Study on Crack Propagation Process of Granite Samples Based on AE and its Location Technique

摘要

Acoustic emission (AE), which is produced by the micro-cracks occurrence or growth, is an ubiguitous phenomenon associated with brittle fracture in many materials. AE technique can monitor the microfractures development in the rock sample continuously and in-real-time, which is better than other methods. In this paper, acoustic emission (AE) and location technique was employed to study rock failure process. It was investigated using different precut crack granite samples (70 mm×70 mm×150 mm),and AE sensors were surface mounted. A Geiger location algorithm allows AE event location from first arrival times to be determined by AE sensors, which was applied to study the crack initiation and propagation process, also to analyze the crack spatial evolution mode with stress changing during the total loading process. The experimental results showed AE activity represents different characters with stress-strain changing during the total loading process ; the quantity of AE events was very little in the initial loading up to crack initiation ; when initial crack generated AE events apparently increased ; AE events was in quiet period after crack initiation up to before crack propagation ; AE activity sharply increased from crack stable propagation up to crack unstable propagation; especially in crack unstable propagation step AE events reach the most quantity in the division strain. There is "void space" of AE events during the AE location results; the "void space" of AE events is the position of macroscopic crack breakthrough, which can be used to predict the crack breakthrough position of rock samples. Meanwhile, AE location results are also direct reflection of interior stress field propagation process. AE location result also reflect directly the spatial position, direction and spatial curved face of crack propagation in the rock sample, which is very significant to study the mechanism of rock failure.