Author(s): Ardito Raffaele, D'Alessandro Luca, Braghin Francesco, Corigliano Alberto
Elastic metamaterials are represented by the periodic repetition of a unit cell, that is suitably designed in order to achieve specific properties, beyond the typical features of natural materials. As an example, auxetic metamaterials are characterized by a negative apparent Poisson ratio, with possible useful applications as shock absorbers, actuators, etc. The present paper is focussed on elastic metamaterials that show a peculiar behavior in terms of wave transmission (so-called phononic crystals, PnC). Among the others, the presence of bandgaps (i.e. the frequency ranges of prevented wave transmission) is one of the most investigated properties: a wide and complete bandgap is generally beneficial to guarantee robust wave attenuation around a certain frequency, in view of the possible application of PnC as acoustic filters. In many cases, a complete bandgap is obtained by a periodic arrangement of two or more materials. Conversely, in this paper some recent developments are presented, with reference to single-phase engineered metamaterials. The unprecedented features of the proposed layouts (i.e. sub-wavelength ultrawide bandgap, overstepping of passing bands, mechanical tuning of wave propagation) are investigated through numerical computations, theoretical analyses and experimental tests. The thorough examination of the computational results and the comparison with a simplified theoretical model allow us to infer that the dispersion properties are directly connected to the capability of the proposed structures to confine the mechanical energy in well separated modes of wave propagation. In order to obtain an experimental confirmation, a set of 3D prototypes is realized via additive manufacturing (selective laser sintering on Nylon PA12). The measurements of the transmission spectrum prove the filtering properties in the audible frequency range. The achieved results open new possibilities for the practical applications of such metamaterials and intriguing themes for future research.
Name: Prof Raffaele Ardito