Factors affecting the relative magnitude of acoustic emissions generated during the fracture of granite

Relative event magnitudes of acoustic emissions (AE) generated during the fracture of granite were examined and have been shown to depend on the proximity to the visible fracture, type of loading, and crystal size of the test specimen. A method was advanced for characterizing the relative strength of acoustic emissions based on a knowledge of the rate at which the signals decayed with distance from the source. In the small crystal size (1 mm) granite, AE events associated with fixed crack-mouth displacement (holding) were approximately twice as energetic as events associated with reduced crack-mouth displacement (unloading). The influence of crystal size on relative event magnitudes was most apparent during unloading, for which AE events in the large crystal size (10 mm) granite were on the average 3.5 times as energetic as events in the 1 mm granite.