****NON-TECHNICAL ABSTRACT**** Granular materials are ubiquitous: from pharmaceutical powders to breakfast cereals to coal to avalanches, they appear in all aspects of life. These materials can flow or act like a solid, properties that are exploited in countless practical applications. Understanding these materials is extremely important, but such understanding is substantially lacking. This award supports a project that focuses on "jamming" one of the most intriguing and poorly understood properties of these materials: how do they transition between solid-like to fluid-like behavior. Implicated in this process are two disparate phenomena: forces are carried on structures known as force chains, and in response to applied forces, particles move very non-uniformly. A key premise of this work is that these processes are intimately connected. Novel experiments will allow a complete characterization of granular systems and the opportunity to probe these two features and their interconnection. This work will test novel theoretical approaches that may provide a rigorous basis for predicting granular behavior, as well as the behavior of other disordered systems. Outreach/educational components will be integrated into all aspects of this project. These include outreach to area elementary and secondary schools, and training/research opportunities for high school students, undergraduate and graduate students and for post-docs. The PI also works with an international consortium of granular industrial users to help transfer knowledge to practical applications.
Jamming occurs for dense disordered systems: granular materials, the subject of this project, as well as colloids, foams, glasses, etc. This award supports an experimental project that will probe two key aspects of jamming: 1) force anisotropy, and 2) possible connections between force anisotropy, as epitomized by force chains, and spatial dynamical heterogeneity. Although isotropic jamming has been well studied, the case of anisotropic stresses is not understood. This case is particularly important because shear induces flow in dense granular materials. This project will also test emerging statistical theories that could provide a fundamental basis for understanding non-conservative systems such as granular materials. Experiments will involve several novel techniques including 2D and 3D photoelastic methods combined with biaxial, shear, and triaxial devices. Outreach/education will be integrated into all aspects of this project, including: outreach to local schools, and training/research opportunities for high school, undergraduate and graduate students and for post-docs. The PI also works with an international consortium of granular industrial users to help transfer knowledge to practical applications.