Modelling the evolution of dislocation structures upon stress reversal

The non-uniform distribution of dislocations in metals causes a material anisotropy that manifests itself through strain path dependency of the mechanical response. This paper focuses on the micromechanical modelling of FCC metals with a dislocation cell structure. The objective is to enhance the continuum cell structure model, developed in Viatkina et al. [Viatkina, E., Brekelmans, W., Geers, M., submitted for publication. Modelling of the internal stress in dislocation cell structures], with an improved description of the dislocation density evolution enabling a correct prediction of strain path change effects under complete or partial stress reversal. Therefore, attention is concentrated on the dislocation mechanisms accompanying a stress reversal. Physically based evolution equations for the local density of the statistically stored dislocations are formulated to describe the formation and dissolution of a dislocation structure under deformation. Incorporation of these equations in the cell structure model results in improved predictions for the effects of large strain path changes. The simulation results show a good agreement with experimental data, including the well-known Bauschinger effect. The contributions of the dislocation mechanisms and the internal stresses to the resulting macroscopic strain path change effects are analysed. The dislocation dissolution is concluded to have a significant influence on the macroscopic behaviour of FCC metals after stress reversals.