Phase field modelling of stress corrosion

The evolution of surfaces exposed to an aggressive environment and mechanical load is studied. This is a process of stress corrosion that leads to pitting, crack initiation and growing cracks. In conventional fracture analyses a known or a postulated crack is required. A serious complication is that a large part of the lifetime of a crack or a surface flaw is spent during the initiation of the crack. The knowledge of the mechanisms leading from a pit, flaw, scratch, etc. to a crack is very limited. The motivation for the present study is to provide a model that will increase the understanding of the transition from stress induced surface roughening and pitting to growing cracks. The evolution of the originally flat surface involves free strain energy, chemical energy and gradient energy. A phase field model is used to capture the driving forces that the free energy causes. The flat surface is unstable and develop a waviness. Initially while the waves are shallow a spectrum of favoured spatial frequencies are found to be in accordance with the Asaro-Tiller-Grinfeld theory. Later the surface curvature becomes larger at the depressions than at the higher parts of the surface. This increases the growth rate of formed pits. The pits finally develop into cracks. Also massive branching of pits and cracks is observed. (C) 2014 Elsevier Ltd. All rights reserved.