Local Measurement of Stress-Strain Behaviour of Ductile Materials at Elevated Temperatures in a Split-Hopkinson Tension Bar System

A split-Hopkinson tension bar system is modified to allow for measuring the stress-strain behaviour of ductile materials at large strains, high strain rates and elevated temperatures. The specimen is heated by induction, and a pyrometer provides a laser-based temperature measurement that controls the testing temperature in a feed-back loop. A high-speed digital camera system and an edge detection algorithm are used to obtain local measures of strain after necking of the axisymmetric specimens. Using the local strain measurements and Bridgman's analytical formulas, it is feasible to find the equivalent stress-strain curve to fracture for different levels of strain rate and temperature. Thermal and thermo-mechanical finite element simulations of the test set-up are used to evaluate the validity of the proposed experimental method.