JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012 - 37

Applied Market Information Ltd. (AMI) organised a global networking conference on wind turbine blade manufacture in Dusseldorf, Germany, in December 2011 to bring together energy companies, wind industry players and the composites supply chain, with top blade manufacturers and researchers reviewing the latest innovations and the issues.

Focus

foam preparation); prefabrication of the structural supports such as the spar cap and root insert; moulding; wet and dry finishing; then assembly with metal parts and lightning connections. The company has in-house testing facilities and works to GL, DNV and CWET (India) standards. Structural design optimisation of blades is being studied by Acentiss, which is working with Airworks of Italy and IABG to form A2Wind in order to focus on rotor blade development using aerospace technology. The structural constraints of blades include a minimum stiffness to avoid collisions with the turbine tower and a minimum buckling factor. There are manufacturing constraints too and cost is an important factor. Studies show that carbon fibre will be needed for structural and cost optimisation as blades get longer.

Carbon fibre In blade design, there are limits due to aerodynamic stress, rotational stress, mass-dependent stress and frequency. The SGL Group both manufactures wind turbine blades and supplies carbon fibre. It has studied the use of carbon fibre in the spar cap load-carrying structure of rotor blades, compared to glass fibre. The carbon fibre blades were 20% lighter and had about 25% lower mass moment. In addition, the use of carbon fibre significantly reduced blade root fatigue loads, which means that the root and pitch system can be smaller, with a longer blade. The trend towards carbon fibres requires new expertise as they are finer than glass and more difficult to infuse with resin. BASF supplies epoxy to the wind blade market and Dr Gregor Daun has conducted research to improve infusion for large blades. With geometric scale-up of structures, most forces are squared and torques are cubed, so laminate thickness needs to increase. Over long flow paths, infusion fronts slow down and become more viscous, so BASF has a new latent system with slower gelation. This can assist with the thicker parts too as it improves homogeneity of curing. Euros Entwicklungsgesellschaft was founded in 1996 in Berlin to focus on blade design and has since started two plants in Poland (Ustron and Zory-

Fig.2: Wind turbine installation

©Gamesa Corp

Warszowice) for blade and master plug/ mould manufacturing. It supplies around 1% of the European market. The Materials department is carrying out research on foam cores for spar webs and the shell, looking at resin absorption into the slits in the sandwich and the cellular structure, which depends on the cell diameter and wall thickness. The shear stiffness after resin absorption increases by a factor of approximately 3.2, which can be taken into account in the design process and used to reduce blade weight. Fiberline Composites, a manufacturer of blade subcomponents, has been involved in studies of carbon fibre composites which showed that carbon fibre is very sensitive to wrinkles. There are several methods for measuring fibre misalignment including multiple field image analysis (MFIA), confocal laser scanning microscopy (CSLM), X-ray tomography and Fourier transform misalignment analysis (FTMA). Shear properties can be monitored using methods such as the Iosipescu shear test combined with Digital Image Correlation (DIC). Fiberline has developed an injection pultrusion processing method that gives highly aligned fibres. Owens Corning OCV Technical Fabrics is a supplier of glass-based fabrics for the global composites industry including wind blade manufacturers. The Ultrablade fabric helps to improve modulus and strength in the vacuum infusion process (VARTM) supporting the longer blades, while reducing spar weight by around 17% in a study using the IEC 61400-1 class II blade model. Headquartered in California, Clipper Windpower is a relatively young company producing 2.5 MW Liberty wind turbines and developing 10 MW Britannia models for the offshore market. It is now affiliated to United Technologies Corp. (UTC) and can develop wind projects. According to the American Wind Energy Association, it had 66% market share of the 2.5 MW and larger turbine market in the United States in 2009. It has a new blade to enter the market in the 3rd quarter of 2011, and is focussing on innovative production processes such as mechanisation and

No70 January - February 2012 /

jec composites magazine 37

Feature Wind Energy

JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012