Dynamics of Brittle Fracture with Variable Elasticity

Simulations show that brittle cracks approach six-tenths the Rayleigh speed and follow the highest surface energy path. Using an interatomic potential recently developed by J. P. Sethna, we find that the crack's limiting speed now approaches the theoretical prediction of the Rayleigh speed, but the crack path is still associated with greatest elastic stiffness and surface energy. We conclude that the crack's dynamics is governed by the anisotropic mean-field elasticity associated with large strains ( $\ge 7\%$).