Non-associated anisotropic plasticity of metal sheets based on the distortional concept

The anisotropic plastic behavior of metals is important and commonly necessary in industry for accurate sheet metal forming simulations. An efficient model would greatly improve the final simulation results for forming processes and component designs. In this paper, an alternative plastic method is proposed where a distortional yield surface is adopted under the non-associated flow rule (NAFR) to accommodate the complex anisotropic behavior of the stress and strain evolution. This plastic model bypasses a multistep numerical procedure in calculating the first derivative of homogeneous anisotropic hardening (HAH) [1] function. Thus, it is an efficient model with low computational cost. The capability of prediction and a detailed application are investigated considering material data of dual phase steel sheets. The plastic constraints are derived to obtain stable flow conditions during plastic deformation accumulation. The experimental calibration and nonlinear verification through tension-compression and tension-tension (including cross-loading) tests are performed, where a good prediction and agreement are observed. The integration procedure, as well as its corresponding material subroutine, is developed and implemented into the finite element program for structural simulations.