A new model was developed for the hardening behavior of cell-forming crystalline materials at large strains. The model considered a cellular dislocation structure that consisted of 2 phases: cell walls and cell interiors. The dislocation density evolution in the 2 phases was considered in conjunction with a mechanical analysis of a cell structure in torsional deformation, in which the cell walls lay at 45º to the macroscopic shear plane. They were also greatly elongated in the direction perpendicular to the applied shear direction. On the basis of recent data on the volume fraction of cell walls, the cell-wall volume fraction was considered to decrease as a function of strain. All stages of large-strain behavior were correctly reproduced within a single formulation for Cu in torsion. The strain rate and temperature effects were accounted for correctly, and the predicted dislocation densities were in agreement with experimental measurements. It was suggested that the factor which was responsible for hardening-stages IV and V was a continuous decrease in the volume fraction of the cell walls at large strains.

A Dislocation-Based Model for all Hardening Stages in Large Strain Deformation Y.Estrin, L.S.Tóth, A.Molinari, Y.Bréchet: Acta Materialia, 1998, 46[15], 5509-22