Applicability of Hill48 Yield Model and Effect of Anisotropic Parameter Determination Methods on Anisotropic Prediction

In this paper, the limitations of the Hill48 yield model in predicting directional yield stresses and plastic strain ratios (r-values) were investigated. According to a theoretical derivation, there are several inherent forms of the variation law of uniaxial tensile yield stress and r-value with angles calculated by Hill48. Three types of materials, DC04, DP600 and AA3104, were taken as research objects, and the anisotropic parameters and prediction errors were obtained by direct solution methods and the non-associated flow rule (non-AFR) methods based on different numbers of experimental data were analyzed. The results show that the prediction accuracy of the Hill48 yield model mainly depends on whether the anisotropic behavior of the material satisfies the above change law and is not directly related to the value of r. On this basis, under the associated flow rule, an anisotropic parameter identification method based on the conditional extremum of the cost function was proposed. It can significantly improve the prediction accuracy of low-carbon steel materials compared with the direct solution method. The research results provide detailed insight into the reasonable application of the Hill48 model in sheet metal forming and a reference for investigating the limitations of other advanced yield models.