Self-similar solutions for stress driven material dissolution

During corrosive dissolution of metal ions from a body surface an oxide compound is produced. This compound form a protective film that reduces the dissolution rate. When a fraction of a millimetre depth is dissolved the dissolution become insignificant. However cylic load will damage the film with continued dissolution as a result. In connection with this a threshold strain should be exceeded. A relation between this threshold and the remote surface strain is believed to control the shape of the pit. This paper proposes a model where the corrosion process and the mechanical state of the body forms the geometry of a pit. The shape extends from shallow cavity like pit to a thin crack depending on the threshold strain versus remote strain. For small surface strains a crack is formed. The growth rate of the crack is given by the dissolution at the crack tip. No crack growth criterion is used. The growing crack is itself creating conditions for strain concentration, which leads to a high crack growth rate. Computation of the mechanical state is based on finite element calculations. Cracks evolving from surface irregularities are studied. The model simulates how dissolution leads to surface roughness, how pits form and grow to become cracks or cavities in a single continuous process.