Springback prediction of advanced lightweight sheet metal considering evolving plastic behaviors under different reverse loadings

This research investigates the influence of tension-compression asymmetry (TCA) on the plastic behaviors of pressure-sensitive sheet metal under different reverse loadings for QP1180 steel and AA7075 T6 aluminum. A new constitutive model is proposed based on the HAH20 distortional hardening framework for both proportional and non-proportional loadings. The new model couples the five stress states-sensitive (Five-SSS) analytical yield function for proportional loading to model the TCA evolution. A direct-separate calibration approach is proposed to calibrate the reverse loading related-parameters directly from the experimental data to accurately predict the evolution of Bauschinger effect, transient hardening and permanent softening at different pre-strain levels. The proposed model highly improves the prediction accuracy of the plastic behaviors under cyclic shear loading for the investigated materials. The U-draw bending simulation of QP1180 under different blank holding forces is conducted to validate the accuracy of the proposed model. Compared with the HAH20 model, the proposed model improves the prediction accuracy of springback angle θ₁ by approximately 56.25 % and 75 % under blank holding forces of 10 kN and 20 kN, respectively.