Prediction of forming-limit curves of dual-phase steels based on a multiple length scale modelling approach considering material instabilities

In this contribution a decoupled sequential multiple length scale modelling approach to estimate forming-limit curves of dual-phase steels is presented. Two-dimensional Voronoï tessellated representative volume elements, based on the periodic microfield approach and under the assumption of plane stress are utilised to investigate the onset of material instabilities in the microstructure. Here, material instabilities, also termed as local stability problem or shear band, refer to a critical state of mechanical equilibrium where further strain increments do not lead to an increase of stress. To capture the influence of different microstructures and strength levels on shear band formation, DP500 and DP1000 dual-phase steels are analysed. The results of the micromechanical investigations are subsequently used to derive a damage criterion to predict material instabilities in finite element models of Nakajima-tests. Utilising this multi-scale approach enables the prediction of forming-limit curves which give a good estimation of the tendencies of experimentally determined curves.