Characterization of ultra-thin sheets with the in-plane torsion test

• Applicant: Professor Dr.-Ing. A. Erman Tekkaya
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551704509

There are various test methods available for determining material properties that are necessary for the design of forming processes. In addition to established methods such as the tensile test, the in-plane torsion test (IPT) is becoming increasingly important for science and industry. Currently, the in-plane torsion test is already being successfully applied to thin sheets with a thickness between 0.5 and 3.0 mm for characterizing the hardening behavior up to high strains, the kinematic hardening and the maximum fracture strain. For many applications in the packaging and other industries, the sheet thicknesses required to be characterized fall below the limits of the established methods. For example, a low sheet thickness in the in-plane torsion test without suitable countermeasures leads to large measurement inaccuracies and also to a very early failure of the specimens due to wrinkling. This completely negates the general advantages of the in-plane torsion test.For this reason, the application of the in-plane torsion test for ultra-thin sheets between 0.1 and 0.5 mm thickness is to be extended in the present proposal. The necessary requirements for the method and the test systems are be investigated so that the technology can be successfully transferred to industry. The influence of the testing equipment and the measuring sensors on the results and the process limits during the testing of ultra-fine sheets is investigated for this purpose. In order to avoid wrinkling, two methods for wrinkle suppression is considered in the course of the project. On the one hand, the artificial increase of the sheet thickness by means of glued specimen stacks is analyzed. Here, the influence of the adhesive layer on the results and the process limits of this method are considered. Another method is the reduction of the inner clamping diameter. For this purpose, the influence of the technology and materials are estimated analytically and numerically. These results serve as the basis for the development of a testing machine designed for testing ultra-thin sheets with small clamping radii. This machine will be built and used for validation of the numerical simulation. Isotropic and kinematic hardening on several steel and aluminum alloys is determined. Finally, the influence of yield curve determination up to high strains on the results of a numerical simulation is quantified. A numerical model of an application-oriented forming process is created and the deviations when using different methods for flow curve extrapolation are investigated. Both extrapolated yield curves from the tensile test, which are based on different approaches, are compared with experimental and extrapolated yield curves from the in-plane torsion test.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: ERICHSEN GmbH & Co. KG; Novelis Deutschland GmbH; thyssenkrupp Rasselstein GmbH
• Co-Investigator: Dr.-Ing. Heinrich Traphöner