Spar cap for windmill blade using carbon fiber

Abstract

Provided is a spar cap for a windmill blade having an overall length of 97 m or more, the spar cap being at least partially made of a carbon fiber-reinforced plastic to achieve both sufficient rigidity and lightness in an ultra-long blade to be used for a large windmill, the carbon fiber-reinforced plastic satisfying all of the following A to C. A: The carbon fiber-reinforced plastic to be used has a tensile fracture strain of 0.9% or more in the 0° direction and a compressive fracture strain of 0.6% or more in the 0° direction. B: The average single filament diameter of carbon fibers to be used is not less than 6 μm and not more than 9 μm. C: A crystallite size Lc (nm) and a crystal orientation degree π002(%) of carbon fibers to be used satisfy the relationship of formula (1). Formula (1): π002 ≥ 4.0 × Lc + 73.3

Description

Carbon fiber spur caps for wind turbine blades

[0001] This invention relates to a spur cap, which is part of the beam structure inside the blades of a wind turbine.

[0002] In wind power generation, the size of wind turbines is increasing in order to increase power generation volume and efficiency, and turbines with blades exceeding 85 meters in length are now appearing. A wind turbine rotor is a rotating body in which multiple blades (typically three blades) are connected to a hub connected to a rotating shaft. The amount of electricity generated by a wind turbine is roughly proportional to the mass of air passing through this rotor. The mass of air passing through the rotor is proportional to the area over which the rotor catches the wind as it rotates (wind-receiving area, rotational sweep area). In other words, the amount of electricity generated increases in proportion to the square of the blade length. To put it simply, the amount of electricity generated per turbine improves with larger blades, which in turn allows for a reduction in the number of wind turbines installed in a wind farm of the same size, thus reducing related costs such as the number of foundation works and power cables for transmission. This is the motivation for increasing the size of wind turbines.

[0003] On the other hand, typical wind turbines are upwind type, with the rotor located on the windward side when viewed from the tower. Therefore, if the blades flex significantly in strong winds, the blade tips may come into contact with the tower, potentially leading to accidents such as blade breakage. For this reason, one of the basic design requirements for blades is to provide sufficient rigidity to prevent contact with the tower, taking into account the expected wind speed distribution, the load on the blades due to the wind, and the blade length. To ensure this rigidity, almost all blades have a structure in which a beam structure called a spar runs through the longitudinal direction of the inside of the blade. Within this spar structure, the part closest to the blade surface is called the spar cap, and fiber-reinforced plastic is used for it.

[0004] Glass fiber reinforced plastic (GFRP) has traditionally been widely used for spur caps. GFRP spur caps are the mainstream for blades with lengths of several tens of meters. Sometimes, spur caps are made by bundling extruded material manufactured by pultrusion and joining them together as a single unit. Even in the case of a downwind-type wind turbine where the tower is on the windward side relative to the rotor, it is unlikely that a structural design that would cause the huge blades to flex significantly is conceivable, and rigidity remains important for the blades.

[0005] As the pursuit of wind turbine power generation efficiency increases, wind turbine blades typically use thin, teardrop-shaped cross-sections that offer superior aerodynamic characteristics. While thicker blades are advantageous in terms of rigidity because they increase the second moment of area, this significantly sacrifices aerodynamic performance. Although it would be desirable to increase blade thickness as blade length increases, the strong demand for a thin, efficient blade shape means that blade thickness is either maintained or increased very gradually even as blade length increases, which is the trend in large wind turbines. In other words, the space available for placing spars inside the blade is limited, and the height of the spars (beams) cannot be freely set. Naturally, there are also limitations on the thickness of the spar caps, and the maximum possible thickness is automatically determined by the blade cross-sectional shape.

[0006] Patent Document 1 describes a spur cap made of extruded material that is embedded in a blade. However, despite the fact that its design should differ significantly depending on the length of the blade and spur cap, there is no specific explanation of these differences. Furthermore, regarding the characteristics of the optimal extruded material to be used for the spur cap, it only states that it is a glass fiber material or a carbon fiber material, but there is absolutely no description of the specific physical properties or performance that should be achieved or are desirable.

[0007] European Patent No. 3418556

[0008] As mentioned above, for blades with lengths of several tens of meters, GFRP spur caps are the mainstream. For blade lengths of this magnitude, a blade with sufficient rigidity can be obtained using GFRP spur caps. Typically, the structure of a spur is a composite beam in which a pair of flat-flange spur caps 10 are connected by a shear web 14, as shown in Figure 2. To simplify the spur structure for consideration, if we assume that the cross-section of the spur is constant (constant width and height) in the direction of the blade length, and that it is a cantilever beam with a uniformly distributed load applied, then the amount of deflection at the tip increases rapidly in proportion to the fourth power of the beam length.

[0009] While there is a demand for increasing the size of the wind turbine (rotor diameter or blade length) to increase power generation, it is obvious that extending the blade length beyond a certain point without changing the structure and configuration of the spar (beam) has limitations due to the sudden increase in tip deflection. This is because it would no longer satisfy the aforementioned basic design requirement of configuring the system so that the blade tips do not come into contact with the tower even in strong winds.

[0010] In this analysis, the beam height is assumed to be constant, so the only things that can be changed are the elastic modulus of the material used for the flat plate equivalent to the spur cap and the thickness of the plate. While increasing the thickness of the spur cap can improve rigidity, there is a limit to how thick it can be, and naturally, this will lead to an increase in weight. If the spur cap / blade becomes heavier, the equipment such as cranes for wind turbine installation will also have to be correspondingly larger. Furthermore, if the wind turbine head (the rotor, nacelle, etc., composed of blades) becomes heavier, the supporting tower or foundation structure (monopile or jacket in the case of fixed-bottom offshore wind turbines) will also have to be made heavier, which will increase the total cost of the wind turbine system. In the case of floating offshore wind power generation systems, a floating structure or mooring system is required instead of a foundation structure, but if the wind turbine head becomes heavier, these will also have to be made heavier, a trend similar to that of onshore wind turbines and fixed-bottom offshore wind turbines. In other words, reducing the weight of the spur cap / blade can contribute to a certain extent to reducing the total cost of the wind power generation system.

[0011] To meet the growing demand for larger wind turbines and longer blades in power generation systems, while simultaneously addressing challenges such as blade tip deflection (blade tip displacement) and the need to increase the weight of spur caps, changing the material used for the spur caps is the most effective approach. Specifically, by increasing the elastic modulus of the material used for the spur caps, it is possible to suppress blade tip deflection within the limited space available for spur placement, without significantly altering the basic structure of the blade, and to provide a configuration with reduced mass.

