围压卸荷条件砂岩动静组合加载碎块分维特性

Fractal characteristics of sandstone fragmentation under coupled static and dynamic loading and confining pressure

利用带轴向静压和主动围压加载装置的分离式霍普金森压杆试验设备,研究了砂岩试样在不同轴向静载等级(0MPa^72MPa)、不同冲击能量下的动态力学特性,结合分形理论和能量原理,分析高应力试样破裂块度分布规律及其能量的相关性。试验结果表明:在轴向静载一定的情况下,砂岩试样的动态压缩强度随冲击能量的增大而提高;试样发生临界破坏,冲击能量随轴向静载的增大出现先增加后减小,试样破坏形态由中心破裂向更为复杂的压剪破裂转变;在较高轴向静载下,碎块分维数与冲击能量之间呈现非线性递增关系,表明较小的冲击能量有助于诱发高轴向静载储能释放,提高砂岩试样破碎程度。

The dynamic failure characteristics of sandstone with different axial static pressures （0 ~72MPa）and impact energy were investigated using the improved split Hopkinson pressure bar （SHPB）with axial static pressure and confining pressure.Combining the fractal theory and energy principle,the distribution law of fragments of sandstone specimens and its correlation with strain energy were investigated.The results showed that the dynamic compression strength of sandstone increases with increase in impact energy when the axial static pressure is constant;during the critical failure of sandstone specimens,the impact energy firstly increases and then decreases as the axial static pressure increases;the compression-shearing damage is the principal failure mode of sandstone specimens;the relation between fragment fractal dimension and impact energy is nonlinear and progressive under higher axial static loading,it means lower impact energy is helpful to induce the release of the elastic strain energy of sandstone specimens under higher axial static loading and to increase their rupture level.