Propagation of solitary waves in 2D granular media: A numerical study

The impact-induced wave propagation in a model granular material composed of closely packed linearly elastic spherical particles interacting through Hertzian contact is investigated numerically using a specially adapted molecular dynamics framework. Of particular interest is the effect of the stiffness and density mismatch between main and interstitial beads on the anisotropic nature and speed of propagation of the primary compressive wave generated by a localized impact event in an extended square-packed granular medium. Two propagation regimes are observed in the numerical simulations: the first one described by a solitary wave pattern emanating from the point of impact, and the other characterized by a directional propagation of the impact energy in the principal directions of the pack. A simple model is proposed to describe the bounds between these two propagation regimes in the parametric space defined by the mass and stiffness ratios between main and interstitial particles. Maps of the normalized maximum compressive force and wave speed are presented to quantify the anisotropy of the wave propagation response.