Deterioration of the fire structural resistance of sandwich composite under tension due to water absorption

The effect of water absorption on the fire structural resistance of a sandwich composite is investigated. A sandwich material consisting of E-glass/vinyl ester laminate skins and balsa wood core was environmentally aged in hot (70 °C) and humid (85% relative humidity) conditions for an increasing period up to and exceeding the saturation time. The face skins displayed Fickian diffusion behaviour in the absorption of water whereas the core exhibited significant mass loss due to water causing hydrolysis of bioorganic compounds in the wood. Water absorption decreased the fire structural resistance of the sandwich composite under tensile loading. The saturated sandwich composite exposed to fire failed at lower tensile stresses and within shorter times compared to the dry composite. The reduction in fire resistance was primarily due to moisture-induced weakening of the laminate skins. The reduction to the fire structural resistance caused by water absorption was predicted using a thermal-mechanical model.