The Role of Melting and Vaporization in Hypervelocity Impact

Abstract

Abstract : The memorandum discusses the thermodynamics associated with the flow processes in hypervelocity cratering. Qualitative, graphical arguments are presented to show that previously proposed thermal-impact theories, which postulate that the kinetic energy of impacting projectiles goes entirely into breaking of chemical bonds of fusion, considerably overestimate the transference of energy into heating. Work conducted on the evaluation of release temperatures and phases of nine metals as a function of shock strength is summarized, and similar information is estimated for ten additional metals. The data on release temperature as a function of maximum shock pressure provide a basis for calculating the threshold impact velocities of various projectiles that cause incipient and complete melting in the target material. The results indicate that a quantitative evaluation of the effects of heating in an impact process requires a detailed knowledge of the maximum shock pressures as a function of position within the target.