A rigid-viscoplastic finite element program for sheet metal forming analysis

Abstract A finite element modeling (FEM) program has been formulated to simulate a general three-dimensional sheet stretching operation. The program is based on an anisotropic, rigid-viscoplastic material model and utilizes triangular, plane stress elements incorporating a membrane approximation. These features are aimed at reducing CPU time for realistic industrial applications while retaining the necessary complexity of material behavior. An incremental theory of plasticity based on Hill's new theory of anisotropy and on a minimum plastic work path over the time step is employed. Special algorithms for dealing with die contact condition, material unloading and Coulomb friction have been developed. Simulations of stretch forming using two punch-and-die configurations are presented, and one of the results is compared with results appearing in the literature. Simulations of these operations using finer meshes and smaller time steps demonstrate the robustness of the formulation. Although the program is unoptimized, initial CPU times suggest that the program is suitable for large-scale industrial forming simulations.