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ADMIRE Athens meeting, June 20-21, 2002 1

THE INFLUENCE OF COLD-WORKON THE STRESS INTENSITY FACTOR

OF CRACKED HOLESAND PIN LOADED JOINTS

Silvestre T Pinho, Helder B M Martins,Pedro P Camanho, Paulo M S T de Castro

IDMEC - Porto, Portugal


2/22


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to develop a simplified procedure to relate holeexpansion (internal pressure / mandrel interference) of

an infinite isotropic plate, with the residual stress fieldand plastic zone

to assess the reduction of Kresulting from the cold-work process, in both open and riveted holes.

objectives


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-110

-90

-70

-50

-30

-10

10

10 12 14 16 18 20 22 24 26 28 30

r [mm]

MPa]

Semi-analytical Solution

Numerical Solution

rr

semi-analytical and numerical

residual stress fields (von Mises)


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-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7

r/ri

y

von Mises

Tresca

rr

residual stresses

obtained using von Misesand Tresca yield criteria


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plate with open hole

a

ri


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-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

r/ri

y

Residual c ircumferencial stress

Stress due to uniform remote tensile load

Resulting stress

stress field due to cold-workand remote loading


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2.5

3

3.5

4

4.5

5

5.5

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85

Elastic-perfectly plastic material

Alclad alloy

p

3 3/ 10 10ir

relationship between appliedpressure and radial interpenetration

central hole in infinite plate


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1

1.05

1.1

1.15

1.2

1.25

1.3

0.55 0.6 0.65 0.7 0.75 0.8 0.85


Alclad alloy

mesh size

(semi-analytical)

(finite element)

p

cr

plastic/elastic interface coordinateas a function of the pressure applied;

von Mises yield criterion;central hole in infinite plate


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0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 1.1 1.2 1.3 1.4 1.5

dimension of the plastically deformed region / hole radius

y

a/ri=1.00

a/ri=1.05

a/ri=1.10

a/ri=1.15

a

ri

remote stress requiredto open two symmetrically located

cracks in a cold-worked hole


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2024 Alclad

uniaxial stress-strain relations


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14

15

16

17

18

19

20

21

22

23

24

12 12.5 13 13.5 14 14.5 15 15.5 16 16.5

a (mm)

Alcalad Al 2924-T3


No cold-work

Case 1

Case 2

Case 3

MPa mK

285MPay

100MPat

a

ri10mm

ir

Kas a function of crack lengthand cold-working

Alclad Al 2024-T3


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a

ri

riveted joint


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comparison between Ksolutionsfor a plate with a riveted hole

2.4

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

2.85

2.9

1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65a/r

K/K0

rigid pin

Ref. [24]

a

ri


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cosine and calculated distributionsof radial contact stress

0

2

4

6

8

10

12

14

0 15 30 45 60 75 90

a ( )

s rr/ s o

rigid pin

Ref. [24]


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7.045E-4

1.409E-3

2.113E-3

2.818E-3

equivalent plastic straindue to cold-work


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yystress gradientcracked cold-worked pin-load joint


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yystress gradient

cracked cold-worked pin-load jointdetail


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Kas a function of crack lengthand cold-work

111

112

113

114

115

116

117

118

119

12 12.5 13 13.5 14 14.5 15 15.5

Elastic-perfectly plastic m aterial

Alclad Al 2924-T3

a (mm)

Case 3

Case 2

Case 1

No cold-work

MPa mK

a

ri

1mmu Al 2024-T3


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analytical and semi-analytical solutions are derivedfor the characterization of the residual stress fieldand plastic zone sizes of cold-worked holes forelastic-perfectly plastic materials

the cold-working process is shown to reduce Kfordifferent dimensions of plastically deformed regions,and for different crack lengths, for both a remotely

loaded plate containing an open hole, and for ariveted joint.

conclusions I


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the reduction of stress intensity factor value for thecracked open hole problem was found to be greater

than the Kvalue reduction for the pin-loaded joint.This implies that claims of fatigue enhancementsolely based upon the performance of open holespecimens may be optimistic in actual connections

conclusions II

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