Effect of size on characteristic of acoustic emission in rock specimen

A series of uniaxial-compression tests were conducted on some granite specimens. A multi-channel, high-speed AE signal acquiring and analyzing system was employed to acquire and record the characteristics of AE events and demonstrate the temporal and spatial distribution of these events during the failure process. The test results show that in the primary stage, many low amplitude AE events are developed rapidly and distributed randomly throughout the entire specimens. In the second stage, the number of AE increases much slower than that in the first stage, while the amplitude of most AE events became greater. Contrarily to the primary stage, AE events clusteres in the middle area of the specimen and distributes vertically conformed to the orientation of compression. The most distinct characteristic of this stage is a vacant gap formed approximately in the central part of the specimen. In the last stage, the number of AE events increases sharply and their magnitude increases accordingly. The final failure location coincidently inhabited the aforementioned gap. The main conclusion is that most macrocracks are developed from the surrounding microcracks existed earlier and their positions occupy the earlier formed gaps, and the AE activity usually becomes quite acute before the main rupture occurs. Supported by the Special Subject of 863 Programm(2007AA06Z107) and the Younth Foundation of HPU(Q2008-51)