Dynamic Wave Dispersion and Loss Properties of Conventional and Negative Poisson's Ratio Polymeric Cellular Materials

This article describes experimental investigations of the dynamical behaviour of conventional and negative Poisson's ratio foamed materials in torsional vibration. Dispersion of standing waves and cut-off frequencies were observed. Consequently, foamed materials do not obey the classical theory of elasticity or viscoelasticity. The dynamical effects were attributed to microvibrations of the cell ribs in a structural view and were associated with microstructure or micromorphic elasticity in a continuum view. Cut-off frequencies were lower in re-entrant foams with negative Poisson's ratios than in the conventional foams from which they were derived. An analytical model was developed in which the ribs of the conventional foams were modelled as free-free vibrating beams. The predicted cut-off frequencies were comparable to those observed experimentally.