Full field strain measurement in split Hopkinson tension bar experiments by using ultra-high-speed camera with digital image correlation

In this work the digital image correlation (DIC) technique was used for the full field measurement of the dynamic tension strain in traditional split Hopkinson tension bar (SHTB) experiments using the commercial image correlation software and the digital ultra-high-speed camera. This system was used to study the dynamic tensile response of nylon and aluminum alloy. The dynamic tensile stress-strain curves of nylon and aluminum alloy were accurately obtained to verify the validity of the dynamic tensile strain measured by the DIC technique. The results show that the average strain thus determined agrees well with the strain measured with a strain gauge attached to the specimen, but the traditional SHTB experiment's analytic strain is larger than the strain measured from the DIC method, which can be rectified by using the effective gauge length in consideration of the effect of rounded fillets. The effective gauge length does not depend on the strain rate. Based on the full filed strain measurements of the specimen, the strain distribution within the gauge length is uniform for the brittle nylon specimen, but the strain distribution for the ductile aluminum alloy specimen is not uniform due to the effects of the necking.