Study on Cyclic Impact Failure Characteristics of Quartz Sandstone under Medium Strain Rate

Quartz sandstone samples were tested under cyclic impact loadings by the drop weight impact test equipment to study its mechanical properties and failure process under medium strain rates. Three specimens were selected at each impact height of 0.3~0.6 m, and each specimen was subjected to 8 cycles of impact with medium strain rates of 26.33 s^-1, 29.7 s^-1, 32.03 s^-1 and 35.17 s^-1, respectively. Then, the influence of cyclic loading times on the dynamic compressive strength, elastic modulus and energy efficiency of quartz sandstone were discussed. The results show that under different medium strain rates, the dynamic compressive strength of the specimens under the impact loading of the 8th cycle is about 13 MPa, which is lower than that of the first cycle. During the process, the resistance to deformation is weakened, and the elastic modulus is significantly reduced. The dynamic compressive strength of the specimens has a positively correlation with the elastic modulus. From the perspective of energy, the dissipated energy, energy efficiency and unit volume dissipated energy of the specimen are improved after 8 cycles of impact loading. The effect is most obvious when the impact energy is 70.27 J, the dissipated energy of rock is increased by 6 J, the energy efficiency is increased by 8.8%, and the unit volume dissipated energy is increased by 50%. For fracture fractal, the fracture morphology of rock under medium strain rates includes splitting failure, edge collapse failure, block failure and crushing failure. When the strain rate increases from 26.33 s^-1 to 35.17 s^-1, the characteristic value of the average particle size of the sample fragments decreases from 24.49 mm to 21.15 mm. The fractal dimension increases from 1.07 to 1.75 linearly.