The formability of twinning-Induced plasticity steels predicted on the base of Marciniak-Kuczynski theory

Abstract

The purpose of this work is to predict and analyze the formability of twinning - induced plasticity steels through the Marciniak-Kuczynski (MK) theory with emphasis on the solutions for improving the prediction results. The selected constitutive equations involve the Yld00-2d of Barlat et al. (2003) plane stress yield function, the Swift strain-hardening power law and the dislocation density based constitutive model proposed by Kim et al. (2013), taking into account the dislocation glide, twinning and dynamic strain aging. Three types of high manganese content TWIP steels sheet were selected. To understand the formability of the TWIP steel and the factors influencing it, a sensitive study on the effect of the mechanical properties of the TWIP steel on the MK theory concept and the predicted forming limits is performed. Using the dislocation density based microstructural model, the deformation twinning effect and the contribution of dynamic strain aging to the FLDs of TWIP steel is analyzed. The relevant influence of the sharpness of the yield surface in the biaxial stretching region in the prediction of FLDs of TWIP steels is highlighted. The extended MK model can be adapted to predict the forming limits of the TWIP steels by using an unusual high initial geometrical defect imposed by their high strain hardening. In this way it was showed that the MK theory cannot be applied for predicting the forming limits of TWIP steels unless by applying imperfection factors that are not physically reasonable. Therefore, new failure models are required for TWIP steel.