ANALYSIS OF ELASTIC-MODULUS OF CONVENTIONAL FOAMS AND OF REENTRANT FOAM MATERIALS WITH A NEGATIVE POISSONS RATIO

Foam materials with negative Poisson's ratio can be made by transforming the cell structure from the convex polyhedral shape of conventional foam cells to a concave or ''re-entrant'' shape. Mechanical behavior of re-entrant foams differs from that of conventional foams. Most of the difference is attributed to the change in cell shape. In this study, Young's moduli of conventional and re-entrant open cell foams are obtained by modeling the three-dimensional unit cell as an idealized 14-sided unit cell. Young's modulus of re-entrant foams decreases with permanent volumetric compression ratio in both modeling and experiments.