Study on the influence of design parameter variation on the dynamic behaviour of thermoplastic honeycomb panels

摘要

Sandwich panels are layered structures that consist of at least five layers : two thin face sheets that are bonded with bonding layers to the thick core. The core has a very low density whereas the face sheets are stiff and strong. The entire panel combines high mechanical properties with a very low areal mass. Most of the structural characteristics of the panel (material selection and thickness of each layer) can be selected independently of other parameters, and the overall characteristics of the panel depend on the particular selection of parameters. Because of the wide range of panel parameters, numerical modelling is useful to provide insight into the structural characteristics of a particular panel.This paper studies the effect of design parameter variations on the dynamic behaviour of honeycomb sandwich panels. The dynamic behaviour includes natural frequencies, mode shapes and damping of such panels with free boundary conditions.In the first section the structure of honeycomb sandwich panels is illustrated, in particular those with a ThermHex core. For a typical honeycomb panel the different design parameters are outlined.Natural frequencies and mode shapes can be predicted approximately using analytical models. Some of the methods are outlined in this article.The second section of the paper presents the numerical modelling of a sandwich panel using commercial finite element codes. Different core modelling strategies are compared, e.g. geometrically correct or as a homogenised equivalent material. Advantages and drawbacks of the different methods are outlined. Different ways of modelling damping in the panels are also presented.The third section discusses the experimental validation. To validate the finite element models, measurements are carried out on some test panels. Free-free boundary conditions are provided by elastically suspending the panels. To make measurements totally contactless, the test panels are excited acoustically and the vibration measurement is performed with a laser vibrometer. The way the data are captured and processed is also outlined.Measured natural frequencies and mode shapes are compared with the calculated results from the different FE models and the analytical models. The techniques that are used for this comparison are briefly discussed.The different FE models are updated using results from a sensitivity analysis. This analysis is performed theoretically for every design parameter and is discussed in detail. Results from the updated models are again compared with those obtained from measurements.The uncertainty on different design parameters is studied and discussed. The influence of these various uncertainties on the natural frequencies and mode shapes is investigated using Monte Carlo simulations.