Experiments and Simulations on the micromechanics of single- and polycrystalline metals

Crystallographic slip, i.e. movement of dislocations on distinct slip planes, is the main source of plastic deformation of most metals. The Crystal Plasticity FEM combines this basic process with the Finite Element Method by assuming that the plastic velocity gradient is composed out of the shear contributions of all slip systems. To apply the method to forming simulation of "real" parts suffered from the fact, that a huge number of single orientations is needed to approximate the crystallographic texture of such parts. This problem was recently solved by the introduction of the Texture Component Crystal Plasticity FEM (TCCP-FEM), which uses orientation distributions (texture components) for the texture approximation instead of single orientations. Excellent agreement of experiments and numerical simulations for different forming operations has shown the feasibility of this idea. Most crystal plasticity codes use simple empirical constitutive equations. However, as crystal plasticity is build on dislocation movement it was an obvious idea to introduce a constitutive model based on dislocation densities (internal state variables) instead of strain (external, variable) into the crystal plasticity. The dislocation model used is based on five main ingredients: 1) For every slip system mobile and immobile dislocations are distinguished. 2) A scaling relation between mobile and immobile dislocations is derived. 3) The immobile dislocations are divided into parallel and forest dislocations for every slip system. 4) The Orowan equation is used as kinetic equation. 5) Rate equations for the immobile dislocation densities are formulated based on distinct dislocation processes, e.g. lock formation or annihilation by dislocation climb. For a wide range of temperature and strain rate the constitutive behavior of single and polycrystals is studied and simulation results are checked by comparison with experiments.