Cumulative damage characteristics of rock samples under cyclic low energy inclined plane impact

To investigate the cumulative damage characteristics and unstable failure mechanism of rock samples under cyclic inclined plane impact loads, an experimental device simulating inclined plane impact, and a drop hammer loading test machine were used to conduct cyclic low-energy impact tests on sandstone samples with five inclined plane angles. The porosity of the sandstone samples was measured using a low magnetic field nuclear magnetic resonance (NMR) detection system, obtaining the porosity, T ₂ spectrum distribution, and NMR images of the samples after different numbers of impacts at different slope angles. Under the action of cyclic inclined plane impact loads, the larger the slope angle, the smaller the extent of sample damage. The rock samples with a large inclined angle is more inclined to rupture at the tip of the inclined plane, mainly primarily characterized by shear-tensile failure. The porosity of the small slope angle changes sharply, resulting in greater damage. Under the same impact energy, as the number of impacts increases, the porosity of the samples first decreases, then increases, and then decreases again. This is manifested by large porosity closure after the first impact, followed by small pore expansion into large pores after 5 impacts, leading to gradual degradation of the samples until failure. The main factor affecting the rock samples is the presence of large-sized pores with a spectral area of over 95%. As the number of impacts increases, the quantity of small pores decreases, while the size and quantity of large pores both increase, indicating continuous deterioration of rock sample.