Earing predictions based on asymmetric nonquadratic yield function

A nonquadratic yield function (Yld96; Barlat, F., Maeda, Y., Chung, K., Yanagawa, M., Brem, J.C., Hayashida, Y., Lege, D.J. Matsui, K., Murtha, S.J., Hattori, S., Becker, R.C., Makosey, S., 1997. Yield function development for aluminium alloy sheet. J. Mech. Phys. Solids, 45, 1727) which simultaneously accounts for the anisotropy of uniaxial yield stresses and r values was newly implemented in a finite element code. Yield surface shapes, yield stress and r-value directionalities of Yld96 were investigated and compared with those of the previous yield function, Yld91 (Barlat, F., Lege, D.J., Brem, J.C. 1991a. A six-component yield function for anistropic metals. Int. J. Plasticity, 7, 693). Complete formulations for Yld96 implementation and the calculation of coefficients were also discussed for the convenient use of Yld96. A 2090-T3 aluminum alloy sheet sample was modeled and earing formation during a cup drawing test was simulated using the FEM code. The results of earing and thickness strain profiles were compared with the results obtained with Yld91. Investigations were further carried out with a translated yield surface to account for the strength differential effect observed in this material. Computation results with the translated yield surface were in very good agreement with experimental results. It was shown that the yield surface shape and translation have a significant influence on the prediction of the cup height profile during the drawing of a circular blank.