Theory of High-Temperature Breakaway of Dislocations from a Row of Randomly Placed Pinning Agents

Abstract

This paper discusses the decrement, at temperature T, of a sound wave of stress amplitude σ0 due to the breakaway of dislocations from pinning agents placed at random along a line. Attention is confined to the high-temperature low-amplitude region; then many pins are involved in the saddle configuration for breakaway. This region is found to consist of two regions P and Q of qualitatively different behavior. For each region, an expression is obtained for the dominant (exponential) factor in the decrement; the same expression is also the dominant factor in the modulus defect and in the fraction of dislocations breaking away during one cycle. In region Q, the decrement varies as exp(− A/σ0 + BT), where A and B are approximately independent of both σ0 and T at sufficiently low amplitudes. This approximate behavior has been found previously in experimental results.