Influences of bedding properties on the mixed-mode fracture behavior of shale under different dynamic loadings

Abstract

Understanding the dynamic mixed fracture behavior of shale is crucial for determining parameters in explosive fracturing. Therefore, a split Hopkinson pressure bar (SHPB) was adopted to conduct dynamic fracture tests on cracked straight-through Brazilian disk (CSTBD) shale under different impact loadings. The results revealed that the effective fracture toughness K_eff of shale increased linearly with the loading rate. The enhancing effect of the loading rate on K_eff increased with the pre-fabricated crack angle, and the effect of loading rate on shale with vertical bedding was greater than that of shale with horizontal bedding. Furthermore, the dissipated energy correlated positively with K_eff. A SHPB simulation system was established on the basis of the coupling between FLAC^3D and PFC^3D. The fracture characteristics of shale samples with different bedding tensile strengths were subsequently investigated. The simulation results indicated that the K_eff of shale with horizontal bedding tended to increase in a power function relationship with the bedding tensile strength, and an increase in pre-fabricated crack angle increased the rate of increase. In contrast, the K_eff of shale with vertical bedding was more significantly influenced by the mixed mode than by the bedding tensile strength. The ratio of kinetic energy to dissipated energy was approximately 15%. The fracture energy increased with increasing bedding tensile strength, and shale with horizontal bedding had a more significant effect on the fracture energy. Finally, the effect of bedding properties on shale crack propagation is discussed.