Fractal study on the dynamic fracture of red sandstone after F-T cycles

Rock is an easily weathered material. Especially in alpine regions, freeze–thaw (F-T) cycles have a significant effect on the mechanical behavior of rock. A dynamic disturbance load further complicates the problem. Rock is also a multi-scale material; it may be more suitable to investigate the change in the macroscopic behavior from a microscopic perspective. Since rock fractures exhibit self-similarity, the material responses can be analyzed using fractal theory to determine the chaotic morphology of macroscopic fractures. We use a Φ 100 mm split Hopkinson pressure bar (SHPB) to perform dynamic tests on red sandstone after F-T cycles at three impact strength levels to obtain the dynamic fracture morphology. The fractal dimension of the dynamic fracture is calculated. The macroscopic fracture degree is quantitatively characterized. The relationship between the fractal dimension and the F-T cycles and impact strength are established. A scanning electron microscope (SEM) is used to obtain microscopic images of the dynamic fracture, which are processed to extract quantitative information, including the number, area, length, and width of the pores. The relationship between the fractal dimension and the pore information is investigated to reflect the macro-microscopic characteristics of rock under the coupling environment of F-T cycles and impact loads.