Influence of flow rule and calibration approach on plasticity characterization of DP780 steel sheets using Hill48 model

Anisotropic plasticity of DP780 steel sheets is characterized using Hill48 model in this paper. Both associated and non-associated flow rules (AFR and non-AFR) for Hill48 model are taken into account, and in total four approaches are used to calibrate model parameters under the plane stress state. For the non-AFR Hill48 model, the yield function is calibrated by equivalent stress values and meantime the plastic potential is calibrated by Lankford r-values. The other three calibration approaches are respectively implemented for the AFR model, which achieves three specified models, i.e. von Mises model (a reduced form), stress-calibrated (calibrated by equivalent stress) and r-calibrated (calibrated by r-value) AFR Hill48 model. Each model as well as the calibrated parameters is used to simulate the same group of tests including uniaxial tension, notched tension, shear and punch. A comparison between the test results and the four groups of simulation indicates that the non-AFR Hill48 model achieves the most accurate characterization of both the force-displacement curve and the local strain evolution. Among the three AFR models, the stress-calibrated one leads to the most acceptable simulation as far as the force response is concerned. Recommendations are finally made in terms of flow rule selection, calibration approach and validation in simulation of high strength steels using Hill48 model.