Dynamic Contact Networks in Granular Systems: New Insights into Fracture &Segregation

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。****非技术摘要****了解颗粒物质如沙子或砾石如何以及何时对应力做出反应并开始流动是地震预测，岩石雪崩灾害预测和土木工程等广泛领域的重要问题。这个项目将通过观察颗粒之间的接触点网络来研究颗粒物质的流动，并研究这些网络如何随着颗粒物质的流动而变化。其他理解颗粒流动的方法侧重于单个颗粒的运动或将系统视为流体状连续体。本研究将运用网络理论的工具，突出中间尺度。触摸颗粒的集合-并将因此提供颗粒流动的新视角。该项目将重点关注颗粒材料中发生的两个关键过程，颗粒材料流动过程中接触网络的破坏，以及颗粒在颗粒流动中按尺寸的偏析。拟议的研究将训练研究生进行最先进的实验和计算研究，并指导本科生和高中生。研究小组还将对他们的工作进行公开展示，以简单的例子强调沙子的流动，这些沙子具有迷人的、技术上重要的特性，但尚未完全被理解。****技术摘要****本项目的目标是通过实验测量三维颗粒流场，并利用网络理论来表征流动行为。网络理论度量关注的是连接对象集合的大规模结构。由于颗粒物质的强度来自于颗粒接触的密集网络，因此网络理论将为理解颗粒材料的性质提供一种新的观点。重点将放在两个关键的颗粒流动过程上。断裂和偏析。第一个目标是表征堵塞颗粒材料断裂的开始，即颗粒物质开始流动时形成的大规模结构重排，如剪切带。了解颗粒物质如何以及何时破裂并开始流动对地震预测、岩石雪崩灾害预测和土木工程等广泛领域都很重要。第二个目标是描述颗粒流动过程中导致不同粒径混合物分离的颗粒重排。研究生将接受实验工具（3D成像）和理论概念（网络理论）的独特组合训练，并将为本科生提供指导。该小组已经开发了一些演示，突出了干扰和颗粒隔离的最显著特征，这些演示将在公开讲座和推广活动中展示。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).****NON-TECHNICAL ABSTRACT****Understanding how and when particulate matter such as sand or gravel will respond to stress and start to flow is an important problem in a wide range of fields such as earthquake prediction, rock avalanche hazard prediction, and civil engineering. This project will study the flow of granular matter by looking at the networks of contact points between particles, and examining how these networks change as the granular material flows. Other approaches to understand granular flow focus on the motion of individual particles or look at the system as a fluid-like continuum. The proposed research will apply the tools of network theory, which will highlight the intermediate scale ? ensembles of touching particles - and will thus provide a novel perspective on granular flow. The project will focus on two key processes that occur in granular materials, the breaking of the contact network during flow of granular material, and the segregation of particles by size in such a granular flow. The proposed research will train graduate students in state of the art experimental and computational research and in mentoring of undergraduate and high school students. The research team will also conduct public demonstrations of their work, highlighting -on simple examples- flows of sand that possesses fascinating, technologically important properties which are not yet fully understood.****TECHNICAL ABSTRACT****The goal of this project is to measure three dimensional granular flow fields experimentally, and to utilize network theory to characterize the flow behavior. Network theory metrics focus on the large scale structure of ensembles of linked objects. Since granular matter derives its strength from a dense network of particle contacts, network theory will provide a novel viewpoint relevant to understanding granular materials properties. The focus will be on two key granular flow processes ? fracture and segregation. The first goal is to characterize the onset of fracture of a jammed granular material, i.e. the formation of large scale structural rearrangements such as shear zones when granular matter starts to flow. Understanding how and when granular matter will fracture and start to flow is important to a wide range of fields such as earthquake prediction, rock avalanche hazard prediction, and civil engineering. The second goal is to characterize the particle rearrangements that lead to segregation of a mixture of particle sizes during granular flows. Graduate students will be trained in a unique combination of experimental tools (3D imaging) and theoretical concepts (network theory), and will contribute to mentoring of undergraduate students. The group has developed demonstrations that highlight the most striking features of jamming and granular segregation, which will be presented at public lectures and outreach events.