Heterogeneity, Anisotropy, and Fluctuations in Dense Granular Materials

*非技术摘要*颗粒材料无处不在：从药粉到早餐麦片，从煤炭到雪崩，它们出现在生活的方方面面。这些材料可以像固体一样流动或发挥作用，这些特性在无数实际应用中得到了开发。理解这些材料是极其重要的，但这种理解实际上是缺乏的。该奖项支持一个项目，该项目的重点是“干扰”这些材料最耐人寻味、也最鲜为人知的特性之一：它们如何从类固体行为转变为类流体行为。在这个过程中牵涉到两种截然不同的现象：力在被称为力链的结构上传递，粒子在外力的响应下运动得非常不均匀。这项工作的一个关键前提是，这些过程是密切相关的。新颖的实验将允许对颗粒系统进行完整的表征，并有机会探索这两个特征及其相互联系。这项工作将测试新的理论方法，这些方法可能为预测颗粒行为以及其他无序系统的行为提供严格的基础。外联/教育部分将纳入该项目的所有方面。这些措施包括对地区小学和中学的外联，以及为高中生、本科生和研究生以及博士后提供培训/研究机会。PI还与国际颗粒工业用户联盟合作，帮助将知识转移到实际应用中。*技术摘要*干扰发生在密集无序系统中：颗粒材料，本项目的主题，以及胶体，泡沫，玻璃等。该奖项支持一个实验项目，该项目将探索干扰的两个关键方面：1)力各向异性，2)力各向异性，如力链的缩影，与空间动力学异质性之间的可能联系。虽然各向同性干扰已经得到了很好的研究，但对各向异性应力的情况还不清楚。这种情况特别重要，因为剪切会在致密的颗粒材料中诱导流动。这个项目还将测试新兴的统计学理论，这些理论可以为理解非保守系统，如颗粒物质提供基本基础。实验将涉及几种新技术，包括结合双轴、剪切和三轴装置的2D和3D光弹性方法。推广/教育将纳入该项目的所有方面，包括：与当地学校进行推广，为高中生、本科生、研究生和博士后提供培训/研究机会。PI还与一个由颗粒状工业用户组成的国际联盟合作，帮助将知识转化为实际应用。

****NON-TECHNICAL ABSTRACT****Granular materials are ubiquitous: from pharmaceutical powders to breakfast cereals to coal to avalanches, they appear in all aspects of life. These materials can flow or act like a solid, properties that are exploited in countless practical applications. Understanding these materials is extremely important, but such understanding is substantially lacking. This award supports a project that focuses on "jamming" one of the most intriguing and poorly understood properties of these materials: how do they transition between solid-like to fluid-like behavior. Implicated in this process are two disparate phenomena: forces are carried on structures known as force chains, and in response to applied forces, particles move very non-uniformly. A key premise of this work is that these processes are intimately connected. Novel experiments will allow a complete characterization of granular systems and the opportunity to probe these two features and their interconnection. This work will test novel theoretical approaches that may provide a rigorous basis for predicting granular behavior, as well as the behavior of other disordered systems. Outreach/educational components will be integrated into all aspects of this project. These include outreach to area elementary and secondary schools, and training/research opportunities for high school students, undergraduate and graduate students and for post-docs. The PI also works with an international consortium of granular industrial users to help transfer knowledge to practical applications.****TECHNICAL ABSTRACT****Jamming occurs for dense disordered systems: granular materials, the subject of this project, as well as colloids, foams, glasses, etc. This award supports an experimental project that will probe two key aspects of jamming: 1) force anisotropy, and 2) possible connections between force anisotropy, as epitomized by force chains, and spatial dynamical heterogeneity. Although isotropic jamming has been well studied, the case of anisotropic stresses is not understood. This case is particularly important because shear induces flow in dense granular materials. This project will also test emerging statistical theories that could provide a fundamental basis for understanding non-conservative systems such as granular materials. Experiments will involve several novel techniques including 2D and 3D photoelastic methods combined with biaxial, shear, and triaxial devices. Outreach/education will be integrated into all aspects of this project, including: outreach to local schools, and training/research opportunities for high school, undergraduate and graduate students and for post-docs. The PI also works with an international consortium of granular industrial users to help transfer knowledge to practical applications.