A cohesive zone global energy analysis of an impact loaded bi-material strip in shear

摘要

The numerical results show clearly that at low cohesive stresses inter-sonic crack speeds approaching the axial wave speed are predicted. At higher cohesive stresses the crack speeds are much lower and Needleman (1999) reported that they ran at the Rayleigh wave velocity. In Williams et al. (to be published), however, a range of speeds was observed from about the Rayleigh velocity to significantly lower values. All the numerical studies showed transitions from the lower speeds to the higher under certain conditions. Such transitions are observed experimentally though it is difficult to prescribe the cohesive stress, or indeed GO, in the tests and the numerical results are able only to infer the values. The analytical solution gives a sensible description of the numerical values. The most basic of solutions predicts the intersonic speeds and when a cohesive zone is involved these speeds occur for low stress values. The crack speed dependency on the cohesive stress shows a region of rapid change which coincides well with the transitions observed numerically. This arises from the elastic constraint in the region beyond the cohesive zone.