Toward physically-based rate laws for dislocations

Rate laws of the Becker type are inappropriate for dislocations. They were developed for independent particles, not for lines where the motions are highly correlated. Since one end of a line cannot communicate with the other end faster than sound speed will allow, there are serious correlation problems when the activation area is considered to be larger than a few atomic squares; e.g. there are difficulties with conventional kink nucleation theory. Without arbitrary modifications, this theory does not describe the observed temperature dependence of flow stresses satisfactorily. It is shown how the intrinsically one-dimensional Becker-type theory can be combined with a two-dimensional theory to yield a physically consistent model that provides a better description of the temperature dependence of plastic flow stresses without being arbitrary. It is also indicated how the behavior of covalent crystals with intrinsic resistance to dislocation motion can be described.