A shape memory polymer based syntactic foam with negative Poissonʹs ratio

In this study, a shape memory polymer (SMP) based syntactic foam was prepared and programmed by a two-dimensional (2-D) stress condition (tension in one direction and compression in a transverse direction). Thermomechanical properties and microstructures of the foam were characterized. The results show that the 2-D programming method leads the foam towards anisotropy from original isotropy. It is found that, depending on the strain levels in the post-programming uniaxial compression or uniaxial tension tests, the programmed foam exhibits negative Poissonʹs ratio in the two programmed directions, regardless of the loading direction during the uniaxial testing of the programmed foam. The negative Poissonʹs ratio may be beneficial for some applications such as sealant in expansion joint, car bumper, seat cushion, and crash helmet in auto industry, nose-cone and wing panel in aircraft, etc.