In-Plane Torsion Test - Analysis of the Tool Design

The in-plane torsion test is more frequently used in various research facilities to obtain flow curves and the Bauschinger-coefficients of sheet materials. The execution and the experimental setup of the test currently depend on the experience, available machines as well as tools at the respective testing laboratories. For this reason, the author’s aim is to standardize the in-plane torsion test in order to create a common basis for carrying out the tests and to enable the characterization of comparable material parameters. The shape and structure of the inner clamping are often selected based on experience without knowing the exact effects on the process. Although the clamps appear less relevant, they are the only component in contact with the specimen and have a major influence on the process limits of the in-plane torsion test, such as wrinkling and slippage. To provide such a base, the shape and the surface structure of the clamping on the process limit of slipping are investigated. Results show that a ring-shaped clamping surface can transmit up to 50% more torque at the same clamping force compared to a full-circle clamping surface. It is derived analytically that torque transmission through plain clamping surfaces is not possible for a part of thin sheets (t = 0.5 and 3.0 mm). For such cases, structured clamping surfaces were used to enable successful torque transmission.