Strain localization analysis using a large strain self-consistent approach

Abstract

The development of a relevant constitutive model adapted to sheet metal forming simulations requires an accurate description of the most important sources of anisotropy, i.e. the slip processes, the intragranular substructure changes and the texture development. During plastic deformation of thin metallic sheets, strain-path changes often occur in the material resulting in macroscopic effects. These softening/hardening effects must be correctly predicted because they can significantly influence the strain distribution and may lead to flow localization, shear bands and even material failure. The main origin of these effects is related to the intragranular microstructure evolution. This implies that an accurate description of the dislocation patterning during monotonic or complex strain-paths is needed to lead to a reliable constitutive model. A crystal plasticity model coupled with an intragranular microstructure description, inspired by Peeters' works, is used to determine the single crystal behaviour and to describe the dislocation cells evolution. The scale transition between the local behaviour and the polycrystalline one is realized thanks to a large strain self-consistent approach. Moreover, the introduction of a ductility loss criterion, first introduced by Rice, based on the ellipticity loss of the elastic-plastic tangent modulus, is used to plot Ellipticity Loss Diagrams (ELD). Qualitative comparisons are made with experimental Forming Limit Diagrams (FLD) for ferritic steel for simple and complex loading paths. In particular, it is shown that numerical ELD have a shape close to experimental FLD and reproduce qualitatively the effects due to complex loading paths.