Study on fractal characteristics of acoustic emission and crack propagation in rocks

In this paper, the fractal nature of crack propagation in rocks is demonstrated by means of acoustic emission (AE) method. AE behavior is monitored during fracture toughness tests conducted on compact tension specimens of three types of rocks. It is shown that the microcrack fracture process zone proceeds the macroscopic crack extension, resulting in nonlinear fracture behavior. Iidate granite, Tohoku marble and Akiyoshi limestone were used. In Iidate granite, the fracture process zone grows in narrow region. Tohoku marble shows that the fracture process zone consists of distributed microcracks surrounding the macroscopic crack. In Akiyoshi limestone which is preheat treated, extensive crack branching is observed. The AE behavior is characterized by a fractal dimension b which is the slope of the log - log frequency and AE energy distribution. The trend in variation of b-value is shown to correspond to the crack propagation behavior. In addition, it is found that the fluctuation of b-value can also be characterized by fractal. This observation implies that the self-similarity lies in the rock fracture process.