颗粒体系中的骨架及力链网络

颗粒物质是大量离散的固体颗粒相互作用而组成的复杂体系,具有非连续和接触耗散等基本特征,其物理机制研究是近20年科学前沿之一.砂土就是典型的颗粒物质,土体中的有效应力是作用在土体骨架上的平均应力,土体变形主要来源于骨架上的颗粒位置,但对土体骨架并没有一个清晰的物理描述.近期颗粒物质力学研究认为,体系中颗粒相互接触形成的网络结构是外荷载传递路径的物理基础,可能就是土力学所指的骨架.同时还发现,较大的力通常沿着准直线的路径传递,人们常把传递较大力、与该准直线路径对应的若干颗粒组成的链状结构,称为强力链;弱力链则传递较小力.力链结构及其演变规律的描述是颗粒物质研究的核心之一.以单轴侧限压缩数值模拟为例,对比说明了土体颗粒骨架与力链结构的关系,明确提出强力链网络决定颗粒体系的宏观力学行为.

Skeleton and force chain network in static granular material

A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact. Soil is a typical granular material in nature. The concept of effective stress is one of Karl Terzaghi's most important contributions to soil mechanics. It is a measure of the stress on the soil skeleton (the collection of particles in contact with each other), and determines the ability of soil to resist shear stress. However, the soil skeleton is an imaginary concept, and it is hard to measure the geometric and mechanical properties. A few conflicts on its understandings are still remaining. The newly developed granular material mechanics may be helpful to provide insights to soil skeleton. We propose that skeleton is actually the particle connection diagram, and more importantly we found the interparticle forces were transmitted through quasilinear chain structures affiliated to the skeleton. It is necessary to compare the skeleton and force chains. In this work, a series of discrete element simulations were conducted on a uniaxial compression system consisting of 12,400 poly-dispersed particles. We find that skeleton corresponds to the geometric architecture of particle connection, while force chains sensitively response to external loadings though the skeleton is kept constant.