PARTICLE ROTATIONS IN GRANULAR MATERIALS

Abstract eng:
Particle rotations can have a dominant influence on the behavior of granular materials, particularly in materials with circular or spherical particles. The paper briefly reviews experimental evidence of the magnitude and variability of particle rotations and their effect on a granular material’s stiffness and strength. Evidence of rotational patterning is reported from DEM simulations of a large square assembly of multi-sized circular particles. The translational velocities of the particles were used to compute the rotation and deformation rates within small polygonal regions of material. The material rotation could then be compared with the rotations of the particles themselves. Two meso-scale phenomena are described in the paper: rotating clusters and rotation chains. During biaxial tests, the local deformation rates are highly variable, with banded regions having deformation rates much greater than the mean rate, and with clustered regions in which very little deformation occurs. Material within a nearly-rigid region usually rotates in either an entirely clockwise or entirely counter-clockwise manner. The direction of this material rotation matches the direction of particle rotations in these regions. In a second rotational pattern, the most rapidly rotating particles are aligned in chain-like patterns oblique to the principal stress directions. These rotation chains are usually located within intensely deforming band-like regions.

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