High Strain Rate Testing of a Low Carbon Steel to High Strains over a Range of Temperatures, Using a Torsional Hopkinson-bar Apparatus

A recent version of a torsional Hopkinson-bar apparatus, capable of high strains such as found in metal working, is briefly described. The magnitude of axial forces and bending waves in the system during a test is determined and their effects on measured flow stress shown to be negligible. Test results for a low carbon free-machining steel are given, for shear strain rates up to 4330/s and temperatures up to 500C. In all but one case this material fractured in the dynamic tests before the potential strain was realized, but shear strains of about 1.3 were usually obtained. Because of the large strains, adiabatic heating during the dynamic tests had a substantial effect on the stress-strain curves. The dynamic strain ageing effect was clearly evident from the tests at 400C and 500C.