Extending the annular in-plane torsional shear test specimen to applications at high strain rates

In-plane torsional shear testing is a well-established material testing technique in the metal forming community. The corresponding specimen is designed to be machined from sheet metal with a continuous annular shear zone intended to deform in simple shear. Consequently, there are no geometric discontinuities or “edge-effects” to induce volumetric changes or instabilities with the result that large true plastic strains up to 1.0 can be achieved. This paper presents an extension of the in-plane torsional shear test to the dynamic regime. Dynamic experiments were performed using a torsional split Hopkinson bar (TSHB) on specimens manufactured from Al 1050 H14. The experimental results show that the adopted technique can be used to determine the material behavior accurately and reliably in the dynamic regime.

FRACTURE PHENOMENOLOGY AND TOUGHNESS OF FILLED NATURAL RUBBER COMPOUNDS VIA THE PURE SHEAR TEST SPECIMEN

ABSTRACT Material anisotropy induced by strain in filled vulcanized rubbers strongly affects fracture toughness. The influence of carbon black content on fracture phenomenology and fracture toughness was investigated by performing video-recorded tests adopting a suitable grooved notched pure shear test specimen. In such a way, it was possible to analyze the so-called “knotty tearing” deformation mechanism occurring at the crack tip: sideways cracks perpendicular to the notch plane develop before the onset and propagation of a forward crack parallel to the notch plane. The J-integral fracture mechanics approach was adopted and digital image correlation analysis was performed to measure the strain at the crack tip. The presence of carbon black modifies the maximum chain extensibility and strain-induced crystallizability of the rubber matrix in the compound. The formation of sideways cracks occurred in all filled compounds and resulted in a link to the maximum chain extensibility. Nevertheless, toughness enhancement was observed only when strain-induced crystallization took place at the crack tip before the onset of the forward crack.