Geometry and Mechanics of Nonthermal Packings

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****Technical Abstract****The proposed experiments are designed to probe on the same footing, the structure, linear response and failure of assemblies of (a) compact grains, (b) extended one-dimensional filaments, and (c) two-dimensional sheets. Since the elements in these packings are macroscopic, the packings are nonthermal, and are therefore far from equilibrium. The award contributes to understanding whether untargeted packing protocols lead to final states with statistically reproducible properties. The proposed experiments will study the three-dimensional structure of model systems of each type. At the same time, forces of shear and compression will be applied to probe the mechanical strength of the material. Simultaneously, small loads will be applied to characterise the linear response. The spatial elements that bestow rigidity on a material are often most clearly exposed by studying how the material fails under external loading, so loads large enough to generate yielding will also be imposed. The proposed work gives graduate and undergraduate students exposure to a variety of techniques and the opportunity to work in newly-emerging areas of physics. The PI is also an organizer of an annual summer school hosted at UMass Amherst for early-career graduate students in soft matter physics.****Non-Technical Abstract****The mechanical properties and structure of assemblies of large particles are much more poorly understood than that of assemblies of molecules or atoms. The proposed work will study three geometrically different classes of these systems: (1) Granular materials which range from range from pharmaceutical powders to mineral ores, and from food grains to the soils they grow in. (2) Fibrous materials are the main constituent of plant matter, as well of human products ranging from paper to fabrics and insulants. (3) Crumpled sheets appear in flowers and leaves, as well as in trash compaction and shock absorption. The goal is to study idealized versions of these systems by 3-dimensional imaging techniques that allow the structure to be visualized while forces are applied to the material. This will give important clues as to the structural elements in these materials that are responsible for their mechanical properties. The proposed work gives graduate and undergraduate students exposure to a variety of techniques and the opportunity to work in newly-emerging areas of physics. The PI is also an organizer of an annual summer school hosted at UMass Amherst for early-career graduate students in soft matter and statistical physics.