Mechanism of low-temperature slip in organic single crystal

To account for the temperature dependence of the yield-stress of body centred cubic metals, Feltham (1969) proposed a model, in which slip is considered to be induced by stress assisted, thermally activated, formation of arcs of screw dislocation trapped in Peirels troughs. For the saddle point configuration in the forward movement of a screw dislocation segment over the Pieierls hill, Feltham arbitrarily assumed in the model a fixed activation distance equal to one Burgers vector, which was criticized by Taylor. In this paper, a more plausible range of activation distance for the saddle point configuration has been considered on physical and energy grounds, and the model has been further developed to obtain analytical formulations for the inter dependence of yield stress, activation volume and temperature. Available data for anthracene single crystals in the range 80 to 200 K are found to be fully explicable in terms of the modified model. (author)