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An evolving non-associated Hill48 plasticity model accounting for anisotropic hardening and r-value evolution and its application to forming limit prediction
Experimental and numerical investigations on the characterisation and prediction of cold formability of a ferritic steel sheet were performed in this study. Tensile tests and Nakajima tests were conducted for the plasticity characterisation and the forming limit diagram determination, respectively. For the plasticity behaviour description, an evolving non-associated Hill48 anisotropic plasticity model was formulated to accurately characterise the anisotropy evolution under monotonic loading, including anisotropic hardening as well as the r-value evolution. The detailed model parameter calibration procedure was also demonstrated. Eventually the model was applied to the forming limits prediction in conjunction with the modified maximum force criterion. A systematic and detailed study was performed addressing the impacts of the evolving and non-associated characteristics of the model formulation on the forming limits prediction by comparing the proposed model with the classical ones. Both the plasticity model and its application to the formability prediction were validated by the experimental results.