Threshold for dynamic re-crystallization in shock loaded aluminum alloy

Shock loading of D16 aluminum alloy within impact velocity range of 30-450 m/s reveals two regimes of dynamic deformation. Three dynamic variables -- particle velocity $U_{p}$, particle velocity dispersion $D^{2}$ and velocity deficit at the plateau of compressive pulse \textit{$\Delta $U} are registered in real time at every shock. At the impact velocities lower 380 m/s, velocity deficit (which quantitatively characterizes an intensity of meso-macro energy exchange) is very small or absent at all. In this region of impact velocities the structure of material remains invariable. At 380 m/s a catastrophical growth of velocity deficit occurs, which corresponds to start of dynamic re-crystallization process as adaptation mechanism to loss of structural stability of dynamically deformed material. The size of grains decreases from 30 $\mu $m to 1,5 -2 $\mu $m. The catastrophical growth of velocity deficit happens when rate of change of velocity dispersion becomes higher than rate of change of mean particle velocity, i.e. a criterion$\left( {\frac{D}{u}\frac{\dot {D}}{\dot {u}}} \right)\ge 1$ is fulfilled.