A finite element method is developed and validated for the estimation of loss factors of a viscoelastically damped plate. Viscoelastic layer is used as constrained layer and is sandwiched between an aluminum base plate and a constraining layer. Frequency-dependent material properties are used for the viscoelastic material in the finite element model. The derived dynamic equations of motion are used to carry out harmonic analysis to determine the natural frequencies and loss factors of sandwich plate and validated with experimental results for cantilever boundary condition. The validated finite element model is then used to estimate the loss factors of sandwich plate with various boundary conditions and different thicknesses of constraining and constrained layer for a given base plate thickness. The results show that the loss factor is maximum for a constraining layer to sandwich plate thickness ratio of 0.40–0.45 and is independent of boundary condition. The loss factor increases with increase in thickness of the viscoelastic layer. The loss factor increases for higher mode for all boundary conditions.
Various types of sandwich beams with viscoelastic cores are currently used in aerospace and automotive industries, indicating the need for simple methods describing the dynamics of these complex structures. In order to understand the effectiveness of the sandwich structures, the dynamics of bare beam with unconstrained and constrained viscoelastic layers are investigated in this study. The viscoelastic layer is bonded uniformly on the beam. The effects of distributed viscoelastic layer treatment on the loss factors are studied. From the experiments it is observed that beams with constrained viscoelastic layer provide higher loss factors than those with unconstrained layer. The dynamics of sandwich beams is modeled using Euler and Bernoulli beam theory. Frequency-dependent Young's modulus and loss factors are considered in the model of viscoelastic material. The predicted Eigen frequencies obtained from the model are compared with the experimental results for two viscoelastic materials with aluminum base material. Frequency response functions are obtained from the finite element model and compared with experimental results for harmonic input. Reductions in vibration amplitudes for two viscoelastic materials (EAP-2 and EAP-43) are also compared. Based on the experimental results, it has been observed that the loss factors of EAP-43 are higher than that of EAP-2.
Statistical Energy Analysis is extensively used framework for predicting the transmission of vibration and sound through complex structures. The prediction of noise and vibration levels in such structures depends on precise estimation of three parameters viz. modal densities, the damping loss factors and the coupling loss factors between the subsystems. Damping is usually characterized by the amount of energy dissipated and the most common measure of this dissipation is damping loss factor. This paper describes the effect of materials used for plate on damping loss factor. The experimental results of conventional and composite plates are compared. Damping loss factor has been determined by Half-power bandwidth method for the plates.
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