In the early stage of the development of wind power blades, due to the small blades, there are wood blades, cloth skinned blades, steel beam glass fiber skinned blades, aluminum alloy blades, etc. As the blades develop in the direction of large-scale development, composite materials have gradually replaced other materials. The only material available for large blades.
One of the advantages of composite materials that other single materials cannot match is its designability. By adjusting the direction of the single layer, the required strength and rigidity in this direction can be obtained. More importantly, the anisotropy of materials can be used to couple the different deformation forms of the structure. For example, due to the bending and torsion coupling, the structure is twisted when only the bending moment is applied.
In the past, the cross-section coupling effect of the blade was a headache for designers, and the design engineering tried every means to eliminate the coupling phenomenon. But in the aviation field, people began to use the bending-torsion coupling and tension-shear coupling effect of composite materials to improve the performance of the wing. On the blade, the design concept of inducing bending and torsion coupling controls the aeroelastic deformation of the blade, which is the aeroelastic tailoring. Through aeroelastic cutting, the fatigue load of the blade is reduced and the power output is optimized.
Glass fiber reinforced plastic (FRP) is the most commonly used composite material for modern fan blades. With its low price and excellent performance, FRP occupies the dominant position of large fan blade materials. However, as the blades gradually become larger, the diameter of the wind wheel has exceeded 120m, the longest blade has reached 61.5m, and the weight of the blade has reached 18t. This puts more stringent requirements on the strength and stiffness of the material. All-glass fiber reinforced plastic blades can no longer meet the requirements of large-scale and lightweight blades. Carbon fiber or other high-strength fibers are then applied to the local area of the blade, such as NEGMiconNM82.40m long blades, LM61.5m long blades all use carbon fiber in high stress areas. As the blades increase, stiffness has gradually become important and has become the key to the design of a new generation of MW-class blades.
The use of carbon fiber has greatly improved the stiffness of wind turbine blades, but has not increased its own weight. Vestas uses carbon fiber on the main beam of the 44m series blades for the V903.OMW model. The weight of the blade is only 6t, which is the same as the weight of the V802MW, 39m blade. Research reports in the United States and Europe pointed out that the load-bearing glass fiber laminate containing carbon fiber is a very effective alternative to MW-class blades. In the research project funded by E.C., it is pointed out that the use of carbon fiber in the blades of the 120m diameter wind turbine can effectively reduce the overall self-weight by 38% and reduce the design cost by 14%. However, carbon fiber is expensive, which greatly limits its use on fan blades.
Today, the carbon fiber industry still focuses on the development of lightweight, good structure, and thermal properties with high added value for aviation applications. However, many researchers boldly predict that the application of carbon fiber will gradually increase. The cost-effectiveness of wind energy will depend on the way carbon fiber is used. If a large number of glass fibers are to be replaced in the future, low prices are necessary to be competitive.
