The Effect of Water Immersion on the Mechanical Properties of Polystyrene Bead Foam Used in Soft Shell Cycle Helmets

Polystyrene bead foam mouldings were subjected to water immersion. The kinetics of the water absorption depended on whether there were open interbead channels near the surface of the mouldings. High strain rate measurements showed that the fracture toughness is low and independent of the foam density or water immersion for 24 hours. The fracture toughness is related to the interbead tensile strength, and SEM examination of the fracture surfaces shows that the fracture path is usually near, but not at, the bead boundary. The compressive yield stress decreases significantly after water immersion. The consequences for the testing of soft shell bicycle helmet mouldings is discussed