CRACK-PROPAGATION IN A NONLINEARLY VISCOELASTIC SOLID WITH RELEVANCE TO ADHESIVE BOND FAILURE

The problem of crack propagation through a material possessing nonlinearly viscoelastic material response is considered, including the influence of stress-induced free- volume changes on the rheology, as well as the formation of voids as material failure is approached. This particular material response is confined to a thin layer along the crack propagation axis, while the bulk of the material behaves in a linearly viscoelastic manner, thus simulating the situation arising in the growth of a crazeled crack, or the failure of a bonded joint with a thin adhesive layer strained uniformly across its thickness. The nonlinear material behavior thus governs simultaneously the stress and strain distribution at the crack tip as well as the crack speed solely in dependence on the applied load (stress intensity factor). Only quasi-static motion is considered the velocities being understood to be ''reduced'' by temperature according to a time-temperature superposition principle. Comparisons with a model based on linearly viscoelastic considerations and rate-insensitive properties of the damaged material are presented.