Achieving high strains in sheet metal characterization using the in-plane torsion test Q. Yin 1, a , J. Kolbe 1, b , M. Haupt 1, c , and A. E. Tekkaya 1, d 1 Institute of Forming Technology and Lightweight Construction, TU Dortmund University, Baroper Str. 301, D-44227 Dortmund, Germany a Qing.Yin@iul.tu-dortmund.de, b Joerg.Kolbe@iul.tu-dortmund.de, c Marco.Haupt@tu-dortmund.de, d Erman.Tekkaya@iul.tu-dortmund.de Keywords: In-Plane Torsion Test, Sheet Metal Characterization, Flow Curve. Abstract. The in-plane torsion test is used to determine plastic flow curves for sheet metals. Very high strains of up to an equivalent strain of 1.0 can be measured since there are no edge effects in a plane torsion specimen. In combination with optical strain measurement, an efficient evaluation method for this test was developed. However, the achievable strain varies for each material. The slippage between the inner clamps and the specimen was found to be one main limiting effect. In order to improve the clamping capability, different surface corrugations are applied at the inner clamping tool. Four sheet materials, DC06, DP600, AA6016, and AA5182 are selected for testing this new clamping setup. While the flow curve of DC06 is determined until a strain of 1.0 and above, such high values cannot be achieved for the other materials. It can be shown that the measurable strain can be increased by the choice of the surface corrugation features at the inner clamping. For the DP steel and the aluminum alloys, the flow curve can be determined until equivalent plastic strains of 0.5 to 0.6, which is also a significant improvement compared to many other sheet metal testing methods. Introduction In order to design sheet metal forming processes using numerical simulation, the material behavior has to be identified and described. Modern high strength sheet materials create new challenges for material characterization. Predicting the strain distribution, sheet thickness, springback behavior, and formability, numerous material parameters need to be determined. Thus, the measurement of flow curve, anisotropic yield locus, or kinematic hardening are typical tasks. For sheet metal characterization various experimental methods to identify the hardening curve are known from literature. These tests can be classified according to the stress state (Fig. 1a). The well-known uniaxial tensile test can be seen as a reference test due to its standardized testing procedure and specimen geometry. On the first quadrant of the yield locus the equi-biaxial stress state can be achieved by the hydraulic bulge test [1], the biaxial tensile test [2], and the stack compression test [3]. On the third quadrant uniaxial and biaxial compression tests for sheet material are known from literature [4]. However, these experiments show a high buckling tendency and, therefore, require more effort in order to reach noteworthy strains. For the second and fourth quadrant shear tests are available. One advantage is the constant shear area, which does not change during deformation. However, shear tests show inhomogeneous stress and strain distribution due to edge effects. Mainly three different kinds of geometry exist for shear specimen. The one-sided simple shear specimen represents the basic idea of a simple shear test [5] (Fig. 1b). By applying a parallel translation at the opposing edges of the shear zone, a rectangular shear bridge is deformed to a parallelogram. Since the free edges cause inhomogeneity the width to height ratio of the shear zone should be designed accordingly to ensure an appropriate size of quasi- homogeneous area in the center. Due to the resulting reaction moment the clamping tools of the one-sided shear test are very highly loaded. Extensive experimental effort in the clamping procedure Key Engineering Materials Vols. 554-557 (2013) pp 77-85 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.554-557.77 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 129.217.226.67-10/04/13,12:37:21)