Characterization of Flow Curves for Ultra-Thin Steel Sheets With the In-Plane Torsion Test

The in-plane torsion test is a shear test that has already been successfully used to determine flow curves up to high strains for thin sheets with thicknesses between 0.5 mm and 3.0 mm. In the same way as with other shear tests, the formation of wrinkles is a major challenge in determining flow curves with the in-plane torsion test, especially when testing ultra-thin sheets with a thickness between 0.1 mm and 0.5 mm. A new method for suppressing wrinkling is introduced, in which the formation of wrinkles is avoided by arranging and gluing single sheets to multi-layered specimens. The influence of the used adhesive on the determination of flow curves is negligible. The proposed method is used to identify flow curves for two materials, the high strength steel TH620 and the soft steel TS230, used in the packaging industry. The Materials are tested in sheet thicknesses between 0.17 mm and 0.6 mm. The determined equivalent plastic strains for the TH620 with a sheet thickness of 0.20 mm, could be increased from 0.38 (bulge-test) to over 0.8 with the new method by using four-layered specimens.