颗粒破碎的三维离散元模拟研究

3D numerical simulation of particle breakage using discrete element method

采用PFC等离散元方法研究岩土材料的颗粒破碎已经成为热点。采用考虑局部应力集中的点荷载破碎准则,利用阿波罗填充和膨胀法保证破碎前、后颗粒之间的种群平衡,并引入尺寸因子来表征不同粒径的颗粒强度。在此基础上,开展了石英砂、钙质砂和萨克拉门托河砂3种不同破碎难易程度材料的数值试验,并与室内试验结果进行对比。结果表明:建立的三维颗粒破碎模型能够很好地描述破碎难易程度不同的颗粒材料的压缩特性;考虑应力集中效应的点荷载破碎准则比基于平均应力Mohr-Coulomb理论的颗粒破碎准则更能真实地反应颗粒材料的破碎现象。同时,所建立的模型能够揭示破碎对颗粒材料各向异性消散和级配曲线演化的影响规律。

Discrete element method （DEM）, such as particle flow code （PFC）, has become one of the current highlights to investigate the particle breakage process in the geotechnical field. In this study, based on the point load crushing criterion considering the local stress concentration, a three-dimensional （3D） particle crushing model was established. Particually, the particle balance among particles before and after crushing is ensured by the Apollo filling and expansion method, and a size effect factor is used to characterize strength of particles with different sizes. Then, numerical simulations were performed on three types of sand with different degrees of breakage, namely silica sand, calcareous sand and Sacramento River sand. The comparisons of numerical and experimental results show that the established model can well describe compressive properties of granular materials with different degrees of breakage. Comparing with the failure criterion rooted in Mohr-Coulomb theory on the basis of mean stress, the criterion in the established model shows a better manner in reflecting the real fragmentation phenomena under the same loading condition. At the same time, the established model reveals the influence of crushing on the anisotropic dissipation and gradation evolution of granular materials.