[0012] Therefore, in the past, GFRP was used for spar caps because the blade length was limited. However, with the increase in the size of wind turbines and the lengthening of blades, the rigidity required for the blades has increased dramatically, as mentioned above. At the same time, under the need to maintain a thin airfoil shape that is excellent for power generation efficiency and to ensure design freedom within that thin airfoil shape, CFRP has gradually come to be used for spar caps. Thus, general-purpose carbon fiber with a higher modulus of elasticity than glass fiber has come to be used for spar caps, but the carbon fiber selected has not necessarily been optimized for wind turbine blade applications, especially for long blades that will accommodate even larger wind turbines in the future. In the trend of blades continuing to become longer, spars require both high rigidity and great deformation resistance. When designing wind turbine blades, verification is required under various load cases to ensure that the blades do not break due to wind load, not only under the wind force at wind speeds assumed during normal power generation, but also under various conceivable conditions such as when the turbine is stopped or when the wind turbine control system fails. The conditions to be considered are defined as DLCs (Design Load Cases) in standards such as the IEC 61400 series. Various DLCs are used to account for different wind speeds and wind direction / speed changes (turbulence), and it is required that design strength > design load. Which DLC is most severe for the blade is determined to differ depending on the assumed wind turbine class and installation conditions (wind conditions, etc.), but in any case, the blade must not break even when subjected to large deformations. This is why simply designing the blade with rigidity is insufficient, and it must be a structure that can tolerate large strains.

[0013] Therefore, for future ultra-long blades, the carbon fibers used in the spur caps must have a thicker single-fiber fineness for superior production efficiency, high breaking strain, and an optimized crystal structure compared to conventional products. Furthermore, it is desirable that they also possess a higher modulus of elasticity while meeting all of these requirements.

[0014] A typical manufacturing condition for improving the elastic modulus of carbon fiber is to increase the firing temperature of the precursor. However, increasing the firing temperature affects the crystallite size Lc (nm) and crystal orientation π of the carbon crystallites that make up the fiber. ００２ While the elastic modulus improves as the crystallite size increases, the increase in crystallite size also acts to weaken the fibers. Brittle carbon fibers, in other words, carbon fibers with low fracture toughness, are prone to fracture due to even slight defects within or on the fiber surface, resulting in low fracture strain when tensile or compressive stress is applied. Carbon fiber reinforced plastics using such low fracture strain carbon fibers have low tensile fracture strain and compressive fracture strain in the 0° direction. Thus, with conventional technology, it has been difficult to provide a spur cap that uses carbon fibers with excellent production efficiency, exhibits high fracture strain when tensile or compressive stress is applied, and also exhibits high elastic modulus and rigidity. Therefore, the present invention aims to provide such a spur cap.

[0015] The present invention, which solves the above problems, comprises one of the following configurations: (1) A spur cap for a wind turbine blade, having a total length of 97 m or more, wherein at least a portion of it is made of carbon fiber reinforced plastic, and the carbon fiber reinforced plastic satisfies all of the following A to C: A: The tensile fracture strain in the 0° direction of the carbon fiber reinforced plastic used is 0.9% or more and the compressive fracture strain in the 0° direction is 0.6% or more. B: The average monofilament diameter of the carbon fibers used is 6 μm or more and 9 μm or less. C: The crystallite size Lc (nm) and crystal orientation degree π of the carbon fibers used. ００２ (%) satisfies the relationship in equation (1). π ００２≥4.0 × Lc + 73.3 ...Equation (1) (2) The spar cap according to (1), wherein the carbon fiber reinforced plastic is an extruded material obtained by pultrusion molding, and is constructed by bundling and joining multiple extruded materials together. (3) The spar cap according to (2), characterized in that the carbon fiber reinforced plastic composed of the extruded material is used as the outermost layer of the spar cap. (4) The spar cap according to (3), characterized in that the thermal conductivity of the carbon fibers in the extruded material is 20.0 W / m·K or higher. (5) The spar cap according to any one of (2) to (4), wherein the volume content of carbon fibers in the extruded material is 63 volume% or more and 70 volume% or less. (6) The spar cap according to any one of (2) to (4), wherein the volume content of carbon fibers in the extruded material is 63 volume% or more and 65 volume% or less. (7) A spur cap according to any one of (2) to (6), wherein the tensile fracture strain in the 0° direction of the drawn material is 0.95% or more and the compressive fracture strain in the 0° direction is 0.65% or more. (8) A spur cap according to any one of (1) to (7), wherein 50% by weight or more of carbon fibers with a fiber tensile modulus of 243 GPa or more are used. (9) A spur cap according to any one of (1) to (7), wherein 50% by weight or more of carbon fibers with a fiber tensile modulus of 255 GPa or more are used. (10) A spur cap according to any one of (1) to (9), wherein the total length is 115 m or more. (11) A spur cap according to any one of (1) to (9), wherein the total length is 140 m or more. (12) A wind turbine blade having a spur cap according to any one of (1) to (11). (13) A method for manufacturing a spur cap for a wind turbine blade, having a total length of 97 m or more, in which at least a portion is made of carbon fiber reinforced plastic, wherein the spur cap is made of carbon fiber reinforced plastic that satisfies the following A to C: A: The carbon fiber reinforced plastic used has a tensile fracture strain of 0.9% or more in the 0° direction and a compressive fracture strain of 0.6% or more in the 0° direction. B: The average monofilament diameter of the carbon fibers used is 6 μm or more and 9 μm or less. C: The crystallite size Lc (nm) and crystal orientation degree π of the carbon fibers used. ００２ (%) satisfies the relationship in equation (1). π ００２≧4.0×Lc+73.3...Formula (1)

[0016] According to the present invention, it is possible to provide a spur cap that uses carbon fiber with excellent production efficiency, yet exhibits high fracture strain when subjected to tensile and compressive stress, as well as high elastic modulus and rigidity. Therefore, it is possible to achieve both sufficient rigidity and lightness even in ultra-long blades used in large wind turbines.

[0017] This is a side view of a wind turbine. It also includes an explanatory diagram of the turbine blade structure and spur caps.

[0018] Figure 1 is a side view of a wind turbine. A typical wind turbine is an upwind type, as shown in Figure 1, where the rotor (a rotating body typically composed of three blades) is located on the windward side when viewed from the tower, and the rotor is connected to the nacelle at a constant angle of elevation.

