Study on acoustic emission characteristics and energy evolution of Brazilian splitting tests of coal samples with different height-diameter ratio
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摘要:
为探究不同高径比对圆盘煤样抗拉强度及能量演化机制的影响，对5组直径相同、高度不同的煤样进行巴西劈裂试验，并同步声发射监测系统及三维形貌扫描技术探究不同高径比煤样的抗拉特性、声发射特征、破断模式及断面形貌特征。结果表明：随着煤样高径比的增加，煤样抗拉强度呈现逐渐减小的趋势，当高径比在0.4∶1至1∶1范围内时，高径比为0.4∶1的煤样抗拉强度最大。圆盘煤样宏观破坏模式逐渐由拉−剪混合裂纹主导的多裂纹复杂破断模式转变为单一断面拉伸裂纹破坏。累积声发射能量逐渐增大，且累积能量曲线的聚丛现象较为显著，呈阶梯式上升趋势。较低应力水平阶段的耗散能占比逐渐增大；当荷载增至弹性极限时，耗散能及其占比逐渐减小；当煤样趋近破裂阶段时，弹性应变能与耗散能占比趋于平稳；当煤样进入峰后破裂阶段时，积聚在煤样内的弹性应变能迅速释放，耗散能占比急剧增加，煤样内部宏观裂纹迅速扩展并贯通。多重分形谱宽度（Δα）逐渐增大，频谱测度子集（Δf）小于零，表明煤样拉伸破裂过程中小破裂尺度信号占主导优势。另外，不同高径比工况下煤样破断面高程的相对频率呈现出拟合度较高的高斯型函数分布，分形维数呈逐渐增大趋势，表明高径比越小，其破裂后断面的复杂程度越低，反之高径比越大的煤样破裂后断面粗糙程度越复杂。
Abstract:In order to explore the influence of different ratios of height-diameter on the tensile strength and energy evolution of disc coal samples, Brazilian splitting tests were carried out on five groups of coal samples with the same diameter and different heights. The tensile behavior, acoustic emission (AE) characteristics, fracture modes and section morphology characteristics of coal samples with different height-diameter ratio are investigated using a synchronous AE monitoring system and three-dimensional morphology scanning technology. The results show that the tensile strength of coal gradually decreases with the increase of the ratio of height to diameter, and the peak strength of coal reaches the maximum when the height-diameter ratio is 0.4∶1. The failure mode of coal samples gradually changed from the complex fracture mode of multiple cracks dominated by tensile-shear mixed cracks to the tension cracks of single section. The cumulative AE energy increases gradually, and the clustering phenomenon is more significant, showing a stepwise upward trend. The proportion of dissipated energy increases gradually at the lower stress level. When the load increases to the elastic limit, the dissipated energy and its proportion decrease gradually. The ratios of elastic strain energy and dissipated energy tend to be stable when the coal sample approaches the failure stage. When the coal sample enters the post-peak stage, the accumulated elastic strain energy releases rapidly, the proportion of dissipated energy increases sharply, and the macroscopic cracks in the coal sample rapidly expand and coalesce. The width (Δα) of the multifractal spectrum gradually increases, and the spectral measure subset (Δf) is less than zero with the increase in height-diameter ratio, which indicates that the small fracture scale signal dominates in the splitting tests. In addition, the relative frequency of broken section elevation of coal samples under different height-diameter ratios presents a good Gaussian function distribution, and the fractal dimension shows a gradually increasing trend. The smaller the height-diameter ratio, the less complex the fractured section will be, whereas the larger the height-diameter ratio, the more complex the roughness of the broken section will be.
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Keywords:
- Brazil splitting /
- mechanical properties /
- acoustic emission /
- micro cracking /
- multifractal
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图 3 不同高径比圆盘煤样应力峰值
Figure 3. Peak stress of disk coal samples with different height-diameter ratio
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图 4 不同高径比圆盘煤样应力−时间曲线
Figure 4. Stress-time curves of disk coal samples with different height-diameter ratio
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图 5 不同高径比典型煤样最终破裂模式
Figure 5. Fracture modes of typical disk coal samples with different height-diameter ratio
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图 6 不同高径比煤样应力及声发射能量随时间演化曲线
Figure 6. Evolution of tensile strength and AE energy of disk coal samples with different height-diameter ratio
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图 7 煤岩耗散能与弹性应变能关系
Figure 7. Relationship between dissipated energy and elastic strain energy of coal rock
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图 8 不同高径比煤样能量演化曲线
Figure 8. Evolution of energy for coal samples under different height-diameter ratio
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图 9 不同高径比煤样弹性应变能与耗散能占比曲线
Figure 9. Curves of elastic strain energy and dissipated energy of coal samples under different height-diameter ratio
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图 10 不同高径比煤样微裂纹分布特征
Figure 10. Distribution of microcrack in coal samples with different height-diameter ratio
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图 11 不同高径比圆盘煤样全应力段多重频谱特征曲线
Figure 11. Multifractal spectrum curves of coal samples with different height-diameter ratio
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图 12 不同高径比煤样破断面形貌特征
Figure 12. Fracture surface morphology of coal samples with different height-diameter ratio
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图 13 不同高径比煤样破断面粗糙度高程分布拟合
Figure 13. Fitting of elevation distribution on fracture surface of coal sample with different height-diameter ratio
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