双轴压缩下颗粒物质接触力与力链特性研究

Investigation on contact force and force chain of granular matter in biaxial compression

为探究双轴压缩过程中颗粒物质接触力与力链特性,采用离散元法研究双轴压缩过程,得到双轴压缩过程中颗粒体系宏观力学特性,即偏应力、体积应变变化规律,并通过对接触力大小分布规律、接触力角度分布规律等细观层次分析,完成接触力大小、力链方向性量化描述,同时探究围压对颗粒物质力学特性的影响。研究表明,双轴压缩过程经历应力强化、应力软化、应力波动三个阶段。在各阶段,强接触与总体接触的各类型接触力大小分布规律可采用高斯函数或指数函数拟合,弱接触的法向与总接触力分布较为均匀;直径较大颗粒上具有接触力集中现象,集中程度随着围压升高而加强;力链网络形态经历"鱼鳞"状-"柱"状-"拱"状-"龟壳"状演变,由初始时基本各向同性,逐渐向最大主应力y向偏转,表现出强烈各向异性,最后又经历小幅度偏转偏离y向。不同围压下力链分量比变化规律证实了该发现,接触力角度分布规律也从力链承载方向验证了此结论。研究结果将为探究双轴压缩中颗粒物质力学特性提供理论基础。

In order to study the characteristics of contact force and force chain of granular matter in biaxial compression, the biaxial compression is investigated by DEM. Then the microscopic mechanical properties(variation of deviatoric stress and volumetric strain) of granular system are obtained, and the quantitative descriptions about the magnitude of contact force and orientation of force chains are completed through analyzing the distribution of orientation and the magnitude of contact force at mesoscopic and micro levels. And the effects of confining pressure on granular matter are investigated. The results demonstrate that process of biaxial compression is divided into three stages: the stress hardening stage, the stress softening stage and the stress fluctuation stage. The magnitude distribution of contact force of total contact and strong contact can be fitted by Gaussian function or exponential function, but the magnitude distribution of the normal and total contact force of weak contact is uniform. The contact force concentrates on the larger diameter particles, and the concentration degree of contact force is strengthened with the increase of confining pressure. The shape of force chain network evolves through ‘scale'-‘column'-‘arch'-‘turtle shell', and the orientation of it turned from isotropy to the direction of maximum principal stress(Y-axis) that shows anisotropy, finally it turns away from Y-axis slightly, the findings are also confirmed by the component ratio of force chains under different confining pressure and the distribution of contact force-degree through the bearing direction of force chains. The results of this paper provide a theoretical basis for the study of mechanical properties of biaxial compression.