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

Johns Hopkins University, Baltimore MD

Investigators

Abstract

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.