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

非技术摘要颗粒材料是我们日常生活中不可或缺的许多部分，从为我们的早晨提供燃料的咖啡豆，到治愈我们的药片，再到为我们的发电厂提供燃料的煤炭。然而，这类材料仍然很难在工业环境中成功处理，很难对易发生山泥倾泻的山坡进行危险评估，也很难确保土木工程基础设施(如堤坝或堤坝)的稳定性。通过这个项目，PI将进行受控的实验室实验，旨在确定稳定的颗粒材料开始流动的过程。测量单个粒子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界和物理界的各种方法的有效性，并找出它们之间的联系。他们将与北卡罗来纳州国家科学之家一起组织一个名为LEAP的年度研讨会！(启动您的优秀物理冒险)既为高中女生提供了接触尖端物理的实践机会，也培训了物理研究人员将他们的研究转化为可公开访问的格式，以及我们实验室致力于工业和地球物理应用的合作者。最后，他们将继续与本科生研究人员合作，包括特别重视招收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受训人员能够在教育、工业或政府部门找到工作，因为他们的兴趣一致，拥有实验技术和数据科学方面的关键专业知识。技术摘要当颗粒材料失去刚性时，它会在已知的约束条件下，集体重新排列其颗粒和内力。这种材料不会自发地转变为一种新的构型，但必须越过某个门槛，无论是摩擦的还是含能的。通过这个项目，PI将对慢流进行实验，以确定颗粒材料开始变形/流动从一种有效状态到另一种状态的机械过程，以及如何选择这一系列状态。对于给定的质点构型，内力不是简单地由外部载荷决定的：许多简并解是可能的。这表明，从统计物理中提取的方法将是捕捉颗粒现象的必要手段。该小组的目标是测试多个框架，并寻求解决问题的工程方法(非局部流变学、莫尔-库仑失效)和统计物理方法(干扰、刚性渗流、非热统计系综)之间的联系。它们将通过来自边界的机械压力以及粒子尺度活动的内部压力来驱动材料失去刚性，以建立这些联系。实验将提供各种应用的基本知识关键：岩土工程和危险评估；制药、农业和采矿行业的散装材料处理；以及太阳系探索任务。国际和平协会将与北卡罗来纳州国家科学研究所一起组织一次名为LEAP的年度研讨会！(启动您的优秀物理冒险)既为高中女孩提供亲身接触尖端物理(包括颗粒材料)的机会，又培训物理研究人员将他们的研究转化为公开可访问的格式。最后，他们将继续与本科生研究人员合作，包括特别强调招收和支持来自代表性不足和历史上被边缘化的群体的学生。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.