Crack Kinematics of Rock-Like Materials by Quantitative Acoustic Emission

Abstract

The moment tensor corresponding to acoustic emission (AE) source contains kinematical information on crack motion in a material. In order to determine the moment tensor components from AE waveforms, the SiGMA (simplified Green's functions fro moment tensor analysis) procedure is developed, where AE sources can be located, classified into tensile cracks and shear cracks, and then the directions of crack motions are determined. In this paper, the SiGMA procedure is further extended in rock-like materials, and a crack micrography is proposed. To this end, a relation between a damage parameter in damage mechanics and the moment tensor is clarified. Thus, damage evolution of the notched beam under bending is estimated from the trace components of the moment tensor. The scalar damage parameter is closely related with the crack density consisting of the crack volume. Therefore, the crack volumes are quantitatively estimated in unaxial compression tests of plate specimens with a slit. In the linear elastic fracture mechanics (LEFM), the direction of crack extension can be determined from the concept of the maximum circumferential stress. Since the direction of crack motion can be derived from the eigenvectors of the moment tensor, the relation is applied to estimate the normalized stress intensity factors.