Morphological transformation of the process zone at the tip of a propagating crack. I. Simulation.

Stress concentration at a crack tip engenders a process zone, a small domain containing a phase, different from that in the bulk of the solid. We demonstrate that this zone at the tip of a propagating crack exhibits a morphological transformation with an increase of the crack velocity. The concave zone shape with an invagination in its back that is characteristic of a slow crack transforms into a droplet-shaped convex zone upon exceeding a critical velocity value, v_{G}. In this latter case, a metastable wake follows the propagating zone. We obtained this result by computer simulation of a crack propagating in a solid exhibiting a first-order phase transformation.