| It is essential to model the Bauschinger effect correctly for sheet metal forming process simulation and subsequent springback prediction when material points are subjected to cyclic loading conditions. The combined nonlinear hardening model for time independent cyclic plasticity, proposed by Chaboche and coworkers, is examined and a simple modification is suggested for the isotropic part of hardening rule to utilize the conventional tensile test data directly. This modification is useful for the materials whose reversal loading curves saturate to the monotonic loading curve.; In addition, an anisotropic nonlinear kinematic hardening model (ANK model) is proposed in attempt to represent the Bauschinger effect more realistically.; The inverse method developed by Zhao and Lee (1999, 2000, 2000a) is modified to take into account of the current development. For two grades of steels (SPRC, DQ steel) and one aluminum alloy (AL6022-T4), the associated material parameters of sheet metals are identified.; The section integration through the thickness for plate/shell elements is also investigated in this study. The motivation is that the elasto-plastic solution of plate/shell element in the simulation of sheet metal forming and springback prediction highly depends on the section integration. An adaptive integration scheme is suggested to improve the integration through the thickness which keeping the number of integration points at minimum. The locations of integration points are varied to detect and to trace the kink points of stress distribution through a thickness during the incremental deformation. Thus, the nonlinear stress distribution through the thickness can be integrated accurately with a small number of integration points. From the simple bending and a square cup indentation problem, it is shown that the proposed integration scheme is very effective without a loss of solution accuracy. (Abstract shortened by UMI.)... |
