Discrete Dislocation Plasticity

Abstract

Plastic deformation of metals governs several length scales, Fig. 1. At the large length scale of the macroscopic world, plastic deformation is conveniently described by a phenomenological continuum theory. When zooming in, one will first start to observe that, in most engineering cases, the material is polycrystalline. At that scale, plastic deformation is a physical process that is inherently inhomogeneous and anisotropic. This is caused by the fact that each grain is anisotropic with a finite number of slip systems where glide can take place. When zooming in further, one will see that plastic deformation within each grain involves the collective motion of many dislocations. Zooming in on a single dislocation will reveal that it is an atomic line defect. It is the lattice distortion around this defect that contains sufficient energy that slip of close-packed atomic planes is possible by motion of dislocations, as any elementary materials textbook, such as Callister (2000), describes. This chapter is concerned with the bottom two length scales in Fig. 1, namely dislocations as discrete entities. The motion of individual dislocations and the creation of new ones, is what leads to plastic deformation. Crystal plasticity is a continuum description where the motion of many dislocations is averaged out in terms of an effective slip —this will not be discussed here; an excellent review is given by Asaro (1983).