THE LEVICH INSTITUTE ANNOUNCES THE FOLLOWING SEMINAR

Tuesday, 12/1/98
4:00 PM
Steinman Hall, Room #1M-22
Professor Bob Behringer
Duke University
Physics/Mechanical Engineering & Materials Science/Computer Science
"Dynamics of Granular Materials: Friction, Fluctuations and Instabilities"


ABSTRACT


Granular materials are ubiquitous, yet display complex and only partially understood behavior that I will explore here through a series of experiments. These materials appear solid-like under moderate shear, but can flow like fluids. Thus, convection and various wavy states occur. However, the physics behind these flows is quite different from that of conventional fluids. Without a continuous supply of energy, flow rapidly stops due to the inelasticity of collisions and the friction at contacts. Segregation by size or other properties occurs; these effects would not take place in fluids where entropy/temperature play an important role. For slowly deforming dense systems, the stress is carried nonuniformly in space on filimentary structures known as stress chains. That is, there are strong spatial and temporal fluctuations in the local force. Conventional models have neglected these fluctuations, but they may play a key role in many slow granular flows. In recent experiments on a 2D system, we have found that the qualitative nature of the force fluctuations varies significantly as the density is varied. In particular, there appears to be a critical density near which there is critical slowing down, an order parameter, and an increasing length scale.

BRIEF ACADEMIC/EMPLOYMENT HISTORY: RESEARCH INTERESTS:


Return to Fall, 1998 Seminar Schedule