Corrosion crack growth in a bi-material system

Bi-materials composed of thin layers ideally bonded to large substrates are considered. Cracks emerging from an almost flat surface and propagating through the bi-materials are studied. The cracks acquire realistic geometrical shapes, where the tips are integral parts of the crack surfaces. Crack propagation is related to surface evolution resulting from material loss due to corrosion. Controlling mechanism for the evolution is the rupture of a brittle passive film, which is frequently building-up along the surface. The evolution rate is a function of the degree of film damage caused by the surface straining. The model leads to a moving boundary formulation, for which a numerical solution is used. The mismatch of the material plastic properties is being varied in the study. The results show how cracks pass the interface. The growth rate variation close to the interface is studied. Typical surface evolution for a crack passing through a soft-hard material interface is presented. The resulting crack morphology of the model resembles what has been observed in reality. It is shown how the results can be used in designing bi-material systems to inhibit corrosion crack growth