Shell Models with Enhanced Kinematics for Finite Elements in Sheet Metal Forming Simulations

Beyond the shell model of Reissner and Mindlin, which is available in LS-DYNA® for example in shell ELFORM=2/16, there have been many developments in the field of 3d-shell models in recent years [1]. 3d-shell models can be beneficial in sheet metal forming simulations because they allow for three-dimensional stress states. 3d-shell elements are available in LS-DYNA®, e.g. ELFORM=25. In the doctoral dissertation of Fleischer[2] it has been found that under certain conditions this element formulation suffers from an artificial stiffening effect. Although this finding dates back to 2009, this phenomenon has remained unexplained so far. In this contribution, the authors explain the reason for this stiffening effect and show a possibility to remove it. Moreover, an outlook on the development of higher order shell models for sheet metal forming simulation is given.