parameters according to FAT 71 (see table) � construct fatigue curve for LS

� FEA for plates � merge fatigue curves for different joints

FATFATFATFAT LLLLoad cyclesoad cyclesoad cyclesoad cycles, LW, LW, LW, LW

5×105×105×105×104444 3×103×103×103×105555 2×102×102×102×106666

71 215 133 71

100 303 177 100

125 333 235 125

FAT 71 FAT 71FAT 125


32


FAT 71 FAT 71FAT 125


-3

4x10-3

Reference FAT 71

10-4

10-3

PFS

[-]

Längssteife - R=0 mit Einspannen (FAT 71)

Längssteife - R=-1 mit Einspannen (FAT 71)

Platte t=10 mm - R=0 quer zu Naht (FAT 71)

Platte t=10 mm - R=-1 quer zu Naht (FAT 71)

Platte t=10 mm - R=0 längs zu Naht (FAT 125)

Platte t=10 mm - R=-1 längs zu Naht (FAT 125)

FAT 71 � adjust

FAT 125 - OK


33


104

105

106

107

Schwingspielzahl


Reference FAT 71

-3

4x10-3

FAT 100 (adjusted)

FAT 125 - OK

10-4

10-3

PFS

[-] Längssteife - R=0 ohne Einspannen (FAT 71)

Längssteife - R=-1 ohne Einspannen (FAT 71)

Längssteife - R=0 mit Einspannen (FAT 71)

Längssteife - R=-1 mit Einspannen (FAT 71)









34


104

105

106

107

Schwingspielzahl



Estimating crack propagation

Beach marks due to variable amplitude loadingCrack propagation phase ~700,000 cycles


35


FCG calculations

Analytical model

� Stress gradient in both thickness and width directions

� Stress input

� Stabilized WRS distribution

� Stress distribution due to external loading

Initial crack a×2c = 0.2×1 mm²� Initial crack a×2c = 0.2×1 mm²

� Final crack depth 12 mm


36


Fatigue crack growth rates for steel S460

Data by M. Vormwald


37


FCG curves for steel S460

Fit according to BS 7910

1.E-02R = -1

1.E-05

1.E-04

1.E-03

da/d

N, m

m/c

ycl

e

R = -0.4

R = 0

R = 0.4

R = 0.7

BS 7910, steels in air, R ≥ 0.5, 50%

BS 7910, steels in air, R ≥ 0.5, 98%


38


1.E-07

1.E-06

1 10 100

∆K, MPa√m

FCG curves for steel S460

Fit by Mettu-Forman equation (NASGRO)

1.E-02R = -1

1.E-05

1.E-04

1.E-03

da/d

N, m

m/c

ycl

e

R = -1

R = -0.4

R = 0

R = 0.4

R = 0.7

NASGRO, R = -1

NASGRO, R = -0.4

NASGRO, R = 0

NASGRO, R = 0.4

NASGRO, R = 0.7


39


1.E-07

1.E-06

1 10 100

∆K, MPa√m

Results of FCG calculations, R = 0

Fmax, kN σσσσn,max, MPa N, cycles

160 223 74,000

120 167 138,000

80 111 400,000

40 56 3,314,000

80

no WRS relief considered

111 361,000

Load a

mplit

ude F

a,

kN

Nom

inal str

ess a

mplit

ude σ

n,a,

MP

a

PredictedS-N failure curve


40


N, cycles

Load a

mplit

ude F

Nom

inal str

ess a

mplit

ude

� Numerical analysis of welding residual stresses and consideration of their

redistribution under in-service loading provide a rational way for transferring

S-N data obtained on particular welded joints to another geometries

� When doing so, damage parameters can be applied to derive correlation between

different geometries and loading conditions (including stress triaxiality and mean

Conclusions

different geometries and loading conditions (including stress triaxiality and mean

stress effects)

� Parameters according to Fatemi and Socie and Smith, Watson and Topper seem to be

most appropriate damage parameters for the material considered

� For the longitudinal stiffener, crack propagation makes a major contribution to fatigue

life

� Given S-N curve at crack initiation, the fracture mechanics approach reasonably

predicts the S-N curve at failure, and vice versa


41


predicts the S-N curve at failure, and vice versa

� No significant effect of the WRS relief on fatigue crack growth rates in the stiffener

was observed. This result may be due to specific geometry (small hot spot at the

notch root) and should not be generalised

Acknowledgements

IGF Project No. 15.913 N / DVS-Nr. 09.049 funded by „Forschungsvereinigung funded by „Forschungsvereinigung Schweißen und verwandte Verfahren e.V.

des DVS“, Aachener Str. 172, 40223 Düsseldorf


42


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Consideration of the Residual Stress Relief in Fatigue ... · Fatigue testing of welded specimens...

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