[0019] In the case of upwind wind turbines, if the blades deflect significantly due to strong winds, the blade tips may come into contact with the tower, potentially leading to accidents such as blade breakage. Therefore, considering the expected wind speed distribution, the load on the blades due to the wind, and the blade length, providing the blades with sufficient rigidity to prevent contact with the tower is one of the basic design requirements for blades. As mentioned above, the required rigidity of the blade increases exponentially with increasing blade length, but if the blades are extended while maintaining the conventional blade configuration and rigidity, they will easily come into contact with the tower. Therefore, in practice, a standard is set in the design to ensure that the blade tip deflection (blade tip displacement) is below a certain level, taking into account the distance to the tower. This will be explained below as the tower proximity standard at maximum displacement. Thus, providing rigidity to the blades is one of the most important items for long blades, but because an elevation angle is also set when the rotor is installed, even if rigidity is provided to the blades to prevent contact with the tower (tips deflection is suppressed), it is necessary to anticipate that the blades will undergo considerable deformation.

[0020] Figure 2 illustrates the structure of a wind turbine blade and its spar cap. To ensure high rigidity, almost all blades have a beam structure called a spar that runs through the inside of the blade in the longitudinal direction. The spar is connected between two flanges by a shear-deformable connecting member called a shear web 14. The thickness and width of the spar may also vary in the longitudinal direction to match the airfoil shape. In this spar structure, the part closest to the blade surface is called the spar cap 7, as shown in Figure 2. In this figure, there are two spar caps 7, one above and one below, and fiber-reinforced plastic is used here. This spar cap is the part according to the present invention. In this invention, taking into account the three-dimensional shape of the spar and the structural members constituting the spar as described above, we present an industrially effective configuration (spar cap) that takes into account the necessary suppression of tip deflection and a blade using it.

[0021] The carbon fiber reinforced plastic used in the spur cap of the present invention has a tensile fracture strain of 0.9% or more in the 0° direction and a compressive fracture strain of 0.6% or more in the 0° direction. In the following description, the 0° direction of the carbon fiber reinforced plastic refers to the orientation direction of the carbon fibers in the carbon fiber reinforced plastic. Having a tensile fracture strain of 0.9% or more in the 0° direction and a compressive fracture strain of 0.6% or more in the 0° direction is an important characteristic for the spur cap, which is the main structure of the blade and requires resistance to large deformations in strong winds and other conditions.

[0022] While this characteristic itself is relatively easy to obtain when using carbon fibers with a standard modulus of elasticity, using carbon fibers with a higher modulus of elasticity usually results in a significant decrease in fracture strain. Therefore, achieving such a fracture strain is difficult unless carbon fibers with a specific structure / properties are used. In summary, increasing the modulus of elasticity of carbon fibers is effective in suppressing blade tip deflection due to blade lengthening, but to overcome the disadvantages associated with increased modulus of elasticity, it is effective to keep the physical properties within the range described above.

[0023] Furthermore, in the present invention, in order to achieve such strain characteristics even for high-modulus carbon fibers, the carbon fiber-reinforced plastic constituting the spar cap has an average single filament diameter of 6 µm or more and 9 µm or less, and the crystallite size Lc (nm) and the crystallite orientation π ００２ (%) satisfying the relationship of formula (1) is used as the carbon fiber. π ００２ ≧4.0×Lc+73.3 ・・・Formula (1) The nano-level structure of the carbon fiber is controlled, and the crystallite size Lc (nm) and the crystallite orientation π ００２ The carbon fiber obtained by adjusting the parameters within an appropriate range exhibits high breaking strain, and even when the elastic modulus of the carbon fiber is improved, the reduction in breaking strain is suppressed to a minimum.

[0024] Conventionally, grades with increased elastic modulus of carbon fibers (those called medium-modulus fibers or high-modulus fibers) have, in most cases, an average single filament diameter of 5 µm. This is because an average single filament diameter of about 5 µm is more advantageous for achieving high elastic modulus performance, but this comes at the expense of productivity and cost. According to the present invention, even for relatively low-cost carbon fibers with an average single filament diameter of 6 µm or more and 9 µm or less that are excellent in productivity, the crystallite size Lc (nm) and the crystallite orientation π ００２ (%) by highly controlling the carbon fiber production conditions so as to satisfy the relationship of formula (1), it has been found that a 0° direction tensile breaking strain of 0.9% or more and a 0° direction compressive breaking strain of 0.6% or more can be achieved in the carbon fiber-reinforced plastic.

[0025] In general, when production conditions for increasing the elastic modulus of carbon fibers are adopted, the crystallite size Lc and the crystallite orientation π of the carbon fiber ００２Both increase, but the tendency for the crystallite size Lc to increase can be suppressed by controlling the structure of the carbon fiber at the nanoscale, and the carbon fiber used in this invention is obtained. Furthermore, suppressing the increase in crystallite size also suppresses the embrittlement of the fiber. Carbon fibers that are brittle and have low fracture toughness are prone to breaking due to slight defects in the fiber or on the fiber surface, and the fracture strain when tensile or compressive stress is applied is low, but in this invention, this tendency for the fracture strain to decrease can also be suppressed. In particular, when the elastic modulus of the carbon fiber used is set high, the decrease in fracture strain, which would normally decrease easily, can be kept to a minimum, and both the low tip deflection and resistance to large deformation required for the blade can be achieved. Specifically, the crystallite size Lc (nm) and the degree of crystal orientation π of the carbon fiber ００２ To ensure that (%) satisfies the relationship in equation (1), it is particularly effective to control the number of twists and tension of the fiber bundles during the carbonization process when manufacturing carbon fibers. Alternatively, it is also preferable to strengthen the interaction between the single fibers constituting the pre-carbonized fiber bundle instead of twisting. Strengthening the interaction here refers to measures that increase the unity of the fiber bundle by causing interference between the single fibers, such as entanglement. In this invention, all carbon fiber reinforced plastics constituting the spur cap may have the above characteristics, but it is sufficient if at least some of the carbon fiber reinforced plastics have the above characteristics.

