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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.

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Strain path dependency in FCC metals is often associated with the anisotropy induced by the dislocation cell structure in deformed metals. In this paper, the mechanical behaviour of metals under various nonuniform deformation paths is studied with the use of a recently developed dislocation cell structure model. It is shown that this model correctly captures the essential features of strain path change effects for moderate strain path changes, i.e. the anisotropy and the dependency on the amount of prestrain. Next, a numerical analysis is performed to assess the micromechanical origin of the modified reloading yield stress and the transient hardening after strain path changes. The separate influence of anisotropic effects due to the cell structure morphology and residual internal stresses are thereby addressed and illustrated. The transient hardening behaviour after a strain path change is related to the adjustment of the internal stresses to the new loading. Results obtained are consistent with related experimental findings reported in literature.