Investigation On The Failure Features Of Coal Under Uniaxial Loading Condition By Micro X-Ray Computed Tomography

To visualize and analyze the failure features in coal specimen under uniaxial compression condition, a micro X-ray Computed Tomography (CT) system and associated loading device were used to obtain slice images in detail with resolution of 30 mu mx30 mu m. The volumetric images of specimen were reconstructed based on two-dimensional images. Thus, the coalescence, branching and propagation of micro cracks in space were observed. Fractal analysis was employed to quantify the damage or cracking process. Two-and three-dimensional box-counting methods were applied to analyze slice images and volumetric images respectively. Comparison between fractal dimensions calculated from two-and three-dimensional box-counting method was carried out. The results show that the fractal dimension increases with the propagation of micro cracks at pre-failure stage. Moreover, the fractal dimension obtained by the 3D algorithm does not approach the fractal dimension of 2D data set obtained by slice images analysis if the value is simply added to one. The fractal dimension of fractures in specimen under uniaxial loading conditions can also be used as a precursor to estimate the structural failure.