Dislocation Plasticity: Overview

An arbitrary deformation of a material can always be described as the sum of a change in volume and a change in shape at constant volume (shear). Assuming constant structure, the change in volume is recovered when the load is removed, since the atoms can simply relax back to their equilibrium sizes. The change in shape, on the other hand, may or may not be recovered, since the atoms can relax into new positions that are configurationally identical to the original ones, but displaced from them. The part of the shear that is recovered is elastic, the part that remains is plastic. Plastic deformation is a permanent change in shape through shear.