Influence of the plasticity model in sheet metal forming simulations

The influence of the plasticity model adopted in sheet metal forming simulations is investigated in this work by means of a numerical study of three types of experimental tests, namely, the hemispherical punch stretching, the cup-drawing and a bending-drawing test proposed recently. The simulations are performed with the finite element code Abaqus wherein the yield criterion proposed by Ferron et al. [Int. J. Plas. 10 (1994) 431] has been implemented. For the sheet metal forming operations where the loading paths are not too sharply non-linear, as is the case of the hemispherical punch stretching and the cup-drawing tests, it is shown that the numerical predictions of strain distributions mainly depend on the yield surface shape in the stress range of interest. Furthermore, the isotropic hardening assumption provides a good fit of experiments for these tests where the sheet is submitted to relatively linear loading paths. On the other hand, the strains obtained in the bending-drawing test and, in particular, the amount of widening of the strip cannot be accounted for with the assumption of isotropic hardening. This suggests that this assumption should be relaxed to take account of the kinematic hardening effects associated with stress reversals undergone in the bending-drawing test.