Novel In-Plane Torsion Specimen for the Characterization of Damage and Hardening

Funding: German Research Foundation (DFG)
Project: TE 508/65-1
Contact: Heinrich Traphöner M. Sc.

Equivalent strains much larger than 1.0 are obtained for ductile materials in the in-plane torsion test with circumferential groove.

This fact is attributed to the almost ideal simple shear stress and strain state. While the stress can be easily calculated from the measured torque, it is no longer possible to measure strains above this value by conventional optical strain measurement. The optical pattern deforms severely so that an accurate strain measurement is no longer possible. By the development of new methods for measuring very high shear strains in the in-plane torsion test the determination of flow curves of very ductile materials is made possible. On the one hand, the feasibility of applying a new undeformed optical pattern to the sample in several steps is investigated. Thus, flow curves are determined cumulatively. On the other hand, a new method allows to determine the flow curve incrementally from torque and angle of rotation. In this way, the limitations of the optical measurement can be overcome.

 

Flow curves for DC04 with 2 mm sheet thickness from the tensile test and the in-plane torsion test with groove