MICROMECHANICAL STUDY OF DISPERSION AND DAMPING CHARACTERISTICS OF GRANULAR MATERIALS

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.