Influence of the Poisson's ratio on the efficiency of viscoelastic damping treatments

An efficient way of mitigating noise and vibration is to embed viscoelastic patches into the host structure. Viscoelastic properties are of significant importance in determining the performance of the passive damping treatment. The behaviour of homogeneous isotropic materials is described by two elastic constants (generally the Young modulus and the Poisson ratio, or the shear and bulk moduli), which are frequency- and temperature-dependent in the case of viscoelastic materials. In practice, the Poisson's ratio is often considered as independent of temperature and frequency. One goal of this work is to numerically evaluate the validity of this assumption and its limitations (frequency range, thickness of the viscoelastic layer). To this end, a thermo-mechanical characterization of a viscoelastic material is carried out by dynamic measurements of the complex shear and bulk moduli, allowing the indirect measurement of the frequency- and temperature-dependent Poisson's ratio. Moreover, the measurements of the Poisson's ratio (direct or indirect) can lead to considerable uncertainties. For instance, large discrepancies have been observed when characterizing the Poisson's ratio of polymer foams. Another goal of this work is to investigate the influence of those uncertainties on the dynamic response of a damped structure.

Comparison of passive damping treatments based on constrained viscoelastic layers and multi-resonant piezoelectric networks.

This work aims at comparing the damping performances of two passive damping treatments based on piezoelectric or viscoelastic patches. The motivation for such a comparison stems from the fact that the two damping techniques have been developed fairly independently, and are rarely compared. First, the dynamic response of a simply-supported metallic plate is measured experimentally after being equipped with constrained viscoelastic patches or piezoelectric patches connected to an electrical network. In order to extend the comparison, a numerical model of the structure is set up and validated to evaluate the damping performances of both passive treatments under different configurations (for instance equal-mass and equal-thickness configurations). Finally, with regard to these experimental and numerical results, the advantages and the limitations in using viscoelastic or piezoelectric treatments are discussed.

Topology Optimization of Free Damping Treatments on Plates Using Level Set Method

Application of level set method to optimize the topology of free damping treatments on plates is investigated. The objective function is defined as a combination of several desired modal loss factors solved by the finite element-modal strain energy method. The finite element model for the composite plate is described as combining the level set function. A clamped rectangle composite plate is numerically and experimentally analyzed. The optimized results for a single modal show that the proposed method has the possibility of nucleation of new holes inside the material domain, and the final design is insensitive to initial designs. The damping treatments are guided towards the areas with high modal strain energy. For the multimodal case, the optimized result matches the normalized modal strain energy of the base plate, which would provide a simple implementation way for industrial application. Experimental results show good agreements with the proposed method. The experimental results are in good agreement with the optimization results. It is very promising to see that the optimized result for each modal has almost the same damping effect as that of the full coverage case, and the result for multimodal gets moderate damping at each modal.

Active damping of geometrically nonlinear vibrations of smart composite shells using elliptical smart constrained layer damping treatment with fractional derivative viscoelastic layer

In this article, the performance of elliptical smart constrained layer damping treatments on active damping of geometrically nonlinear vibrations of doubly curved smart laminated composite shells is analyzed. The constraining layers of the smart constrained layer damping treatments comprised vertically/obliquely reinforced 1–3 piezoelectric composites, while the constrained layers of isotropic viscoelastic materials are modeled using the three-dimensional fractional order derivative model. A mesh-free model of the smart composite shells is developed for analyzing their nonlinear transient responses within the framework of a layerwise shear and normal deformation theory considering the von Kármán–type geometric nonlinearity. Thin, doubly curved laminated composite shells integrated with elliptical/rectangular smart constrained layer damping patches with different stacking sequences and boundary conditions are considered for presenting the numerical results. The numerical analyses demonstrate the higher effectiveness of the elliptical smart constrained layer damping treatments over the rectangular ones in attenuating the nonlinear vibrations of laminated composite shells.