Effect of Anisotropic Yield Functions on the Accuracy of Material Flow and its Experimental Verification

This paper evaluates the performance of anisotropic yield functions based on mathematical methods which consider the prediction accuracy of yield stresses and R-values. The anisotropic yield functions being evaluated include one quadratic yield function and six non-quadratic ones. These yield functions are applied to describe the anisotropy of steel sheets and aluminum alloy sheets to evaluate their predictability. The root-mean-square errors (RMSEs) are computed to quantitatively assess their performance. The computation results of RMSEs demonstrate that the Yld2004-18p yield function exhibits the highest accuracy but requires extensive tests to calculate anisotropic parameters. The Yld2000-2d and BBC2000 yield functions are the same and thus have the same prediction accuracy. The application to cylindrical cup drawing shows that, associated with the Yld2004-18p and Yld2000-2d yield functions, the finite element (FE) simulations of cup drawing process can predict cups with six or eight ears. Considering both efficiency and accuracy, the Yld2000-2d and BBC2000 yield functions, which have less anisotropic parameters to be calculated, are recommended for metals with intermediate anisotropy.