Quantitative characterization and evolutionary patterns of coal cracks based on crack tensor analysis.

The internal crack structure of coal significantly influences its deformation and failure. Hence, quantitatively characterizing the crack features and their evolutionary patterns in coal is crucial. This study utilized a computerized tomography (CT) system to investigate the evolution of cracks in loaded coal samples. At different stages of uniaxial compression failure, crack evolution was observed, and crack tensor theory was applied to calculate crack tensor parameters for each stage. The results show that the crack direction tensor accurately reflects the average directional characteristics of the cracks, the crack fabric tensor accurately reflects the size and damage features of the cracks, and the crack tensor can quantitatively describe the multi-dimensional characteristics of the cracks. additionally, the trace of the coal crack fabric tensor quantifies the evolution pattern of coal cracks, exhibiting a trend of slow increase, steady increase, and rapid increase. finally, an exponential function relationship was found between the trace of the coal crack tensor and stress, enabling the assessment of coal damage degree based on stress levels.