Comparative study on stress acoustic emission changes in damage and failure of raw coal and briquette
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摘要: 在研究声发射特征与煤样和断裂的关系时，原煤和型煤都可用作实验样本。大多煤层材质较软，制造标准的原煤试样较为困难，因此使用型煤作为研究样本的实验较普遍，但型煤改变了煤的原始结构，影响了其物理和力学性质，使用型煤替代原煤作为实验样本的适用性一直是学术界讨论的焦点。此外，目前对于原煤和型煤在假三轴压缩实验中表现出的声发射特征差异的研究相对有限。针对上述问题，开展了原煤和型煤假三轴压缩声发射实验，从力学性能、断裂模式和声发射时空演化、频带能量分布、非线性特征等方面着重讨论和分析。结果表明：加载过程中释放的声发射能量和峰值应力总能量与煤样强度密切相关，原煤主要为剪切和拉伸混合破坏模式，型煤主要为拉伸轴裂破坏模式；煤样的声发射位置分别对应其宏观破裂形态，但发生时间和空间分布不同；在峰前加载阶段，原煤的声发射信号相对较少，而型煤的声发射响应剧烈，并在峰值应力时刻达到最大值；通过小波包分析得到型煤的声发射频带能量分布范围小于原煤，原煤的声发射信号频率主要集中在10～120 kHz，而型煤的声发射信号仅在0～100 kHz频率范围内活跃，说明型煤的微破裂规模大于原煤；原煤和型煤的波形能量90%活跃在0～150 kHz；当加载试样接近失稳破坏时，即加载应力为峰值应力的99%左右时，原煤和型煤声发射信号的Hurst指数均大于0.5，表明声发射时间序列与加载过程具有长期相关性。Abstract: When studying the relationship between acoustic emission features and coal samples and fractures, both raw coal and briquette can be used as experimental samples. Most coal seams have soft materials, making it difficult to manufacture standard raw coal samples. Therefore, it is common to use briquettes as research samples in experiments. However, coal briquettes change the original structure of coal, affecting its physical and mechanical properties. The applicability of using briquettes instead of raw coal as experimental samples has always been a focus of academic discussion. And currently, there is relatively limited research on the differences in acoustic emission features between raw coal and briquette in pseudo triaxial compression experiments. In order to solve the above problems, pseudo triaxial compression acoustic emission experiments are conducted on raw coal and briquette, with a focus on discussing and analyzing mechanical properties, fracture modes, spatiotemporal evolution of acoustic emission, frequency band energy distribution, nonlinear features, and other aspects. The results show that the acoustic emission energy released during the loading process and the total peak stress energy are closely related to the strength of the coal sample. The raw coal mainly exhibits a mixed failure mode of shear and tension, while the briquette mainly exhibits a tensile axial crack failure mode. The acoustic emission positions of coal samples correspond to their macroscopic fracture morphology, but their occurrence time and spatial distribution are different. In the pre peak loading stage, the acoustic emission signal of raw coal is relatively small, while the acoustic emission response of briquette is intense and reaches its maximum value at the peak stress moment. Through wavelet packet analysis, it is found that the energy distribution of the acoustic emission frequency band of briquette is smaller than that of raw coal. The acoustic emission signals of raw coal are mainly concentrated in the frequency range of 10-120 kHz, while the acoustic emission signals of briquette only jump in the frequency range of 0-100 kHz, indicating that the micro fracture scale of briquette is larger than that of raw coal. 90% of the waveform energy of raw coal and briquette is active at 0-150 kHz. When the loaded sample approaches instability failure, i.e. around 99% of the peak stress, the Hurst index of the acoustic emission signals of raw coal and briquette are both greater than 0.5. It indicates a long-term correlation between the acoustic emission time series and the loading process.
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图 1 假三轴压缩声发射实验装置
Figure 1. Pseudo triaxial compression acoustic emission experimental device
图 8 原煤和型煤声发射信号的时间序列特征
Figure 8. Time series characterization of acoustic emission signals from raw coal and briquette
图 9 不同应力水平下原煤和型煤声发射的空间分布和能量
Figure 9. Spatial distribution and energy of AE from raw coal and briquette at different stress levels
图 11 原煤和型煤在σ/σc=99%时的波形能量比分布
Figure 11. Distribution of waveform energy ratios of raw coal and briquette at σ/σc=99%
图 12 原煤和型煤在σ/σc=99%时的Hurst统计量
Figure 12. Hurst statistic at σ/σc=99% for raw coal and briquette
表 1 原煤和型煤的基本力学参数
Table 1. Basic mechanical parameters of raw coal and briquette
煤样类型 试样编号 轴向应
力/MPa弹性模
量/GPa泊松比 密度/
（g·cm−3）原煤 M–01 53.10 13.13 0.54 1.28 M–02 64.98 10.55 0.46 1.32 M–03 59.12 13.84 0.42 1.31 型煤 XM–01 21.46 1.43 0.71 1.08 XM–02 23.05 1.54 0.83 1.12 XM–03 23.16 1.96 0.77 1.16 
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表 2 声发射信号的分形结果
Table 2. Fractal results of AE signal
试样编号 Hurst指数 分形维数 相关系数 M–02 0.999 8 1.000 3 0.999 6 M–03 0.999 7 1.000 6 0.999 8 XM–02 0.999 5 1.000 4 0.999 4 XM–03 0.999 6 1.000 7 0.999 5
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