Local and equivalent stress intensity factors for tortuous cracks under remote mode II loading

Abstract

In metallic materials the paths and fronts of fatigue cracks usually exhibit a certain tortuosity caused by microstructural heterogeneities. Our previous calculations for remote mode III loading revealed that the in-plane tortuosity of pre-crack fronts was associated with significant local k2 components of the effective stress intensity factor (SIF), thus enabling small segments growing in the local mode II to gradually advance the whole “mode III” crack front. In this work, the local effective SIFs at both in-plane and out-of-plane (3D) serrated crack fronts in the compact-tension-shear specimen under the remote mode II loading are numerically investigated by neglecting the friction stresses. The changes in local and global effective SIFs are presented separately for in-plane and out-of-plane tortuous crack fronts and, on the global level, also for their combination. Local k3 components appeared at in-plane serrated crack fronts and, for the out-of-plane roughness, local k1-values were present. Forequal levels of the remote mode II loading, a geometrical shielding effect induced by the crack tortuosity, i.e., a uniform decrease of an averaged k2-value with increasing roughness of the crack front was revealed. When all three local loading modes along the tortuous crack front were considered in terms of equivalent SIFs, the shielding effect was also revealed in an entire or a prevailing range of roughness characteristics. However, some of equivalent SIF definitions predicted an unexpected slight anti-shielding effect in a certain small range of roughness characteristics close to those associated with crack fronts in real metallic materials.