On Parameter Identification for the GISSMO Damage Model

In order to improve predictiveness of crashworthiness simulations, great effort has been made regarding the treatment of crack formation and propagation. To achieve this, a consistent prediction of pre-damage, accumulated during manufacturing of a sheet-metal part, can help to improve accuracy. The constitutive models used for crash simulations are usually isotropic and based on the von Mises flow rule or the Gurson, Tvergaard & Needleman approach. For forming simulations, a more sophisticated and anisotropic description of yield loci – often based on the Hill or Barlat (1989) criteria – is considered important, which makes it necessary to use different constitutive models for both parts of the process chain. A damage model suitable to be used for both disciplines therefore has to be able to correctly predict damage regardless of the details of the constitutive model formulation. To fill this gap the damage model GISSMO (Generalized Incremental Stress-State dependent damage MOdel) has been developed at Daimler and DYNAmore (Neukamm et al. (2009), Haufe et al. (2010)). It combines proven features of damage and failure description available in crashworthiness calculations with the possibility of mapping various history data from sheet metal forming to final crash loading. The meanwhile carried out applications in everyday simulation work show excellent results based on carefully fitted material parameters. The present paper will focus on the parameter identification for the GISSMO damage model in crashworthiness simulation. A correct indication of damage and failure requires material data gained from several experimental tests. Starting from the treatment of the raw data, a procedure will be given, that shows how to calibrate the elastic-plastic behavior. In the following, a method is introduced which allows to capture damage and failure characteristics of a material. Step by step the determination and validation of particular GISSMO parameters will be discussed from a practical point of view. The objective is to give a complete overview of the calibration of a GISSMO material card.