Symmetric Branching of Mode II and Mixed-Mode Fatigue Crack Growth in a Stainless Steel

Symmetric branching was found in all fatigue experiments carried out in 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 loading was biaxial, sinusoidal along each axis and out-of-phase from a each other. Stress intensity factor calculations using finite element methods showed {Delta}K{sub II} was almost zero along each branch for all four branches so that all branches were Mode 1 cracks. The propagation of branched Mode 1 cracks in the initial Mode 2 damaged zone was faster than in their own Mode 1 zone created afterwards. The two dominantly branched cracks shielded the other small cracks appeared during the initiation of branching.