Energy Absorption and Low Velocity Impact Response of Open-Cell Polyurea Foams

Abstract

The energy absorption and impact attenuation of low density polyurea (PU) foams (140–220 kg/m3) is presented. The stress–strain behavior, energy absorption, cushioning efficiency, and energy return (resilience) are measured at a quasi-static strain rate using an Instron load frame. In addition, the low velocity impact attenuation of the polyurea foams at 5 J and 7 J impact energies were investigated according to the American Society for Testing and Materials (ASTM) test methods F1976. The polyurea foams were then compared with widely used ethylene vinyl acetate (EVA) and thermoplastic polyurethane (TPU) foam technologies at similar densities. The PU foams displayed a 5% increase in cushioning efficiency and 30% greater energy absorption over TPU and EVA foams under quasi-static compression. Under impact testing, PU foams resulted in a reduction of up to 28.6% and 36.9% in peak transmitted impact forces when compared to EVA and TPU foams of the same thickness (20 mm) at 5 J and 7 J, respectively. These properties should allow these materials to have a wide range of cushioning/impact applications, especially as midsoles in athletic footwear.