Mechanical behaviors of auxetic polyurethane foam at quasi-static, intermediate and high strain rates

Abstract

We experimentally determined the uniaxial compressive stress-strain responses of an auxetic polyurethane (PU) foam at quasi-static (0.01/s), intermediate (1/s, 10/s and 745/s) and high (1430/s, 1870/s and 2290/s) strain rates. A hydraulically driven materials testing system (MTS) was used to perform the experiments at the strain rate of 0.1/s, 1/s and 10/s, while higher intermediate (745/s) and high strain-rate compressive loadings were introduced using long and regular Kolsky bars, respectively. The Poisson effect of the auxetic PU foam was also investigated during the experiments using a precision LED optical micrometer system (OMS) (0.01/s–10/s) or an ultra-high speed camera (745/s–2290/s). Our results show that the compressive stress-strain curves of the auxetic PU foam are non-linear and strain-rate sensitive. In all the experiments, the Poisson's ratio, with an initial negative value at small strains, progressively increased toward 0 as the specimen was further compressed. The strain-rate effect on the material's Poisson's ratio is also evident in our study, as the specimens subjected to high strain-rate loadings exhibited smaller negative Poisson's ratios (NPR) in absolute sense at small strains in comparing with those at quasi-static and intermediate strain rates.