STATIC AND DYNAMIC LOADING BEHAVIOUR OF AUXETIC THERMOPLASTIC FOAMS

摘要

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.