Modelling the evolution of dislocation structures upon stress reversal

The nonuniform distribution of dislocations in metals causes a material anisotropy that man-ifests itself through strain path dependency of the mechanical response. This paper focusseson the micromechanical modelling of FCC metals with a dislocation cell structure. The ob-jective is to enhance the continuum cell structure model, developed in Viatkina et al. (2007),with an improved description of the dislocation density evolution enabling a correct predictionof strain path change effects under complete or partial stress reversal. Therefore, attention isconcentrated on the dislocation mechanisms accompanying a stress reversal. Physically-basedevolution equations for the local density of the statistically stored dislocations are formulatedto describe the formation and dissolution of a dislocation structure under deformation. Incor-poration of these equations in the cell structure model results in improved predictions for theeffects of large strain path changes. The simulation results show a good agreement with experi-mental data, including the well-known Bauschinger effect. The contributions of the dislocationmechanisms and the internal stresses to the resulting macroscopic strain path change effectsare analysed. The dislocation dissolution is concluded to have a significant influence on themacroscopic behaviour of FCC metals after stress reversals.