Comparative study of phase-field damage models for hydrogen assisted cracking

Hydrogen assisted cracking (HAC) usually causes premature failure of metallic materials and results in unexpected collapse of structures under the environmental exposure of hydrogen. Therefore, computational modeling of HAC is of paramount significance to quantify the adverse effects of HAC on the integrity and safety of structures. In this respect phase-field models for fracture are promising since they are able to seamlessly deal with complex crack patterns like nucleation, branching, merging and even fragmentation in a standalone framework. In this work we provide a comparative study of three frequently adopted phase-field models for hydrogen assisted cracking. Both the phase-field models for brittle fracture (e.g., the AT1/2 and WN models) and the phase-field regularized cohesive zone model (PF-CZM) are considered within the unified phase-field theory for damage and fracture, and are extended to incorporate the hydrogen enhanced decohesion mechanism. The numerical implementation of the phase-field models for HAC is also presented, with a simple scheme for calculating the gradient of the hydrostatic stress. Representative numerical examples show that, the PF-CZM with an increasing Irwin's characteristic (internal) length and the PF-CZM with a constant one are both insensitive to the regularization length scale parameter. This merit make them promising for the computational modeling of HAC.