Investigation on the compressive properties of auxetic foams under different loading rates

Auxetic materials or materials with a negative Poisson's ratio have a great potential to be used in many industries because of their specific mechanical properties such as high stiffness and strength with significant weight saving. In this article, the effect of various parameters of the fabrication process on the microstructure of a polyurethane auxetic foam was investigated. Moreover, the compression behavior of this foam in different situations, from quasi-static to high strain rate loading, was studied comprehensively. Results indicated that 70% volume reduction, being heated to 180°C and kept at that temperature for 1 h and 45 min could maximize the auxeticity of the foam. Microscopic images demonstrated that the foam structure cells were transformed from honeycomb to re-entrant, causing the Poisson's ratio to become negative. With increasing the re-entrant cells, the auxeticity of the foam increased, which leads to increasing the absorbed energy in quasi-static compression up to 443%, and in high strain rate loading up to 617%.