Matteo Bianchi

Vibro-acoustic properties of auxetic open Cell foam: Model and experimental results

The combined mechanical and acoustic properties of auxetic (negative Poisson’s ratio) foams are described both from a numerical and experimental point of view. Samples of open cell PU-PE foams with negative Poisson’s ratio are produced using a dedicated manufacturing process, and subjected to tensile quasi static and cyclic loading, as well as sound absorption measurements based on ISO 10-534-2 Standard. A homogenization model based on the Biot’s theory is also derived to calculate the poroelastic parameters of the foam. The experimental and numerical results are compared and commented to provide explanations regarding the unusual acoustic absorption of these porous materials.

Blocked Shape Memory Effect in Negative Poisson's Ratio Polymer Metamaterials

We describe a new class of negative Poissons ratio (NPR) open cell PU-PE foams produced by blocking the shape memory effect in the polymer. Contrary to classical NPR open cell thermoset and thermoplastic foams that return to their auxetic phase after reheating (and therefore limit their use in technological applications), this new class of cellular solids has a permanent negative Poissons ratio behavior, generated through multiple shape memory (mSM) treatments that lead to a fixity of the topology of the cell foam. The mSM-NPR foams have Poissons ratio values similar to the auxetic foams prior their return to the conventional phase, but compressive stress-strain curves similar to the ones of conventional foams. The results show that by manipulating the shape memory effect in polymer microstructures it is possible to obtain new classes of materials with unusual deformation mechanisms.