The rate dependence of confor polyurethane foams

A low resilience polyurethane foam was compressed under impact, constant strain rate and creep loading conditions, over a range of temperatures. The foam was characterised by scanning electron microscopy and image analysis. The compressive collapse stress was found to be strongly strain rate and temperature dependent, with the maximum rate effect in the impact velocity range from 1 to 10 m/s. The highly viscoelastic response is due to the glass transition temperature being about 20°C, and the low crystallinity of the foam. The foam creep response is similar in many ways to that of conventional flexible PU foam, but the creep strain can stabilise at intermediate values.