Optimizing Reinforced Polyurethane as a Combined Structural and Damping Component

Abstract

In many engineering applications, mechanical vibration can cause structural failure or other problems. While traditional composite systems are typically more heavily damped than metal structures, there may still be insufficient energy dissipation for vibration control. When more control is required, additional mechanical damping treatments may be applied, commonly in the form of viscoelastic free or constrained layers. Reinforced polyurethane has been shown to be both a structural system, and one that dissipates significant amounts of vibration energy. This material system has been shown to significantly enhance the damping loss factor of cylindrical and flat plate structures. For these structures, mechanical strength and flexibility were the primary design requirements. The level of damping for each structure was quantified, but the material systems were not optimized for energy dissipation. The high level of damping in these reinforced polyurethane systems was attributed to a combination of the flexibility, i.e. high strains, of the material, coupled with energy dissipation within the matrix. As the system deforms, the matrix is subject to time-varying shear, and energy is dissipated in the matrix. This mechanism can be likened to micro-mechanical constrained layer damping. This paper presents an experimental technique for the determination of the damping of thin fiber reinforced damping layers. A conventional composite beam with varying thicknesses of reinforced polyurethane was modally tested. The results of the modal analysis were then processed to yield the damping of the free layer. The experimentally determined levels of damping were significantly higher than conventional free layer treatments, especially at low frequencies.