Numerical Modelling of Combined Forming and Punching of Sheet Metal for Heat Exchanger Applications

Abstract: In this work a strategy for numerical simulation of punching during concurrent pressing of stainless steel sheet metal has been investigated accounting for the stress triaxiality and Lode angle parameter. Modelling of the damage evolution of a sheet metal is a useful tool within the field of engineering and materials science, and can provide useful information regarding material capabilities in a design process. An inverse modelling approach was used, where both a material model and a damage model were developed. The damage model was developed using the GISSMO damage model (Generalized Incremental Stress State dependent damage MOdel) which incorporates the dependence on the stress triaxiality and the Lode angle parameter. The fracture strain is defined in the stress triaxiality and Lode angle parameter space as a surface and experiments were conducted to cover the space of the stress states. The modified Mohr-Coulomb fracture criterion was used to predict fracture strain in every stress state. The simulation software LS-DYNA was used for numerical modelling and the software LS-OPT was used to identify damage parameters. The results show good agreement with experimental data but due to issues with stress state characterization of the experiments, further validation is necessary before the damage model can be used in practice. The results from this work show a strong potential for the inverse modelling approach to model the evolution of damage using GISSMO. It was concluded that, in order to accurately describe the material behavior during punching, experimental data from a wide variety of stress states is necessary and the results from this work highlight the need of complete and accurate experiments. These findings are important for future development of damage models.