Interfaces in Dynamic Brittle Fracture of PMMA: a peridynamic analysis

Abstract

Recent experiments in bonded PMMA layers have shown dramatic changes in dynamic crack growth characteristics depending on the interface location and toughness. In this paper we present a peridynamic (PD) analysis of this phenomenon and determine three elements that are essential in a model reproducing the observed fracture behavior: (1) softening near the crack tip to account for changes in PMMA due to heat-generation induced by the high strain rates reached around the crack tip in dynamic fracture; (2) independent extension (mode I) and shear (mode II) modes of fracture; (3) a two-parameter fracture model, which matches both strength and fracture toughness for any horizon size. Once these elements are in place, the PD model captures the experimentally observed dynamic fracture characteristics in bi-layer PMMA: crack branching or not at the interface, depending on the interface location; crack running along the interface for a while before punching through the second PMMA layer; slight crack path oscillations near the far end of the sample. The computed crack speed profiles are close to those measured experimentally. The model produces an enlargement of the fracture process zone when the crack running along the interface penetrates into the second PMMA layer, as observed in the experiments. This is where nonlocality of the PD model becomes relevant and critical.