A strain gradient plasticity model to investigate diffusion and dynamic segregation of hydrogen

This paper presents a finite element implementation of strain gradient plasticity (SGP) and coupled hydrogen diffusion. The model encompasses stress-assisted diffusion, solute swelling, and multiple trap sites. The primary achievement of this paper is that a new transport term, that is driven by plastic strain gradients, has been developed and implemented with the finite element method (FEM). The model is applied to the problem of biaxial loading of a solid, under plane strain conditions, featuring a circular hole to investigate the extended transport equation. The results show that the hydrogen concentration increases significantly compared to conventional stress-assisted diffusion. In addition, the localization of hydrogen occurs in regions where there is a restriction on the plastic strain state, such as is often the case around microstructural sites. Together with other mechanisms at play during hydrogen embrittlement this preferential segregation could be used to explain the intergranular fracture mode often observed in experiments.