Identification through mesoscopic simulations of macroscopic parameters of physically based constitutive equations for the plastic behaviour of fcc single crystals

The objective of this work is to derive the parameters of macroscopic constitutive equations for the plasticity of fee single crystals with the help of simulations performed at a dislocation level. The macroscopic model is based on the leading physical mechanisms which are involved in the plastic deformation. The three involved constitutive laws use the total dislocation densities on each glide system as fundamental variables. Those three expressions are derived from physical precesses governing the behaviour of a single dislocation and adapted to be used at the macroscopic scale. Literature results could be widely used for the identification of the material parameters for different fee materials but some of the parameters are mean values and must be seen as phenomenological parameters so that a good way to determine such values consists to use a numerical tool where each dislocation is individually simulated in a three dimensional network. Such a tool works at a mesoscopic scale (typically several microns) and deals with dislocations discretized into pure screw and edge segments. It includes all the well-known elementary events governing the dislocation motion such as the line tension effect, the Frank-Read multiplication mechanisms, the cross-slip events and the junction formations. The cross-analysis of several specific mesoscopic simulations allows to determinate the values of some macroscopic parameters and also to check the validity of both models.