Using Acousto-Optic Coupling Technology to Investigate the Fracture Evolution of Rock-Like Materials during Inclined Shear Tests

Abstract

This study used synchronized acoustic and optical nondestructive AE and ESPI technology with an inclined shear test to investigate the micro- and macroscopic failure mechanisms of cement mortar specimens under shear force. Crack opening displacement feedback was used to control stable damage to obtain complete loading curves of specimens sheared at different shear angles (β). AE technology was used to investigate the time and space distributions of the occurrence of microseismic sources produced by shearing within rocks. Synchronized comparisons were made using the interference images caused by the exterior of the rock material changing shape because of the shearing detected by electronic speckle pattern interferometry (ESPI). This was then used to examine three characteristics of the fracture evolution of rock-like material: localization, initiation of cracks, and crack propagation. The results indicate that shearing stiffness and shear strength are reduced following increases in the shear angle. In addition, the fracture propagation angle tends to change direction and its value also increases. Using AE methods to observe the evolution of microcracks in materials, the time and position of their localization were determined. These results were then compared with the crack initiation and propagation positions detected using ESPI. It is found that the fracture trends observed using these two methods were largely identical.