Effect of natural crack distributions on coal failure process based on fluorescent epoxy impregnation method and phase-field FEM simulation.

Natural crack structures significantly affect coal damage, and are a critical problem in mining engineering. In this paper, we introduced the fluorescent epoxy impregnation method (FEIM) to coal failure research, which can obtain cracks with an accuracy of 1 μm by a much lower experimental cost compared with CT scanning. Then we proposed a way to combine FEIM method and the phase-field finite element method (FEM), and established the tensor characterization theory of crack propagation to fully explore the effects of fracture structures on coal failure properties. The results demonstrated that the distribution of initial cracks in coal significantly affected the subsequent failure path at the micro level. Initiation of cracks occurred at the tips of inflection points of existing cracks. The cracks mainly propagated along or perpendicular to existing cracks. The cracks were tightly connected, forming larger crack networks and developing new cracks. The crack tensor theory can describe the crack initiation and propagation process well. The trace of the crack fabric tensor is equal to the total length of all cracks, while the crack orientation tensor describes the direction characteristics of the crack field. Natural cracks in coal greatly affected the initiation location, but the ultimate failure pattern was always shear failure. The proposed method combined experiments and numerical simulations can provide a basic reference for mining engineering. [ABSTRACT FROM AUTHOR]