STRESS EQUILIBRIUM EFFECTS WITHIN HOPKINSON BAR SPECIMENS

In the compression testing version of the split Hopkinson pressure bar technique a small disc-shaped specimen, sandwiched between two high-strength steel bars, is compressed by a stress pulse. The stress/strain properties of the specimen can be derived from the amount of the stress pulse reflected and transmitted by the specimen, assuming that stress equilibrium exists throughout the specimen. However, during the initial loading phase the multiple reflections generated at the two specimen/bar interfaces cause a non-uniform stress distribution, leading to possibly inaccurate estimates of the initial stress/strain properties. The paper describes a microcomputer analysis to study many of the important parameters affecting the build-up to elastic stress equilibrium and to predict the reflected and transmitted pulse shapes for different loading pulses.