Testing of hydrophobically coated composite materials with marine energy applications

Abstract

Tidal turbine applications will place composite materials such as glass-fibre-reinforced polymers (GFRPs) and carbon-fibre-reinforced polymers under surprisingly high pressure due to the significant water depths they operate in (to depths of 50 m). The technical reliability of tidal turbines must be guaranteed despite the high dynamic loads resulting from the combination of plant operation, wind and waves with irregular swell. These external effects could lead to operation downtime and accelerated degradation. Research has already established that (unpressurised) moisture saturation is detrimental to both the tensile and fatigue strengths of a GFRP material compared with its dry laminate performance. This degradation has been shown to be stress dependent. It is possible that hydrophobic coatings could help protect the material while in service. Therefore, two commercially available coatings were applied to five variations of composite materials. These materials are commonly used in tidal and wave turbine blades, as they have excellent corrosion resistance and mechanical properties. All five were subjected to the same conditioning processes: non-pressurised and pressurised immersion conditioning in water. A glass-fibre epoxy (Ampreg) composite, along with a glass-fibre powdered epoxy composite, a glass-fibre polyether ether ketone composite and a carbon-fibre powdered epoxy composite, was investigated. The glass-fibre epoxy (Ampreg) was also subjected to static/fatigue tensile tests.