CAREER: The Kinematics of Localized Failure and Flow in Granular Materials

颗粒状材料，如砂，药丸和筒仓中的谷物，表现出非常有趣的行为：它们由固体颗粒组成，在静态载荷下表现为固体;但在开始不稳定时，它们像液体一样流动。 《科学》杂志最近将缺乏颗粒物质运动的一般理论列为科学界目前未回答的100个问题之一。 该教师早期职业发展（CAREER）项目旨在通过研究局部密集颗粒流问题，为更好地理解颗粒材料行为做出贡献。 这个问题将在三个方面进行研究：地质力学的剪切带在砂中，断层泥的作用，在地震断层的启动，和致密颗粒流的热力学变量的量化。 具体来说，我们将使用实验成像技术来检测和表征微观和细观尺度的变形，这些变形被认为是颗粒柱的堆积和坍塌的特征，这构成了颗粒材料中应力传递的基本机制。 由于颗粒系统（例如沙子，玉米）的固有不透明性，大多数以前的研究仅限于理想材料的2D实现。 这项工作将提供一个第一次的机会，通过成像砂，因为它沿着沿着玻璃边界变形，表征颗粒流在真实的材料。 对颗粒材料行为的更好理解将广泛影响涉及颗粒材料的许多科学和工程问题，例如改进岩土工程破坏中安全裕度的量化，防止筒仓流动中的颗粒堵塞，以及提高地震成核的可预测性。 从这一努力中产生的跨学科的施肥将有助于提高地质力学，地球物理学和颗粒物理学的科学发现。 这项研究工作的教育部分利用了拟议实验的基于图像的性质，为颗粒材料中的故障和流动现象的可视化创造了途径，用于本科课程，K-12推广和继续教育。 研究活动将直接涉及本科生，并将特别针对妇女与南加州大学？妇女在科学和工程（WiSE）计划。

Granular materials, such as sands, pharmaceutical pills, and grains in a silo, manifest quite intriguing behavior: they are comprised of solid particles and behave as solids under static loading; but upon the initiation of instability, they flow like liquids. Science magazine recently has cited the lack of a general theory for the motion of granular materials as one of the top 100 currently unanswered questions in science. This Faculty Early Career Development (CAREER) project aims to contribute to the pursuit of better understanding of granular material behavior by looking at the problem of localized, dense granular flow. The problem will be studied in three contexts: the geomechanics of shear banding in sands, the role of fault gouge in the initiation of earthquake faulting, and the quantification of thermodynamic variables for dense granular flows. Specifically, we will use experimental imaging techniques to detect and characterize micro- and meso-scale deformations that are presumed to be signatures of the buildup and collapse of grain columns, which form the basic mechanism for stress transfer in granular materials. Due to the innate opacity of granular systems (e.g. sand, corn), most previous studies have been limited to 2D realizations of idealized materials. This effort will provide a first-of-its-kind opportunity to characterize granular flow in a real material by imaging sand as it deforms along glass boundaries. An improved understanding of granular material behavior will broadly impact a host of science and engineering problems involving granular materials, such as improved quantification of safety margins in geotechnical failures, preventing grain clogging in silo flow, and improved predictability of earthquake nucleation. The cross-disciplinary fertilization deriving from this effort will serve to heighten scientific discovery in each of geomechanics, geophysics, and granular physics. The educational component of this research effort capitalizes on the image-based nature of the proposed experiments to create avenues for visualization of failure and flow phenomena in granular materials, for use in undergraduate courses, K-12 outreach and continuing education. The research activities will directly involve undergraduates, and will particularly target women in conjunction with USC?s Women in Science and Engineering (WiSE) program.