A novel method to obtain the dynamic tensile stress–strain curve of rocks

The dynamic tensile stress–strain behaviour is desirable in evaluating the stability of geo-structures subjected to dynamic loading. However, the dynamic direct pull test is rather difficult to conduct due to experimentation difficulties; its common alternative the traditional Brazilian disc (BD) test cannot provide the stress–strain curve. This research study proposes a method to obtain the dynamic tensile stress–strain curve of rocks based on the modified dynamic BD test using a split Hopkinson pressure bar system in combination with a high-speed camera. The stress history of the disc centre is obtained following the International Society for Rock Mechanics and Rock Engineering suggested method on rock dynamic tests, while its strain history is estimated using the digital image correlation technique. Due to the rock heterogeneity, a small rectangular sensing region (RSR) enclosing the disc centre is chosen and the average strain of RSR is used to estimate the strain of the disc centre. As compared with the conventional strain gauge method, the strain calculation method in this study has many advantages, including non-contact measurement and high accuracy. The proposed method is thus more reliable and can be readily applied for determining dynamic tensile stress–strain curves of rocks.