Microcracking in tensile fracture of a brittle rock

Acoustic emission (AE) and digital image correlation were used to monitor mode I fracture in center notch and smooth boundary specimens. The AE source was characterized as a microcrack and represented by the moment tensor, which was obtained by minimizing the error between displacements calculated from an elastodynamic solution and those measured, subjected to the constraint of a microcrack source. Results showed that microcracking was locally mixed-mode dominant because of oblique microcrack planes within a tortuous fracture. However, the microcrack mechanisms decomposed in the global coordinate system indicated mainly mode I opening with modes II and III ten times smaller.