A freely expanding ring technique for measuring the tensile properties of polymers

The measurement of the stress-strain properties of materials at high strain rates is principally carried out using the split Hopkinson pressure bar (SHPB) technique, in which high compressive strain rates, typically in the range 10(2)-10(4) s(-1), are achievable with small solid discs as the test materials. Torsional SHPB systems have also been developed for test specimens in the form of small hollow cylinders. Another version of the SHPB technique has enabled high-strain-rate tensile measurements to be made, but inertial effects tend to limit the strain rate to about 10(3) s(-1) for the dogbone-shaped specimens. To achieve higher tensile strain rates, the authors have developed an expanding ring technique. This involves placing a thin ring of polymer as a sliding fit around a hollow, thick-walled, polymeric cylinder, the internal wall of which is loaded with a blast wave generated by an exploding wire. The tensile stress-strain properties of the ring material have been determined, at strain rates up to 1.6 x 10(4) s(-1), by observing the movement of the ring as it freely expands away from the cylinder. Several polymers have been studied and comparisons made with compressive stress-strain behaviour.