CAREER: Quantifying Local Rearrangements and Their Effects in 3D Granular Materials

这个职业项目的目标是了解局部粒子重排如何引起颗粒材料的宏观性质。颗粒状物质在自然界和工业中随处可见，如沙子、土壤、粉末和药丸。这些材料的力学和动力学特性是工程设计、地质事件和工业过程的核心。理论和数值模型提供了粒子重排等微观过程与这些材料中的力学和动力学行为之间的联系。然而，这项先前的大部分工作都是针对二维系统进行的，而假设的联系的细节还没有得到实验测试。这个项目将使用新的X射线测量来量化三维颗粒材料中粒子尺度的运动和应力。这些测量将被用来测试和改进现有的粒子尺度假设，这些假设低于将局部粒子重排与宏观行为联系起来的理论。随着这些测量和测试，将开发新的工具来预测粒子尺度重排事件的位置、细节和影响。这项研究产生的数据和知识将被整合到一门新的研究生水平的颗粒材料力学课程中。该项目将涉及高中或本科的研究人员，并聘请当地艺术家开发和传播对研究和研究过程的引人入胜的解释。该项目将使用剪切加载和点力加载的3D颗粒材料的原位X射线断层扫描和3D X射线衍射测量，以了解局部粒子重排的原因、细节和影响。这些测量将被用来定量测试将粒子重排与宏观行为联系起来的理论(例如，剪切变化区(STZ)和非局部流动性(NLF)理论)所依据的假设。特别是，X射线测量将使定量评估局部重排的运动学，相关的粒子级应变和应力，以及三维摩擦颗粒材料中重排影响的长度范围。此外，该项目将开发新的衡量标准，用于预测影响宏观行为的颗粒尺度过程的位置和影响，这些宏观行为利用解决颗粒旋转和颗粒间滑动的能力。该项目的成果将是对粒子尺度过程如何在3D中产生连续尺度的力学和动力学行为、摩擦行为以及用于验证和扩展现有理论的新数据的基本理解。该奖项反映了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。

The goal of this CAREER project is to understand how local particle rearrangements give rise to the macroscopic properties of granular materials. Granular materials are found throughout nature and industry as sand, soil, powders, and pills. The mechanical and dynamical properties of these materials are central to engineering design, geological events, and industrial processes. Theories and numerical models have provided links between microscopic processes like particle rearrangements and mechanical and dynamical behavior in these materials. However, much of this prior work has been performed for two-dimensional systems, and the details of the hypothesized links have not been experimentally tested. This project will employ novel X-ray measurements to quantify particle-scale motion and stresses in three-dimensional granular materials. These measurements will be employed to test and improve the existing particle-scale hypotheses that underly theories linking local particle rearrangements to macroscopic behavior. Along with these measurements and tests, new tools will be developed to predict the location, details, and effects of particle-scale rearrangement events. The data and knowledge generated by this research will be integrated into a new graduate-level course on the mechanics of granular materials. The project will involve high-school or undergraduate researchers and engage local artists to develop and disseminate captivating interpretations of the research and research process.This project will use in-situ X-ray tomography and 3D X-ray diffraction measurements of shear-loaded and point-force-loaded 3D granular materials to understand the causes, details, and effects of local particle rearrangements. These measurements will be used to quantitatively test hypotheses underlying theories linking particle rearrangements to macroscopic behavior (e.g., shear transformation zone (STZ) and non-local fluidity (NLF) theories). In particular, the X-ray measurements will allow quantitative assessment of the kinematics of local rearrangements, the associated particle-level strains and stresses, and the length scale of influence of rearrangements within 3D frictional granular materials. In addition, the project will develop new metrics for predicting the locations and effects of particle-scale processes that affect macroscopic behavior that leverage the ability to resolve particle rotations and inter-particle slip. The outcome of the project will be a fundamental understanding of how particle-scale processes give rise to continuum-scale mechanical and dynamical behavior in 3D, frictional behavior, and novel data for validating and extending existing theories.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.