The vibroacoustic behaviour of aluminium foam sandwich panels in similitude

Aluminium Foam Sandwich (AFS) panels are a type of structural configuration in which two aluminium thin layers enclose a core made of foamed aluminium. Both the metallic characteristic of the matrix and the foam porosity lead to a remarkable combination of properties which range from high specific stiffness to thermal and acoustic isolation. However, these characteristics, depending on core properties as foam density, pores morphology, type and size of gas bubbles, are obtained by means of a manufacturing process that is not fully controlled. Thus, in order to reduce the financial and temporal costs of the campaign of experimental tests needed for completely understanding the properties and potentialities of AFS panels, similitude methods can be used so that scaled-down models can be tested in place of the full-scale structure. In this work, the similitude conditions and scaling laws of Alulight® AFS panels with two different boundary conditions (simply supported and free-free) are derived and validated. In particular, two different sets of conditions are derived: the first by expliciting all the geometrical and material properties, the second by combining some parameters into just one with physical meaning, the bending stiffness. The analysis in similitude is addressed towards the prediction of vibroacoustic properties such as natural frequencies, Frequency Response Function (FRF) and radiated acoustic power. Both models in complete and partial similitude are investigated. While the former allow to reconstruct the vibroacoustic characteristics of the prototype, the latter does not. Furthermore, it is proved that it is possible to derive a simplified set of similitude conditions if many parameters are gathered into just one parameter with physical meaning.