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

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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.