围压对砂岩动态冲击力学性能的影响

 利用带围压装置的霍普金森压杆设备对砂岩在不同围压等级、不同应变率下的动态力学性能进行试验研究，分析砂岩单轴动态抗压强度和比能量吸收值的应变率效应，围压状态下砂岩在冲击荷载循环作用下的力学特性以及累积比能量吸收值与入射能量、围压等参量之间的关系。研究结果表明，砂岩的动态杨氏模量与静态杨氏模量相比明显增加，两者比值达3.21～3.81；而当应变率为50～100 s－1时，动态杨氏模量随应变率有所增加，但变化不大。砂岩单轴动态压缩试验的比能量吸收值与应变率 呈线性关系，而单轴动态抗压强度增长因子 (即动态抗压强度)与 成线性关系。在围压状态下，砂岩具有明显的脆性–延性转化特征，其应力–应变曲线出现明显的屈服平台，呈近似的弹塑性特征。围压的加载作用对阻止试件产生剪切失稳的作用相当明显。随着冲击荷载循环作用次数的增加，试件的杨氏模量变小，屈服应力降低，屈服应变增加。砂岩的破坏形态随围压大小不同而发生变化，砂岩从轴向拉伸破坏形态向压剪破坏形态转变的临界围压值为10 MPa。在能量相同的入射波作用下，砂岩试件在低围压时比在高围压时的比能量吸收值大，且砂岩的比能量吸收值、入射波能量和围压三者具有良好的规律性，并得到比能量吸收值随入射波能量和围压变化的关系式。

EFFECTS OF CONFINING PRESSURE ON MECHANICAL BEHAVIORS OF SANDSTONE UNDER DYNAMIC IMPACT LOADS

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(ε.),dynamic strength increasing factorη and strain rate(ε.)1/3at 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.