Structural rearrangements and transport properties of cyclically sheared granular packings

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0853943KudrolliIntellectual Merit The PI proposes to apply a state of the art fluorescent index matching technique to measure the three dimensional positions of particles in the bulk to investigate the elastic and plastic response of a dense granular system undergoing cyclic shear. The proposed research will be transformative because it allows one to systematically examine the packing structure and transport coefficients of the particles over a volume fraction ranging from random loose packing to hexagonal close packings in a regime which is most common to industrial applications. There is a need for such a study because athermal granular matter lacks a sound hydrodynamic description in spite of their preponderance in industrial processes leading to ad hoc solutions. The proposed work builds on preliminary experiments where it is found that velocity auto correlation function for sheared dense granular media show a fast decay, which raises the possibility that hydrodynamic calculations can be extended to significantly greater range of volume fractions compared with elastic hard sphere liquids at equilibrium. A cyclic shear cell apparatus is developed, and a broad shear zone is obtained in the bulk. Three dimensional particle tracking allows one to measure nearest neighbor distribution, the icosahedral order parameter, besides the Voronoi volume distribution as a function of volume fraction and strain, much in the way this is being accomplished in colloidal glasses with confocal microscopy, but here at a 100 times larger scale. Such information can reveal fundamental assumptions about granular systems and understanding of their properties in relation to other particulate matter such as colloidal glasses and suspensions, besides help develop a computational model. The cyclic and quasi static nature of the shear application, will allow us to identify parameters over which one can experience an elastic response in finite, rigid multi contact particulate systems. Furthermore, once plastic deformation has occured, detect heterogenities, identify irrevisible shear transformation zones and determine their topology. Then, the PI will investigate the effect of polydispersity on granular packing and transport properties. It is well know that particulates segregate even if minor differences between them exist. In particular, we will examine the motion of an intruder particle in a cyclically sheared system and study the competition between size, roughness, density and gravity. The application of the fluctuation-dissipation principle to their motion will be tested. The comparison with theoretical calculations will be conducted in collaboration with Professor V. Kumaran of the Department of Chemical Engineering at the Indian Institute of Sciences, Bangalore. Further, the PI proposes to build a database downloadable from the web, containing the trajectories of all the particles as a function of shear cycle that other members in the field can use to carry out their own analysis.Broader Impact The proposed work will have significant impact on undergraduate, graduate and post doctoral student training, besides fostering international collaborations. The involvement of underrepresented members in STEM careers will be positively impacted because the graduate student working on the project is female, and the post doctoral student has partial African heritage. The grant will enhance summer research experience of undergraduate students and help accomplish their honor thesis projects in the laboratory. Aspects of the research will be also adapted into a course on mechanics currently being developed by the PI.