Formability Modeling with LS-DYNA

This paper presents how the process of loss of stability, as described by the classical theory of Marciniak and Kuczynski, can be represented in non-linear finite element analyses with LS-DYNA. As will be seen, this is strongly dependent upon proper constitutive equations and parameters for the sheet material at hand. Of this reason two user-defined sub-routines for weakly and strongly textured aluminum alloys, respectively, have been implemented. Further, a non-local instability criterion has been implemented in order to detect incipient plastic instability. Next, some inhomogeneity must be introduced in the finite element model. In further analogy to the work of Marciniak and Kuczynski the inhomogeneity can be introduced either to the material properties or to the thickness. In order to perform the calculations in an efficient way, an automated procedure – called an FLD-calculator – has been created. Finally, the FEM-based calculations are compared with analytical and experimental results.