基于声发射多重分形特征的层状板岩失稳前兆研究

为探究层状板岩失稳前兆，开展了5组不同层理倾角（0°、30°、45°、60°、90°）板岩的单轴压缩试验，分析了其破坏形态、声发射参数及多重分形特征，讨论了多重分形谱宽Δα与损伤演化的关系，得到了基于多重分形的破坏前兆及预警时间。结果表明：当层理倾角由0°增加到90°时，板岩先由张拉劈裂破坏向劈裂剪切破坏转变，接着变为剪切滑移破坏，最终转变为张拉劈裂破坏；振铃计数突增以及低频-高幅信号比例的持续增加可作为板岩失稳前兆，且层状板岩在裂纹贯通阶段低频-高幅信号占比随层理倾角的增大呈先减后增的变化过程；多重分形谱宽?α先突减再突增也可作为不同层状板岩的失稳前兆，且Δα的突增时间提前于损伤突变，Δα预警时间随层理倾角的增大呈先增后减再增的变化过程，层理倾角为30°时预警时间最长。

Research on the failure precursors of layered slate based on multifractal characteristics of acoustic emission

In order to explore the failure precursors of layered slate, uniaxial compression tests of five groups of slate with different bedding angles (? = 0o, 30o, 45o, 60o, 90o) were carried out. The failure modes, acoustic emission (AE) parameters and multifractal characteristics were analyzed, and the relationship between multifractal spectrum width (Δ?) and damage evolution was discussed. In addition, the precursor and warning time of final failure based on multifractal were determined. The results show that when the ? increases from 0o to 90o, the failure modes of slate change from tension-splitting failure to splitting-shear, then to shear slip, and finally to tension-splitting. Moreover, the abrupt increase of AE counts and the continuous increase of low-frequency (LF) and high-amplitude (HA) signals can be identified as precursors. And the proportion of LF-HA signals in the crack coalescence stage decreases first and then increases with the increase of ?. The sudden decrease and the following increase of Δ? can also be the precursor. Furthermore, the sudden increase time of Δ? is ahead of the damage mutation. Specifically, with the ? increasing, the early warning time of Δ? increases first, then decreases and then rebounds. The slate with ? = 30o has the longest early warning time.