Forming limit diagrams for anisotropic metal sheets with different yield criteria

Abstract

For thin metal sheets subject to stretching under various in-plane tensile stress histories, localized necking is analyzed by using the M–K-model approach, and forming limit diagrams are drawn based on the critical strains for localization. The analyses account for plastic anisotropy, and predictions are shown based on four different anisotropic plasticity models, which have all been fitted to agree with the same set of experimental data. Situations where the tensile axis is along one of the orthotropic axes of the anisotropy are studied, as well as situations where the tensile axis is inclined to the orthotropic axes. Furthermore, the effect of allowing for nonzero shear strains outside the necking band is considered. In all analyses the rotation of the orthotropic axes is accounted for, and a few studies are used to evaluate the effect of assuming the development of a plastic spin.