Processes Occurring in Solids Under the Action of Powerful Shock Waves

Abstract

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