Fatigue Crack Paths 2003

10

10505

b a

bbb

1201AT

A M G 6

DB 9156 A T1

8

01419

6

A M G 6

= 45 E 0 o

45O

A M G 6

1 1 6 3 A T M

4

01419

= 0 = 0.5 K K

0 15 30 45 6 0

coordinate X [ m m ]

02

0

15 30 4 coordinate X [ m m ] 5

m m

icnritaiacl k wSt=ee8l 0Am m a/w=0.50 V V=0.040

68 w S=te8e0l A

= 0 ==2455

d

ac

a/w=0.540 V V=0.020

= 65 E EE 0 o 0 0 o o

E = 45 0 o

024

10

0 15 30 45 60 C O O R D I N AXT [EMM]

o

a /w=0.6 0

initial crack

30

75

0

10 20 C O O R D I N AXT[EM M ]

30

20

Figure 3. Theoretical (curves) and experimental (points) fatigue crack growth

trajectories for (a,b) eight-petal and (c,d) compact tension shear specimens

angle, . So, the situation in biaxially loaded eight-petal specimen for

K=0.5 and

0 E

0 E

0 E

0 E

=0q (or

K = 2 and =90q) concerns the state of unstable equilibrium, and the

irregularity in crack behavior is greater than for =65q. The zig-zag path of a

propagating crack may be explained by considering the advancement of a crack as

consisting of distinctive steps, where voids and other discontinuities of the material,

surrounding the crack tip, coalesce and create each kink for the crack. If the biaxial

stresses are tensile (K>0) then a crack is directionally unstable and, following a small