单轴压缩条件下大理岩破裂过程声发射频谱演化特征实验研究

Spectrum evolution characteristics of acoustic emission during the ruptureprocess of marble under uniaxial compression condition

开展大理岩单轴压缩声发射实验,采用快速傅里叶变换获得声发射信号二维频谱图,提取其主频及次主频,进一步选用表征声发射信号频谱的主频与次主频的比值α和主频幅值与次主频幅值的比值β,结合分形理论研究大理岩破坏过程声发射频谱演化特征。研究结果表明,(1)大理岩破裂过程声发射次主频特征绝非全部波形的共有现象,仅为部分信号所特有,可以将声发射信号分为仅存在主频、不存在次主频的A类信号与主频、次主频同时存在的B类信号;(2)在岩石损伤的裂隙扩展至破坏阶段,A、B两类信号事件率中的较低值减少消失,累积事件数增长速率明显增大;(3)声发射信号主频带与次主频带分布规律相似,表现为连贯密集的条带状演化特征;(4)α、β均具有分形特征,其关联维数随着岩石损伤的增加表现出不同特征的降维现象。

The acoustic emission experiments on marble under the uniaxial compression are carried out.The fast Fourier transform is applied to obtain the two-dimensional spectrum of the acoustic emission signal,and the spectrum parameters such as dominant-frequency,secondary dominant-frequency are extracted.Then,a-value,i.e.,the ratio of the dominant-frequency to secondary dominant-frequency,andb-value,i.e.,the ratio of the dominant-frequency amplitude to secondary dominant-frequency amplitude,are adopted to characterize the spectrum characteristics of acoustic emission signal.The fractal theory is also used to study the characteristics of acoustic emission spectrum during the rupture process of marble.The results show that(1)the secondary dominant-frequency characteristics of acoustic emission in marble fracture process are not the common phenomenon of all waveforms,but are unique to some signals.The acoustic emission signals can be classified into two types:class A signals have only dominant-frequency characteristics,class B signals have both dominant-frequency and secondary dominant-frequency characteristics.(2)From the rock crack growth to failure stage,the low value event rates of two types of signals(i.e.,class A and class B)decrease and gradually disappear the increase rate of the cumulative number of events presents a significant increase.(3)Both the dominant-frequency band and the secondary dominant-frequency band of the acoustic emission signal have the similar distribution characteristics,showing a continuous and dense strip-like evolution feature.(4)Both thea andbhave fractal characteristics.With the increase of rock damage,their correlation dimension declines to some extent.