Crack Paths 2009

2050T851

2050T851

8090 T651

8090 T651

air

air

2024AT351

2024AT351

101-010-109 -8 7 6 3 4 5 6 7 8910 2022 T351

20

-6

2022 T351

10

2022 T851

2022 T851

2050T851

2050T851

vacuum

8090 T651

8090 T651

vacuum

-7

2024AT351

2024AT351

10

a)

b)

2022 T351

2022 T351

2022 T851

2022 T851

/cy l e )

/cy c l e )

-8

10

( m

( m

-9

d a / d N

10

d a / d N

-10

10

-11

10

1

10

∆K(MPa.m1/2)

∆Keff (MPa.m1/2)

Figure 4: Influence of ambient environment on fatigue crack propagation:

a) da/dN vs ∆K, and b) da/dN vs ∆Keff.

a

10µm

c

b

1 µ m

d

Figure 5: S E Mmicrographs of 2050 T851.

Figure 6: a) S E Mmicrographs

a) ambient air at ∆ K= 6 MPa.m1/2;

of 8090 T651in high vacuum;

b) (111) facet identified from

b) vacuum at ∆ K= 6 MPa.m1/2; c) Transition

triangular etch pits.

stage II to stage I-like at ∆ K= 5 MPa.m1/2;

d) stage I like at ∆ K= 4.5 MPa.m1/2

89