A theoretical study on forming limit diagrams prediction

Abstract

The paper develops a theoretical study on forming limit diagrams using a new general code for forming limit strains prediction. Treating the Marciniak and Kuckzinsky (M–K) theory by a new approach, the code consists of the main part and several subroutines, which allow the implementation of any hardening law, yield function or constitutive equation, changing the respective subroutine. The strong influence of the constitutive law incorporated in the analysis on the predicted limit strains is shown by use of different yield functions like von Mises isotropic yield function, quadratic and non-quadratic criterion of Hill (Hill, 1948 and Hill, 1979) and Barlat Yld96 yield function. The difference in the stress–strain curve based on two hardening models (namely Swift hardening law and Voce equation), up to the maximum equivalent strain is presented and the effect on the predicted limit strains is also studied. In this work an aluminum alloy sheet metal AA6016-T4 is studied. Yield surface shapes, yield stress and R-value directionalities simulated by the respective yield functions were investigated and compared with experimental data. A successful correlation is observed between the experimental FLDs and the computed limit strains when the shape of the yield locus is described by Yld96 criterion and the hardening law represented by Voce equation.