Integrated acoustic-optic-mechanics (AOM) multi-physics field characterization methods for a crack: Tension vs. shear

Rock macrofracturing often involves the tension-shear coexistence mechanism on the microscopic scale. This paper addresses the occurrence of tension and shear mechanisms in rock macrofracturing process based on the self-developed integrated acoustic-optic-mechanics (AOM) multi-physics field monitoring technique. With this advanced technique, three-point bending (3-p-b) tests with conventional loading and unconventional loading, as a control of the conditions that produce the different mechanisms, are first carried out on sandstone to establish AOM criteria for crack nature classifications. By using the AF-RA-based Kernel density median criterion and the optical angular bisector criterion, a coupled analysis of acoustical-optical data for the distinction of tension- vs shear-induced cracks in two different flaw configurations under uniaxial compression has been available. Results show that the crack initiation mode in tension-type rock bridge tests is dominated by the tension mechanism, while the ultimate failure pattern is shear-dominated. Comparably, failure of shear-type rock bridge is faithfully dominated by the shear mechanism. The paper, therefore, makes two contributions—a better understanding of rock fracturing process and providing a method of establishing the simple and intuitive criteria to justify the crack natures.