Enhanced characterization of the yield behavior of sheet metal at torsional load using digital image correlation methods

This work describes an approach for strain determination at the “in-plane” torsional test using digital image correlation (DIC) without brushing a statistical pattern on the specimen. It is well known, that the in-plane torsion test represents a appropriate test method for material characterization of sheet metal in terms of yielding and kinematic hardening . However, the gained measurement data does not allow the exact reading of material models for direct use in numerical analysis. The determination of shear values represents thereby the main challenge. Beside well established methods for stress-strain analysis mentioned in this contribution, the applicability of digital image correlation methods for the direct read of distortion on the specimen has been investigated. Therefore a torsion test rig has been developed and torsion tests using specimen out of mild- and high strength steel have been conducted. The in-plane situation allows the distortion tracking of single points on the specimen by using a 2D image correlation software. The needed pictures were taken by using a common digital lens reflex camera (DSLR). It has been shown, that the resolution of the inherent specimen pattern is sufficient for the use of common 2D image correlation software. Torsional test results in form of computed yield curves of mild- and advanced high strength steels are aimed to be presented in this contribution.