Dynamic failure behavior and damage evolution process of holed sandstone under impact loads

In this research, the damage process and dynamic failure behavior of some sandstone rocks, containing an elliptical hole, were evaluated. For this reason, a series of laboratory tests under both static and dynamic loads in 4 different orientations of the elliptical hole was performed. Modified Split Hopkinson Pressure Bar testing machine was employed to apply impact load. Dynamic fracture evolution was recorded by utilizing a high-speed camera to evaluate the macro damage evolution process. Scanning electron microscope analysis and thin section studies were also used to assess mineral's behavior regarding micro-crack evolution. Furthermore, the experimental tests were numerically simulated, and strain energy density and dynamic stress concentration factor were measured to evaluate the effect of elliptical hole inclination on dynamic response. The results indicated that when the largest diameter is perpendicular to core axis, the rock shows the lowest strength in both static and dynamic loading conditions. Also, with increasing hole inclination, both strain energy density and dynamic stress concentration factor decreased. Evaluation of fracture surface indicated that grain-boundary cracks are the dominant type of cracks and iron oxide cement distribution has a vital role in the development of the cracks.