Crack tip blunting and cleavage under dynamic conditions

Abstract eng:
Because many structural materials comprise two or more phases, fracture often involves growth of cracks from one phase to another. Researchers have hypothesized that dynamic effects are important in these processes, and can promote brittle failure in engineering alloys. We assess this hypothesis of “dynamic embrittlement” using molecular dynamics (MD) simulations. We focus on whether dynamics affects the energy barriers for crack tip dislocation emission or cleavage, and what happens in the dynamically overloaded situation, when both processes are energetically possible. In the MD simulations, we employ a novel potential, with a tunable energy barrier for dislocation emission, and a novel simulation technique, termed a “dynamic cleavage test.” Our simulation results indicate that the competition between cleavage and emission—i.e., the intrinsic ductility of the material—is unaffected by dynamics. Finally, we discuss the implications of this finding for understanding the micromechanisms of fracture in engineering alloys.

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