the effects of residual tensile stresses induced by cold ...€¦ · the effects of residual...

The Effects of Residual Tensile Stresses Induced by Cold-Working a Fastener Hole

A. Brot and C. MatiasEngineering Division

Israel Aerospace Industries

Presented to the:USAF Aircraft Structural Integrity Program (ASIP)

ConferencePalm Springs, CA

4 December 2007

ASIP 2007, Palm Springs, CA Unclassified

2

Photoelastic Measurements of the Stress Field at a Cold-Worked Hole (provided by Fatigue Technology Inc.)


3

Crack Growth from a Notched Edge towards a Cold-Worked Fastener Hole for 7475-T7351 Aluminum Alloy(detail was cut-away from a component test specimen)

10mm Radius Edge

Cold-Worked Fastener Hole


4

Test Specimen Used to Measure Residual Stresses Induced by Cold-Working (10mm notch radius)

Fastener Hole


5

Measured Stress Distribution along Edge of Notch

Cold-Work Residual Stress Along Edge With Radius 10mm; Opposite of c'sink side; Hole #2

-5

0

5

10

15

20

25

30

-2 -1 0 1 2 3 4 5 6 7 8 9 10X Coordinate [mm]

Res

idua

l Stre

ss [k

si] C W Stage

C'Sink Stage

X = 0X

Cold-Work Residual Stress Along Edge With Radius 10mm; C'sink side; Hole #2

-5

0

5

10

15

20

25

30

-2 -1 0 1 2 3 4 5 6 7 8 9 10X Coordinate [mm]

Res

idua

l Stre

ss [k

si]

C W StageC'Sink Stage

X = 0X

Cold-Work Residual Stress Along Edge With Radius 30mm; Opposite of c'sink side; Hole #2

-5

0

5

10

15

20

25

30

-2 0 2 4 6 8 10 12 14 16 18 20 22X Coordinate [mm]

Res

idua

l Stre

ss


X = 0X

Cold-Work Residual Stress Along Edge With Radius 30mm; C'sink side; Hole #2

-5

0

5

10

15

20

25

30

-2 0 2 4 6 8 10 12 14 16 18 20 22X Coordinate [mm]

Res

idua

l Stre

ss


X = 0X


6

Stress Field around a Cold-Worked Hole near an Edge (e/D = 1.95) showing a residual stress of about 31 ksi.

Elastic-plastic (ABAQUS) FEM, using quadratic reduced integration, courtesy of Fatigue Technology Inc.

ABAQUS FEM mesh


7Test Results for the 30mm Radius Coupon with Cold-

Worked and Countersunk Holes

• Failure of a 30mm radius test coupon under 20 ksi (R = 0.05) loading.

• Failure originated from the outer diameter of the countersunk holes.

• Mean life of first failure(3 coupons, 12 holes): 186,000 cycles.

30mm Radius


8Test Results for the 10mm Radius Coupon with Cold-

Worked and Countersunk Holes

• Failure of a 10mm radius test coupon under 20 ksi (R = 0.05) loading.

• Failure originated from the 10mm radius edge, adjacent to the cold-worked hole.

• Minimum life (1 coupon, 4 holes): 57,000 cycles.

10 mm Radius

Origin


9

Symmetryplane

Symmetryplane

P-level DOF

Total Potential Energy

Convergence Rate

% Error

1 119 1.230594E+03 0 31.35

2 342 1.131074E+03 1.11 9.72

3 579 1.125535E+03 0.7 6.71

4 920 1.121601E+03 1.63 3.15

5 1365 1.120756E+03 1.81 1.54

6 1914 1.120553E+03 2.11 0.76

7 2567 1.120506E+03 2.23 0.39

8 3324 1.120494E+03 2.23 0.22

52 Elements, p = 8, nonlinear solution

StressCheck (ver. 7.1) Analysis of Cold-Worked Specimen

Quarter Model


10

Residual Stress Distribution for

e/D = 2.78

External stress = 20 ksi

Produced by StressCheck ver 7.1, (Courtesy of ESRD)

S1 stress along the curved edge (psi)

Mandrel removal

Remote load T = 20 ksi

10 mm Radius

[inch]


11

Comparison of Measured Stresses and those Calculated by the StressCheck (ver. 7.1) FEM

Notch stresses after cold-working (no external loading)

