Our previous time-of-flight studies with two-dimensional polygonal simulations and one- and three-dimensional experiments showed that the sound-velocity in granular materials in one and two dimensions is of the order of 10% of that of the bulk material, while in three dimensions with spherical beads, it is only of the order of one percent. The conclusion was that the force network in three dimensions leads to a reduction of the sound velocity compared to two dimensions. With our newly completed fully three dimensional discrete element method with polyhedral particles, we investigate the relation between particle shape, size dispersion and sound velocity. The force-law is able to reproduce the sound velocity of the bulk material for space-filling particle packings. We find that the sound velocities in polyhedral assemblies are about 3% to 5% of the bulk sound velocities. This means that the influence of the particle geometry on the contact is significant. Aggregates with particles with many surfaces show higher sound velocities than those with sharp edges. Additionally, solitonic waves were observed which propagated in front of the sound-waves, but only in a relatively short range.
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