Measuring impact responses of foamed polymers

A unique dual pendulum system was developed to measure single-impact com-pression responses of foamed polymers. The data, complemented with a math-ematical model of impact, led to measures of the material’s energy absorption, compression modulus, and damping. Results are presented for a class of open-celled foamed polymers specifically developed for shock mitigation. The exper-iments employed such materials of four different densities, with impact times ranging in the 1 to 5ms range and mean impact stresses up to 160 kN/m2. The results for these materials showed: (1) energy losses of up to 50 % of incident energy, with a peak energy absorption per unit volume of 18 kJ/m3; (2) peak compression modulus of 880 kN/m2 with strain rates approaching 200 s−1; (3) a mean damping factor of 0.258 with a standard deviation of 0.029. Such data are of practical importance in many shock-mitigating applications, including pros-theses, floor pads and cushions, gloves for hand-held vibrating tools, grips for hockey sticks and tennis rackets, and soles for sports shoes.