A nonlinear-discrete model of dynamic fracture instability

Molecular-dynamics simulations of dynamic fracture show that local shear deformation at the crack tip increases, and local potential energy builds up, eventually triggering dislocation emission — the instability that leads to crack branching. Neither the build-up nor the instability can be predicted by linear-continuum theories. We propose a simple nonlinear-discrete model, which demonstrates that the excitation of nonlinear modes generates this instability.