12 - Microstructural changes in materials under shock and high strain rate processes: recent updates

Abstract

High strain rate deformation and shock-wave-assisted processes find applicability in a variety of applications including material processing. Design of a processing unit utilizing shock phenomenon and design of a material for protection from explosion shock mandate thorough understanding of material behavior under shock and high strain rate conditions. The material response to high strain rate and shock is very different from conventional deformation. It is marked by generation of abundant defects in material exposed to shock for a comparatively low amount of strain generated in it. The material response can vary widely and depends on various material parameters along with the parameters of shock wave. It is well known that the materials with different crystal systems deform by means of different active slip and twin systems. Moreover, for a class of crystal systems the response can further depend on a system’s specific material parameter such as stacking-fault energy in a face centered cubic (FCC) material. With an extensive amount of research dedicated to understanding of the phenomenon of defect evolution in a material under shock, the phenomenon is nonetheless not completely comprehended. The present chapter aims to give the readers a brief overview of the response of materials to shock. Various experimental methods used for research are discussed briefly. The material behavior under shock with a focus on materials with FCC, hexagonal close packed, and body-centered cubic crystal systems is reviewed. The effect of peak pressure and pulse width is explored thereafter. Recent studies have shown that residual strain in the material can have a strong effect on its microstructure under shock. The role of residual strain, which has largely evaded the discussion till now, on defects in shocked microstructure is discussed. Theories of defect generation mechanism under shock compression are reviewed with a focus on recent developments suggesting an atomic shuffling–based defect formation mechanism.