[0026] Various methods can be used to manufacture the fiber-reinforced plastic for obtaining the spur cap in the present invention. For example, prepreg molding or resin infusion molding can be used. The spur cap of the present invention is not limited by the manufacturing method used, but it is most desirable to obtain it by bundling multiple fiber-reinforced plastics (extruded material) obtained by pultrusion molding and joining them together as a single unit. Pultrusion molding is a general term for molding methods in which reinforcing fibers are wetted and impregnated with a matrix resin, and then passed through a heated mold of approximately constant cross-section to continuously obtain fiber-reinforced plastics of constant cross-section. The mold may have multiple heating and cooling areas at different temperatures, and there are no restrictions on the reinforcing fibers or matrix resins used. The matrix resin is typically a thermosetting resin such as vinyl ester resin, epoxy resin, or polyurethane resin, but it may also be a thermoplastic resin, or it may be a reactive pultrusion molding in which polymerization of the resin proceeds during passage through the mold. The advantage of a spur cap made by bundling multiple extruded materials and joining them together as a single unit lies in the excellent straightness of the fibers in the extruded material and the relatively easy ability to increase the volume content of reinforcing fibers in the extruded material. These characteristics allow the properties of the reinforcing fibers to be expressed more efficiently. There are no restrictions on the method of joining and integrating multiple extruded materials, but a typical method involves bundling the extruded materials into a predetermined configuration, and then injecting / curing resin into the gaps between the extruded materials using the resin infusion method. Other methods such as adhesive bonding can also be used. The extruded material can be used anywhere in the spur cap as long as it satisfies the strength and rigidity requirements of the blade, but it is more preferable if the extruded material exhibiting the aforementioned properties as a carbon fiber reinforced plastic is used in the outermost layer of the spur cap, as this not only provides strength and rigidity as a blade, but also makes it easier to implement measures for heating the blade surface to melt snow. Here, the outermost layer refers to the layer closest to the skin 11 on the outside in the thickness direction of the blade, among the multiple bundles of extruded materials used in the spur cap 10 in Figure 2.In order to heat the blade surface and perform snow melting treatment, methods include circulating air heated by a heater inside the blade to raise the surface temperature of the blade and melt ice, and directly heating the blade by applying electricity to heating wires or carbon fibers embedded in or inside the blade surface. In order to more effectively exert the snow melting effect in these methods, it is preferable that the thermal conductivity of the carbon fibers constituting the pultruded material is 20.0 W / m·K or more. When the value is equal to or higher than this, it becomes possible to apply the heating required for snow melting with lower power. Here, the thermal conductivity of carbon fibers can be measured by a general laser flash method or the like. In the case where the thermal conductivity has anisotropy, the maximum value of the measured values is taken as the representative value of the thermal conductivity of the carbon fiber.

[0027] In the above embodiment, it is preferable that the volume content of carbon fibers in at least one pultruded material constituting the spar cap is 63% by volume or more and 70% by volume or less. The fiber volume content of general fiber-reinforced plastics is often about 55% by volume to 62% by volume. In contrast, a higher fiber volume content can improve the elastic modulus of the pultruded material. On the other hand, when the fiber volume content exceeds 70% by volume, the amount of matrix resin becomes insufficient, voids are generated in the pultruded material, or the contact between the reinforcing fibers and the mold during pultrusion molding becomes excessive, and the mold gradually wears out, making it difficult to maintain the pultrusion manufacturing parameters. A more desirable range is 63% by volume or more and 65% by volume or less.

[0028] In addition, regarding the range of breaking strain required for a carbon fiber reinforced plastic (pultruded material), as described above, the 0° direction tensile breaking strain is 0.9% or more and the 0° direction compressive breaking strain is 0.6% or more, and a more desirable range is that the 0° direction tensile breaking strain is 0.95% or more and the 0° direction compressive breaking strain is 0.65% or more. Higher deformation resistance is required for installation in environments exposed to strong winds such as offshore wind turbines, or environments exposed to storms and turbulence such as typhoons. This is because, as described above, even if the design is intended to suppress blade tip deflection, complicated loads may be applied to the blade depending on wind conditions (such as turbulence and gusts).

[0029] The tensile modulus of the carbon fibers used in the carbon fiber reinforced plastic for spur caps described above may be around 230 to 242 GPa (so-called standard modulus yarn), but a more desirable range is 243 GPa or higher (slightly higher modulus than the standard modulus yarn generally sold), and the effects of the present invention become particularly pronounced in this range. That is, even a slight increase in modulus contributes to reducing the deflection of the blade tip, and the aforementioned crystallite size Lc (nm) and crystal orientation degree π ００２ Satisfying the (%) relationship effectively contributes to improving the performance of the spur cap. Furthermore, a desirable range for the fiber tensile modulus is 255 GPa or higher, and even more preferably 280 GPa or higher. When the blade length / spur cap length is 115 to 139 m, considering the balance between blade stiffness and fracture strain, a fiber tensile modulus in the range of 255 to 279 GPa is preferable. When the blade length / spur cap length is 140 m or more, it is desirable that the tensile modulus of the carbon fiber be 280 GPa or higher. To suppress blade tip deflection, the higher the tensile modulus of the carbon fiber, the better, but it becomes more difficult to achieve the aforementioned tensile fracture strain and compressive fracture strain in the 0° direction. When the tensile modulus of the carbon fiber used is, for example, 280 GPa or higher, the crystallite size Lc (nm) and the degree of crystal orientation π ００２ It is more desirable that the (%) relationship satisfies equation (2). π ００２ ≧4.0×Lc+73.8...Formula (2)

[0030] The crystallite size Lc (nm) and crystal orientation π shown here ００２ (%) can be measured using the method described below. Even from CFRP members such as drawn materials, carbon fibers can be extracted to obtain their Lc and π ００２ It is possible to measure this and determine whether the component, and by extension the blade, falls under the scope of the present invention.

[0031] In many cases, the reinforced plastic constituting the spar cap is formed only of carbon fiber reinforced plastic (CFRP), but this does not preclude use thereof as a mixture with other types of materials such as glass fiber reinforced plastic (GFRP). However, in order to develop sufficient rigidity, it is desirable that carbon fibers account for 50% by weight or more of the reinforcing fibers constituting the spar cap, and in particular, that the aforementioned high-modulus carbon fiber grade is used.

[0032] Regarding the length of the spar cap, generally, the longer the blade, the more difficult it is to achieve the aforementioned suppression of blade tip deflection and deformation tolerance. Therefore, the ratio of total blade length to spar cap length for which the present invention is particularly effective is 97 m or more. The invention is even more effective for blades having a total length of 115 m or more. Further, in order to achieve a total spar cap length of 140 m or more, it is generally necessary to increase the thickness of the spar cap even when CFRP is used, but by utilizing the present invention, the degree of design freedom can be increased, and a lightweight spar cap can be obtained.

