Use of high-speed photography to study localisation during high-strain-rate torsion testing of soft iron

A technique has been developed for using high-speed photography to study the continuous formation of regions of localised shear in thin-walled tubular specimens of very ductile Remco iron tested in a torsional split Hopkinson pressure bar apparatus at nominal strain rates of ∼3000 s−1. A fibre-optic flash unit provides adequate illumination at framing rates up to 200 000 s−1. Photographic grids having 5 or 10 lines (or squares) per mm allow strains up to the order of 1000% to be estimated and the start of ductile tearing to be observed.