Dynamic Tensile Behavior of Anisotropic Rocks: Crack Evolution, Energy Dissipation, and Mechanical Mechanism

Abstract

Evaluating the dynamic mechanical properties of rocks is the foundation for preventing and controlling relevant disasters. To investigate the dynamic tensile failure mechanism of transversely isotropic rocks, Brazilian disk tests were conducted via the split Hopkinson pressure bar. Then, numerical rock models with different bedding plane angles were constructed based on the discrete-element method and validated by comparing the results of simulations with those of laboratory experiments. After the microcrack evolution and energy transition process of the model were determined, the full-field stress distribution during loading was analyzed to explore the effects of weak bedding planes on the mechanical properties and failure characteristics. The microfracturing mechanism of transversely isotropic rock was also illustrated by determining the relationship between broken energy and Brazilian disk behavior. The results revealed that crack propagation in the dynamic Brazilian disk of transversely isotropic rock was induced mainly by tensile stress. The Brazilian disk strength, related to the angle β between the bedding plane's normal direction and the loading direction, exhibited a similar trend to the number of cracks formed in the matrix rather than the total number of cracks. For the specimens with low bedding plane angles, a few bedding planes lost bearing capacity, whereas the percentage was > 15% for the specimen with β = 45°, 67.5°, or 90°. The energy required for the failure of the bedding plane was almost negligible compared with the energy consumed by the bond breakage of the matrix, which was why cracks are more easily initiated in the bedding plane for the specimens with high β. A new anisotropic tensile strength criterion was proposed on the basis of microdamage evaluation and tensile mechanics mechanism. Subsequently, the effectiveness of the criteria was checked by experimental data reported in other studies. It was demonstrated the developed criterion is a useful method for describing the tensile strength of transversely isotropic rocks with different bedding plane angles.