The Tensile Failure Characteristics of Black Shale Under Dynamic Brazilian Test

Abstract

Abstract Dynamic tensile failure is one of the main failure modes of layered shale during the horizontal drilling and hydraulic fracturing. To comprehensively understand the failure behaviors under dynamic loading, a series of split Hopkinson pressure bar (SHPB) tests are conducted on black Longmaxi shale under different loading rate at seven loading-bedding angles β. The results indicate that both static and dynamic Brazilian tensile strength (BTS) increase with the angle β. But the dynamic BTS are far greater than the static BTS. However, as the loading rate increases, the anisotropic index decreases gradually. In addition, there is a positive correlation between dynamic BTS and loading rate, which is that the dynamic BTS increases with loading rate. In this study, the relation between dynamic BTS and loading rate is fitted by a power function with correlation coefficients higher than 0.92. The failure samples show that there are four typical fracture patterns, which are central tensile failure as β=0° and β=90°, bedding activation shear failure as β=15°, non-central arc fracture at β=30° and 45°, mixed mode fracture as β=60° and 75°, respectively. This study provides significant data to evaluate the mechanical properties of layered black shale for safety and stability under dynamic loading.