Damage Analysis and Prediction of Forming Limits for IF Steel

Abstract

Based on Continuum Damage Mechanics, an isotropic damage model is developed to give a damage-coupled localized necking criterion. Hill’s 1948 quadratic yield criterion and flow theory are employed to describe anisotropic plasticity of sheet metal during forming procedure. Sheet forming experiments in three stress states and density measurement test have been performed on IF steel, and then the damage data obtained are used to validate numerical results based on the damage-coupled model. As for the proportional loading, a simple expression of limit strains has been obtained to predict the forming limit curve. Then the forming limit diagrams predicted by this damage-coupled anisotropic model have been validated with experimental data for two kinds of sheet metal. Also the influences of material properties on forming limit curves are discussed.