Intragranular localization induced by softening crystal plasticity: Analysis of slip and kink bands localization modes from high resolution FFT-simulations results

Abstract

We investigate the ability of local continuum crystal plasticity theory to simulate intense slip localization at incipient plasticity observed experimentally in metals exhibiting softening mechanisms. A generic strain softening model is implemented within a massively parallel FFT solver framework to study intragranular strain localization throughout high resolution polycrystalline simulations. It is coupled to a systematic analysis strain localization modes: Equivalent plastic strain and lattice rotation fields are processed to create binary maps of slip and kink bands populations, estimate their volume fraction and mean strain level. High resolution simulations show the formation of an intragranular localization band network. The associated localization maps are used to identify accurately slip and kink bands populations and highlight the distinct evolution of kink bands, influenced by lattice rotation. Results highlight that the analysis of the nature of localization bands in numerical studies is fundamental to asses the validity of polycrystalline simulations. Indeed, it is evidenced that selection between slip or kink localization modes is only due to grain to grain incompatibilities as these two localization modes are equivalent in classical crystal plasticity models. As a result they predict the formation of a large amount of kink bands in contradiction with experimental observations of softening metals. We show that this holds for complex physics based models too. Hence, the use of classical crystal plasticity for strain localization simulation should be reconsidered in order to predict realistic localization modes.