Macro- and Meso-Damage Evolution Characteristics of Coal Using Acoustic Emission and Keuence Testing Technique

Acoustic emission (AE) experiments of Yuwu and Guangli coal samples under uniaxial compression were carried out by using the electro-hydraulic servo pressure testing machine (TAW-3000 and DS5-16B model of holographic AE signal analyzer) to study macro- and meso-damage evolution characteristics of different types of coal. The relationship between meso-damage and macro-damage processes of different types of coal was discussed based on AE localized results and the VHX-6000 Digital Microscope System test results. The results revealed that AE signals are generated mainly in the unstable fracture propagation stage under uniaxial compression, and the number of AE signals is related closely to the evolution process of original cracks and other defect structures of specimens. In addition, the AE space-time evolution process of coal has good correspondence with the stress-strain curve. Besides, the macro-damage modes of different types of coal are different. A typical split-shear composite failure mode was observed in Yuwu coal sample, while Guangli coal sample experienced the typical multi-shear fracture failure mode. The results also suggested that the macro-fracture surface roughness of coal sample is correlated strongly with the generation of internal secondary cracks with good fractal characteristics, and AE positioning technology can be used to monitor the initial fracture source location and high energy concentration area in coal.