Full-field deformation measurements from Brazilian disc tests on anisotropic phyllite under impact loads

Abstract

To explore the dynamic fracturing behaviours and failure mechanisms, transversely isotropic phyllite rocks with five bedding plane angles were investigated for full-field strain Brazilian disc tests under different strain rates using a split Hopkinson pressure bar and high-speed digital image correlation (DIC) technology. Two kinds of crack evolution processes: the cracks in specimens with low bedding angles activated near the non-loading point, and other cracks initiated at the centre of the disc prior to exceeding the peak stress were observed. Considering the four types of failure modes characterized by different mechanisms, the dynamic failure mechanism of transversely isotropic rock was discussed. The Brazilian disc strength of transversely isotropic rock subjected to impact loads was computed by introducing the patchy weakness model to reflect the dominant role of the rock matrix in the dynamic test. The DIC results demonstrated that additional random orientation defects are activated and the competition for evolving into cracks becomes intense, indicating that cracks develop less along bedding planes as the strain rate increases. Moreover, the fracture patterns of the transversely isotropic phyllite specimens changed under static and dynamic conditions. Therefore, it is necessary to study the properties of transversely isotropic rocks under dynamic impacts rather than simply using inferences from static results.