[0033] As mentioned above, one aspect of the present invention is that a portion of the spur cap is made of glass fiber reinforced plastic, that is, by mixing carbon fiber reinforced plastic and glass fiber reinforced plastic. In this case, it is desirable to use a glass fiber grade with a fiber tensile modulus of 75 GPa or higher. Even more desirable is to use a glass fiber grade with a fiber tensile modulus of 95 GPa or higher. Glass fibers with an elastic modulus of 95 GPa or higher have recently come to be used in blades, and a suitable spur cap can be obtained by combining them with the carbon fibers described herein. There are no restrictions on the method of mixing carbon fibers and glass fibers, but as mentioned above, one desirable form of the spur cap is one in which multiple fiber-reinforced plastics (extruded material) obtained by pultrusion are bundled together and joined together. In this case, one example is to mix CFRP extruded material and GFRP extruded material, bundle multiple pieces together, and join them together. Alternatively, a form in which multiple pieces are bundled mainly of CFRP extruded material, with a thin GFRP layer between each extruded piece, can also be exemplified. This thin GFRP layer can be, for example, made by impregnating one or two layers of glass fiber fabric with a matrix resin. Furthermore, a blend of glass fibers and carbon fibers is also acceptable. Even materials other than fabrics, such as mats, can be used as examples.

[0034] Regarding the CFRP portion, it is also possible to use a mixture of carbon fibers with different properties. Any combination is acceptable; for example, it is possible to mix multiple types of carbon fibers with different tensile moduli, multiple types of carbon fibers with different surface treatments, or multiple types of carbon fibers with different crystallite sizes Lc. It is also acceptable to combine extruded materials with different tensile fracture strains or 0° direction compressive fracture strains. As an example, it is possible to prepare multiple carbon fiber reinforced plastic extruded materials manufactured using such carbon fibers with different properties, bundle these extruded materials in an intended ratio or arrangement, and then join and integrate them to create a spur cap. Since spur caps are typically used under bending forces, one preferred example is to construct the low-stress layer near the neutral axis and the high-stress layers in other parts of the spur cap with fiber-reinforced plastics having different properties.

[0035] The design of wind turbine blades is carried out using established analysis software that conforms to the IEC 61400 series. This software includes HAWC2 developed by the Technical University of Denmark (DTU), Bladed by the certification body DNV, and OpenFAST by the National Renewable Energy Laboratories (NREL), and these are the most common. While the detailed specifications of each software differ, they share similar basic functionality. Many modern wind turbine blades are over 85 meters long, and the spars / spar caps embedded within them are correspondingly massive. Typically, the actual fabrication and deformation measurements of such large components are only performed in the final stages of wind turbine development; most of the basic design is done using software. The software examples mentioned earlier have a proven track record, and it has become industry standard practice to complete most of the design using software calculations. Therefore, the examples and comparative examples in this specification also use the results of software analysis.

[0036] For the basic blade models, we used various Reference Wind Turbines (RWTs) publicly available from research institutions for research purposes, as well as some modified versions thereof. The RWTs are designs completed by research institutions that meet the basic requirements for wind turbines, and although they are not commercial machines, they are designed to be similar. We referenced the aeroelastic analysis model of the blade section and the coefficients used therein, and performed calculations such as blade tip deflection in a typical DLC (Design Load Case) compliant with the IEC 61400 series using the analysis software Bladed. Even when the model was in the format of OpenFAST or HAWC2 software, we performed the analysis after converting it to the Bladed format. Furthermore, we verified whether this blade tip deflection met the tower proximity criteria for wind turbine blades, in accordance with the original RWT design. If necessary, a three-dimensional finite element model (hereinafter referred to as the FEM model) of the blade was reconstructed while referring to the RWT report. The material or thickness of the spur cap in this model was changed to adjust the stiffness of the FEM model to match the coefficients of the aeroelastic model mentioned earlier. The mass of the spur cap was then determined using the adjusted FEM model. The results of these studies are shown in Table 1.

[0037] The following reports summarize the RWTs referenced: Reference 1: The DTU 10-MW Reference Wind Turbine Reference 2: Definition of the IEA Wind 15MW Offshore Reference Wind Turbine (2020) Reference 3: The Definition of the IEA Wind 22-Megawatt Offshore Reference Wind Turbine

[0038]

[0039] Comparative Examples 1 to 4 show the results for spur caps and blades using the prior art.

[0040] Comparative Example 1 is a GFRP spur cap made of glass fiber. If the total length is 86m, it satisfies the proximity requirements and is viable as a wind turbine blade. However, even at this length, the spur cap mass is 14.3 tons, indicating that it is not viable unless it is a very thick and heavy spur cap. Comparative Examples 2 to 4 are CFRP spur caps made of carbon fiber. Comparative Example 2 uses Zoltek PX35 carbon fiber, which is currently standard for spur caps. A CFRP pultruded material with a 5mm thick rectangular cross-section (fiber volume content 62%) was prepared, and an analytical model was constructed assuming that multiple of these were bundled together and resin injected to obtain a single spur cap. The length of the spur cap was set to 115m. In Comparative Example 2, the spur cap had to be made thick to ensure rigidity in order to meet the tower proximity requirements for the blade, and the spur cap mass was 15.7 tons.

[0041] Comparative Example 3 used Toray Industries, Inc.'s "Torayca" (registered trademark) M40J carbon fiber. While its high tensile modulus of elasticity (377 GPa) allows for a relatively lightweight spur cap, the carbon fiber reinforced plastic exhibited remarkably low tensile and compressive fracture strains in the 0° direction. This is because the carbon fiber undergoes a graphitization process at extremely high firing temperatures, resulting in a large crystallite size (Lc). Such low fracture strains raise serious concerns about fracture due to large deformations of the spur cap caused by wind turbulence or gusts, or localized stresses that may occur under extreme conditions such as wind turbine control system failures. While a high tensile modulus of elasticity is one requirement for long blades / spur caps, it is insufficient on its own. High-modulus grades of carbon fiber, like those used in this comparative example, have existed for some time, but they are not necessarily suitable for wind turbine blades.

[0042] Comparative Example 4 uses the same PX35 as Comparative Example 2, but investigates an ultra-long blade with a blade / spur cap length of 140m. An attempt was made to ensure the rigidity of the spur cap by making its thickness as thick as possible. However, the external dimensions and profile of the blade are determined taking aerodynamic conditions into consideration, and the shape of the spur cap that penetrates the inside of the blade cannot be freely set due to the constraints of the internal space dimensions of the blade. Furthermore, in terms of molding the spur cap, it is difficult to inject resin beyond a certain thickness, so an upper limit on the thickness is naturally set. We investigated with a spur cap mass of 18.9 tons, which is the upper limit possible for this 140m long blade shape, but we were unable to sufficiently suppress the deflection of the blade and could not meet the tower proximity standards. In other words, this wind turbine design using a 140m blade could not be made feasible using the conventionally used PX35.

