密集颗粒物质的介观结构

The mesoscopic structures of dense granular materials

密集颗粒物质由大量颗粒组成的多体相互作用体系,在一定条件下,颗粒互相连接,形成相对稳定的介观尺度结构,其几何和动力学性质较大程度上决定了颗粒体系的宏观物理和力学性质,因此开展颗粒的介观结构研究具有重要的理论价值,是科学的前沿之一.自然界的堆石坝、堰塞体和碎屑流,以及工程中的高温气冷堆堆芯颗粒流和先进核裂变能系统(ADS嬗变)的颗粒散裂靶等都是典型的颗粒体系,研究颗粒体系宏观力学性质是灾害预测和调控技术的关键.本文首先介绍颗粒接触力理论和简化模型的研究进展,接着介绍介观尺度结构分析方法与测量技术,颗粒体系Jamming转变、软点和颗粒微位移测量技术等,最后列举了几个关键的科学问题.颗粒介质中很多基本力学问题的解决需要借鉴物理和数学等学科的最新成果,建立新的概念和范式,从新的角度、思路、理念去认识颗粒介质的基本问题.同时,颗粒介质的基础研究还要紧密结合工程应用领域的大量相关的核心技术,与工程领域专家共同合作,使得颗粒介质的研究有的放矢,更具生命力.

A dense granular material （GM） is composed of dense random packing of solid particles and posses disorder structures which has been a long-standing mystery. On the one hand, GMs are amorphous materials with no long-range structural order; on the other hand, both topological and mechanical short range order are pronounced in these materials, due to their high granular packing density. The unique internal structure of GMs underlies their unique mechanical ad physical properties, which render GMs are useful for various applications in more and more engineering and industries in recent years, such as rock-filled dams, granular type debris flows, and the pebble-bed High Temperature Reactor. However, fundamental knowledge on the structural aspect of GMs remains seriously lacking. For example, how the granular mesoscopic structures are formed on the short-to-medium range, how the structure differs in different GMs and changes with granular composition, external loadings, and processing history and methods, and more importantly, how the structure influences the properties of GMS, are still well answered questions. Granular materials are currently the most actively studied materials. In this paper, we review the tremendous efforts over the past decades devoted to unraveling the particle-level structure of GMs and the structural origin of their unique mechanical behaviors, including the simplified inter-particle contact models and the structure measurement techniques and analysis methods. The failure of granular materials play a vital role in transition from solidto fluid-like states. The related jamming transition, the concepts of ＂soft spots＂ and the micro-displacement measurement techniques are then analyzed. Outstanding questions in this research area will be outlined.Suggestions are proposed as well. The studies on the fundamental problems of granular materials should employ the cutting edge studies of the condensed physics and mathematics to establish new concepts. Because of extensive uses in engineering and industries, the fundamental studies are suggested to closely connect with engineering and industries by focusing on the core technologies, which would greatly prompt the development of this research area.