Comminution is an old art. Unfortunately the analysis of the unit operations has been handicapped by the lack of both theoretical and experimental information. Two types of information are needed, one an understanding of what happens when a particle breaks in a brittle manner; and two, an understanding of what happens when the daughter fragments pass through the mill.
Recently, successful theoretical attacks on the fracture of brittle solids have yielded significant results. New experimental techniques are yielding insight into the physical phenomenon occurring during brittle fracture. Many of the re-doubtable shiboliths of the last century are either being laid to rest or verified.
The problem with a shock wave is that, from its beginning to its decay into a compressive elastic wave we do not fully understand the dynamics. The shock wave proceeds into the target material as well as into the projectile material. The shock wave moves both perpendicularly into the target and the projectile. However a rarifaction wave originating at the edge of the material eats into the compressive shock wave, attenuating it.
Hypervelocity impacts are spectacular phenomenon. Material in the liquid state is ejected from the early crater at velocities exceeding that of the impacting projectile. Associated with the