Bob Behringer

Force Fluctuations and Transmission in Granular Materials

Abstract: Granular materials present a host of challenges, and the main focus of this talk will be understanding their statistical properties in the dense phase. In the dense phase(s), forces are carried preferentially on complex filimentary structures known as force chains. The way in which these mesoscopic structures come into play on larger scales is a topic of intense debate, but it seems likely that an understanding of this issue is fundamental to further progress. Open questions include how static forces are transmitted, and how changes in the force chain structure come into play in deforming samples, for instance samples under shear. In the latter case, fluctuations can be very large, an order of magnitude greater than the mean. In addition, it is interesting to ask whether the statistical properties of dense granular materials can be related to corresponding properties for equilibrium systems. These issues will be explored through a series of experiments, first to determine the 'Green's function' for static forces, and then to characterize the nature of force fluctuations.