EFFECTS OF CONFINING PRESSURE ON MECHANICAL BEHAVIORS OF SANDSTONE UNDER DYNAMIC IMPACT LOADS
LU Xiaocong1，XU Jinyu1，2，GE Honghai3，ZHAO Dehui1，BAI Erlei1
(1. Engineering Institute，Air Force Engineering University，Xi¢an，Shaanxi 710038，China； 2. College of Mechanics and Civil Engineering，Northwestern Polytechnical University，Xi¢an，Shaanxi 710072，China； 3. Air Force Engineering Design and Research Bureau，Beijing 100068，China)
Abstract：Experiments of dynamic behaviors are carried out for sandstone specimens by split Hopkinson pressure bar(SHPB) equipment with confining pressure device at different confining pressures and different strain rates. The effects of strain rate on uniaxial dynamic compression strength and specific energy absorbency，as well as the mechanical characteristics of sandstone at the triaxial state under the circular action of impact loads are analyzed. It is demonstrated that the rates of dynamic and static Young¢s moduli increase evidently with values of 3.21–3.81. Dynamic Young¢s modulus increases slightly with the changes of strain rates，which ranges from 50 s－1 to 100 s－1. The linear relationships of specific energy absorbency and strain rate ，dynamic strength increasing factor and strain rate at the uniaxial state are all presented. It has clear brittle-ductile transformation(BDT) property for sandstone；and the stress-strain curve is shown under the yield platform at triaxial state. Along with the increase of circular action times of impact loads，the Young¢s modulus and the yield stress of specimens decrease，and the yield strain increases. The failure configurations of sandstone change with the confining pressure from axial tensile failure to compression-shear failure；and the critical confining pressure is 10 MPa. Specific energy absorbency value against lower confining pressure level is more than the value under higher confining pressure with the same energy of incident wave. The formulas among with the specific energy absorbency，the incident energy and confining pressure are put forward.
