Mechanics of Crystallization, Deformation and Phase Transformation in Granular Materials with Engineered Grain Geometries

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This grant will focus on the engineering, modeling, fabrication and testing of new types of solid granular materials. Granular materials like sand are seemingly simple, but their mechanics is remarkably rich and complex. In this project, the geometry of individual grains will be manipulated to generate crystallization and deformation mechanisms not seen in traditional granular materials, creating “granular materials by design”. This project will establish a mechanics-based fundamental understanding of crystallization in granular materials, enabling manipulation and assembly at large scales. This project will also generate mechanics-based models for the inelastic deformation of granular crystals based on contact mechanics and geometrical hardening. The new granular materials that will emerge from this work will have high strength, unique combinations of assembly / disassembly, strength and self-healing, making them attractive as lightweight materials and aggregate architectures. The reversible nature and the large deformation capabilities of these granular materials will also make them attractive as shape morphing materials, programmable “smart” matter, robotics and biomedical materials. Vigorous outreach activities will be developed in this project including curriculum development at the University of Colorado, research projects for undergraduate students, active learning module for high school students, as well as promotion and improvement of diversity in STEM. A major scientific objective for this project is to create a unified and mechanics-based framework that captures the assembly, phase transformations, deformation and failure of engineered granular materials. Granular systems of specific interest and critical scientific questions include: (i) high packing and space filling in “granular crystals” with stiffness and strength orders of magnitude higher than traditional granular materials; (ii) steering of grains through amorphous-crystalline transitions using mechanical stimuli; (iii) effects of confinement and unlimited deformations to create and control attractive functionalities such as shape morphing, healing, tuning of stiffness and strength; (iv) mechanics of interlocking in branched particles to generate high strength and toughness in tension. Methods include discrete element modeling using geometry-sensitive contact algorithms, 3D printing of grains, and mechanical experiments with in-situ 3D imaging (refractive index matching scanning). A fundamental understanding of these new “engineered” granular materials will lead to new paradigms for the manufacturing and mechanics of granular materials and structures, and for the generation of advanced functionalities such as adaptability, shape morphing or self-healing.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.