Achieving High Strains in Sheet Metal Characterization Using the In-Plane Torsion Test

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.

Accurate springback prediction in deep drawing using pre-strain based multiple cyclic stress–strain curves in finite element simulation

“…Calculation of shear strain is carried out by d r dr    (2) at radial position with the rotation angle as the slope of the tangent to material line that was radial before deformation [31]. The calculation of equivalent stress and equivalent plastic strain in dependency of the normal anisotropy ( for isotropy) 7 which describes the relation between width and thickness change, is done using the Hill yield criterion [32].…”

A new test for determining fracture toughness in plane stress in mode II

“…The relative rotation is provided by means of the outer clamping, which fixes the specimens with screws (Figure 3(a)). The stationary inner clamp applies a vertical fixing load of 40 kN to the central region of the specimen in accordance to the procedure proposed by Yin et al 16 for the conventional plane torsion test (Figure 3(b)). The rotation angle was measured by means of an incremental rotary encoder with 5000 marks, which enables a resolution of 0.018°.…”

“…More recently, Brosius et al 15 changed the geometry of the plane torsion test specimens to include two twin bridges in order to avoid the disadvantages of conventional test specimens regarding high torque requirements and possibility of buckling. More recently, Yin et al 16 enhanced the testing conditions of torsion test specimens by improving clamping of the specimens by means of surface corrugations in order to avoid slippage and by incorporating an optical strain measurement system.…”

“…Picture and schematic representation of the experimental setup that was utilized in the fracture toughness tests performed with the double-notched torsion test specimen.Source: Adapted from Yin et al16 …”