Theoretical Prediction of the Limit Curves for Simulation of Plastic Instability

Summary In sheet metal forming operations, the forming limit is usually governed by strain localisation due to plastic instability and fracture. A great number of parameters may influence the forming limitations such as strain hardening, strain rate sensitivity, damage, anisotropy and strain path. The recent advances in finite plasticity, damage modelling and instability theory offer new tools for the prediction of the Forming Limit Diagrams (FLDs). In the present work, a series of tests to assess strain path effects in metal deformation were performed with different materials. A numerical simulation of necking phenomena under complex strain paths using Hill's theory of orthotropic anisotropy and time dependent constitutive relations was carried out. The validity of the model was tested through the comparison of theoretical results with experimentally determined FLDs.