冲击荷载作用下岩石动态力学特性及破裂特征研究

采用分离式霍布金森压杆(split Hopkinson pressure bar,SHPB)试验系统对灰岩,白云岩和砂岩3类岩石进行动态冲击试验,得到岩石的动强度因子,耗散能密度及破碎尺寸与应变率的变化关系。在此基础上结合晶体离散元方法,采用高分辨率扫描和图像处理技术建立了晶体尺度试样模型,研究岩石材料高应变率力学特性和损伤特征。通过与室内SHPB试验对比,验证数值模拟的准确性。结果表明:岩石材料的动态屈服强度具有明显的率相关性,但弹性模量没有随应变率的增加而显著增加;在高应变率下,材料的动强度因子与应变率更符合Ханукаев公式;随着应变率的增加,岩石的破坏形态出现完整型→劈裂破坏→粉碎性破坏转化,这是由细观裂纹的激活数目以及裂纹间的相互作用关系所决定的。裂纹密度的变化和扩展路径的选择是材料动断裂机制,其宏观表现为材料的率效应和破碎成形。

Dynamic properties and fracture characteristics of rocks subject to impact loading

Split Hopkinson pressure bar(SHPB) apparatus was used to study the factor of dynamic strength increasing，the density of dissipation energy and the fragment size of limestone，dolomite and sandstone subject to impact loading. SHPB has some difficulties to measure the higher strain rate and dynamic damage process for rock materials. The grain-based model was thus built by using the high resolution scanning and image processing technique combined with the discrete element method. The accuracy of numerical simulation was verified with the experimental SHPB results. The results indicated that the dynamic failure strength of rock material was rate dependent strongly，but the elastic modulus did not increase significantly with the increasing strain rate. The semi-empirical formula for evaluating the factor of dynamic strength increasing is consistent with the Ханукаев equation. The failure pattern of the rock transforms from the intact→splitting damage→pulverized damage with the increasing strain rate. This phenomenon is determined by the number of the micro cracks activated and the interaction between the cracks. The increase of the crack density and the change of the crack propagation path are the mechanism of the dynamic fracture of the rock，and the macrosopic responses are the rate effect and fragmentation of the material.