Contraction of extended dislocations at high speeds

It is argued that, at high velocities, extended dislocations become contracted because this can lower their kinetic energies enough to offset the stacking fault energies that determine their extensions. When they are contracted, screw dislocations can cross-glide without the aid of thermal activation. This is consistent with the fact that cross-gliding is more frequent at low temperatures than at high ones. The critical velocity for contraction is about one-third the velocity of shear waves.