Effects of Density and Temperature on the Mechanical Shock Mitigation Response of Polymethylene Diisocyanate (PMDI) Based Rigid Polyurethane Foams

Understanding the shock mitigation characteristics of foams is critical in material design, selection, and evaluation under extreme mechanical and environmental conditions. Energy dissipation is a key factor in quantifying the efficiency of shock mitigation. Energy dissipation in the time domain generally provides an overall energy dissipation capacity of the shock mitigation material while energy dissipation in the frequency domain may facilitate tailoring shock mitigation schemes to frequency-sensitive payloads. In this study, a Kolsky compression bar combined with frequency-based energy analysis was employed to characterize the shock mitigation response of polymethylene diisocyanate (PMDI) based rigid polyurethane foams with different densities at different temperatures. All PMDI foam materials exhibited energy dissipation ratios of 95% or above. The energy dissipation ratio decreased with increasing density but was independent of temperature within the temperature range (− 56 to 71 °C) investigated. The energy dissipation ratio also decreased with increasing specimen strain although little change in energy dissipation ratio was observed when the strain was less than 40% at ambient temperature. The cutoff frequency, which is the frequency above which nearly all energy was reflected back or otherwise rejected by the specimen, decreased with increasing specimen strain and was independent of specimen density and temperature.