加卸载条件下冲击性岩石动态力学特性研究

Dynamic mechanical performance of impact rocks under loading and unloading condition

为探究矿井基本顶周期来压路径对冲击性矿柱动力学特性的影响,借助分离式霍普金森压杆冲击加载设备,对不同循环加卸载预处理的冲击性砂岩开展动态压缩实验。探讨不同循环加卸载路径、冲击气压对岩样断裂强度、破坏耗能、碎块分布的影响。结果表明:动态应力–应变曲线分为弹性变形阶段、非稳定断裂发展阶段、断裂后阶段。在非稳定断裂发展阶段,应变硬化现象和跃进特性明显。在断裂后阶段,岩样破坏程度与冲击气压呈正相关。反射能、透射能、耗散能密度与入射能线性增长关系显著。平均反射能、平均耗散能密度随循环上限应力增大呈先下降后上升的“U”型变化特性。岩样密实度越高,冲击破坏时反射能、耗散能密度越小,透射能越大。冲击荷载下,岩样主要表现为粉碎破坏、岩块碎裂、岩块侧面剥落脱离、岩块劈裂。冲击扰动越剧烈,岩样平均碎块粒径越小,平均分形维数越大,破坏越彻底,岩屑分布越均匀。

To investigate the influence of the main roof's periodic weighting path on the dynamic characteristics of impact pillars,dynamic compression experiments were conducted on the impact sandstones which were preprocessed with different cyclic loading and unloading,by using the split Hopkinson pressure bar.The effects of the cyclic loading and unloading paths and the impact pressure on the fracture strength,energy dissipation and fragmentation distribution of rock samples were discussed.The results show that the dynamic stress-strain curve can be divided into the elastic deformation stage,the unstable fracture development stage and the post-fracture stage.In the unstable fracture development stage,the strain hardening phenomenon and the leaping characteristic are obvious.In the post-fracture stage,the damage degree of rock samples is positively correlated with the impact pressure.The reflected energy density,the transmitted energy density and the dissipated energy density increase linearly with the incident energy.The average reflected energy density and average dissipated energy density decrease first and then increase with the upper cyclic stress,showing a "U"-shaped varying characteristic.The higher the rock sample density is,the smaller the reflected energy density and the dissipated energy density are.By contrast,the transmitted energy is larger.Under the impact loading,the rock samples mainly show the crushing failure,the rock fragmentation,the rock side spalling and the rock splitting.The severer the impact disturbance is,the smaller the average particle size.By contrast,the average fractal dimension of the rock samples is larger.The rock samples are destroyed more thorough.The rock debris are distributed more uniformly.