A revisited criterion for crack deflection at an interface in a brittle bimaterial

An asymptotic analysis is carried out to model the mechanism of deflection of a crack at an interface in a brittle bimaterial. Necessary conditions are derived from an energy analysis based on seeking the path which provides the maximum of additional energy released by the fracture process. In the case of a stationary crack impinging perpendicularly on the interface and submitted to progressive loading, the energy criterion depends on the elastic mismatch of the bimaterial constituents and the ratio of the crack extensions in the deflected and the penetrated directions. The criterion reveals high sensitivity to the value of this ratio. Applying this criterion thus requires an arbitrary assumption concerning the value of the crack extension ratio, as was proposed by He and Hutchinson (He, MY, Hutchinson JW. Crack deflection at an interface between dissimilar elastic materials. Int J Solids Structures 1989;25:1053–67). Considering now a crack propagating towards the interface, an improved criterion which does not require any assumption concerning the extension ratio is established by using a quasi-static approximation and assuming that the deflection mechanism occurs under constant loading.