A composite dislocation cell model to describe strain path change effects in BCC metals

Sheet metal forming processes are within the core of many modern manufacturing technologies, as applied in, e.g., automotive and packaging industries. Initially flat sheet material is forced to transform plastically into a three-dimensional shape through complex loading modes. Deviation from a proportional strain path is associated with hardening or softening of the material due to the induced plastic anisotropy resulting from the prior deformation. The main cause of these transient anisotropic effects at moderate strains is attributed to the evolving underlying dislocation microstructures. In this paper, a composite dislocation cell model, which explicitly describes the dislocation structure evolution, is combined with a BCC crystal plasticity framework to bridge the microstructure evolution and its macroscopic anisotropic effects. Monotonic and multi-stage loading simulations are conducted for a single crystal and polycrystal BCC metal, and the obtained macroscopic results and dislocation substructure evolution are compared qualitatively with the published experimental observations.