Keywords: layerwise models, sandwich plates, viscoelastic damping.

Light and thin structures, usually applied on spacecraft and aeronautical assemblies, are very sensitive to cycling or random loading, which promote high levels of mechanical vibration, noise and fatigue failure, leading to structural disturbance and premature failure [1]. Soft core sandwich panels, using viscoelastic layers, are usually applied on these structures in order to improve their dynamic behavior [2,3]. A high damping soft viscoelastic core inserted inside a sandwich plate can improve its dynamic response due to the high level of energy dissipation that occurs in the viscoelastic layer as a result of the polymeric molecular chain reaction to the imposed cycling deformation.

Though its mechanical performance, low cost and damping efficiency, this kind of structures with integrated viscoelastic treatment demand a special and complex simulation task in order to properly determine the treatment parameters, like material type, thicknesses, number of layers, location and treatment coverage. The usual approach applies a layered scheme of plate and brick finite elements, using a solid brick finite element to model the viscoelastic layer [4]. This modelling approach can provide a simple and reliable mean to simulate the sandwich structures using the finite element method, being able to describe accurately the high shear deformation that is developed inside the viscoelastic layer, promoted by the constraining effect of the outside skins. However, it demands a cumbersome spatial modelling task, that must be recreated to account for any thickness change, which is not recommended to model multiple layer sandwich panels, using more than one viscoelastic core, and requires special care when simulating non planar structures.

To overcome the layered modelling scheme limitations a layerwise finite element model is proposed which proved to provide results similar to those obtained using the layered approach. With this new model the sandwich plate is spatially modelled by 4-node planar finite elements, using a conventional plate or shell mesh generator, while the layers parameters, namely its thickness and material properties, are simply described in a numerical table that is directly used in the finite element routine. Thus, the redefinition of treatment configuration, i.e. the number of layers, the layering order, thickness of each layer and material properties, is easily allowed by simple redefinition of the input data file.

In the present work three different layered models [4] along with the layerwise model are used to simulate single core sandwich plates, giving special attention to the numerical efficiency, namely the numerical locking protection issue, and accuracy of both modelling approaches. The two modelling approaches are validated through a set of frequency response functions measured on two sandwich specimens with integrated viscoelastic damping treatments. The numerical results are obtained using the direct frequency analysis method, along with the complex modulus approach [4], to account for the variation of the viscoelastic material properties with frequency and generate the frequency response model.

1

D.I.G. Jones, "Handbook of Viscoelastic Vibration Damping", John Wiley & Sons, 2001.

2

C.D. Johnson, "Design of Passive Damping Systems", Special 50th Anniversary Design Issue, Transactions of the ASME, 117, 171-176, 1995.

3

A.D. Nashif, D.I.G. Jones, J.P.Henderson, "Vibration Damping", John Wiley & Sons, 1985.

4

R.A. Moreira, J.D. Rodrigues, "Constrained damping layer treatments: The finite element modelling", Journal of Vibraton and Control, 10(4), 575-596, 2004. doi:10.1177/1077546304039060

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