PSI - Issue 82

Andreas Taucher et al. / Procedia Structural Integrity 82 (2026) 295–301 A. Taucher et al. / Structural Integrity Procedia 00 (2026) 000–000

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use a tool that is integrated in AutoForm, which defines the failure threshold according to the maximum edge strain. The threshold parameters are defined by a methodology that is standardized in each company, and some interview partners use the hole expansion test to determine the threshold parameter for different sheet edge qualities. The simulation software developer confirmed that reliable physical models for predicting edge cracks are still lacking. 4. Discussion Based on the information collected in the interviews, a basic methodology for the efficient definition of the material behavior in FE simulations of sheet metal forming processes can be supposed. A typically material model includes the flow curve, the yield surface and the forming limit curve for describing the plastic behavior and failure initiation, respectively. Combining the true stress-true strain curve obtained from uniaxial tensile testing and bulge testing and extrapolating this curve using a mathematical criterion that is selected based on the best-fit of the experimental data is recommended for defining the flow curve. Using the BBC05 criterion for defining the yield surface is supposed especially for simulating aluminum sheet forming, as this criterion provides a good description of biaxial yielding. The interview partners suggest determining model parameters based on material data from uniaxial tensile and bulge tests. The Nakajima test is recommended for creating the FLC. If the testing equipment is not available, a synthetic model can be alternatively employed. Because of the high experimental effort, considering strain rate dependency and kinematic hardening is only recommended, if the material is expected to be sensitive to these effects. Results of sheet metal forming simulations are usually associated with uncertainties, as they are just more or less accurate approximations of the reality. Therefore, most of the companies use their specific procedures for considering these uncertainties during the evaluation of the simulation results. A possibility to consider varying material properties is to generate “worst-case” and “best-case” material models according to tolerances specified in the material standards. Considering both extrema in the simulations allows for predicting the maximum variation of the component geometry and for assessing the sensitivity to failure formation. In general, highly accurate material data improve the predictive quality of the simulations. However, the experimental efforts and thus the costs for the acquisition of these data can Semi-structured interviews with experts from the automotive industry were conducted regarding their strategies and methodologies for the acquisition of material data used in finite element (FE) simulations of sheet metal forming processes. The following conclusions can be drawn based on the information collected in these interviews:  The interview partners reported similar procedures for obtaining material parameters and selecting models for their FE simulations. The main differences were in the definition of safety margins, tribological conditions and forming limits by using the classical strain-based forming limit curve (FLC).  Uniaxial tensile tests and bulge tests are the material testing methods used by the interview partners. Moreover, most of the partners employ the Nakajima test for determining the FLC. These three testing methods are state of the art and they just require limited effort compared to other material tests.  Because of cost and equipment restrictions, the interview partners cannot afford many different material tests to obtain the parameters required in complex material models. The efficiency of a material model or testing method (achieving acceptable results at comparatively low effort) seems to be the key factor for being selected.  Based on the recommendations of the interview partners, an efficient methodology for the material characterization includes only 2-3 established material tests. However, the methodology does not cover strain rate dependency and kinematic hardening, which are rather of minor interest, especially for aluminum alloys.  Increasing the number of interview partners would be beneficial to improve the applicability of the results of this basic study. Especially, more manufacturers of forming tools and developers of simulation software should be consulted. be considerable. 5. Conclusions