CAREER: State Variables in Granular Materials

North Carolina State University, Raleigh NC

Investigators

Abstract

Nontechnical Abstract Granular materials are ubiquitous in both natural and engineered systems, from sand to pharmaceuticals to corn, and behave unpredictably due to their ability to act like either solids or liquids. This Faculty Early Career Development project at North Carolina State University aims to improve our understanding of granular and other complex materials by utilizing tools from nonequilibrium statistical mechanics to conduct carefully controlled laboratory experiments in model systems. The project will test the relevance of various state variables (such as temperature-like variables, pressure, void space, or degree of ordering) to describing dense granular systems. In particular, it will build experiments which, for the first time, directly address the degree to which these variables can equilibrate between two parts of a system and change under shear. An improved understanding of which of these variables are necessary/sufficient to describe the state of the system will broadly impact processing industries, geotechnical engineering, and earthquake hazard estimation by providing diagnostics to measure the state of a granular system before it fails. The project will integrate research with undergraduate education through providing laboratory research opportunities for undergraduates, as well as developing and disseminating a course on nonlinear/nonequilibrium systems. Students from both the course and the laboratory will develop, in collaboration with NC State's Science House, hands-on outreach activities for use with local school/youth groups. Technical Abstract Granular materials are ubiquitous in both natural and engineered systems, from sand to pharmaceuticals to corn, and behave unpredictably due to the presence of both solid-like and liquid-like states. This Faculty Early Career Development project at North Carolina State University aims to improve our understanding of granular and other complex materials by utilizing tools from nonequilibrium statistical mechanics to conduct carefully controlled laboratory experiments in model systems. The project will test the relevance of various state variables (such as ``temperature'', pressure, packing fraction, fraction of static contacts, or degree of ordering) to describing dense granular systems. In particular, it will build experiments which, for the first time, directly address the degree to which temperature-like variables (compactivity/angoricity from Edwards entropy and effective temperature from the fluctuation-dissipation theorem) equilibrate between two subsystems and change under shear. An improved understanding of which of these variables are necessary/sufficient to describe the state of the system will broadly impact processing industries, geotechnical engineering, and earthquake hazard estimation by providing diagnostics to measure the state of a granular system before it fails. The project will integrate research with undergraduate education through providing laboratory research opportunities for undergraduates, as well as developing and disseminating a course on nonlinear/nonequilibrium systems. Students from both the course and the laboratory will develop, in collaboration with NC State's Science House, hands-on outreach activities for use with local school/youth groups.