Étude expérimentale de la dynamique d’endommagement microscopique accompagnant la rupture dynamique du PMMA

Experimental study of the dynamics of microscopic damage during fracture in PMMA. Crack propagation is the fundamental mechanism responsible for catastrophic breakdown of brittle materials, and is usually described by the linear elastic fracture mechanics theory. However, tins theoretical framework is only relevant to slow crack propagation and fails at high velocities. In particular, it accounts neither for the experimentally observed maximal crack velocities, nor for the roughness of the post-mortem fracture surfaces. In order to investigate these phenomena, we have designed an experimental setup that allows studying the fracture mechanisms in a model brittle material, namely PMMA, over a wide range of velocities at small space and time scales. This apparatus has enabled us to evidence a new critical velocity beyond which crack propagation is accompanied by microscopic damage through the nucleation and growth of microcracks ahead of the front. The analysis of the morphology of the fracture surfaces suggests that a purely geometric model could account for the conic marks observed. Applying such model to real fracture surfaces might shed light on the mechanisms of microcracking damage spreading and revisit the origin of the discrepancy between theory and experiments at large fracture velocities.