On Closing the Constitutive Gap Between Forming and Crash Simulation

With increasing requirements on crashworthiness, and light-weight car body structures being a central issue in future automotive development, the use of high strength steel qualities has become wide-spread in modern cars. Since these materials often show significantly lower ductility than conventional steels, it is of great importance to precisely predict failure under crash loading conditions. Hence constitutive models in crashworthiness applications – as for instance the Gurson/Johnson-Cook model which is applied widely at Daimler AG – need to be initialized with correctly determined internal variables mapped from a corresponding sheet metal forming simulation. Here two principle ways could be used theoretically: On the one hand different understanding of damage and failure in crashworthiness and sheet metal forming applications may be unified by a generalized incremental stress state dependent damage model (GISSMO). This approach can be considered as an attempt to replace the currently used FLD for the failure description in forming simulations. Furthermore, an advantage would be the inherent ability to account for load-path dependent failure behavior. On the other hand the already applied Gurson model in crash simulations may be fed by an estimation of the internal damage value from the forming simulation. The idea here would be to perform the forming simulation with a state-of-the-art anisotropic material model like e.g. the Barlat model, with a simultaneously executed estimation of Gurson’s damage evolution law. The present paper will enlighten these two possible approaches. Furthermore it will be shown that damage prediction in metal forming processes and subsequently the use of the results as initial damage values in crash simulations is possible and necessary to predict structural failure in crashworthiness simulations.