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Wind turbine blades are being manufactured using polymer matrix composite materials, in a combination of monolithic (single skin) and sandwich composites. Present day designs are mainly based on glass fiber-reinforced composites (GFRP), but for very large blades carbon fiber-reinforced composites are being used increasingly, in addition to GFRP by several manufacturers to reduce the weight. The size of wind turbines have increased significantly over the last 25 years, and this trend is expected to continue in the future. Thus, it is anticipated that wind turbines with a rated power output in the range of 8—10 MW and a rotor diameter about 170—180 m will be developed and installed within the next 10—15 years. The article presents an overview of current day design principles and materials technology applied for wind turbine blades, and it highlights the limitations and important design issues to be addressed for up-scaling of wind turbine blades from the current maximum length in excess of 61 m to blade lengths in the vicinity of 90 m as envisaged for future very large wind turbines. In particular, the article discusses the potential advantages and challenges of applying sandwich type construction to a larger extent than is currently being practiced for the load-carrying parts of wind turbine blades.

A means of enhancing electrical and thermal conductivities of carbon fibre reinforced polymer (CFRP) composites is investigated for the purpose of reducing damage when electric current and/or heat is introduced into a CFRP structure. The addition of commercially available graphene oxide (GO) nanoflakes dispersed into an epoxy resin is studied; quantities up to 6.3 vol% are used in a vacuum infusion process with carbon fibre fabric to form CFRP laminates. Measurements of the anisotropic electrical and thermal conductivity of the laminate were conducted on CFRP specimens with and without the GO nano-flakes. It is shown that the electrical conductivity in the through-thickness direction increased markedly, reaching values up to 0.18 S/cm, when 6.3 vol% of GO was added into the epoxy, showing a threefold increase compared to the neat CFRP. Similar improvement was also found in the thermal throughthickness conductivity for the same filler content, where the laminate exhibited identical values in both transverse and through-thickness directions. However, the properties transverse to the fibres were not greatly affected by the GO addition. To assess the effect of the GO on the mechanical properties, interlaminar shear strength tests were conducted that showed that the addition of the GO significantly enhanced the through-thickness shear strength.

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