煤与砂岩复合岩声发射统计效应的试验与最大似然理论

岩石类材料破裂损伤的声发射统计效应近年来在理论、试验和模拟方面已开展了大量研究,并且近年来以声发射为实验基础,采用统计物理学的方式分析声发射信号,继而关于材料内部损伤机制的相关研究也得到了发展,但是针对不同材料声发射统计效应及其相互作用与临界行为研究还较为缺乏。为此在实验室条件下采用日本岛津AGI-250高精度材料试验机对由分别取自内蒙古和重庆地区的煤与砂岩组成的复合岩开展了单轴压缩试验,利用DISP系列全数字声发射工作站采集压缩条件下试样中煤与砂岩层位的声发射信号,对信号进行了概率密度分布分析,并建立了考虑叠加效应的幂律指数最大似然估计方法。研究发现:复合岩在单轴压缩条件下煤层和砂岩层的声发射信号与纯煤和纯砂岩表现出了不同的统计性质,其整体声发射能量概率密度分布受煤层影响较大,砂岩层整体服从单幂律分布,而煤层则服从双幂律分布;叠加效应的幂律指数最大似然估计方程由上下限幂律指数α,β,与声发射数量比例x三参数控制,方程预测结果与试验中拥有较低幂律指数层位的分析结果一致,且随着声发射能量的增加逐渐趋近于下限幂律指数值;随着声发射能量级的增加,复合岩中煤层对整体统计结果的影响程度逐渐增加,而砂岩层的影响程度变化不明显。

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 fracture damage in theory,experiments and simulation recently.Based on the test approach of acoustic emission,the research on the mechanism of internal damage of materials has also been conducted to analyze the AE signal by statistical 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 established.The results showed that more influenced by the coal layer of composite rock,the acoustic emission energy probability 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 estimation equation of power-law exponent under superposition effect was determined by power-law exponent’s upper limitation 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 emission energy.With increasing level of acoustic emission energy,the influence degree of coal layer on the whole composite rock increased gradually,while that of sandstone layer had no significant change.