Damping of metallic wool with embedded rigid body motion amplifiers

The use of entangled metallic wires as vibrational dampers and shock isolators is of interest in a variety of applications. By taking advantage of the frictional contact between the contiguous wires, it has been shown that significant amounts of energy dissipation can be achieved. The amount of energy dissipation is highly dependent on many factors with one in particular being the excitation amplitude. When the excitation amplitude is low, a combination of the number of contact points, in which have relative motion, and the contact pressure are lessened often leading to a sacrifice in energy dissipation. In this paper, spherical metallic rigid bodies are embedded within metallic wool. These rigid bodies act as motion amplifiers in which, locally within the metallic wool, amplify the excitation amplitude leading to an increase in vibrational damping. Presented are experimental modal results from various metallic wool/embedded rigid body arrangements within a prismatic hollow aluminium tube. It is found that the incorporation of the embedded rigid bodies into the steel wool significantly improves the damping within the system. It is demonstrated that an increase in damping by 2328% has been achieved at only a 3.8% penalty in mass. It is found that the level of damping from the embedded rigid bodies depends not only on the excitation amplitude but their quantity and the accompanying steel wool configuration. A finite element procedure coupled with an analytical model is proposed which accounts for the strain energy produced within the steel wool to estimate the damping effect that this filler material has on the behaviour of the overall structure. The model treats the metallic wool/rigid sphere combination as a homogeneous equivalent solid with amplitude dependent damping properties, thereby reducing the complexities of the physics-based model while still providing an estimate of the vibrational damping while in the frequency domain.