A Geometric Phase Field Model for Hydrogen Enhanced Decohesion in Porous Ductile Metals

Abstract A finite strain, multi-field model for hydrogen embrittlement in porous ductile metals is presented, based on a geometric phase field approach applied on the Gurson–Tvergaard–Needleman model. The hydrogen enhanced decohesion mechanism is incorporated by augmenting the damage driving force with a Rankine-type, hydrogen-dependent term governed by the maximum principal stress. This allows the model to capture both ductile and brittle fracture modes, as well as the transition between them. The phase field formulation introduces an intrinsic length scale that regularizes the solution and eliminates mesh dependency. To address volumetric locking, a mixed finite element formulation with pressure variation is employed. The model successfully captures key experimental observations, including the strain-rate dependence of tensile failure, the transition from internal to surface fracture with increasing deformation rate, and the significant reduction in fracture toughness under hydrogen exposure.