Intersonic crack propagation in homogeneous media under shear-dominated loading: Numerical analysis

The transition from subsonic to intersonic propagation of a planar crack subjected to mixed-mode loading is investigated numerically using a spectral form of the elastodynamic boundary integral equations. The spontaneous motion of the propagating crack is simulated with the aid of a quasi-linear rate-independent cohesive failure model coupling normal and shear failure modes. It is observed that, when the loading amplitude is shear-dominated and represents a substantial fraction of the fracture plane strength, the dynamic crack undergoes a rapid transition to intersonic regime. In some cases, the transition takes place through the temporary creation ahead of the main crack of a secondary cohesive zone which quickly coalesces with the primary cohesive zone. In most cases, however, the subsonic-to-intersonic transition takes place through a rapid but smooth acceleration of the main cohesive failure zone. Intersonic crack propagation can be achieved under mixed-mode conditions when the shear component of the external loading is sufficiently large. However, under steady-state intersonic conditions, cohesive failure occurs exclusively in shear, even when the remote loading of the crack is of mixed-mode nature.