Characteristics of Impact Fragmentation and Energy Dissipation of Cylindrical Rock Specimens with Various Aspect Ratios

To investigate the crushing behavior and energy dissipation patterns of rocks subjected to impact loads, impact experiments were performed on limestone samples with various aspect ratios using a split Hopkinson pressure bar testing apparatus. The effects of aspect ratio and impact velocity on the failure modes and energy consumption during the fragmentation process of the specimen were examined. High-speed photography techniques and scanning electron microscopy technology were utilized to investigate the morphological features of the fracture surfaces in rock fragments. The results indicated that at a constant aspect ratio, an increase in the impact velocity resulted in a decrease in the equivalent particle size and an increase in the fractal dimension. At the same impact speed, the equivalent particle size increased with an increase in the aspect ratio, whereas the fractal dimension decreased as the aspect ratio increased. The failure modes of the limestone specimens gradually shifted with higher aspect ratios, transitioning from axial splitting to compressive shear as the dominant failure mechanism. The fractal dimension of the fragments increased with a higher energy dissipation density. As the aspect ratio of the specimen increases, the length-to-thickness ratio of the fragments increases linearly. The proposed prediction function model for the variation of the equivalent particle size of fragments with dissipated energy agrees well with the experimental results. Numerical simulations employing the finite element method confirmed the dynamic crushing characteristics of limestone. These simulations illustrated the variations in crack propagation paths in limestone specimens with various aspect ratios under impact conditions.