Acoustic emissions produced by discrete fracture in rock part 2—Kinematics of crack growth during controlled Mode I and Mode II loading of rock

Abstract

Abstract A well-characterized experimental programme was undertaken to study acoustic emission (AE) waveforms produced during discrete fracture propagation in rock. Large chevron-notched specimens were loaded in controlled conditions, and characteristic AE associated with Mode I and II fracture were isolated. Tested rock included medium-grained granite and micritic dolostone. The AE waveforms belonged to five characteristic classes. The variety of AE event classes was the same in Mode I and II loadings for both rock types. By far the most common three classes are related to basic step impulses. The mechanism for crack propagation in rock is indicated to be due to localized tensile failure for both tensile and shear loadings. Relative roughness of the crack surface corresponded closely with relative distributions of the different characteristic event classes. A ratio of event types was formulated which is a good indicator of the amount of out-of-plane crack growth. Rates of occurrence of AE events varied during loading modes, and between the two materials. Very few events occurred during load increase to peak or during unloading. Event rates increased as the crack propagated through the notch, and AE rates for subsequent constant-length crack propagation were constant.