Hydrogen-assisted localized plasticity driven by dislocation pinning-depinning: Finite element simulations

For the development of a hydrogen energy society, understanding hydrogen-assisted fatigue crack propagation is crucial. Hydrogen-assisted fatigue crack propagation exhibits an exceptionally rapid growth rate, with only small plastic deformation observed at the macroscopic level. Nevertheless, the presence of dislocation structures, typically associated with conventional fatigue failure, has been reported near the crack tip. Explaining this phenomenon solely based on hydrogen-induced softening or hardening is challenging. Therefore, this study focuses on the newly proposed concept of temporary hardening resulting from hydrogen-induced pinning and depinning. In this research, we conducted a numerical analysis using an elastoplastic analysis coupled with hydrogen diffusion analysis to simulate the pinning and depinning effects caused by hydrogen. Our simulation results demonstrated that hydrogen-induced pinning and depinning led to higher strains at the crack tip compared to cases without these effects, resulting in small-scale macroscopic plastic deformation.