Study on Dynamic Mechanical Properties and Meso-Deterioration Mechanism of Sandstone Under Cyclic Impact Load

The laboratory experiment of the spilt Hopkinson pressure bar is carried out, and the cyclic load simulation is realized by a new method based on two-dimensional particle flow code (PFC^2D) program. The dynamic damage and failure process of sandstone under cyclic impact load are further observed and analyzed from the view of mesoscopic scale. The results are as follows: (1) The numerical calculation method based on particle flow discrete element can effectively reproduce the Hopkinson bar impact compression experiment. (2) Under the cyclic impact load, the number of cracks in the specimens increases continuously, showing the effect on mechanical properties such as strength deterioration, elastic modulus reduction and peak strain increase. The number of cracks increases sharply at the moment of failure, and the peak strain and elastic modulus change significantly. (3) Along with the increase in cycle numbers of impact load, the failure modes of sandstone specimens develop from the mode of local meso-cracks at the end of the specimen and a small amount of rock debris to axial splitting failure mode dominated by main meso-cracks and extended from the end to the middle of the specimen. Compared with impact test with high strain rate, the failure evolution trend of sandstone specimens with axial preferential development of main meso-cracks is more significant. (4) The dynamic deterioration characteristics and evolution laws of meso-cracks in rock under cyclic impact load, such as nucleation, propagation, connectivity and interaction, are studied using PFC^2D program, making up the shortcomings of laboratory experiment.