Mechanical degradation of foam-cored sandwich materials exposed to high moisture

Sandwich specimens composed of E-glass/polyester face sheets bonded to a PVC foam core were exposed to high moisture (95% RH) and immersed in sea-water for extended periods of time. Degradation of mechanical properties of the face sheets, foam core and face/core interface were progressively evaluated using flexural testing of the laminates, through-thickness tension of the foam core and interfacial sandwich DCB fracture testing. Testing reveals substantial flexural stiffness and strength reductions for the laminated composites, and only minor reduction in the tensile stiffness and strength of the foam. Degradation of the interfacial face/core fracture toughness is weak for specimens subjected to elevated moisture and more pronounced for sandwich specimens immersed in sea-water. After 30 days of exposure to high moisture, foam damage is visible in the form of cracks and pits on the cell walls. Optical examinations of expansional strains show that moisture absorbed by the foam penetrates only about to 2–3 mm from the core free surface for the 95% RH condition, while penetrates deeply for the immersed condition.