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Statistics of Dense Granular Materials
Bob Behringer (Duke University, North Carolina, USA)
Abstract:
Dense granular materials present a number of interesting challenges. They are many-body systems with dissipative interactions. As suggested by Edwards et al., one would like to have a statistical approach analogous to Boltzmann statistics for energy-conserving systems. But the dissipative character of dense granular materials challenges conventional notions. New approaches require a careful examination, and suggest a number of experiments. This talk will focus on recent experiments that seek to characterize the statistics of dense granular systems and to test recent models. In particular, we have carried out experiments to determine the microscopic distributions of contact forces, the nature of jamming, the effect of stress anisotropy, the role of affine and non-affine motion in sheared granular systems, the effect of particle rotation, and the importance of particle shape. Many of these experiments use photoelastic particles. This allows the tracking of particle motion, and perhaps most importantly, the determination of the contact forces by the solution of a nonlinear inverse problem.
Our results are consistent with predictions from the force ensemble approach, but much more needs to be done.
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