Intra-particle dynamics and the impact response of granular chains

Low-frequency waves generated by an impact on an isostatic granular medium with vanishing confinement pressure are theorized to depend on rigid-particle collisions. According to this model, an impact generates a solitary wave spanning several particle diameters. High-frequency waves with wavelengths smaller than a typical granule size behave differently, and their propagation can be modeled as diffusive. In this paper, experiments and simulations based on a one-dimensional chain of spheres are performed to measure surface and bulk waves in individual granules. Results show that an impact also generates high-frequency waves, due to the dynamic behavior of the individual granules, appearing simultaneously with the solitary wave. Intra-particle Rayleigh waves play a key role in generating and transmitting macroscopic wave modes. The exchange energy between intra-particle wave modes also influences the decay of the solitary wave. Copyright (C) EPLA, 2013