Experimental study of the mechanical and fracture behavior of flawed sandstone subjected to coupled static-repetitive impact loading

In nature, rock masses, particularly underground rock structures, are subjected not only to static stress but also to frequent dynamic disturbances. In this paper, dynamic tests were carried out on single flawed sandstone specimens using a split Hopkinson pressure bar (SHPB), aiming to investigate the mechanical and fracture behavior of fractured rocks subjected to coupled static-repetitive impact loading. The results show that the dynamic strength of the flawed specimens decreases gradually with increasing the flaw length and repetitive impact number. The flaw length and axial prestress significantly affect the dynamic mechanical behavior of the flawed specimens. A longer flaw length produces lower dynamic strength and fewer repetitive impacts for a given axial prestress. The repetitive impact counts and the cumulative absorbed energy peak at an axial prestress of 20 MPa. Tensile strain, characterized by the digital image correlation (DIC) technique, is concentrated on the flaw tips and progressively extends approximately along the loading direction with increasing repetitive numbers. Wing and anti-wing cracks are the dominant cracks under repetitive impact loading conditions. Under repetitive impact without axial prestress, wing cracks play a key role in the failure of the specimen, while anti-wing cracks dominate the fracture process when the specimens are subjected to coupled static-repetitive impact loading. The findings in this paper could deepen the knowledge of the mechanical and fracture behavior of rocks subjected to coupled static-repetitive impact loading.