Experimental study on crack evolution and fracture mechanism of coal under loading based on various nondestructive monitoring technologies

It is very important to understand the internal correlation mechanism between microcrack evolution and macromechanical response of coal. Based on acoustic emission monitoring, VIC-3D noncontact full-field measurement and high-resolution CT scanning test system, combined with digital image processing technology and statistical analysis, the crack propagation and damage evolution of coal under loading are studied. The results show that the coal crack propagation has obvious stage characteristics. In the unstable development stage of cracks, the stress–strain curve of coal shows a nonlinear growth trend, and the cracks expand rapidly and lead to final failure. Acoustic emission parameters reflect the types and quantities of cracks in different loading stages. The fracture porosity and fractal dimension of coal show a trend of decreasing first and then increasing during the whole loading process. The change of fracture volume and surface area reflects the dynamic response of coal from passive compression to active expansion under external force. In addition, the uneven distribution of coal internal structure has a significant impact on its failure mode. The research results clarify the crack propagation and fracture mechanism of coal from the microscopic point of view, and provide theoretical basis for early warning and control of deep engineering disasters.