Rock is a typically inhomogeneous and anisotropic material, which contains several natural defects with various scales, such as micro-cracks, pores, fissures, joints inclusions, and precipitates. Large numbers of acoustic emission (AE) signals will be generated when rock is loaded until failure. Experimental study on rock damage process under cycling load based on acoustic emission technique was carried out. Mathematical relation between rock damage and AE counts based on damage theory and load/unload response ratio theory was established to study rock damage process and Kaiser effect. The Experimental results show that acoustic emission can reflect the rock damage process. Under cycling loading, rock damage is increasing during unload process with load increasing. There is internal relation between load/unload response ratio of AE and Kaiser effect. The damage during unload phase may be the induced factor for the occurrence of AE before the previously applied stress reached when specimens under re-load.
Acoustic emissions (AE) are transient elastic waves generated by the rapid release of energy from localized sources within materials such as metal, rock and concrete, when they undergo changes in the mechanical, thermal and hydraulic environment (Katsuyama 1996). AE technique is a helpful tool to study the unstable failure process because it can monitor the process of initiation and propagation of micro-cracks in brittle material continuously and in real-time, which is much superior compared with other methods and is applied to study failure mechanics of brittle material widely. For the importance of AE technique, many researchers applied AE technique to study the unstable fracture process of rock and have obtained many valuable results. Tang & Chen (1990, 1997) established quantify relationship between AE and failure units' distribution in rocks through the studies on mechanics of Kaiser effect based on statistical damage model.