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This paper describes an approach allowing aging to be included in the design of marine structures. Two types of aging are considered, physical aging and seawater saturation. The latter is shown to be more severe for this material, with losses in properties of up to 30% being measured after aging. A complete set of in-plane and out-of-plane properties was generated for a carbon/epoxy composite, and these were then used as input data to model the response of a flexural beam under a mixed shear/bending load. Reasonable agreement is found between model and test results; both show the strong influence of seawater conditioning on the composite performance, with a reduction in strength after aging of around 35%. This approach can be applied to account for seawater aging during the design of composite structures.

In recent years, many tidal turbine projects have been developed using composites blades. Tidal turbine blades are subject to ocean forces and sea water aggressions, and the reliability of these components is crucial to the profitability of ocean energy recovery systems. The majority of tidal turbine developers have preferred carbon/epoxy blades, so there is a need to understand how prolonged immersion in the ocean affects these composites. In this study the long term behaviour of different carbon/epoxy composites has been studied using accelerated ageing tests. A significant reduction of composite strengths has been observed after saturation of water in the material. For longer immersions only small further changes in these properties occur. No significant changes have been observed for moduli nor for composite toughness. The effect of sea water ageing on damage thresholds and kinetics has been studied and modelled. After saturation, the damage threshold is modified while kinetics of damage development remain the same.