<title>Damping of flexural vibration by coupling to low-density granular materials</title>

Abstract

Heavy structures (such as machine-tool bases) are sometimes filled with granular materials (such as sand, gravel, or lead shot) to increase their damping. Traditionally, relatively dense granular fills have been selected for such applications in order to obtain strong coupling between the structure and the granular material. But recent experiments indicate that a low-density granular fill can provide high damping of structural vibration if the speed of sound in the fill is sufficiently low. We describe a set of experiments in which aluminum beams are filled with a granular material whose total mass is three per cent of that of the unfilled beam and damping coefficients as high as 0.04 are obtained. The experiments indicate that the damping at high frequencies is essentially a linear phenomenon. We present a simple model that qualitatively explains the essentially linear high-frequency damping observed in the experiments.