[0043] Examples 1 to 5 illustrate typical cases of the present invention, but these examples do not limit the present invention in any way.

[0044] Example 1 uses a spur cap length of 115 m and prototype carbon fiber A. The prototype carbon fiber A has a crystallite size Lc (nm) and a crystal orientation degree π. ００２ The (%) represents the scope of the present invention, and the manufacturing method will be described later. The prototype carbon fiber A has a significantly higher tensile modulus of elasticity compared to PX35, and its value is almost the same as that of the aforementioned M40J. Nevertheless, the decrease in tensile fracture strain and compressive fracture strain in the 0° direction is kept to a minimum. The average single filament diameter is 7 μm, and the productivity of the carbon fiber is superior to that of M40J. By using such a carbon fiber with a high tensile modulus of elasticity and large fracture strain in the spur cap, the spur cap mass is effectively kept down to 10.8 ton (low carbon fiber usage), and it can withstand large deformations.

[0045] Example 2 also uses a spur cap length of 115 m and employs prototype carbon fiber B. This prototype carbon fiber B also has a crystallite size Lc (nm) and a crystal orientation degree π. ００２The (%) range of this invention is defined as the tensile modulus of the fiber, which is set between PX35 and M40J, slightly higher than PX35. The tensile modulus of the fiber does not differ drastically from that of PX35, and it has properties similar to PX35, which has a proven track record in wind turbine blade / spur cap applications. Manufacturing costs and fracture strain do not deviate significantly from those of PX35. Therefore, it is possible to easily change the design and specifications from spur caps using PX35, while also reducing the mass of the spur cap.

[0046] Example 3 uses a spur cap length of 140 m and employs prototype carbon fiber B, as in Example 2. While the spur cap needed to be made nearly as thick as possible to ensure the required rigidity of the blade, unlike Comparative Example 4, the blade tip deflection could be kept within the design specifications. In other words, while the wind turbine system was not feasible in Comparative Example 4, the use of prototype carbon fiber B allowed for a feasible design even with a spur cap length of 140 m. In short, this demonstrates that the present invention increases design flexibility for wind turbines, blades, and spur caps, enabling the creation of larger wind turbines.

[0047] Example 4 uses a spur cap length of 140 m and employs the same prototype carbon fiber A as in Example 1. While Example 1 had a spur cap length of 115 m, Example 4 has a length of 140 m. However, by using carbon fiber with a high modulus of elasticity, it was possible to construct the spur cap with ample margin. Furthermore, the mass of the spur cap is equivalent to that of Comparative Example 2, which has a length of 115 m. This means that by selecting an appropriate carbon fiber, it is possible to extend the spur cap / blade while suppressing the increase in weight while satisfying other design requirements.

[0048] Example 5 uses a spur cap length of 155 m and employs the same prototype carbon fiber A as in Example 1. Although Example 5 has a spur cap length of 155 m, the mass of the spur cap is equivalent to that of Example 3. This demonstrates that by selecting an appropriate carbon fiber, it is possible to extend the spur cap / blade while suppressing the weight increase while satisfying other design requirements.

[0049] Prototype carbon fiber A can be obtained by the following manufacturing method. The polyacrylonitrile-based carbon fiber precursor bundle (precursor), which is the basis of the carbon fiber, can be obtained by spinning a spinning solution of a polyacrylonitrile-based polymer.

[0050] The polyacrylonitrile polymer may be not only a homopolymer obtained solely from acrylonitrile, but also a copolymer obtained by copolymerizing acrylonitrile, the main component, with other monomers, or a mixture thereof. Specifically, it is preferable that the polyacrylonitrile polymer contains 90 to 100% by mass of structures derived from acrylonitrile and less than 10% by mass of structures derived from copolymerizable monomers.

[0051] Examples of monomers copolymerizable with acrylonitrile include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allyl sulfonic acid, methallyl sulfonic acid and their salts or alkyl esters.

[0052] The aforementioned polyacrylonitrile polymer is dissolved in a solvent in which the polyacrylonitrile polymer is soluble, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, aqueous zinc chloride solution, or aqueous rhodane solution, to obtain a spinning solution. When solution polymerization is used to produce the polyacrylonitrile polymer, it is preferable to use the same solvent for polymerization and for spinning, as this eliminates the need to separate the obtained polyacrylonitrile polymer and redissolve it in the solvent used for spinning.

[0053] By spinning the spinning solution obtained as described above using a wet or wet-dry spinning method, a polyacrylonitrile-based carbon fiber precursor fiber bundle can be produced.

[0054] The spinning solution obtained as described above is introduced into a coagulation bath and coagulated. The resulting coagulated fiber bundle is then subjected to a water washing step, a bath stretching step, an oil application step, and a drying step to obtain a polyacrylonitrile-based carbon fiber precursor fiber bundle. The coagulated fiber bundle may be stretched directly in the bath without the water washing step, or the solvent may be removed in the water washing step before stretching in the bath. Bath stretching is usually preferably carried out in one or more stretching baths that are temperature-controlled to 30 to 98°C. In addition, a dry heat stretching step or a steam stretching step may be added to the above steps.

[0055] Carbon fiber bundles, which are the form of continuous fibers that form the basis of carbon fibers, can be obtained by flame-retardant treatment of the aforementioned polyacrylonitrile-based carbon fiber precursor fiber bundle, followed by a pre-carbonization treatment and then a carbonization treatment. These treatment steps may also be referred to as the flame-retardant treatment, pre-carbonization treatment, and carbonization treatment, respectively.

[0056] The flame-retardant treatment of polyacrylonitrile-based carbon fiber precursor fiber bundles is preferably carried out in an air atmosphere at a temperature range of 200 to 300°C.

[0057] Following the flame-retardant treatment, a pre-carbonization treatment is performed. In the pre-carbonization step, the obtained flame-retardant fiber bundle is subjected to a density of 1.5 to 1.8 g / cm³ in an inert atmosphere at a maximum temperature of 500 to 1000°C. ３ It is preferable to heat-treat until it reaches this state.

[0058] Furthermore, following the pre-carbonization, a carbonization treatment is performed. In the carbonization process, it is preferable to heat-treat the obtained pre-carbonized fiber bundle in an inert atmosphere at a maximum temperature of 1000 to 3000°C. From the viewpoint of increasing the elastic modulus of the single carbon fibers obtained, a higher maximum temperature in the carbonization process is preferable. However, if it is too high, the adhesive strength between the carbon fibers and the matrix resin may decrease, so it is best to set the temperature considering such a trade-off. For the above reasons, it is more preferable that the maximum temperature in the carbonization process be 1400 to 2500°C, and even more preferable that it be 1700 to 2000°C.

