New criterion for evaluating plastic anisotropy in sheet thickness direction

In sheet metal forming simulations, an increasing number of anisotropic yield functions take account of the full stress state, i.e. the plastic anisotropy associated with the in-plane and out-of-plane behaviour. However, the benefits of incorporating out-of-plane anisotropy into sheet metal forming simulations remain unclear. This paper analyses the effect of out-of-plane anisotropy on sheet metal forming simulations and proposes a new criterion for its evaluation. To this end, a parametric study of a cylindrical deep drawing/embossing process with varying punch-die clearances and tool radii was conducted. The results indicate that the effect of out-of-plane anisotropy is correlated with both the clearance and the radius, resulting in significant variations in the local stress as well as the local plastic strain fields. Furthermore, the results support the overall applicability of the new criterion for evaluating the sensitivity of sheet metal forming processes to out-of-plane anisotropy.