Applications Of Numerical Simulation To The Analysis Of The Forming Limit Of Sheet Metals

The forming limit of sheet metals is the maximal deformation extent that can be obtained before fracture occurring during forming process, from which one can obtain the forming limit diagram (FLD). FLD is the most convenient and intuitionistic method of estimating the forming capability of sheet metals, which can resolve majority problems in sheet material stamping and mould design, such as prediction of wrinkle and fracture, confirmations of pressure-pad-force and forming-force, estimation of bank size, analysis of spingback, et al. In recent years, numerical simulation technology has been widely used to analyze problems of wrinkle, fracture, et al. during the forming of sheet metals, which lays foundations for obtaining FLD via numerical simulation.Finite element simulation could not gain accurate and reliable FLD without the guide of theory of forming capability. This paper predicted the forming limit of sheet metals by using the mechanical property parameters of materials and combining the ductile fracture criteria with finite element simulation. The characteristics and influencing factors of various ductile fracture criteria were compressively analyzed. Ductile fracture criteria built on the theoretical basis of Lemaitre's continuous medium damage-mechanics was chosen, and materials constants used in the ductile fracture criteria were calculated through the Role of Mixture.The FLDs of the two blanks—A15754 and SPCC—have been predicted by combining numerical simulations with the ductile fracture criteria. The influence of speed on the FLD was discussed. The predicted results of ductile fracture criteria were compared with the theoretical calculation values of limit strain calculating formula for the two yield criteria—Hill48 and Hill93, and the former are in good agreement with the latter.The bulging forming limit of the three automotive cover materials—X611-T4, A6111-T4 and A5754-O—were predicted applying Oyane ductile fracture criteria, Brozzo ones and Yu Zhongqi ones while stress hydrostatics was considered. The predicted results were compared with experimental values, which indicate that the results of Oyane ones and Yu Zhongqi ones are well consistent with experimental ones while that of Brozzo ones are not. The effects of pressure-pad-force, friction...