Meso-structures evolution rules of coal fracture with the computerized tomography scanning method

• The real time loading and monitoring system for coal or rock were established.
• CT images show that the raw coal is a kind of heterogeneous material.
• Fractures happen between skeleton and matrix or on the weak region.
• 3D reconstruction images were conducted under the different stress status.

In order to observe the meso-structure and fracture process of coal interior, the computerized tomography (CT) scanning experimental system was developed. This system includes the nonmetal cylinder shell, loading head, strain test equipment, hydraulic pump and vacuum pump, which can scan coal or rock samples with or without gas under uniaxial and triaxial load. The uniaxial compression experiments of coal were done and CT images were obtained at different stress level. The results show that the raw coal is a kind of heterogeneous material and the internal distribution of density is inhomogeneous. The cracks are uneven and their directions are random. During the loading process the inner structures of coal changed. The density of the coal increases at the beginning of load and decreases with the increment of stress. The fractures of coal occur mainly between the skeleton and matrix and on the weak region of the skeleton. Moreover, CT images from the experiments were used to reconstruct 3D images of coal under different stress states. The deformation and fracture process can be observed obviously. These investigations can provide theoretical foundations for understanding of fracture mechanism of coal.