It was recalled that recent experimental observations of the effects of temperature and cumulative strain upon dislocation structures, and upon the cyclic stress-strain behavior in single crystals, had shown that new ideas were required in the dislocation theory of cyclic saturation. The observations permitted a static-dynamic model for the process to be carefully checked. The model provided quantitative account to be taken of the available observations, and clearly showed that cyclic saturation was not a steady state, but was a dynamic process of continued matrix hardening and persistent slip-band formation. The model included features which were based upon the idea that edge dipole walls in fatigue were metastable but impenetrable to uniform slip. Previous rejection of this idea was answered on the basis of a simple dislocation description, of slip uniformity, which related the wall spacings of the static structure to the density of the dynamic structure of gliding dislocations. This static-dynamic picture also included a line tension model for the observed motion of primary matrix and persistent slip-band walls. By assuming only conservative dislocation motion, the model offered the advantage that it remained valid even at very low temperatures; where point defects were immobile. The line tension model permitted the observed fragmentation of primary matrix walls to be explained, and it accounted for a recently discovered relationship between dislocation density in, and spacing of, persistent slip-band walls.

Static-Dynamic Model for Cyclic Saturation in the Fatigue of Metals. O.B.Pedersen: Philosophical Magazine A, 1996, 73[4], 829-58