An Elastoplastic Finite-Element Investigation of Crack Initiation Under Mixed-Mode Static and Dynamic Loading

Abstract

The fracture mechanics techniques needed for materials that fracture in a highly ductile manner must give explicit attention to the extensive plastic deformation surrounding the crack tip. Large-scale crack-tip plasticity has two effects. First, because of crack-tip blunting, crack growth initiation tends to occur under conditions for which conventional linear elastic fracture mechanics analyses are invalid. Second, significant amounts of stable crack growth can occur prior to fracture instability. To cope with these essentially inelastic processes, elastic-plastic fracture mechanics techniques are now being widely pursued [1].2 The research reported in this paper builds on these developments to provide the basis for fracture mechanics treatments under the more general conditions involved in dynamic mixed-mode loading. Current work in elastic-plastic fracture mechanics is largely confined to quasi-static loading conditions and to crack growth in the opening mode (Mode I). Yet, in impact-loaded structures, crack initiation could occur under dynamic conditions with a combination of both the opening mode and the sliding mode (Mode II). Thus, it is necessary to obtain a quantitative understanding of crack growth initiation, propagation, and arrest under initial combined-mode dynamic loading conditions. The research described here is aimed at developing this understanding through a program of integrated experimental and finite-element analysis work.