HYSTERESIS BEHAVIOR AND SPECIFIC DAMPING CAPACITY OF NEGATIVE POISSONS RATIO FOAMS

Previously open cell polyurethane foams have been made to be re-entran t, in that their cell ribs are inwardly bent, which results in the foa m exhibiting a negative Poisson's ratio((1)). Untransformed control an d 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. B oth untransformed and transformed foams exhibited non-linear hysteresi s 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 untran sformed foam. This effect was attributed to the rubbing of the inwardl y buckled cell ribs of the transformed foam. The specific damping capa city varied with both the level of pre-strain and with the amplitude o f cyclic strain about that level.