Anisotropic hardening and evolution of r-values for sheet metal based on evolving non-associated Hill48 model

The uniaxial tensile tests and biaxial tensile tests were carried out to investigate the deformation behavior and yield loci of DC06 steel sheet. The continuous evolution of r-values was calculated by the proposed inverse method, which has higher accuracy and simpler form compared with the previous methods. Based on the equivalent plastic work principle, the anisotropic hardening, the evolution of r-values and subsequent yield loci were investigated. Then, an evolving non-associated Hill48 anisotropic plasticity model was formulated. Where, based on the constructed stress cost-function and constraint conditions of r-values, the anisotropic parameters coupling the distortional hardening and evolution of r-values were developed to characterize the anisotropy evolution. Moreover, the relationship between the uniaxial tensile plastic strain and the equivalent plastic strain was derived. Based on this, the continuous variation curves of anisotropic parameters with real equivalent plastic strain were obtained. The comparison between the experimental and prediction results indicates that the developed model can accurately capture the distortional hardening, evolution of r-values and yield loci simultaneously. Furthermore, the effect of distortional hardening and evolution of r-values on the subsequent yield surfaces and plastic potential is analyzed.