Localization of plastic deformation in stretching sheets with a crystal plasticity approach: Competition between weakest link and instable mode controlled process

The development of plastic strain localization in a stretching tantalum sheet in the form of necking under dynamic loading conditions was investigated by crystal plasticity simulation in the aim of evaluating the role of phenomena taking place at the scale of the material microstructure. Both equi-biaxial and plane strain stretching have been computed and two grain sizes have been considered. As expected from previous studies at the macroscopic scale, pronounced necking is observed for mean deformations much higher than the one for which a maximum force condition is met. Interestingly, a transition between Mott-type fragmentation process and instability-driven necking is observed as a function of the grain size. For large grains (i.e. low number of grains in the sheet thickness) and moderate strain rate, the localization of the plastic strain pattern emerging at the grain scale in the early stages, partly correlated with local slip resistance, seems to play the role of the weakest links in what resembles an obscuration controlled defect interaction process. A pronounced texture may strengthen the role of the local behavior on strain concentration by combining the effects of slip system Schmid factors and self and latent hardening. In contrast, for smaller grains, the memory of the initial strain pattern is much less clear and, for high strain rate, the final neck formation is preceded by the development of strain modulations of larger wavelengths and higher amplitudes than the initial grainwise heterogeneity. These modulations could be interpreted as unstable perturbation modes of the structure. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study revealed that the development of plastic strain localization in a stretching tantalum sheet is influenced by grain size, with large grains showing early localization while smaller grains exhibit larger wavelength strain modulations before neck formation.