Modeling the cold formability of dualphase steels on different length scales

Modern multiphase steels contain constituents of distinctive mechanical properties, so that they develop strong gradients in the local strain distribution during forming operations and this strongly promotes the microstructural damage evolution. Consequently, the material's resistance against ductile crack initiation sets the limits of cold formability and these can even be reached without any macroscopic necking phenomena. The modified Bai Wierzbicki (MBW) model has been proven the capability of providing an impressive accuracy of simulation results when applied to stretch forming tests as it describes ductile crack initiation and propagation. The consideration of the third invariant of the stress deviator on plasticity and ductile failure is a key factor for the model's high accuracy, but due to its phenomenological character its applicability for materials design is currently not given. Furthermore, the quantity of material parameters is so high that an industrial application of this model cannot be expected. Therefore the paper presents an alternative approach for parameter calibration relying on virtual experiments on representative volume elements, where the plastic strain localization theory is applied without any other damage model. (C) 2014 Elsevier Ltd.