Analysis of Mechanical Properties and Failure Modes of Layered Shale in Split Hopkinson Pressure Bar Brazilian Splitting Tests

ABSTRACT Shale is a sedimentary rock widely distributed in the natural environment and frequently exhibits a distinctive layered structure. The damage mode of laminated shale is significantly influenced by the mechanical anisotropy of its laminated structure under dynamic loading. Consequently, to examine the impact of layered structure on the tensile strength and damage mechanism of shale under dynamic loading, we implemented the split Hopkinson pressure bar tests on layered shale. Furthermore, we developed a numerical model of particle flow in the particle flow control (PFC) based on discrete element method theory to investigate the distribution of various types of fractures. The experimental results indicate that the dynamic tensile strength of shale exhibits a clear anisotropy at various loading angles. The dynamic tensile strength of shale is at its lowest when the stratification plane is parallel to the loading direction and at its highest when the stratification plane is perpendicular to the loading direction. Furthermore, the damage mode of shale is determined by the combination of experimental and numerical simulation results, which identified three typical damage fractures. Furthermore, using data acquired from PFC numerical simulation of various cracks and constructing the crack rose diagram, we initially present the notion of crack percentage in this article and investigate the variation pattern of crack inclination angle in space. As the loading rate increases, the proportion of tensile cracks on nonstratified planes experiences a substantial rise, resulting in a more fragmented damage morphology of shale. Conversely, the presence of stratification predominantly contributes to the formation of shear cracks in the shale, exerting a significant influence. Furthermore, the damage patterns obtained from numerical simulations exhibit a high level of concurrence with the experimental findings, thereby showcasing the precision and efficacy of employing diverse crack ratios for ascertaining the damage patterns of shale.