Adiabatic Shearing - General Nature and Material Aspects

Abstract

The phenomenon loosely termed “adiabatic shearing” is one aspect of high velocity deformation that has been receiving substantially greater attention in recent years because of the growing number of areas in which it is now recognized to play a significant role. This will become obvious from the details not only of the rest of the papers in this section, but from others in this conference as well. Although shearing deformation is well known and well understood from a solid mechanics point of view, the term adiabatic shearing will not be found in mechanics texts, the reason being that it is an aspect of real material behavior rather than of an idealized continuum. Moreover, the discussion throughout this paper will concentrate on the behavior of metals although some aspects of adiabatic shearing behavior are also applicable to polymers and other non-metals as well. In metals, plastic deformation takes place by the motion and interaction of dislocations. The work of plastic deformation is partly stored in the metal as elastic strain energy known as cold work while the remainder is converted to heat. It has been experimentally determined that at room temperature 90–95 percent of the work of deformation goes into heat. Ideally, if the deformation took place instantaneously, all would be retained locally and the deformation would be truly adiabatic. During dynamic deformation, however, a certain fraction of the heat generated is lost to the surrounding metal, the exact amount depending both on the rate of deformation and the thermal properties of the material. In any case, if sufficient heat is retained that the deformation process is thought to be significantly modified by it, the deformation is referred to as “adiabatic”.