New criterion for evaluating influences of stress uniformity on results in split Hopkinson bar tests

The split Hopkinson bar (SHB) technique has been widely used to determine dynamic behaviours of materials at high strain rates. In this technique, the non-uniformity of the stress within specimen may lead to errors in test results. In most of the relevant literatures, the relative time duration for stress to approximately equilibrate in specimen was used to evaluate the stress uniformity. But by one-dimensional simulations, it is found that this criterion is not always true. Therefore, two new indices, the degree of stress uniformity and the relative uniformity strain, are defined to characterise the stress uniformity. Then a new criterion is proposed for evaluating the influences of stress uniformity on test accuracy. This study provides guidelines for SHB test designs and data validations.