The effect of moisture and loading rate on the interfacial fracture properties of sandwich structures

The skin‐core interfacial fracture properties of a number of dry and moistureconditioned sandwich structures have been investigated over a range of crosshead displacement rate using the three point bend sandwich (TPBS) structure. It has been shown that the interfacial fracture toughness, Gc, of a crosslinked PVC system decreases rapidly with loading rate, whereas the toughness of a linear PVC remains roughly constant. In contrast, the interfacial fracture toughness of the balsa core material increased steadily with increasing crosshead displacement rate, an effect that was attributed to the rate dependent properties of the glass fibers in the wake of the primary crack. Prolonged seawater exposure in an aluminum honeycomb structure was found to attack the bond between the epoxy matrix and the aluminum core, facilitating crack advance along the skin‐core interface. Finally, it is concluded that great care should be exercised before selecting sandwich structures for hostile marine environments.