煤的直接拉伸力学特性及声发射特征试验研究

为探究直接拉伸荷载作用下煤岩力学特性和损伤演化特征，使用MTS815岩石力学测试系统及PCI-Ⅱ声发射测试系统，对原煤试件进行单轴直接拉伸和实时声发射测试，分析了煤的直接拉伸力学特性及声发射特征，建立了基于声发射的损伤模型。试验结果表明：因煤体孔隙裂纹分布差异，抗拉强度离散性明显，试件平均抗拉强度为0.66 MPa；随拉伸荷载持续作用，煤体损伤累积，试件峰后承载能力逐步下降，但仍保持一定的抗拉承载能力。煤体声发射事件在峰值应力区附近沿破坏面急剧增加和汇合，预示了宏观裂纹面的形成和煤体破坏的发生；峰后试件振铃计数率和声发射能率阶段性反复升降，试件破坏进程逐步推进；声发射测试可良好展示煤体直接拉伸荷载条件下损伤出现、发展和导致破坏的完整演化过程。

Mechanical properties and acoustic emission characteristics of coal under direct tensile loading conditions

To study the mechanical characteristics and the damage evolution process of coal under direct tensile loads，the direct tensile tests and real time acoustic emission (AE) tests on raw coal specimens were conducted using MTS815 rock mechanics testing system and PCI Ⅱ AE testing system.In addition，the direct tensile mechanical characteristics and the AE property of coal were analyzed and a damage model of coal based on AE was built.The test results show that the tensile strengths of specimens，whose average tensile strength is 0.66 MPa，are obviously discrete because of the variations of defect distribution in coal specimens.Under direct tensile loading conditions，the post peak bearing capacity of specimen decreases due to the damage accumulation，but does not directly reach zero.The AE events increase and converge dramatically along the failure surface，which indicates the formation of macroscopic crack surface and the occurrence of coal destruction at the peak stress zoon.As the specimen destruction process gradually advances，the AE count rate and the AE energy rate increase and decrease repeatedly at the post peak region.The AE tests can demonstrate the complete evolution process of coal damage under direct tensile loading conditions：occurrence，development and destruction.