Using acoustic emission technique to monitor damage progress around joints in brittle materials

Abstract

A vast amount of experimental research is available on crack initiation and propagation studies in brittle samples containing joints and rock bridges between them. One of the developed experimental methods is Acoustic Emission (AE) technique which is widely used in different studies as a non-destructive method in order to monitor failure mechanisms. A significant correlation exists between the AE signal characteristics and fracturing of a loaded material. In the present research, in order to monitor failure and damage process of large-scale pre-jointed samples with different geometries, uniaxial compression tests were performed while both AE technique and online photographic monitoring were utilized concurrently to visualize the failure progress around joints and their associated rock bridges. Results showed that by combining stress-time diagram with AE parameters (such as energy and count), failure stages can be identified from onset of loading until complete failure. These include sample compression, wing crack growth, crack coalescence, silence mode (stick-slip phenomenon) and final rupture. Inclination of the joints and their relative alignment with respect to the loading direction control the AE characteristics. Maximum amount of wing crack initiation stress, total AE energy and released energy during coalescence stage were attributed to samples that have shear or mixed failure mode. Furthermore, a two dimensional AE source location method alongside with a simple new algorithm were used to locate crack initiation and follow its growing path and make a comparison with the actual cracks in the loaded sample. Good correlation between AE recordings and actual observed damages showed accurate predictions of AE method is possible for recognizing damage location and its mechanism.