Abstract A series of rock tests including Brazilian indirect tension test (BITT), three-point bending test (TPBT), modified shear test (MST) and uniaxial compression test (UCT) were conducted to investigate the acoustic emission (AE) characteristics and crack classification during rock fracture. The test results show that the rock fracture process presents an obvious segmented variation feature and has a dramatic increasing period, according to the change trends of AE hits and AE energy characteristic parameters. The AE characteristics are closely related to the types of micro-cracks produced in the rock fracture process. The elastic strain energy released by shear crack is greater than that released by tensile crack. Most of AE signals generated in compression and shear failures that mainly produce shear cracks have low average frequency (AF) values and low peak frequencies (below 100 kHz). On the contrary, most of AE signals generated in bending and tensile failures that mainly produce tensile cracks have low RA (ratio of rise time to amplitude) and high peak frequencies (above 100 kHz). In addition, the dividing lines were defined to distinguish the tensile cracks and shear cracks in the AF-RA scatter plots for different rocks. For instance, the AE signals above dividing line accounted for more than 62%, which indicated that the tensile cracks were dominant in TPBT. However, the AE signals below dividing line accounted for more than 74%, and the shear cracks were dominant in UCT. Therefore, the AE characteristics can be used to determine the fracture modes of rock, then to shed light on the micro-crack properties.

中文翻译：

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岩石断裂过程中声发射(AE)特性及裂纹分类的几种基础实验室试验研究

摘要 进行了巴西间接拉伸试验（BITT）、三点弯曲试验（TPBT）、修正剪切试验（MST）和单轴压缩试验（UCT）等一系列岩石试验，研究了其声发射（AE）特性和裂缝。岩石断裂过程中的分类。试验结果表明，根据声发射冲击和声发射能量特征参数的变化趋势，岩石破裂过程呈现出明显的分段变化特征，并具有显着的增加周期。声发射特征与岩石破裂过程中产生的微裂纹类型密切相关。剪切裂纹释放的弹性应变能大于拉伸裂纹释放的弹性应变能。在主要产生剪切裂纹的压缩和剪切破坏中产生的大部分声发射信号具有低平均频率 (AF) 值和低峰值频率（低于 100 kHz）。相反，在主要产生拉伸裂纹的弯曲和拉伸失效中产生的大部分 AE 信号具有低 RA（上升时间与幅度之比）和高峰值频率（高于 100 kHz）。此外，还定义了分界线，以区分不同岩石的 AF-RA 散点图中的拉伸裂缝和剪切裂缝。例如，分界线以上的 AE 信号占 62% 以上，这表明拉伸裂纹在 TPBT 中占主导地位。然而，分界线以下的AE信号占74%以上，UCT中剪切裂缝占主导地位。所以，