Notch stresses after application of 20 ksi stress

Cold-Work Residual Stress Along Edge With 10mm Radius; e/d = 2.78; CW Expansion = 3.89%

-2

0

2

4

6

8

10

12

14

16

18

20

-2 -1 0 1 2 3 4 5 6 7 8 9 10

X Coordinate [mm]

Res

idua

l Str

ess

[ksi

]

SG measurements

STRESSCHECKFEM Analysis

X = 0X

20ksi Remote Loading + Cold-Work Residual Stresses Along Edge With 10mm Radius; e/d = 2.78; CW Exp. = 3.89%

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

-2 -1 0 1 2 3 4 5 6 7 8 9 10

X Coordinate [mm]

Res

idua

l Str

ess

[ksi

]

SG measurements

STRESSCHECKFEM Analysis

X = 0X


12

Residual Stress Distribution for

e/D = 2.10

External Stress = 20 ksi

Produced by StressCheck ver 7.1, (Courtesy of ESRD)

S1 stress along the curved edge (psi)

Mandrel removal

Remote load T = 20 ksi

10 mm Radius

[inch]


13

Photoelastic Measurements of Residual Stresses at the Edge Resulting From Cold-Working

(performed by Vishay Israel Ltd.)


14Measured and Calculated Residual Stresses at the

Edge, Resulting From Cold-Working

0

5

10

15

20

25

30

35

1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 2.80 2.90

Edge distance / Starting hole Diameter

Res

idua

l Str

ess

[ksi

]R=30mm; 3.89%

R=10mm; 3.89%Straight edge 4.26%

R=10mm; 3.1%R=30mm; 3.1%

Abaqus FEM analysis for straight edge 4.26%STRESSCHECK FEM analysis for R=10mm 3.89%


15

Superimposing of Notch Stresses with the Residual Stresses

e

d

Cold-workedhole

Residual Stresses

Notch stress due to external loading: σnotch = σ x Kt

σ

σ

σtotal = σ x Kt + σresidual


16

Fatigue Analysis Results for 7075-T7351 Aluminum alloy:(superimposing notch stresses (R = 0) with residual stresses)

20

25

30

35

40

45

50

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07Mean Fatigue Life (cycles)

Max

imum

Not

ch C

yclic

Str

ess

[R=0

] (ks

i)Residual Stress: 0 ksi

Residual Stress: 10 ksi



30mm radius, e/D = 2.66

Mean Test Fatigue Life > 186,000 cycles

(failed at CW hole)


17


20

25

30

35

40

45

50


Max

imum

Not

ch C

yclic

Str

ess

[R=0

] (ks







(failed at CW hole)


Test Fatigue Life = 57,000 cycles


18


20

25

30

35

40

45

50


Max

imum

Not

ch C

yclic

Str

ess

[R=0

] (ks







(failed at CW hole)





19


20

25

30

35

40

45

50


Max

imum

Not

ch C

yclic

Str

ess

[R=0

] (ks







(failed at CW hole)




No notch, e/D = 2.10


20

SUMMARY AND CONCLUSIONS

1. Testing and analysis confirm that high tensile residual stresses can exist at an edge near a cold-worked hole.

2. These induced residual stresses are a function of:a. edge-distance to hole diameter ratio

b. level of mandrel interference

c. whether the fastener hole was final reamed and countersunk

d. fit of the fastener that is installed in the hole


21

SUMMARY AND CONCLUSIONS

3. When these residual stresses are combined with high cyclic notch stresses that arise from external loading, the fatigue life at the edge can be drastically reduced. This should be accounted for in the design of details near a cold-worked hole.

4. Additional analysis and testing is needed to further quantify these effects.

[To receive a copy of the written paper, please contact me at [email protected]]


22

ACKNOWLEDGEMENT

• The authors would like to thank Len Reid, Vice-President R&D at Fatigue Technology Inc., for his assistance and suggestions in studying this phenomenon and for Tom Poast for performing the elastic-plastic (ABAQUS) finite-element analyses.

• The authors would also like to thank Dr. Ricardo Actis and Dr. Sebastian Nervi of ESRD Inc., for performing the elastic-plastic (StressCheck ver 7.1)finite-element analyses.

the effects of residual tensile stresses induced by cold ...€¦ · the effects of residual...

Documents