动载下层状复合岩石能量耗散及断裂特征研究

Energy dissipation and fracture characteristics of composite layered rock under dynamic load

利用砂岩、大理岩、花岗岩制作6种不同组合方式的层状复合岩石,采用分离式霍普金森压杆试验系统,对不同组合方式的层状岩石进行动态冲击试验,利用高速相机记录其破坏形态,分析复合岩石材料的动态断裂模式、波阻抗效应以及能量耗散规律,探究不同复合岩石试件的动能及断裂能关系.利用离散格子弹簧模型模拟复合岩石试件的动态断裂过程,分析复合试件的应力波传播特性及应力、损伤演化规律.研究结果表明:复合岩石材料的动态断裂特征与上下层材料具有相关性,当下层材料动态起裂韧度较低时,裂纹从起裂至扩展到岩石胶结面历时较短.上层材料对于复合岩石的应力传导作用具有较大的相关性,上层材料密度越大,更有利于透射波传递,应力传导效果越好,而下层材料与上层材料密度相差越大,胶结面上下端应力差越大;受波阻抗效应影响,复合岩石试件应力波的传播行为具有明显差异,波阻抗越大应力波传播速度越快,透射系数越大,产生更多的透射能;复合岩石试件的耗散能时密度、动能及断裂能与上下层岩石材料的密度有关,下层材料不变,上层材料密度越大时,耗散能时密度及断裂能更小,试件完全断裂时获得较大的动能.

Six combinations of layered composite rocks were prepared using sandstone,dali rock,and granite.The composite rock specimens underwent a dynamic impact test using the separated Hopkinson pressure rod test system,and the failure patterns of the specimens were recorded using high-speed cameras.The dynamic fracture mode,wave impedance effect,and energy dissipation nature of these composite rock specimens were analyzed,and the relationship between their kinetic energy and fracture energy was explored.The discrete lattice spring model was used to simulate the dynamic fracture process of the composite rock specimens,and the stress wave propagation characteristics and stress and damage evolution nature of the composite specimens were analyzed.The results show that the dynamic fracture characteristics of composite rock materials are strongly influenced by the uppermost and lowermost layer materials.When the dynamic cracking toughness of the material in the lower layer is low,the crack can maintain a high propagation speed and requires a short time from initiation to expansion to the rock cemented surface.The upper layer material has a greater influence on the stress conduction of the composite rock specimen.The overall transmission capacity depends on the upper layer material such that the greater its density,the more conducive it is to wave transmission and the better the stress conduction.The greater the difference in the densities of the lower and upper layer materials,the greater the difference between the stresses at the upper and lower ends of the rock cemented surface.Wave impedance has a significant effect on the propagation behavior of the stress wave.The propagation speed of the stress wave in the composite specimen is influenced by the porosity and density of the material.The larger the wave impedance,the faster the propagation speed of the stress wave,the larger the transmission coefficient,and the higher the energy transmitted.When energy is dissipated,the density,kinetic energy,and fracture energy of the composite rock specimen are influenced by the densities of the materials in the upper and lower layers.If the lower layer material is unchanged,a higher density of the upper layer material results in a smaller density and fracture energy when the energy is dissipated,yielding more kinetic energy when the specimen is completely fractured.When the upper layer material remains unchanged and the density of the lower material is increased,the cutting tip is more likely to crack,and the density and fracture energy are smaller when the energy is dissipated.