The paper describes the manufacturing and tensile testing of auxetic (negative Poisson's ratio) thermoplastic polyurethane foams, both under constant strain rate and sinusoidal excitation. The foams are produced from conventional flexible polyurethane basis following a manufacturing route developed in previous works. The Poisson's ratio behaviour over tensile strain has been analyzed using an Image Data processing technique based on Edge Detection from digital images recorded during quasi-static tensile test. The samples have been subjected to tensile and compressive tests at quasi-static and constant strain-rate values (up to 12 s -1 ). Analogous tests have been performed over iso-volumetric foams samples, i.e., foams subjected to the same volumetric compression of the auxetic ones, exhibiting a near zero Poisson's ratio behaviour. The auxetic and non-auxetic foams have been also tested under sinusoidal cycling load up to 10 Hz, with maximum pre-strain applied of 12%. The hysteresis of the cycling loading curve has been measured to determine the damping hysteretic loss factor for the various foams. The measurements indicate that auxetic foams have increased damping loss factor of 20% compared to the conventional foams. The energy dissipation is particularly relevant in the tensile segment of the curve, with effects given by the pre-strain level imposed on the samples.

In this study the static and dynamic characteristics of conventional open cell polyurethane (PU), of auxetic (negative Poisson's ratio) and of iso-density foams were analysed. The specimens were produced from conventional gray open-cells polyurethane foam with 30-35 pores/inch and 0.0027 g/cm 3 density, by means of process which has been previously defi ned by the authors. Poisson's ratio measurements were performed under quasi-static conditions using an MTS 858 servo-hydraulic test machine and a video image acquisition system. For the auxetic foams the results suggested similar behaviour to that previously reported in the literature, with signifi cant increases in stiffness during compressive loading, and a signifi cant dependence of the Poisson's ratio on the applied strain. Transmissibility tests, performed in accordance with the ISO 13753 procedure for antivibration glove materials, suggested a strong dependence of the transmissibility on the foam manufacturing parameters. Within the frequency range from 10 to 31.5 Hz the transmissibility was found to be greater than 1, while it was less than 1 at all frequencies greater than 31.5 Hz. The transmissibility results were similar to the mean values for 80 resilient materials tested by Koton et. al., but were higher than the fi ve best materials (not all polymeric) identifi ed by the same researchers. In this study it has been suggested that the resilient behaviour of glove isolation materials should also be evaluated in terms of the indentation characteristics. A simple, linear elastic, Finite Element simulation was therefore performed, and the indentation results suggested that auxetic foams offer a signifi cant decrease in compressive stresses with respect to conventional PU foams.

The paper describes the manufacturing and tensile testing of auxetic (negative Poisson's ratio) thermoplastic polyurethane and polyester urethane foams, under quasi-static and constant strain rate loading. The foams are produced from conventional flexible polyurethane basis following a manufacturing route developed in previous works. The Poisson's ratio behaviour over compressive strain has been analyzed using an Image Data processing technique based on Edge Detection from digital images recorded using camcorders and high speed cameras. The measurements indicate that higher strain rate loading implies stiffening effects on the stress -strain curves, and significant increase of the magnitudes of the Poisson's ratios with increasing compressive strains.

The paper describes the manufacturing and tensile testing of auxetic (negative Poisson’s ratio) thermoplastic polyurethane foams. The foams are produced from conventional flexible polyurethane basis following a manufacturing route developed in previous works. The Poisson’s ratio behavior over tensile strain has been analyzed using an Image Data processing technique based on Edge Detection from digital images recorded during quasi-static tensile test. The samples have been subjected to tensile and compressive tests at quasi-static and constant strain-rate values (up to 12 s−1). Analogous tests have been performed over iso-volumetric foams samples, i.e., foams subjected to the same volumetric compression of the auxetic ones, without exhibiting a negative Poisson’s ratio behavior. A model describing the compressive stress-strain behavior of the auxetic foams has been developed considering the stress-strain performance of single unit cell and making use of statistical distributions of relative densities and buckling loads on auxetic foam cells during loading.