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

Abstract

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 each other. Stress intensity factor calculations using finite element methods showed ΔKII was almost zero along 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 damaged 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 branching.

Experimental study of I + III mixed mode fatigue crack transformation propagation

“…Tong et al 12 studied fatigue threshold behaviour under Mode III and in‐phase mixed Mode III and Mode I loading conditions in a 3.5%NiCrMoV steel, using V‐notched and pre‐cracked cylindrical bar specimens at load ratios R = 0.1 and −1. Qian et al 13,14 tested mixed mode fatigue crack growth in stainless steels under biaxial loading and found the crack was deflected or branched depending on the initial crack growth angle.…”