[0059] The carbon fiber bundles that form the basis of carbon fibers preferably have a twist count of 16 to 120 turns / m during the carbonization process, more preferably 16 to 80 turns / m, and even more preferably 16 to 45 turns / m. This twist count can be controlled by methods such as winding a polyacrylonitrile-based carbon fiber precursor bundle or flame-resistant fiber bundle, or a pre-carbonized fiber bundle, onto a bobbin and then rotating the bobbin in a plane perpendicular to the winding direction when unwinding the fiber bundle, or by applying twist to the fiber bundle while it is moving without winding it onto a bobbin.

[0060] Furthermore, the tension in the carbonization process can be freely set within the range in which a stable carbon fiber bundle can be obtained, but it is preferably 1 to 18 mN / dtex, more preferably 1.5 to 18 mN / dtex, even more preferably 3 to 18 mN / dtex, and still more preferably 5 to 18 mN / dtex. The tension in the carbonization process is determined by dividing the tension (mN) measured at the exit of the carbonization furnace by the total fineness (dtex), which is the product of the average fineness (dtex) of the single fibers of the polyacrylonitrile-based carbon fiber precursor fiber bundle used and the number of filaments. By controlling this tension, the degree of crystal orientation π can be controlled without significantly affecting the average crystallite size Lc of the obtained carbon fibers. ００２ This allows for control of the tension, resulting in carbon fibers that satisfy equation (1) described above. From the viewpoint of increasing the elastic modulus of the individual carbon fibers, a higher tension is preferable. However, if the tension is too high, it may reduce the passability through the process and the quality of the resulting carbon fibers. It is best to set the tension considering both factors. If the tension in the carbonization process is increased without adding twist, breakage may occur in the individual fibers within the fiber bundle, increasing fluffiness, which may reduce the passability through the carbonization process, or the entire fiber bundle may break, making it impossible to maintain the required tension. However, if twist is added to the fiber bundle during the carbonization process, fluffiness is suppressed, making it possible to add high tension.

[0061] In the present invention, examples of inert gases used in the inert atmosphere include nitrogen, argon, and xenon, with nitrogen being preferred from an economic standpoint.

[0062] The carbon fiber bundle, which is in the form of continuous fibers obtained as described above, may be surface-treated to improve the adhesive strength between the carbon fibers and the matrix resin, and functional groups containing oxygen atoms may be introduced. As surface treatment methods, gas-phase oxidation, liquid-phase oxidation, and liquid-phase electrolytic oxidation can be used, but liquid-phase electrolytic oxidation is preferred from the viewpoint of high productivity and uniform treatment. In the present invention, there are no particular restrictions on the method of liquid-phase electrolytic oxidation, and any known method may be used.

[0063] After such electrolytic treatment, a sizing agent may be applied to further improve the handling and processability of the resulting continuous fiber bundle, or to increase the adhesive strength between the carbon fibers and the matrix resin. The sizing agent can be appropriately selected depending on the type of matrix resin used in the carbon fiber reinforced composite material. Furthermore, the amount of sizing agent applied may be finely adjusted from the viewpoint of handling and processability. In addition, if there is concern about a decrease in the adhesive strength between the carbon fibers and the matrix resin due to thermal decomposition products of the sizing agent, such as when using a matrix resin with a high molding temperature, the amount of sizing agent applied may be reduced as much as possible, or the sizing treatment may be omitted.

[0064] Prototype carbon fiber B can be obtained in the manufacturing method of prototype carbon fiber A as exemplified above, by reducing the number of twists in the fiber bundle during the carbonization process and the tension during the carbonization process. However, it is necessary to keep these within the range that satisfies formula (1).

[0065] Crystallite size Lc (nm) and crystal orientation π within the range that satisfies equation (1) ００２ By obtaining (%), it is possible to obtain carbon fibers suitable for spur caps, such as those with high breaking strain. While it is not necessary to strictly follow the manufacturing method described above, the number of twists in the fiber bundle during the carbonization process and the control of tension in the carbonization process are typical examples of suitable manufacturing conditions for satisfying equation (1). In addition, other methods can be used, such as strengthening the interaction between the single fibers constituting the pre-carbonized fiber bundle instead of twisting.

[0066] The performance required of a spur cap varies depending on the design of the wind turbine blade (such as the wind turbine class to accommodate the expected wind conditions) and its length; therefore, it is desirable to use carbon fibers with a suitable tensile modulus of elasticity.

[0067] The following describes a method for measuring the characteristics according to the present invention.

[0068] <Tensile and Compressive Fracture Strain in the 0° Direction of Carbon Fiber Reinforced Plastics> These properties are measured using test specimens cut from spur caps by mechanical cutting or other means, in accordance with the ASTM D3039 and ASTM D6641 test methods.

[0069] <Average Single Fiber Diameter of Carbon Fibers> The diameter of the single fiber was measured by observing the cross-section of the fiber using a scanning electron microscope. Since the cross-sectional shape of the single fiber is not strictly a perfect circle, the equivalent diameter was used as a substitute. The equivalent diameter of a circle refers to the diameter of a perfect circle having the same cross-sectional area as the measured cross-sectional area of ​​the single fiber. The average of the diameters of carbon fibers n=5 or more can be used as the average single fiber diameter.

