Compaction of rods: Relaxation and ordering in vibrated, anisotropic granular material

We report on experiments to measure the temporal and spatial evolution of p acking arrangements of anisotropic, cylindrical granular material, using hi gh-resolution capacitive monitoring. In these experiments, the particle con figurations start from an initially disordered, low-packing-fraction state and under vertical vibrations evolve to a dense, highly ordered, nematic st ate in which the long particle axes align with the vertical tube walls. We find that the orientational ordering process is reflected in a characterist ic, steep rise in the local packing fraction. At any given height inside th e packing, the ordering is initiated at the container walls and proceeds in ward. We explore the evolution of the local as well as the height-averaged packing fraction as a function of vibration parameters and compare our resu lts to relaxation experiments conducted on spherically shaped granular mate rials.