G. Smart

The Effects of Processing on the Topology and Mechanical Properties of Negative Poisson’s Ratio Foams

Combined heat treatment and applied mechanical strains have been employed to modify the structure and properties of polyurethane (PU) foams. Consequently, foams with a range of pore sizes, shapes and orientations have been produced, including those possessing auxetic (negative Poisson’s ratio) behaviour. Four conversion conditions were employed: triaxial, biaxial and uniaxial compression (to linear compression ratios of 0.9, 0.8 and 0.7) and uniaxial tension to (linear extension ratios of 1.1 and 1.2). The converted foams were then observed by either SEM or optical microscopy, as appropriate, to determine the pore structure. Mechanical properties were measured using tensile testing in conjunction with videoextensometry, allowing the values of Young’s modulus and Poisson’s ratio to be ascertained. Increased anisotropy in the pore structure and elastic properties was observed. The biaxial as well as the triaxial conversion routes led to auxetic behaviour for the PU foams.Copyright