Effects of moisture absorption on damage progression and strength of unidirectional and cross-ply fiberglass–epoxy composites

Fiber-reinforced-polymer composites (FRPs) possess superior mechanical properties and formability, making them a desirable material for construction of large optimized mechanical structures, such as aircraft, wind turbines, and marine hydrokinetic (MHK) devices. However, exposure to harsh marine environments can result in moisture absorption into the microstructure of the FRPs comprising these structures and often degrading mechanical properties. Specifically, laminate static and fatigue strengths are often significantly reduced, which must be considered in design of FRP structures in marine environments. A study of fiberglass epoxy unidirectional and cross-ply laminates was conducted to investigate hygrothermal effects on the mechanical behavior of a common material system used in wind applications. Several laminates were aged in 50 ∘C distilled water until maximum saturation was reached. Unconditioned control and the saturated samples were tested in quasi-static tension with the accompaniment of acoustic emission (AE) monitoring. Cross-ply laminates experienced a 54 % reduction in strength due to moisture absorption, while unidirectional laminate strengths were reduced by 40 %. Stress–strain curves and AE activity of the samples were analyzed to identify changes in damage progression due to aging.