Prediction of FLD for sheet metal by considering through-thickness shear stresses

In this study, the effect of through-thickness shear (TTS) stress has been examined on the prediction of forming limit diagrams (FLDs). Determination of the FLD is based on the Marciniak-Kuczynski (M-K) model with some modifications on the stress states for consideration of the TTS stress effects. For solving the equations, the Newton-Raphson method has been used. Furthermore, the Nakazima test has been simulated to investigate the stress state which occurs in the sheet during the test. Results showed that the formability of sheet metal could be better as the through-thickness stress increased. Also, implementation of TTS stress in the present model, the corresponding FLD has better agreement than the conventional FLD with the experimental test result.