A novel Hopkinson-based technique for high-speed biaxial testing of sheet metals

Abstract

Forming processes of sheet metals require knowledge of the material behaviour up to large levels of plastic deformation. To this purpose, biaxial bulge tests are often used. In present paper, a dynamic bulge test is presented. The testing principle relies on conventional split Hopkinson bar testing. Though, as opposed to existing setups, a different positioning of the bars leaves the sample fully accessible for optical measurements. The pressure imposed to a circular sample, together with the sample strain fields, allow to obtain reliable stress-strain data till significantly larger strains compared to tensile tests. The technique is illustrated by tests on an Al2024-T3 sheet. High speed camera imaging of the deforming sample combined with digital image processing is used to obtain full-field strain data. To quantitatively assess the added value of full-field strain measurements, stress-strain curves obtained with and without the strain data are compared.