Impact-induced fatigue of foamed polymers

The fatigue life of foamed polymers in compression impact was measured using a cam-driven compound pendulum system. Impact-induced fatigue data are presented for two open-celled foamed polymers having different densities, which are often used for shock mitigation. Material measurements at constant incident energy included the static compression modulus and peak dynamic stress, which progressively degraded as the number of impacts approached one million. Other indicators of fatigue life were cell breakdown, in which microscopic edge cracks were observed in both dry and water-saturated test specimens. The dry material had the longer fatigue life. In both cases, cell breakdown occurred after a million or more impacts at peak compressive stresses in the 200–300 kN/m2 range.