Experimental and maximum likelihood theory on acoustic emission statistic effect of coal-sandstone composite rock

A lot number of studies have been carried out on the acoustic emission statistic effect of rock material frac- ture damage in theory,experiments and simulation recently. Based on the test approach of acoustic emission,the re- search on the mechanism of internal damage of materials has also been conducted to analyze the AE signal by statisti- cal physics method. However,the study on acoustic emission statistic effect and critical behavior of different materials is rare. In this paper,the uniaxial compression test was carried out on the composite rock composed of coal and sandstone from Inner Mongolia and Chongqing using Japan Shimazu AGI-250 high-precision material testing machine,and the AE signal was captured by the DISP AE station. The probability density distribution analysis has been applied for the AE signals captured in different layers of sample composited by coal and sandstone under uniaxial compression, and a maximum likelihood estimation method for power-law exponent considering superposition effect has been estab- lished. The results showed that more influenced by the coal layer of composite rock,the acoustic emission energy prob- ability density distribution of the composite sample was different from that of pure coal and sandstone,in which coal layer and sandstone layer followed single and double power-law respectively in general. The maximum likelihood esti- mation equation of power-law exponent under superposition effect was determined by power-law exponent’s upper lim- itation α,the lower limitation β and the ratio x of AE amounts,which showed consistency with the experimental results of the layer with lower limitation,and gradually approached to the lower limitation with the increase of acoustic emis- sion energy. With increasing level of acoustic emission energy,the influence degree of coal layer on the whole compos- ite rock increased gradually,while that of sandstone layer had no significant change.