Dislocation accumulation at large plastic strains -- An approach to the theoretical strength of materials

Abstract

The usual method of introducing engineers to the concept of dislocations and their role in plastic flow is to compare an estimate of the theoretical strength of solid (of order {micro}/30 where {micro} is the shear modulus) and the observed strength of either single crystals ({mu}/10{sup 4}) or practical engineering material such as structural steels where the yield stress in shear is of order {mu}/10{sup 3}. However, if one considers the problem in reverse, one can consider the accumulation of dislocations as an important mechanism by which one can produce engineering materials in which the strength level approaches the theoretical strength. If one assumes that the flow stress can be expressed in terms of te mean free path between stored dislocations or as the square root of the global dislocation density, then one can see the influence of dislocation density in a diagrammatic form. It is clear that the strengthening by dislocation accumulation due to large imposed plastic strains represents an important approach both to the development of new, potentially valuable, engineering materials and an important area of basic understanding in terms of the mechanical response of materials close to their theoretical strength. Thus, this article will survey some ofmore » the factors which influence dislocation accumulation at large strains and the consequences of such accumulation processes.« less