Abstract:
A modified split Hopkinson pressure bar (SHPB) system is adopted to load Brazillian disc (BD) samples statically, and then exert dynamic load to the sample through stress wave generated by impact, to simulate the dynamic tensile failure process of rocks under hydrostatic confinement. Five groups of samples are tested under the hydrostatic stress of 0 MPa, 5 MPa, 10 MPa, 15 MPa, and 20 MPa. The rate dependent damage model, dominant crack algorithm (DCA), which is a micro-statistical crack mechanics method, is used to numerically model the failure process of the confined BD rock samples.
The testing result shows that the dynamic tensile strength of the rock increases with the hydrostatic pre-stress, which is reasonable since the confinement closes the microcracks and make it harder to break the rock samples. It is also observed that the dynamic tensile strength increases with the loading rate, revealing the rate dependency that is common for engineering materials. The modeling of the failure process matches well with the experimental results, demonstrating the applicability of the DCA model in predicting the dynamic tensile failure of rock materials.
Introduction
Tensile failure is a main failure mode of rocks in underground rock engineering projects, in which rocks are subjected to dynamic disturbances while under in situ stresses. When disturbed by dynamic loads from blasting, seismicity, or rockbursts, the underground rocks would be vulnerable to tensile failure. Even though the far-field load is compressive, the local stresses may be tensile, as shown in Fig. 1. From a macroscopic point of view, the bending of the roof induces tensile stress at the roof of the opening; from a microscopic view, the discontinuities in the rock result in tensile stress locally around the opening, so the dynamic tensile failure of rocks under pre-tension has been investigated by researchers [1, 2]. However, the far field rocks under hydrostatic prestress can also fail in tension under dynamic loads. Therefore, it is the purpose of this paper to investigate the dynamic tensile failure of rock materials under hydrostatic prestress state.
