Interfaces in dynamic brittle fracture of PMMA: a peridynamic analysis

Recent experiments in bonded PMMA layers have shown dramatic changes in dynamic crack growth characteristics depending on the interface location and its toughness. We present a peridynamic (PD) analysis of the problem and identify three necessary elements in a model aimed at reproducing the observed dynamic fracture behavior at an interface in PMMA: (1) softening near the crack tip to account for changes in PMMA properties due to heat-generation induced by the high strain rates reached around the crack tip in dynamic fracture, (2) independence of extension (mode I) and shear (mode II) modes of fracture, and (3) a two-parameter bond-failure model, that can match both strength and fracture toughness for any horizon size. The PD model with these elements captures the experimentally observed dynamic fracture characteristics in bi-layer PMMA: the presence/absence of crack branching at the interface, depending on the interface location; cracks running along the interface for a while before punching through the second PMMA layer; slight crack path oscillations as the cracks approach the free surface. The computed crack speed profiles are close to those measured experimentally. The simulations help explain the observed behavior of dynamic crack growth through an interface. The model shows an enlargement of the fracture process zone when the cracks running along the interface penetrate into the second PMMA layer, as observed experimentally. This is where nonlocality of the PD model becomes relevant and critical.