Understanding Anisotropy and Forming Limit in 6C16 Aluminum Alloy: Insights from Evolutionary R-Values with Various Calculation Methods

The forming limit curve (FLC) is crucial for evaluating the local forming ability of sheet metal stamping. Considering the evolution of plastic deformation is a significant way to enhance the prediction of the theoretical forming limit. Based on the series anisotropic and forming limit characterization tests for 6C16 aluminum alloy sheet, the influence of calculation methods for evolutionary R-values on the FLC prediction was revealed in this paper. By comparing the calculation processes of plastic strain curves using three evolutionary R-value calculation methods, their calculation principles and limitations were analyzed in detail. In terms of the fitting error for the plastic strain curve, the segmentation linear fitting method had the highest error at 2.62E−3, while the third-order polynomial fitting method had the lowest error at 6.71E−7. Based on the Marciniak–Kuczinsky (M–K) model, the FLC was predicted by different evolutionary R-value calculation methods combined with Hill48, Barlat89, and YLD2000 yield models. The results indicate that the accuracy of FLC prediction is closely related to the fitting accuracy of the R-value solving method on the plastic strain curve. When the third-order polynomial method was used, the prediction accuracy of the FLC based on the YLD2000 yield model could reach 97.82%, which was an increase of 2.76% compared to the other methods. Therefore, optimizing the method of solving the R-value can significantly enhance the prediction accuracy of the FLC. The research findings offer a reference for the selection of appropriate yield models and anisotropic evolution characterization methods for the M–K model.

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