When an object hits the floor, if the object does not break, it rebounds… or not. At least, for sure, the object never comes back at the origin of the falling. Indeed, the brutal impact dissipates energy. Only one single dimentionless coefficient accounts for all this: the coefficient of restitution, i.e. the ratio between the velocity of the object after and before the impact. In this work, we considered hollow objects that are partially filled with a granular material. Consequently, after the impact, the inner grains receive a momentum and allow a greater dissipation of the energy. We found, in the case of cylinders filled with grains, that the coefficient of restitution (of the first rebound) is zero when the mass of the grains contained in the cylinder is larger than 1.5 times the mass and the coefficient of restituion of the empty container. This “perfect’’ granular damper is fullfilled if and only if the cylinder is not full. Finally, we compared the cylinder to the sphere geometry. In this case, we found that the second rebound is always fully damped except when the container is empty…or completely full of grains. This research allows to envisage new way to damp efficiently systems from a spacecraft to a classical hammer.
F. Pacheco-Vázquez, S. Dorbolo, Sci. Rep. 3, 2158 (2013)