Hysteresis Behaviour and Specific Damping Capacity of Negative Poisson's Ratio Foams

Previously open cell polyurethane foams have been made to be re-entrant, in that their cell ribs are inwardly bent, which results in the foam exhibiting a negative Poisson's ratio(1). Untransformed control and transformed negative Poisson’s ratio foams were cyclically loaded at various levels of pre-strain to determine their hysteresis behaviour, and from this, to elucidate their specific damping characteristics. Both untransformed and transformed foams exhibited non-linear hysteresis behaviour at high cyclic strains, regardless of their initial levels of pre-strain. The specific damping capacity of the transformed foam with extreme compressive pre-strain was higher than that of the untransformed foam. This effect was attributed to the rubbing of the inwardly buckled cell ribs of the transformed foam. The specific damping capacity varied with both the level of pre-strain and with the amplitude of cyclic strain about that level.