The sources of cyclic slip irreversibility

The sources of cyclic slip irreversibility in cyclic straining are analyzed. Several physically based models proposed to explain the specific character of the surface relief of persistent slip markings (PSMs) consisting of extrusions and intrusions were reviewed. Two random slip models were further developed and the characteristic reliefs were obtained using simulations under different assumptions on the slip and its distribution within the persistent slip band (PSB). In a model based on static extrusion, the kinetics of extrusion formation was derived. For a model based on the dynamic growth of extrusion basic characteristics were introduced. Characteristic experimental data on the shape of extrusions and intrusions in fatigued polycrystals and the kinetics of their formation were presented. The predictions of individual models were compared with the experimental data and it was concluded that neither the random slip mode nor the static extrusion model can explain the shape and the kinetics of PSM formation. The model based on the dynamic growth of PSMs is in good agreement with experiments on copper. Specific features of materials with planar slip and dislocation arrangement of the PSB and the matrix were discussed.