SYMMETRICAL BRANCHING OF MODE-II AND MIXED-MODE FATIGUE-CRACK GROWTH IN A STAINLESS-STEEL

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.