This paper describes a comparison, both analytically and experimentally, between two widely used loss factor estimation techniques frequently used in statistical energy analysis. Analytical models of simple spring/mass/damper systems were created to compare frequency-averaged loss factor values from the single subsystem power injection method and the impulse response decay method. The parameters of the analytical models were varied to study the effects of the total number of modes, amount of damping, location of modes within frequency bands, and the width of the frequency bands on loss factor estimation. The analytical study shows that both methods give accurate loss factor values as long as the damping values remain realistic for linear systems and at least one modal resonance is present in each frequency band. These analytical results were verified experimentally by measuring the loss factors of simple steel plates, with and without damping treatments applied.
Viscoelastic layered systems provide a simple and flexible solution for damping vibration of sheet metal panels. They also help to effectively eliminate noise from resonant structures and surfaces. This article presents an analytical formulation to predict the stiffness and damping of three layered beams with two different viscoelastic materials adjacent to each other. The complex modulus approach is used to model the elastic and shear moduli of the viscoelastic material and closed-form equations are derived for predicting system stiffness and damping. The model is derived for unsymmetrical setups using variational methods. Experiments are conducted on simply supported three-layered beams at different temperatures to validate theoretical results. Similar results are obtained from both the theoretical model and the experiments. A procedure for the optimization of structural and material parameters for maximizing the damping and minimizing the system mass for a given temperature and frequency range is also presented.
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