三轴压缩下花岗岩声发射Kaiser点信号频段及分形特征
Characteristics of fractal and frequency bands at Kaiser signal of acoustic emission in granite under triaxial compression
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摘要: 采用高、低两种频率的声发射(AE)通道,对花岗岩试件完成了1~30 MPa围压范围内的循环加卸载AE试验。首先根据应力-时间-计数准则确定了Kaiser点。然后运用小波包频段分解法与G-P算法,分别对Kaiser点及相邻点的频段能量分布特征与AE能量关联维数进行了研究。研究结果表明:两种频率通道中接收到的AE振铃计数特征主要区别为数值大小,但整体的变化趋势基本相同,故Kaiser点出现的位置也基本相同;在Kaiser点频段特征方面,围压对Kaiser点特征频段变化规律的影响不明显;轴向相对应力水平小于63.67%时,Kaiser点特征频段为频段0~62.5 kHz和187.5~250 kHz;轴向相对应力水平大于69.06%时,Kaiser点特征频段为62.5~125 kHz;Kaiser点的AE能量关联维数均小于其相邻点。Abstract: Laboratory experiments on the characteristics of acoustic emission(AE)in high and low frequency channels of granite specimens under confining pressures from 1 to 30 MPa with cyclic loading and unloading were carried out.First, Kaiser points were determined by the guideline of stress-time-counts.Second, the characteristics of energy distribution for frequency bands at Kaiser and adjacent points were studied by means of the wavelet packet analysis technique.Third, the relevant fractal dimensions at Kaiser and adjacent points energy were obtained by using G-P algorithm.The results show that:(1) The main difference between characteristics of AE cumulative counts in two frequency channels is the magnitude of the numerical values.But the basic characteristics of AE counts and the locations of Kaiser points are similar in two frequency channels.(2) In the aspect of frequency bands at Kaiser points, the confining pressures have no obvious effect on the variation law of characteristic frequency bands at Kaiser points.The characteristic frequency bands at Kaiser points are 0-62.5 kHz and 187.5-250 kHz at the relative axial stress level less than 63.67% of peak stress, and 62.5-125 kHz as stress level exceeds 69.06% of peak stress.(3) The minimum values of relevant fractal dimensions are at Kaiser points.