Uncovering the dynamic fracture behavior of PMMA with peridynamics: The importance of softening at the crack tip

Recent experimental investigations of dynamic crack propagation in PMMA induced by impact show single cracks running stably at around 300-400 m/s. Existing numerical models for simulating dynamic fracture in PMMA consistently produce crack propagation speeds significantly higher than those measured experimentally. Here we uncover the reason for this puzzle by showing that localized material softening in the fracture process zone (caused by heating due to high strain rates in front of the crack tip), leads to crack propagation speeds that match the observed ones. We introduce a new constitutive model in our peridynamic formulation for PMMA to account for a softer material in the crack tip region. With the new model, the computed crack speed and crack length evolution match very closely those found experimentally.