In recent years the dynamic design of lightweight structures has received increased emphasis. This trend is particularly noticeable in the design of modern aircraft and in engineering transport applications where dynamic loads can produce high amplitude of vibrations. The presence of vibrations often leads to undesirable effects such as structural or mechanical failure, frequent and costly maintenance of machines, decreased positioning performance, human pain and discomfort. The issue of minimising the mass of the structure is also important since it leads to reduced emissions and a reduction of operating costs. Therefore, vibration elimination or reduction is an important item to be considered in mechanical design of structures in order to improve vehicle performance, prevent damage and enhance the comfort of the passengers. In order to reduce undesirable impact on the environment, recyclable thermoplastic honeycomb cores produced from natural fibre composites can be used. This paper investigated the elements which may affect the dynamic characteristics of sandwich panels. The effects of material constituents, fibre length and orientation, as of fibres filled in the core, were investigated. Beams were constructed with honeycomb cores. The damping values of a beam with an unreinforced core was found to be higher than those with fibre reinforced cores, suggesting that the main influence on damping of the material is due to the viscoelastic properties of the matrix material. However, a core made of only matrix material results in poor mechanical properties. So in order to satisfy the trade-off between the requirements of low vibration level and strength of panels, honeycomb cores reinforced with fibre were investigated. Fibre Reinforced cores lead to an improvement of greater than 100% in mechanical properties and a reduction of about 40% in damping capability. Filling the cores with wool fibres results in minimal weight increase and unchanged mechanical properties, plus improved acoustic absorption properties, higher damping, higher resistance to heat transfer and lower smoke emission. From the results shown, it is clear that changes in the material constituents, fibre lengths and orientations yield different dynamic behaviour of the structure: different natural frequencies and damping values for the same geometry and boundary conditions. This gives the designer additional degrees of freedom to design the laminate, the possibility to change fibre length and fibre orientations in order to get a more (or less) damped structure. This possibility makes these materials very attractive since it is possible to obtain an increase in mechanical and damping values, and other functional values, by filling the fibre reinforced honeycomb core cavities with wool fibres.
Vibration characteristics of fiber reinforced honeycomb panels: experimental study
2012
9 Seiten, 8 Bilder, 3 Tabellen, 12 Quellen
Aufsatz (Konferenz)
Englisch
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