On crack path selection and the interface fracture energy in bimaterial systems

The intent of this article is to apply recent solutions for the mechanics of cracks at and near bimaterial interfaces to rationalize crack trajectories observed by experiment and to provide a basis for interpreting measurements of the interface fracture energy, Γ_i. It is demonstrated that the choice of test specimen governs the tendency of cracks to either remain at interfaces or deviate away, based on considerations of the phase angle of loading, ψ. It is further revealed that the measured interface fracture energy may be strongly influenced by the crack trajectory, as governed by ψ, through crack shielding and plasticity effects. Consequently, interfaces do not typically have unique fracture energies, but instead Γ_i depends on ψ which, in turn, is influenced by the test method.