颗粒物质及其多尺度结构统计规律

GRANULAR MATTER AND THE SCALING LAWS

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,在自然界中广泛存在,比如泥石流、岩土和堰塞体等。与之相关的土力学和泥石流动力学等唯象理论发展较为完善,它们侧重于工程应用,对深层次的物理机制并没有深入研究。颗粒物质由于其离散性和强耗散性,相关凝聚态物理学和力学理论不能很好地应用,近20年来其基础研究是科学的前沿,逐渐形成一门新的学科——颗粒物质力学。该文首先简要回顾了颗粒物质的研究历史,理清了发展的脉络,对比了不同学科之间的内在关系,指出基于凝聚态物理学、固体力学和流体力学等科学成就,建立宏观性质的微观理论是颗粒物质力学的主要研究内容;指出了颗粒体系具有典型的多尺度结构特点,认为合理分割结构层次、正确理解不同层次的物理过程、确定它们之间的关联是颗粒物质机理研究取得突破的可行研究途径。以二维颗粒体系的单剪数值模拟实验为例,简单介绍了颗粒体系微观、细观和宏观等三个尺度的统计规律。

The granular material is a conglomeration of discrete solids and macroscopic particles characterized by a loss of energy whenever the particles interact. The typical samples in nature include sand grains, soils, debris flows and so on. The corresponding disciplines have been well developed, such as soil mechanics and debris flow dynamics. However, they are mainly phenomenological theories. The granular matter mechanics, which focuses on the fundamental investigations, is relatively new and stays in its infancy stage so far. In this work, the brief history of studies on granular matter was introduced. The remaining open problems, the relations among the granular matter mechanics, soil mechanics and condensed physics are introduced as well. Granular matter is intrinsically multiscale. In-between the particle scale and the system scale, force chains, as the mesoscale structure, stay quasistatic for a period of lifetime. The crosslink of them forms a heterogeneous network, and acts as the key factor that determines mechanical properties such as stability, elasticity and flowability. Especially, an interpretation to the structure of the strong force chain network represents a major work of granular mechanics. In this study, a series of discrete element simulations were conducted on a granular assembly subjected to simple shear. By taking them as examples, the scaling laws for particle scale and force chain scales are explained in details. Finally, a few opinions about strong force chains and the contact connection diagram are proposed.