Simulation of time-discontinuous chemically-aided intergranular fracture

In this work, based on experimental observations, a model for the pressure dependent diffusion and accumulation of hydrogen ahead of a propagating intergranular crack front is developed. In the model, the pressure dependency of the diffusion is incorporated into the activation energy of an Arrhenius form of the materialʹs diffusivity tensor along high-diffusivity grain boundaries. Inherent to the model is that large amounts of hydrogen can be absorbed into the crackʹs process zone, due to the high triaxial stress in that region, which produces a larger effective diffusivity locally. Further ahead, the effective diffusivity quickly decreases. The combined effect forms a barrier to further rapid penetration, which leads to the mentioned accumulation of the hydrogen in the process zone. Theoretical aspects of the model are discussed and numerical simulations of the transient distributions of hydrogen and subsequent crack front propagation are performed to illustrate the main characteristics of the model.