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对象，目的是捕捉它们的本构行为和变形特征。描述颗粒材料行为的方法有两种，大致可分为连续介质力学模型和基于微观结构的模型。文献中缺乏系统的实验研究来测量压缩/剪切颗粒的接触力及其组构演化。这项拟议的研究利用三维(3D)无损技术来捕捉沙粒之间的应力和应变。将进行三维X射线衍射(3DX射线)和同步辐射微电脑断层扫描(SMT)，以测量颗粒接触处的应变和应力，随着载荷的增加而增加。还将使用纳米压头测量单个沙粒的应力-应变关系、弹性模数和硬度。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，结果将用于提供关键测量，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。据PI所知，将首次进行3DX射线测量，以捕捉一大块天然砂中单个颗粒的应力和应变关系，绘制晶体取向图，并量化导致颗粒破碎的应力。SMT和3DXRD是具有突破单个颗粒应力和应变实验测量的潜力的新技术。该教育计划将包括扩大少数民族本科生参与工程研究的范围，为工科本科生提供丰富的研究经验，并为初中生开发量身定做的教材。

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.