| Molecular Dynamics (MD) simulations of shear-dominated crack propagation by Abraham and Gao (2000) showed that there was finite crack opening when the crack propagated at a sub-Rayleigh speed while the crack opening became negligible when the crack propagated faster than the shear wave speed. On the other hand, the classical linear dynamics theory predicted that there was no crack opening for a pure shear crack. Using the asymptotic method developed by Knowles (1981) which included the effect of geometric nonlinearity, we show that there is indeed finite crack opening even for a pure shear crack when the crack propagates at a sub-Rayleigh wave speed, but the crack opening vanishes when the crack propagates at an intersonic velocity which is above the shear wave speed and below the dilatational wave speed. Our results are consistent with what were observed in MD simulations. |
