Abstract
Instead of occurring simultaneously over regions which are apparently uniformly stressed, plastic flow frequently proceeds in a discontinuous manner, as in the formation of wedge-shaped plastic regions around the periphery of torsion specimens. It is contended in this paper that this phenomenon can be explained as an instability, brought about by stress concentrations which are caused, not by discontinuities in the shape of the specimen, but by the discontinuous behavior of the material around the yield point.
According to this explanation, yielding first occurs at some region of local weakness. The lagging of the stress in this yielded region causes a stress redistribution around the region, somewhat as if it were a hole, which retards stresses and therefore yielding in certain directions while accelerating them in other directions, thus leading to the spontaneous growth of characteristically shaped plastic regions.
