The Effects of Residual Tensile Stresses Induced by Cold-Working a Fastener Hole A. Brot and C. Matias Engineering Division Israel Aerospace Industries Presented to the: USAF Aircraft Structural Integrity Program (ASIP) Conference Palm Springs, CA 4 December 2007
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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
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Photoelastic Measurements of the Stress Field at a Cold-Worked Hole (provided by Fatigue Technology Inc.)
ASIP 2007, Palm Springs, CA Unclassified
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
ASIP 2007, Palm Springs, CA Unclassified
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Test Specimen Used to Measure Residual Stresses Induced by Cold-Working (10mm notch radius)
Fastener Hole
ASIP 2007, Palm Springs, CA Unclassified
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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
Abaqus FEM analysis for straight edge 4.26%STRESSCHECK FEM analysis for R=10mm 3.89%
ASIP 2007, Palm Springs, CA Unclassified
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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
ASIP 2007, Palm Springs, CA Unclassified
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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
Residual Stress: 20 ksi
Residual Stress: 30 ksi
30mm radius, e/D = 2.66
Mean Test Fatigue Life > 186,000 cycles
(failed at CW hole)
ASIP 2007, Palm Springs, CA Unclassified
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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
Residual Stress: 20 ksi
Residual Stress: 30 ksi
30mm radius, e/D = 2.66
Mean Test Fatigue Life > 186,000 cycles
(failed at CW hole)
10mm radius, e/D = 2.78
Test Fatigue Life = 57,000 cycles
ASIP 2007, Palm Springs, CA Unclassified
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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
Residual Stress: 20 ksi
Residual Stress: 30 ksi
30mm radius, e/D = 2.66
Mean Test Fatigue Life > 186,000 cycles
(failed at CW hole)
10mm radius, e/D = 2.78
Test Fatigue Life = 57,000 cycles
10mm radius, e/D = 2.10
ASIP 2007, Palm Springs, CA Unclassified
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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
Residual Stress: 20 ksi
Residual Stress: 30 ksi
30mm radius, e/D = 2.66
Mean Test Fatigue Life > 186,000 cycles
(failed at CW hole)
10mm radius, e/D = 2.78
Test Fatigue Life = 57,000 cycles
10mm radius, e/D = 2.10
No notch, e/D = 2.10
ASIP 2007, Palm Springs, CA Unclassified
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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
ASIP 2007, Palm Springs, CA Unclassified
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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]]
ASIP 2007, Palm Springs, CA Unclassified
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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.