Mechanics of Granular Materials: Rigidity, Nonlocality, and Activated Failure

颗粒材料是我们日常生活中许多部分不可或缺的一部分，从早晨为我们提供能量的咖啡豆，到治愈我们的药物药丸，再到为发电厂提供燃料的煤。然而，这类材料在工业环境中仍然很难成功处理，在我们容易发生山体滑坡的山坡上提供危害评估，或确保堤防等民用基础设施的稳定性。通过这个项目，PI将进行受控的实验室实验，旨在确定稳定颗粒材料开始流动的过程。测量单个粒子的加载和滑动细节的大型数据集将使我们能够测试来自工程和物理社区的各种方法的有效性，并在它们之间建立联系。他们将与北卡罗来纳州立科学学院一起，组织一个名为LEAP的年度研讨会！（启动你的优秀冒险与物理），既提供高中女生动手接触尖端的物理，并培训物理研究人员翻译他们的研究，以公开访问的格式，也为我们的实验室的合作者在工业和地球物理应用工作。最后，他们将继续与本科生研究人员合作，包括特别强调招募和支持来自代表性不足和历史上被边缘化群体的学生。这些活动将使他们的学员在他们的兴趣一致的情况下找到教育、工业或政府的工作，并掌握实验技术和数据科学的关键专业知识。技术摘要：当颗粒状材料失去刚性时，它会根据已知的约束集体重新排列其颗粒和内力。材料不会自发地过渡到一个新的结构，但必须跨越一些阈值，摩擦或能量。通过这个项目，PI将对缓慢流动进行实验，以确定颗粒材料从一种有效状态开始变形/流动到另一种有效状态的机械过程，以及如何选择这一系列状态。对于给定的粒子构型，内力不是简单地由外部载荷决定的：有许多简并解是可能的。这表明，从统计物理学中得出的方法对于捕获颗粒现象是必要的。该小组旨在测试多种框架，并寻求解决问题的工程方法（非局部流变、莫尔-库仑失效）与统计物理方法（干扰、刚性渗透、非热统计集成）之间的联系。为了建立这些连接，它们会通过来自边界的机械力以及来自颗粒尺度活动的内部力来驱动材料失去刚性。实验将提供各种应用的基础知识关键：岩土工程和危害评估；医药、农业和采矿业的散装物料处理；以及太阳系探索任务。PI将与NC州立科学屋一起组织一个名为LEAP的年度研讨会！（启动你的优秀的冒险与物理），既提供高中女生动手接触尖端的物理（包括颗粒材料），并培训物理研究人员翻译他们的研究，以公开可访问的格式。最后，他们将继续与本科生研究人员合作，包括特别强调招募和支持来自代表性不足和历史上被边缘化群体的学生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical AbstractGranular materials are integral to many parts of our daily lives, from the coffee beans that fuel our mornings, to the pharmaceutical pills that heal us, to the coal that fuels our power plants. Yet, this class of materials remains very difficult to successfully handle in industrial contexts, to provide hazard estimation on our landslide-prone hillsides, or to ensure stability of civil infrastructure such as embankments or levees. Through this project, the PI will perform controlled laboratory experiments aimed at determining the processes by which a stable granular material begins to flow. Large datasets measuring the details of loading and slipping for individual particles will allow us to test the efficacy of, and draw connections between, a variety of approaches drawn from both the engineering and physics communities. Together with the NC State Science House, they will organize an annual workshop called LEAP! (Launch your Excellent Adventures with Physics) to both provide high school girls with hands-on exposure to cutting-edge physics, and train physics researchers in the translation of their research to publicly-accessible formats, and also to our lab’s collaborators working on industrial and geophysical applications. Finally, they will continue work with undergraduate researchers, including a particular emphasis on recruiting and supporting students from under-represented and historically marginalized groups. These activities will equip their trainees to find jobs in education, industry, or governments as their interests align, with key expertise in both experimental techniques and data science. Technical AbstractWhen a granular material loses rigidity, it collectively rearranges its particles and internal forces, subject to known constraints. The material does not transition to a new configuration spontaneously, but must cross some threshold, frictional or energetic. Through this project, the PI will perform experiments on slow flows in order to determine the mechanical process by which a granular material begins to deform/flow from one valid state to another, and how this series of states is selected. For a given configuration of particles, the internal forces are not simply determined by the external load: many degenerate solutions are possible. This indicates that approaches drawn from statistical physics will be necessary to capture granular phenomena. The group aims to test multiple frameworks and seek connections between engineering approaches to the problem (nonlocal rheology, Mohr-Coulomb failure) and those of statistical physics (jamming, rigidity percolation, athermal statistical ensembles). They will drive the material to lose rigidity both by mechanical forcing from a boundary, as well as by internal forcing from particle-scale activity, in order to make these connections. Experiments will provide fundamental knowledge key to a variety of applications: geotechnical engineering and hazard estimation; bulk materials handling in the pharmaceutical, agricultural, and mining industries; and solar system exploration missions. Together with the NC State Science House, the PI will organize an annual workshop called LEAP! (Launch your Excellent Adventures with Physics) to both provide high school girls with hands-on exposure to cutting-edge physics (including granular materials), and train physics researchers in the translation of their research to publicly accessible formats. Finally, they will continue work with undergraduate researchers, including a particular emphasis on recruiting and supporting students from under-represented and historically marginalized groups.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.