Development of a strain-gage installation method for high-speed impact of strikers on a Split Hopkinson bar apparatus

Abstract

When designing a split Hopkinson system, the yield strength of the selected pressure bar material determines the maximum stress attainable within deforming samples and also, the maximum striker velocity that is usable to prevent plasticity in bars. In practice, to avoid strain gages stripping, the velocity of the striker is limited by the instantaneous particles acceleration generated in the bars. As a consequence, the full potential of the Hopkinson system can not be used. Therefore, for material having very high yield strength, it is very difficult to induce the required stress wave to create plasticity using a split Hopkinson apparatus. The idea of using an improved method for installing strain gages to withstand very high accelerations is very important for high dynamic loading using the split Hopkinson bar system. This paper compares standard strain gage installation procedures with a new approach. Data obtained for a material showing no plasticity at a normal operating impact velocity range of 22 m/s while showing usable level of plasticity when using a high impact velocity of 37 m/s is discussed.