Crack Paths 2006

400mm

5

x h=10mm z 00mm

q0=850MPaq=q0(1-(x-e)2/c2)1/2 e c=6.0mm c Load movement o y

u=0

w=0

Symmetric planev=0

u=0

Leading crack tip (A) o

Trailing crack tip

m m

B

b/a=0a.49

b

0 0

a = 5 0 m m

b=24.5mm

x

y

A 3D semi-elliptical crack

(Friction coefficient between

v=0

P = 0.0 or 0.5).

fracture surfaces,

P==00.5 Figure 11. F E Mmodel and boundary condition (1/2 model).

26.3MPam26.3MPam 17.6MPam17.6MPam

-121-05050505

0 2 4 6 8 10 12 14 16 -121-05050505 e/c K

PP=0=.05

26.8MPam26.8MPam 12.2MPam12.2MPam

-8 -6 -4 -2 0 2 4 6 8

e/c

(a) KII at the leading edge of the major

(b) KIII at the edge of the minor axis of the

elliptical crack.

axis of the elliptical crack.

Figure 12. Variation of the KII at the leading edge of the major axis of the elliptical crack with

the aspect ratio b/a = 0.49 (point A) and KIII at the edge of the minor axis of the

elliptical crack with the aspect ratio b/a = 0.49 (point B).

C O N C L U S I O N S

(1) The crack in the reversed torsion of SAE52100initiated from several slender M n S

inclusions which are elongated in the longitudinal direction of a cylindrical specimen.

The cracks first propagated up to the size of 2a = 100 ~ 200 P m(which are almost

equal to the length of M n Sinclusion) in the longitudinal direction by ModeII, and

then branched by ModeI to the direction (~ ± 70.5 deg.) perpendicular to the local

maximumnormal stress (VTmax) at the crack tip.