RESEARCH ON CONFINING PRESSURE EFFECT OF SANDSTONE DYNAMIC MECHANICAL PERFORMANCE UNDER THE CYCLICAL IMPACT LOADINGS

Dynamic mechanical performance experiments are carried out for sandstone specimens at different confining pressures and different strain rates by using the split Hopkinson pressure bar equipment with confining pressure device. The paper analyzes the relationship among the accumulative total of special energy absorbency, confining pressure, and damage of sandstone under the cyclical impact load. It is demonstrated that sandstone has BDT(brittle-ductile transformation) property, and the yield platform is observed in the stress-strain curve in triaxial state. Along with the increase of cycle numbers of impact load, the elastic modulus and the yield stress of specimen decrease, and the yield strain increases. Energy absorbency ratio increases with the augment of the strain rate, and decreases with the augment of confining pressure. When the confining pressure increases gradually, the increase rate of damage becomes slow along with the accumulative total of special energy absorbency. In summary, the higher confining pressure is, the more energy is needed for sandstone to reach the same damage level. Finally, the formulas are putted forward.