A Review of Mechanisms and Fracture Mechanics of Moisture Ingress in Composite Systems

Composite materials help realize high strength to weight ratio requirements of the Aerospace Industry. Composite structures and sandwich composite structures are susceptible to moisture ingress. Moisture ingress causes degradation of thermo-mechanical properties of the composite panels. Water accumulation in sandwich composite structures causes rapid degradation of face to core bondline, damage of cells frozen water and even blow off skins owing to sudden pressure build up in the cells of the honeycomb structure. Mechanisms of moisture ingress can be broadly classified into direct and indirect mechanisms. Direct ingress occurs through pre-existing pathways formed by defects in the composite system. Indirect mechanisms are diffusion, Capillary actions, Wicking actions, and Osmosis. The first form of damage in FRP materials is microcracking. The rate of microcracking increases with moisture ingress. Microcracking fracture toughness is a material property for the susceptibility of a composite system to the formation of microcracks. This work implores the mechanisms and the fracture mechanics dominating the formation of microcracks.