Fatigue crack initiation and propagation behaviour of 316L under strain-controlled mode considering the interaction of crack closure and compressive load effect

This work investigates the fatigue crack initiation and propagation behaviour of 316L stainless steel under negative strain ratios. Crack driving force parameters based on different fracture criteria are comparatively discussed. The cyclic deformation response at crack tip region is characterized using digital image correlation (DIC) and electron backscatter diffraction (EBSD). Results show that crack initiation is significantly affected by the variation in notch stress concentration under tensile loads, and the introduction of compressive loads contributes to strain localization. Concentrated strain gradients and de-twinning process under interference of high-density dislocations induce crack initiation. In addition to the primary driving influence of tensile loads, the increasing crack closure level inhibits crack driving force provided by compressive load effect. Moreover, it is observed that the expansion of the residual tensile plastic zone is further inhibited by the plastic wake zone due to the significant crack closure behaviour. Finally, a crack growth rate model is proposed by considering the strain ratio effect and the influence of crack tip plastic zone based on the interaction of crack closure and compressive load effect. It is found that the proposed model is robust in predicting the crack growth rate at both crack initiation and propagations stages.