Dislocation glide in a periodic internal stress field: A computer simulation of the strain transient dip test

Abstract

The glide of a dislocation in a periodic internal stress field is simulated. The velocity of the dislocation is determined by its interaction with a unidimensional random array of short range obstacles. Allowance is made for both forward and backward thermal activation of the dislocation and the following rate determining processes are considered: 1. (i) sideways kink motion, 2. (ii) double kink nucleation and 3. (iii) node unpinning. The importance of backward activation in each case is examined and it is shown that backward activation is suppressed by the presence of the periodic internal stress field. Further, this effect is greater, the shorter the period of the internal stress field. From the distribution of residence times of the dislocation at the obstacles, the probability of finding a dislocation at any position in the internal stress field is computed. The application of this probability distribution to an assembly of non-interacting mobile dislocations allows the strain transient dip test to be simulated. It is found that the critical stress, at which the average dislocation velocity is zero, is the best estimate of the mean internal stress level. The effect of using the various measures of internal stress on the estimation of the forward activation area for glide is also discussed.