Accurate measurement of stress-strain relation under high strain rate condition by using non-coaxial Hopkinson bar method

The non-coaxial Hopkinson bar method (NCHBM) is one of the techniques recently proposed for the high-speed tensile test and is a simple extension of the Hopkinson bar method (HBM). With the apparatus based on NCHBM it is easy to get high strain rates while keeping the high measurement accuracy because of its simplicity. In this study, the primary reason for the transient vibration emerging at the rising part of the stress-time diagram is discussed, and some concrete ideas to get the high accuracy in measuring stress-strain relations are proposed. Especially, by using the strain gauges affixed on the newly designed specimen, the direct measurement of both stress and strain was performed to get the exact stress-strain relation. Those ideas were examined by the experiment and the numerical simulation with using the FEM code LS-DYNA. The target materials employed in this study are SUS316 and SPCC.