In situ three-dimensional x-ray microtomography of an auxetic foam under tension

X-ray microtomography has the potential to unambiguously identify the predominant deformation mechanisms responsible for the auxetic response of polymeric foams. It has been performed in situ on an auxetic polyurethane foam subjected to incremental uniaxial tensile loading. A Poisson’s ratio of -0.20 measured from localized microstructural changes observed during the tomographic sequence compares well with the bulk value of -0.21 obtained by videoextensometry. Evidence obtained by digital image correlation for straightening of bent ribs and rotation of junctions connecting ribs during straining is presented.