Acoustic Emission Characteristics of Loose Particles in Direct Shear Test at Different Rates
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摘要:
松散颗粒堆积体在自然界和工业生产活动中广泛存在. 为研究其力学性质和失稳过程，基于声发射（acoustic emission, AE）技术探究松散体剪切过程的声学特征演化规律. 首先，分析松散颗粒在不同剪切速率下的AE特征参数；其次，结合加载过程的力学特征对AE演化阶段进行划分；最后，利用频谱变化和小波包能量占比进一步验证松散颗粒剪切破坏的AE演化规律. 结果表明：能量和振铃计数随剪切过程而逐步增大，且剪切速率越快，能量和振铃计数增幅越大；小事件数与大事件数的比值（
b 值）在剪切过程中逐渐降低，剪切速率越大，b 值越小；不同速率下的颗粒抗剪强度约为140 kPa，剪切力峰值集中在400 N左右，振铃计数、AE能量与b 值在剪切运动过程中的变化与剪切破坏阶段密切相关；频谱重心会随剪切过程逐步降低，从大约350 kHz降低至250 kHz，同时，较低频带能量占比增加、较高频带能量占比减少，导致频谱重心不断下移.Abstract:Loose particle accumulations are widely present in nature and industrial production activities. In order to study their mechanical properties and instability processes, acoustic emission (AE) technology was used to explore the evolution law of acoustic characteristics of loose particles in a shear process. Firstly, the AE characteristic parameters of loose particles at different shear rates were analyzed. Then, the AE evolution stages were divided based on the mechanical characteristics of the loading process. Finally, the AE evolution law of loose particles under shear failure was further verified with spectral changes and the proportion of wavelet packet energy. The results show that the energy and ringing count increase gradually with the shear process. The faster the shear rate, the larger the increases of energy and ringing count. The number ratio of small events to large events (
b value) decreases gradually during the shear process, and the larger the shear rate, the smaller theb value. The shear strength of particles at different rates is about 140 kPa, and the peak shear force is about 400 N. The changes of ringing count, AE energy, andb value during shear motion are closely related to shear failure stage. The spectral barycenter gradually decreases in the shear process from about 350 kHz to 250 kHz. Meanwhile, the energy proportion of the low frequency band increases, and the energy proportion of the high frequency band decreases accordingly, which results in a spectral barycenter constantly moving down.-
Key words:
- loose particles /
- shear rate /
- acoustic emission (AE) /
- spectrum analysis /
- wavelet packet decomposition
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图 4 不同剪切速率下AE能量变化示意
Figure 4. Schematic of AE energy variations at different shear rates
图 6 松散颗粒体剪切破坏过程分段示意
Figure 6. Sectional diagram of shear failure process of loose particles
图 7 不同速率下剪切破坏过程振铃计数规律
Figure 7. Ringing count law of shear failure process at different rates
图 9 不同速率下剪切破坏过程b值规律
Figure 9. b value rule of shear failure process at different rates
图 10 不同速率下剪切破坏过程频谱重心规律
Figure 10. Spectral barycenter of shear failure process at different rates
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