Experimental Measurements of Stresses and Strains of Granular Materials Using 3D Non-Destructive Technologies

颗粒材料一直是广泛研究的主题，目的是捕捉它们的本构行为和变形特性。有两种方法来描述颗粒材料的行为，可以大致分为连续力学模型和基于微观结构的模型。文献缺乏系统的实验研究来测量压缩/剪切颗粒颗粒的接触力及其结构演变。提出的研究利用三维（3D）非破坏性技术来捕捉砂粒之间的应力和应变。三维x射线衍射（3DXRD）和同步微计算机断层扫描（SMT）扫描将测量颗粒接触时的应变和应力，随着加载的增加，由硅砂组成的样品。应力-应变关系、弹性模量和单个砂粒的刚度也将使用纳米压头进行测量。实验测量将与离散单元和基于微观结构的本构模型进行比较。如果成功，研究结果将用于提供关键的测量，验证和校准本构离散和连续模型，以更好地理解颗粒材料的行为。利用PI的最佳知识，将首次进行3DXRD测量，以捕获天然砂块中单个颗粒的应力和应变之间的关系，绘制晶体取向，并量化导致颗粒破碎的应力。SMT和3DXRD是具有突破性的新技术，可以对单个颗粒的应力和应变进行实验测量。该教育计划的内容包括：扩大少数民族大学生参与工学研究、为工学大学生提供丰富的研究经验、开发适合初高中学生的教材等。

Granular materials have been the subject of extensive research with the objective to capture their constitutive behavior and deformation characteristics. There are two approaches to describe the behavior of granular materials that can be broadly classified as continuum-mechanical and microstructure-based models. The literature lacks a systematic experimental investigation to measure contact forces of compressed/sheared granular particles and their fabric evolution. The proposed research utilizes three-dimensional (3D) nondestructive technologies to capture stresses and strains between sand particles. 3D x-ray diffraction (3DXRD) and Synchrotron Micro-computed Tomography (SMT) scans will be conducted to measure strains and stresses at particle contacts as loading increases for specimens composed of silica sand. Stress-strain relationship, elastic modulus, and stiffness of individual sand particles will be also measured using nano-indenter. Experimental measurements will be compared with discrete element and with microstructure-based constitutive models.If successful, the results will be used to provide critical measurements, validate and calibrate constitutive discrete and continuum models to better understand the behavior of granular materials. To the best of the PI knowledge, the 3DXRD measurements will be conducted for the first time ever to capture the relationship between stress and strain of individual grains within a bulk mass of natural sand, map the crystallographic orientation, and quantify stresses that cause particle crushing. SMT and 3DXRD are new technologies that have the potential of yielding break-through experimental measurements of stresses and strains of individual particles. The educational plan will include broadening the participation of minority undergraduate students in conducting engineering research, providing enriching research experience for undergraduate engineering students, and developing educational materials tailored for middle and high school student.