Stiffness and energy dissipation in polyurethane auxetic foams

Auxetic open cell polyurethane (PU) foams have been manufactured and mechanically characterised under cyclic tensile loading. The classical manufacturing process for auxetic PU foams involves multiaxial compression of the conventional parent foam, and heating of the compressed specimens above the T-m of the foam polymer. Eighty cylindrical specimens were fabricated using manufacturing routes modified from those in the open literature, with different temperatures (135 degrees C, 150 degrees C), compression ratios and different cooling methods (water or room temperature exposure). Compressive tensile cyclic loading has been applied to measure tangent modulus, Poisson's ratios and energy dissipated per unit volume. The results are used to obtain relations between manufacturing parameters, mechanical and hysteresis properties of the foams. Compression, both radial and axial, was found to be the most significant manufacturing parameter for the auxetic foams in this work.