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

颗粒状材料，如沙子、药片和筒仓中的谷物，表现出相当有趣的行为：它们由固体颗粒组成，在静态载荷下表现为固体；但一旦不稳定开始，它们就会像液体一样流动。《科学》杂志最近将颗粒状物质运动的一般理论的缺乏列为目前科学界未解决的前100个问题之一。该学院早期职业发展（Career）项目旨在通过研究局部致密颗粒流问题，促进对颗粒材料行为的更好理解。该问题将在三种情况下进行研究：砂中剪切带的地质力学，断层泥在地震断层发生中的作用，以及密集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尺度和中尺度的变形，这些变形被认为是颗粒柱形成和坍塌的特征，它们构成了颗粒材料中应力传递的基本机制。由于颗粒系统（如沙子、玉米）固有的不透明性，大多数先前的研究都局限于理想化材料的二维实现。这项工作将首次提供机会，通过对沙子沿玻璃边界变形的成像来表征真实材料中的颗粒流动。提高对颗粒材料行为的理解将广泛影响涉及颗粒材料的许多科学和工程问题，例如改进岩土工程失效安全边际的量化，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所提议的实验的基于图像的性质，为颗粒材料中的失败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。这些研究活动将直接涉及本科生，并将特别针对与南加州大学合作的女性。美国科学与工程女性（WiSE）项目。

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.