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The aim of this work is the evaluation of damping ratio in composite materials with orthogonal fiber orientation based on experimental and numerical techniques. In this study, the logarithmic decrement and the envelope techniques calculated using Hilbert transform are used. Carbon fiber/epoxy composites manufactured by filament winding are dynamically tested in free vibration. Post-processing and data analysis are performed with the developed codes. These comprise the use of a band-pass filter to isolate the first fundamental frequency from the other modes of vibration and noise present in the acquired signal. Then, the Hilbert transform is used to estimate the envelope of the vibration signal and the exponential curve is adjusted to obtain the envelope, in order to evaluate the structural damping ratio. Comparisons with a fitted finite element model are used for validation. The results revealed that damping varied proportionally with the number of layers, the ply orientation and, less evidently, with the length of the samples.

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Analytical modeling and numerical simulation of multiphysics coupled systems is an exciting research area, even when it comes to intrinsically linear or linearized formulations, as is usually the case with coupled vibroacoustic problems. The combined effect of many localized geometrical miss-modeling with significant uncertainty in mechanical characterization of some organic materials yields large discrepancies in the natural frequencies and mode shapes obtained. The main goal of this work is to compare two basic approaches for the modeling of stringed musical instruments in the frequency domain: simplified lumped-parameter analytic modeling, considering only the most influential degrees of freedom, and discretized finite element modal analysis. Thus, the emphasis is on a review of some key references in this field, including previous work by the authors, which may shed light on some of the most relevant issues surrounding this problem.