A moving boundary model for fatigue corrosion cracking

Fatigue corrosion crack initiation and propagation is modelled as a moving boundary value problem. The model is based on three physical processes operating at the solid-environment interface – material dissolution, passive film formation and surface straining. The dissolution triggers boundary advancement. The rate of boundary advancement depends on the passive film damage caused by the surface straining. Plane edge cracks, nucleating from surface irregularities, are considered. The cracks obtain realistic geometrical shapes where the near-tip region is an integral part of the crack surface. Elastic-perfectly plastic materials are considered and a low-cycle fatigue load is assumed. The problem is solved using a FEM based program and procedures for moving boundary tracking and interior re-meshing. A crucial ingredient of the boundary tracking is the evolved surface re-meshing, where a scheme based on length and curvature constraints is utilised. The work studies how the choice of these constraints influences the results for crack surface evolution. It is shown that characteristic length parameters in crack nucleation and short crack growth depend on the choice of the constraints. It is concluded that an additional physical process operating at the surface has to be accounted for in order to describe the length scales observed in reality.