Chapter 20 - Dislocations

Abstract

Dislocations are the defects whose motion produces plastic deformation of crystals at stresses well below the theoretical shear strength of a perfect crystal. The dislocation bounds a slipped area and is a line defect. All of the interaction forces have the characteristic feature that varies inversely with the spacing of dislocations. This result has important implications for work hardening and macroscopic descriptions of plastic deformation on the basis of dislocation models. For forest interactions of a dislocation with other dislocations threading its glide plane, the initial interaction is the elastic one. Forest dislocations can be provided by glide on secondary slip systems or by several special mechanisms. The macroscopic flow stress scales inversely with forest dislocation density, or equivalently, directly with the square root of the dislocation density—that is, the total length of dislocation line per unit volume. The exact reasons for such scaling laws remain elusive, but both long-range elastic stresses (the dislocation interaction) and short-range network and junction formation can produce this behavior.