Fatigue Crack Paths 2003

(a)

(b)

Figure 13. (a)Fracture surface of the circumferentially cracked specimen, Wa =

132 M P a 'KIII=11.5

MPa¥m.(b) Formation mechanism of the

factory roof.

Figure 14. Fracture surface of the circumferentially cracked specimen, Wa=

132 MPa, 'KIII=11.5

MPa¥m.Manysmall semi-elliptical cracks

nucleated by modeIII ahead of the initial circumferential crack

tip prior to the formation of factory-roof.

Turning &

Polishing

(a)

(b)

(c)

Figure 15. Profiles of cracks under mode III loading,

MPa¥m, Wa=142

'KIII=13.6

MPa. (a) Slicing and polishing the mode III specimens Formation

mechanism of “factory-roof”. (b) Angle of branched cracks, crack depth

260Pm. (c) Shape of factory-roof crack, crack depth 530Pm.

13