Processes Occurring in Solids Under the Action of Powerful Shock Waves

The action of powerful shock waves on condensed materials can lead to a wide variety of physicochemical changes: polymorphic transformations, decomposition and synthetic processes, polymerisation of monomers, and defect-formation or conversely the formation of a more perfect structure. The study of these processes has shown that many of them take place exceptionally rapidly. The development of methods for the recovery of substances after the action of shock waves made it possible to employ high dynamic pressures for preparative purposes. Examination of the mechanism governing the compression of a substance by a shock wave shows that the transition from elastic monoaxial compression to bulk-phase compression may be identified with phase transformations as regards gas dynamics and thermodynamics and suggests that phase transitions in the shock wave cannot take place at pressures below the dynamic yield point of the substance. The presence of vigorous plastic flow in shock waves together with the operation of pressures reaching millions of atmospheres suggests that in many ways dynamic operations of this kind on various substances are comparable to methods combining high static pressures with shear stresses. Plastic flow in shock waves leads to the appearance of a characteristic mass-transfer mechanism which gives rise to diffusion processes during the very short period of shock-wave compression. Comparison of dynamic and static studies at high pressures reveals a very close correlation between them. However, a number of effects observed by shock-wave techniques are so far inconsistent with the phase diagrams of the corresponding substances.