[0070] <Cryslite size Lc and crystal orientation π of carbon fiber single fibers> ００２> Single fibers are randomly selected from a carbon fiber bundle, and wide-angle X-ray diffraction measurements are performed using an X-ray μ-beam-enabled device. The measurement is performed using a 1.305 angstrom wavelength microbeam, shaped to 3 μm in the fiber axis direction and 1 μm in the fiber diameter direction, while scanning the single fiber in 1 μm steps in the fiber diameter direction. The irradiation time per step is set to 2 seconds. The camera length, which is the distance between the detector and the sample, is set to be within the range of 40 to 200 mm. The camera length and beam center coordinates are determined by measuring cerium oxide as a standard sample. By subtracting the 2D diffraction pattern measured with the sample removed from the detected 2D diffraction pattern, detector-induced dark noise and air-derived scattering noise are canceled out, and a corrected 2D diffraction pattern is obtained. By summing the corrected 2D diffraction patterns at each position in the fiber diameter direction of the single fiber, the average 2D diffraction pattern in the fiber diameter direction of the single fiber is obtained. In this average two-dimensional diffraction pattern, sector integration is performed at angles of ±5° centered on the direction orthogonal to the fiber axis to obtain a diffraction intensity profile in the 2θ direction. The diffraction intensity profile in the 2θ direction is fitted with least-squares using two Gaussian functions to find the angle 2θ that maximizes the diffraction intensity. ｍ The (°) and the full width at half maximum (FWHM) (°) of the composite function of the two Gaussian functions are calculated. Furthermore, the angle 2θ at which the diffraction intensity profile in the 2θ direction is maximized is calculated. ｍ The circumferential integral is performed with a width of ±5° around (°) to obtain the diffraction intensity profile in the circumferential direction. The circumferential diffraction intensity profile is then fitted with least squares using a single Gaussian function to obtain the full width at half maximum (FWHM). β Calculate the (°). Crystallite size Lc and crystal orientation π of the single fiber. ００２ The average crystallite size Lc and average crystal orientation π are obtained by calculating the following formula and averaging the results for each of the three single fibers. ００２ Calculate the following: Lc(nm) = Kλ / FWHM × cos(2θ) ｍ / 2) π ００２ (%) = (180-FWHM β) / 180 × 100 (%) Here, the Scherrer coefficient K is 1.0, the X-ray wavelength λ is 0.1305 nm, and the full width at half maximum FWHM and 2θ ｍ The unit is angle (°). In this embodiment, the second hatch of beamline BL03XU (FSBL) of SPring-8 is used as the device that can utilize the X-ray μbeam, and the charge-integrating SOI detector "SOPHIAS" (pixel size 30 μm × 30 μm) developed by RIKEN is used as the detector. <Thermal conductivity of carbon fiber> The thermal conductivity K of carbon fiber is calculated by the following formula: K = Cp・α・ρ Here, K is the thermal conductivity of carbon fiber (W / m・K), Cp is the specific heat of carbon fiber (J / kg・K), and α is the thermal diffusivity of carbon fiber (m ２ ( / s), ρ is the density of carbon fiber (kg / m³) ３ The specific heat Cp of the carbon fiber was measured according to JIS K7123 (1987). The density of the carbon fiber was measured according to JIS R7602 (1999). The thermal diffusivity α was measured using a LaserPIT thermal diffusivity measuring device manufactured by ULVAC, Inc., on bundles of several dozen carbon fibers.

[0071] <Fiber Content in Fiber-Reinforced Plastics> A sample is cut from a molded product of fiber-reinforced plastic and its mass is measured. Then, the sample is heated in an electric furnace at 500°C for 1 hour to burn off organic matter such as matrix resin. After cooling to room temperature, the mass of the remaining carbon fibers is measured. The ratio of the mass of fibers to the mass of the sample before burning off organic matter such as matrix resin is measured and defined as the fiber content. Another method for removing organic matter such as matrix resin can be immersion in an acid solution. In the case of volume content, the volume ratio is converted using the specific gravity of the fibers and resin composition. <Tensile Modulus of Fibers> A test piece cut from a spur cap by mechanical cutting or the like is used to measure the tensile modulus of fibers according to the ASTM D3039 test method.

[0072] 1: Blade 2: Nacelle 3: Tower 4: Wind (Schematic image of thrust force due to wind) 5: Blade tip deflection (blade tip displacement) 6: Deflection when blade length is extended without changing the blade structure or material composition (Schematic image) 7: Spur cap (part of the spur) 8: Blade internal perspective view 9: Blade cross-section (near the spur cap) 10: Spur cap (cross-section) 11: Skin (glass fiber reinforced plastic) 12: Core material 14: Shareweb

Claims

1. A spur cap for a wind turbine blade, with a total length of 97 m or more, wherein at least a portion of the carbon fiber reinforced plastic satisfies all of the following conditions A to C: A: The carbon fiber reinforced plastic used has a tensile fracture strain of 0.9% or more in the 0° direction and a compressive fracture strain of 0.6% or more in the 0° direction. B: The average monofilament diameter of the carbon fibers used is 6 μm or more and 9 μm or less. C: The crystallite size Lc (nm) and crystal orientation degree π of the carbon fibers used. ００２ (%) satisfies the relationship in equation (1). π ００２ ≧4.0×Lc+73.3...Formula (1) 2. The spur cap according to claim 1, wherein the carbon fiber reinforced plastic is an extruded material obtained by pultrusion molding, and is constructed by bundling and joining multiple extruded materials together.

3. The spur cap according to claim 2, characterized in that the carbon fiber reinforced plastic composed of drawn material is used as the outermost layer of the spur cap.

4. The spur cap according to claim 3, characterized in that the thermal conductivity of the carbon fibers in the extruded material is 20.0 W / m·K or higher.

5. The spur cap according to any one of claims 2 to 4, wherein the volume content of carbon fibers in the drawn material is 63 volume% or more and 70 volume% or less.

6. The spur cap according to any one of claims 2 to 4, wherein the volume content of carbon fibers in the drawn material is 63 volume% or more and 65 volume% or less.

7. The spur cap according to any one of claims 2 to 4, wherein the tensile fracture strain in the 0° direction of the drawn material is 0.95% or more and the compressive fracture strain in the 0° direction is 0.65% or more.

8. A spur cap according to any one of claims 1 to 4, wherein 50% by weight or more of carbon fibers with a fiber tensile modulus of 243 GPa or higher are used.

9. A spur cap according to any one of claims 1 to 4, wherein 50% by weight or more of carbon fibers with a fiber tensile modulus of 255 GPa or higher are used.

10. A spur cap according to any one of claims 1 to 4, wherein the total length is 115 m or more.

11. A spur cap according to any one of claims 1 to 4, wherein the total length is 140 m or more.

12. A wind turbine blade having a spur cap according to any one of claims 1 to 4.

13. A method for manufacturing a spur cap for a wind turbine blade, having a total length of 97 m or more, in which at least a portion is made of carbon fiber reinforced plastic, wherein the spur cap uses carbon fiber reinforced plastic that satisfies the following A to C: A: The tensile fracture strain in the 0° direction of the carbon fiber reinforced plastic used is 0.9% or more and the compressive fracture strain in the 0° direction is 0.6% or more. B: The average monofilament diameter of the carbon fibers used is 6 μm or more and 9 μm or less. C: The crystallite size Lc (nm) and crystal orientation degree π of the carbon fibers used. ００２ (%) satisfies the relationship in equation (1). π ００２ ≧4.0×Lc+73.3...Formula (1)

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