Effect of deformation induced nonlinear and anisotropic elasto-plasticity on sheet forming simulations

Anisotropy in initial yield and subsequent hardening in flow stress has been modeled in the finite element simulations to enhance the accuracy of formability and springback in sheet metal products. As continued efforts in the field of constitutive modeling, the evolution of anisotropy during the plastic deformation and its dependency on deformation path were also studied by many researchers. In addition to the plastic behavior, the elastic nonlinearity in predeformed sheet metals has been also regarded as a key factor which influences the accuracy of the sheet metal forming simulation, particularly in the springback simulation. In this study, recent reviews on the constitutive modeling for the deformation induced nonlinear and evolution of anisotropy are provided mainly using the published data [1,2]. To model the initial anisotropy the Hill 1948 yield function with non-associated flow rule and Yld2000-2d non-quadratic yield function were considered. Also, these yield surfaces evolve as a function of equivalent plastic strain. For better modeling the nonlinearity of elastic behavior during the deformation, recently developed multi-surface elasticity model was implemented in the simulation. To investigate the effect of the considered anisotropic plasticity and nonlinear elasticity on forming simulation, cylindrical circular cup drawing was experimentally conducted and its caring profile and springback after splitting of the formed cup in the circumferential direction were compared with the simulated results. The results showed that the finite element simulations could predict the deformed shapes after forming and springback with enhanced accuracy when the constitutive model could represent the complexity in the anisotropy and nonlinearity during plastic deformation.