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Quicktime movies Closeup movie of stress chains in pentagons File Size ~2.5 Meg Closeup of movie stress chains in disks File Size ~3 Meg Distant movie showing whole shearing apparatus FIle Size ~3.4 Meg Recent papers Kinematics in 2-D shear experiment appearing in Jan 1999 PRE. Can now download a revised version of this paper from the PRE website. (gzipped 136K) Stress fluctuations in 2-D experiment submitted to PRL (gzipped 744K <- one very large picture takes most of room) A granular material is a collection of many individual solid particles that interact through short-range repulsive forces and frictional forces when in contact with other particles or boundaries. The interactions between the particles, inelastic in nature, cause rapid dissipation of energy in the system. Fluids surrounding the particles may also affect the overall dynamics. The growth of interest in this subject by the physics/math community in the past decade, can be attributed to the many unusual phenomena associated with granular flow [Behringer]. One of these phenomena, known as dilantancy, is the property of granular materials to increase in bulk volume when placed under shear. Another interesting feature, referred to as the development of shear bands, arises when an external load overcomes frictional forces in a granular medium. This causes many-particle blocks to separate along planes at certain angles dependent on the internal friction of the substance. Interest is also spurred by the importance of granular flow to many industries. Since many common industrial materials (for example coal, agricultural grains, pharmaceutical products) are granular in nature, an increase in the efficiency of handling processes would be profitable [Ennis]. Our experiment uses a two-dimensional annular geometry to study the effect of shearing on disks made out of a photoelastic polymer. Photoelasticity allows us to visualize the stresses in the material. Viscous drag due to air surrounding the particles is negligible compared to the frictional and shear forces resulting from rotating the shearing surfaces in our experiment. From this system we obtain results for the dynamics and stress fluctuations of slow shear systems, which will provide insight into the importance of these properties in understanding granular flows. [Behringer] H.M. Jaeger, S.R. Nagel, R.P. Behringer, Rev. Mod. Phys. 68, 1259 (1996) [Ennis] B.J. Ennis, J. Green, R. Davies, Chemical Engineering Progress 90, 32 (1994)  Motivation and Experimental SetupVelocity Profiles and Distributions and Density ProfilesStress Measurements
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