Numerical Assessment of the Progressive Rock Fracture Mechanism of Cracked Chevron Notched Brazilian Disc Specimens

Abstract

The International Society of Rock Mechanics (ISRM) suggested cracked chevron notched Brazilian disc method falls into a major testing category of rock fracture toughness measurement by virtue of chevron notched rock samples. A straight through crack front during the whole fracturing process is assumed in the testing principle but is never assessed. In this study, the progressive rock fracture mechanism of cracked chevron notched Brazilian disc rock specimens is numerically simulated for the first time. Two representative sample types with distinct geometry of notch ligaments are modelled. The assumption of a straight through crack front for chevron notched fracture samples is critically assessed. The results show that not only the notch tip but also the saw-cut chevron notch cracks during the experiments. The straight through crack front assumption is never satisfied in the realistic rock fracture progress of chevron notched disc samples. In addition, the crack features prominent curved front, far from being straight. In contrast to the sample type with narrow notch ligament, the acoustic emission (AE) of the simulation on the sample with wide notch ligament depicts obvious biased fracturing of the prescript fracturing route of the notch. The numerically observed progressive fracture mechanism calls for more attention on how to accurately calibrate the critical dimensionless stress intensity factor for a better measurement of Mode I fracture toughness via chevron notched samples.