Cf. Qian et al., SYMMETRICAL BRANCHING OF MODE-II AND MIXED-MODE FATIGUE-CRACK GROWTH IN A STAINLESS-STEEL, Journal of engineering materials and technology, 118(3), 1996, pp. 356-361
symmetric branching was found in all fatigue experiments carried out i
n a cruciform specimen in which the initial crack was in the middle of
the specimen and at 45 deg with respect to the loading axes. The load
ing was biaxial, sinusoidal along each axis and out-of-phase from each
other. Stress intensity factor calculations using finite element meth
ods showed Delta K-II was almost each branch for all four branches so
that all branches were Mode I cracks. The propagation of branched Mode
I cracks in the initial Mode II damage zone was faster than in their
own Mode I zone created afterwards. The two dominantly branched cracks
shielded the other small cracks appeared during the initiation of bra
nching.