The wave-propagation characteristics of dense granular materials have been studied
from the micromechanical viewpoint, in which relationships are sought between
properties at the micro-scale of particles and interparticle contacts and properties at
the continuum, macro-scale. The dispersion and damping characteristics
have been determined from a three-dimensional lattice analysis in which the
particle interaction is modeled with linear elastic springs and linear viscous
dashpots.
Due the presence of rotational degrees of freedom of the particles, optical
branches are observed in the dispersion and damping characteristics, besides the
acoustical branches. The influence of the micromechanical characteristics on the
macroscopic dispersion and damping characteristics has been determined for a
face-centered cubic lattice and a body-centered cubic lattice. For small wave numbers
(large wave lengths) the damping of the optical branches is very large. This
means that the optical branches will not be observed in conditions where a
continuum-mechanical description is appropriate.