Abstract: It is one of the ways to understand the mechanism of rock blasting to explore the dynamic properties of rock in mesomechanics.The dynamic loading of red sandstone under confining pressure was carried out by the split Hopkinson pressure bar,and the microscopic characteristics were characterized by porosity change.Based on the energy dissipation index,the energy dissipation of dynamic damage and fracture of red sandstone was studied.The results show that the overall trend of impact number decreases with the increase of air pressure,and the energy dissipation increases before the specimen is broken,and there is no obvious rebound.In the third or fourth shock,the dynamic characteristics are different.In the initial impact,porosity is closed from mesopores and macropores to micropores.With the increase of impact load,the peak value of micropore porosity difference moves backward.

Key words: split Hopkinson pressure bar,cyclic impact loading,nuclear magnetic resonance,energy dissipation