Fractal characteristics of rocks and mesoscopic fractures at different loading rates

Uniaxial compression tests were conducted on rocks under different loading rates to analyze their effect on rock fragmentation. The fractal dimension of the macroscopic fragmentations of the rocks were then calculated by combining the fractal theory. Based on scanning electron microscopy (SEM), the macroscopic failure characteristics and mesoscopic fracture morphology characteristics of the rocks under different loading rates were compared and analyzed; the mesoscopic fractal dimension of the fracture was calculated using the box dimension method. The results demonstrate that when the loading rate is increased from 0.001 to 0.05 mm/s, the average fragmentation distribution coefficient decreases from 18.99 to 16.37 mm. As the loading rate increases, the fragmentation distribution coefficient gradually decreases, and the rock sample breaks; the degree of failure gradually increases, and the failure mode of the rock transforms from tension to shear failure. The SEM analysis reveals that under low loading rates, an intergranular fracture indicates the primary failure mode. The macroscopic performance primary presents tensile failure; as the loading rate increases, the range of the transgranular fracture gradually increases, and the failure mode evolves from an intergranular to transgranular fracture. The fractal dimension of the mesoscopic structure of the rock fracture tends to increase with an increase in the loading rate, and demonstrates a good positive relationship by fitting with the macrostructure fractal dimension. A larger fractal dimension of the microstructure of a rock fracture indicates more complex structure of the fractured surface. This study provides a better understanding of the meso-rock failure mechanism, and presents significant findings regarding ore rock fragmentation and rockburst prevention.