Dynamic characteristics of sandstone at high strain rates and different confining pressures

The dynamic mechanical properties of rock with confining pressure under high strain rate were investigated using a modified split Hopkinson pressure bar (MSHPB). For the comparison, the quasi-static compression tests were also conducted with a conventional servo-hydraulic testing machine. Before the dynamic loading test, the rock specimen is sandwiched between the two elastic bars of the MSHPB and two strains gauges glued on the surface of the middle of bars are used to record strain histories. The confining pressure system was fixed on the supporting desk of the MSHPB, and the confining pressure can be loaded on the specimen according to the desired pressure value. With a spindle-type striker, a half-sine stress pulse with 100 mu s rise time was generated and will satisfy the request of dynamic stress equilibrium in the specimen. The amplitude of incident pulse can be controlled by adjusting the position of spindle-type striker in launch tube and the gas pressure. The results show that confining pressure has significant effects on the compressive stress-strain behavior of the rock specimens under dynamic loading. The compressive strength will increase with the magnitude of strain rate when the confining pressure is the same, and the strain rate is less than 10(2)/s, and the compressive strength increases with the 1/3 power of strain rate when the strain rate is larger than 10(2)/s. When the strain rate is a constant, the compressive strength of the rock will linear increase with the increases of confining pressure.