Modelling of hydrogen-assisted damage at the deforming single crystal crack-tip

A coupled framework of dislocation density-based crystal plasticity model and slip-rate based hydrogen transport model is developed to simulate hydrogen-assisted damage at the deforming crack-tip. Chemical potential-based boundary conditions and mobile dislocation-assisted hydrogen transport account for the evolving hydrogen concentration. A novel fracture indicator parameter is proposed to quantify the damage that considers the combined effect of local hydrogen concentration, accumulated plastic slip and stress triaxiality. Experimentally-informed critical value for hydrogen concentration is considered to model the crack initiation. Depending on the crystal orientation, the damage is shown to be associated either with an individual hydrogen embrittlement mechanism (hydrogen-enhanced localized plasticity, and hydrogen-enhanced decohesion) or their synergistic effect at the crack tip.