Morphological transformation of the process zone at the tip of a propagating crack. II. Geometrical parameters of the process zone.

The morphological transformation of the process zone at the tip of a propagating crack occurs with the increase of the crack velocity. The zone configuration changes its shape from concave to convex, dropletlike form. The latter exhibits a metastable wake. We prove that the transformation takes place as soon as the crack velocity exceeds Gordon's speed V_{G}. The latter is the velocity of motion of the interface between the stable and overheated metastable phases. We further analyze the dependence of geometrical parameters of the zone and wake on the crack tip velocity. We show that at a constant velocity, the size of the process zone grows with the approach to the binodal. However, it decreases by over three orders of magnitude as the crack's velocity increases. In contrast, the interval length where the zone or the wake comes in direct contact with the crack surface increases at 0≤V<V_{G}, achieves its maximum at V=V_{G}, and then decreases with the further velocity increase. The zone vanishes as soon as the crack's velocity exceeds a critical speed V_{cr}.