A methodology for prediction of forming limit stress diagrams considering the strain path effect

The purpose of this study is to present a methodology for prediction of the forming limit stress diagram (FLSD) and reexamine the effect of strain path on prediction of FLSD. The methodology is based on the Marciniak and Kuczynski model. For calculation of sheet metal limiting strains and stresses, a numerical approach using the Modified Newton–Raphson with globally convergence method has been used. The conditions for non-proportional loading have been achieved by imposing two types of pre-straining on the sheet metal. The effects of grain size, surface roughness and sheet thickness on the FLSD have also been presented. The evaluation of the theoretical results has been performed by using the published experimental data for ST12 low carbon steel alloy.