Dynamic Brazilian splitting experiment of bedding shale based on continuum-discrete coupled method

Abstract

Exploring the dynamic mechanical properties of shale helps to understand the damage of shale reservoirs under dynamic loading. In this paper, static Brazilian splitting experiments were conducted to obtain the static Brazilian strength of shales with loading angles ranging from 0° – 90° (at 15° intervals), and corresponding bedding shale models were developed based on the discrete element method. Then, the split Hopkinson pressure bar system was simulated according to the coupling of the continuous-discrete method, and dynamic Brazilian splitting simulations with loading rates of 100 – 170 GPa/s were carried out. The experimental results show that the Brazilian strengths of the shale at a loading rate of 0.05 mm/s are 4.73 MPa – 7.63 MPa, and the shale matrix and bedding can be simulated using the Flatjoint and Linearpbond models, respectively. The model parameters calibrated by static Brazilian splitting experiments were not applicable under dynamic loading; the microscopic tensile strength of the matrix and bedding increased by 2.7 and 3.1, and the microscopic cohesion increased by 1.8 and 1.7, respectively, for dynamic simulation tests. At a loading rate of 115 GPa/s, the dynamic tensile strength of the shale was 14.5 MPa – 18.2 MPa and increased with the increase of loading angle. There is a linear correlation between the dynamic tensile strength and the loading rate. The loading rate affects the damage pattern of the shale, with cracks tending to expand along the bedding. As the loading rate increases, the primary energy dissipated changes gradually from fracturing the rock to an increase in kinetic energy of the broken fragments.