Vibration-induced densification of granular materials.

摘要

Physical experiments as well as discrete element simulations of vibration are carried out. The use of different amplitudes and frequencies are applied in the experiments to facilitate the observation of densification trends with mono-disperse acrylic spheres and multi-disperse polyethylene pellets. For mono-disperse acrylic spheres, four densification trends are found at different vibration conditions, and attaining the "maximum density" is closely related to the combination of vibration frequency and amplitude, in agreement with experiments in the literature. For multi-disperse polyethylene pellets, there is a substantial increase in solids fraction due to the effects of particle shape and surface friction. Computer simulations applying the discrete element method are then used to investigate the influence of material properties, container geometry and vibration amplitude and frequency on the vibration process. The instantaneous dynamic states have been deeply investigated. The results obtained are in agreement with the experiments of Thomas et al. and consistent with theoretical predictions of Richman et al. at the high relative accelerations. At low relative accelerations, the initial structure of the poured particle bed strongly affects the dynamic behavior. From the analysis of the relaxed states, four densification trends have also been found, and the relationship between the instantaneous dynamic states and final relaxed states is established. Several possible densification mechanisms have been discussed, which is substantiated by evolution of the solids fraction.