Anisotropic yield functions with plastic-strain-induced anisotropy (Q2365390)

In most anisotropic yield functions, the stress exponent, \(M\), associated with the shape of the yield surface, is usually independent of plastic-strain accumulation. This does not allow for different work-hardening characteristics under various strain states, as has been observed in aluminum alloys. Assuming that the coefficients characterizing anisotropy do not change with plastic deformation, but \(M\) varies with plastic strain, relaxing the isotropic hardening assumption, the authors fit well the effective plane stress and effective plane plastic strain in the corresponding stress-strain data obtained in uniaxial tension. These results show that, with all the yield functions tested, the aluminum exhibits substantial variation of \(M\), especially at large strains, while the brass shows a minor change. FEM simulations of the plane-strain sheet forming with 2008-T4 aluminum alloy demonstrates that the implementation of variable \(M\) with Hill's yield function gives better agreement with experimental measurements than the use of Barlat's criterion.