摘要:
为探究白砂岩在动静荷载作用下的损伤演化机制、细观裂纹扩展规律及应变率效应，以细粒白砂岩为研究对象，采用PFC3D软件构建基于平行黏结模型（PBM）的三维离散元模型，对单轴压缩、巴西劈裂和三维分离式霍普金森压杆（SHPB）三种加载条件下白砂岩的力学行为进行数值分析，同时开展相应的室内实验，进行对比分析白砂岩在动静荷载下的宏观力学特征与破坏形态。从细观角度探究了裂纹萌生-扩展-贯通过程、力链演化规律及能量转化特征。引入动态强度放大因子（DIF），定量表征其应变率强化效应。结果表明：所建立的离散元模型能有效表征白砂岩的宏观力学行为，数值分析结果与室内实验结果的抗压强度、抗拉强度相对误差均低于2%，破坏形态较为吻合。白砂岩在单轴压缩、巴西劈裂和动态冲击下的破坏过程裂纹延展的方式存在差异，但均以剪切裂纹为起裂基础，拉伸裂纹为扩展引导，两种裂纹耦合发展的形式形成断裂面，其中剪切裂纹的占比分别为61.8%、52.7%和54.5%，裂纹的萌生和扩展与力链的断裂、重组、集中密切相关，拉伸力链集中区域为裂纹延展的主要路径。在不同应变率加载条件下，白砂岩试样的裂纹扩展方式及破碎形态未发生明显变化。在高应变率冲击条件下能够吸收更多能量，具有更好的承载能力，这是由于在高应变率冲击下试样内部裂纹数量显著增多，贯穿裂纹带更显著，致使白砂岩在高应变率冲击条件下能够吸收更多能量。研究成果可为深部岩体工程在动静联合荷载作用下的稳定性评价与灾害防控提供一定的理论参考。
Abstract:
To investigate the damage evolution mechanism, meso-crack propagation law, and strain rate effect of white sandstone under static and dynamic loads, fine-grained white sandstone was selected as the research object. Taking fine-grained white sandstone as the research object, a three-dimensional discrete element model based on the parallel bond model (PBM) is established using PFC3D software to numerically analyze the mechanical behavior of white sandstone under three loading conditions: uniaxial compression, Brazilian splitting, and three-dimensional split Hopkinson pressure bar (SHPB). Meanwhile, corresponding laboratory experiments are carried out to conduct a comparative analysis of the macroscopic mechanical characteristics and failure modes of white sandstone under static and dynamic loads. The macroscopic mechanical characteristics and failure modes of white sandstone under static and dynamic loads were compared and analyzed. The process of crack initiation, propagation, and coalescence, the evolution law of force chains, and the energy transformation characteristics were explored from a mesoscopic perspective. The dynamic increase factor (DIF) was introduced to quantitatively characterize the strain rate strengthening effect. The results indicate that the established discrete element model effectively represents the macroscopic mechanical behavior of white sandstone, with relative errors of compressive strength and tensile strength between numerical analysis and laboratory results both below 2%, and the failure modes are in good agreement. Under uniaxial compression, Brazilian split, and dynamic impact, the crack propagation patterns of white sandstone differ, but all share a common basis: shear cracks initiate the fracture, tensile cracks guide the propagation, and the coupled development of the two types of cracks forms the fracture surface. The proportions of shear cracks are 61.8%, 52.7%, and 54.5%, respectively. The initiation and propagation of cracks are closely related to the breakage, reorganization, and concentration of force chains, with the concentrated regions of tensile force chains serving as the main paths for crack propagation. Under different strain rate loading conditions, the crack propagation mode and fragmentation morphology of white sandstone do not change significantly. Under high strain rate impact conditions, it can absorb more energy and exhibit better load-bearing capacity. This is because the number of internal cracks in the specimen increases significantly under high strain rate impact, and the penetrating crack zone becomes more pronounced, resulting in the white sandstone absorbing more energy under high strain rate impact conditions. The research findings can provide a theoretical reference for stability evaluation and disaster prevention in deep rock engineering under coupled static-dynamic loads.
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