This paper describes the results of an experimental research in which the fracture toughness of a granitic rock is determined by means of AE technique. ASTM standard specimens of the notched bend type having width from 30 to 508mm were tested.
The deformation and fracture behavior showed a significant nonlinearity and a stable crack growth were observed in all the tests. AE signals were detected at low load level, which indicates the occurrence of microcracking near the initial notch tip. Furthermore an analysis of the waveform and frequency spectrum of AE signals leads to a conclusion that there exists a close relationship between micro-fracture process at the crank tip and AE signals.
J-integral procedure were reasonably used because of the nonlinear deformation behavior. The relationship between the accumulated AE energy and J-integral provides a clear indication of the onset of a stable crack extension, denoted by JiAE The values of JiAE determined on the different specimens are independent of specimen size. This evidence suggests the feasibility of using a J-integral fracture criterion for this materials. A combination of non-linear fracture mechanics and AE technique provides a suitable procedure for determining the fracture toughness of rocks.
