It was pointed out that the 2 main theories (Becker, Mott & Nabarro) of thermally activated plastic glide in ductile crystals differed in their predictions of the stress exponent of the activation energy. When the Becker theory was applied to a problem of the Mott-Nabarro theory (surmounting of a single localized obstacle by a short segment of dislocation line), and account was taken of the stress relaxation caused by the movement of the segment up to the obstacle, this modified Becker theory gave the same stress exponent as the Mott-Nabarro theory. However, the real situation was that long dislocation lines made their way through forests of obstacles. In this case, the interactions between different segments of these lines considerably modified the problem. They led to load shedding, mechanical activation and large glide avalanches. Under these conditions, the original form of the Becker theory (with an unmodified stress exponent) was applicable.

Thermally Activated Plastic Glide. A.H.Cottrell: Philosophical Magazine Letters, 2002, 82[2], 65-70