Static and Dynamic Response of Particulate Media

Southern Illinois University At Carbondale, Carbondale IL

Investigators

Abstract

CBET-0828359 Silbert A sandpile is possibly the simplest and the most common concept of a mechanically stable, granular packing, yet one that exhibits strongly non-linear and complex behavior. A basic understanding of the relation between the microscopic distribution of contact stresses at the grain scale, to bulk, macroscopic, mechanical stability and material strength, persists as one of the most fundamentally challenging questions in contemporary granular matter research. This proposal implements three-dimensional computer simulations of granular materials to address several key features of the mechanical stability of granular packings subject to static and dynamic perturbations. (i) Validate the simulations by comparing results with available experimental data. (ii) Compute linear response profiles in ordered and disordered packings that conclusively resolves the dispute between competing theories of stress transmission based on isotropic/anisotropic elasticity and wave-like propagation models. (iii) Study response crossover effects in small and large packings and correlate this phenomena to emerging length scales that control the stress response. (iv) Determine how friction influences mechanical stability over the range of stable packing fractions, from the close-packed limit down to random loose packing. Compare how different packings approach the onset of failure - loss of mechanical rigidity - with increasing perturbation magnitude, and measure dynamic response of intruder probe particles flowing through the packing. Novel aspects of this work build on current experimental and theoretical results for non-cohesive grains, to include cohesive forces, complex particle shapes, and hydrodynamic effects such as slurries. Intellectual Merit: Fundamental description of the mechanisms of stress transmission inside granular packings, relating how microstructural properties at the grain scale determine macroscopic behavior. Extend our current knowledge on non-cohesive sphere packings, to new and novel systems that include cohesive powders and adhesive grains, composites, and slurries. Broader Impact: Granular materials are found in a wide variety of industrial, natural, and technological settings, and the research has a broad appeal as this study belongs to a large class of problems concerned with mechanical rigidity in amorphous materials including colloidal dispersions, glasses, and polymer and biological networks. Participating students will be encouraged to develop an understanding of these broader aspects of the research. Undergraduate and graduate students are well-suited to the research, and will gain experience in state-of-the-art simulation techniques, computer cluster management, and/or development of computational algorithms, which will be made available as open source software. Simulation configurations, results, and visualizations will be added to a website for collaborative research and public use. Dissemination of research results will follow from publication in refereed journals and attendance at meetings in the physics and engineering communities, and visits to collaborative institutions. The PI continues to implement simulation aides into undergraduate classes and is requesting funds for demonstration materials for class instruction, and future public speaking events. The PI actively promotes the general vision of the department and institution for involving under-represented groups in research, particularly in the physical sciences, and continues to support the recently developed PhD program in the department.