Stiffness and strength analysis of composites for tidal wave turbine applications

Abstract

There has been a rise in renewable energy due to climate change. A specific type of renewable energy is ocean energy, which is derived from tides and waves. Machines that extract energy from the ocean experience transient loads and in turn, fatigue. However, a key component to understanding fatigue is the inherent mechanical properties of the material itself, specifically composites. Due to the nature of the working environment, it is key to understand the influence of moisture on the mechanical properties of composites. Unidirectional carbon fibres are manufactured into composites via VARTM. Specimens are cut out from the finished product and are immersed into seawater for varying durations. Three-point bending tests are conducted onto the specimens after seawater aging and the resulting values are discussed in relation to moisture content. Additionally, the Fickian curve was modelled and compared with measured moisture values of the specimens. Finally, the damage of the specimens was examined under the microscope. The results showed that the mechanical properties do decrease with an increasing amount of moisture ingression. Comparison of moisture uptake shows that the experimental data more or less agreed with the Fickian model. Microscopic damage inspection showed that the fibres failed via compression failure for the most part. It is hoped that this study would be useful in the analysis of fatigue in tidal turbines.