A wind turbine blade spar cap

Abstract

In a first aspect of the present invention there is provided a wind turbine blade spar cap. The spar cap has an upper spar cap surface, a lower spar cap surface, and a spar cap thickness defined between the upper and lower spar cap surfaces. The spar cap has a middle portion throughout which the spar cap thickness is substantially constant, and a tapered end portion in which the spar cap thickness decreases towards an end of the spar cap. The spar cap comprises a plurality of pultrusion layers arranged in a stack. Each pultrusion layer has an upper pultrusion layer surface, a lower pultrusion layer surface, and a layer thickness defined between the respective upper and lower pultrusion layer surfaces. The stack comprises a first substack comprising a plurality of pultrusion layers and a second substack comprising a plurality of pultrusion layers. The stack further comprises an intermediate pultrusion layer comprising a tapered end section in which the layer thickness of the intermediate pultrusion layer decreases towards the end of the spar cap. The tapered end section is located in the tapered end portion of the spar cap. The intermediate pultrusion layer is sandwiched between the first and second substacks such that, in the tapered end portion of the spar cap, the tapered end section of the intermediate pultrusion layer is sandwiched between a plurality of pultrusion layers of the first substack and a plurality of pultrusion layers of the second substack.

Description

[0001] A wind turbine blade spar cap

[0002] Technical field

[0003] The present invention relates generally to wind turbine blades and more particularly to a wind turbine blade spar cap.

[0004] Background

[0005] Modern wind turbine blades typically include a reinforcing spar structure configured to take up bending loads experienced by the blade in use. The spar structure may include a spar cap having longitudinally-extending fibres to provide longitudinal stiffness to the blade. In some wind turbine blades, the longitudinally-extending fibres of the spar cap are provided in the blade by way of a plurality of longitudinally-extending pultrusions. Pultrusions are typically pre-manufactured strips or rods of composite material which, as a result of the manufacturing process, can have a high percentage of longitudinally-extending fibres.

[0006] Due to the differing load requirements along the length of the blade, the pultrusions may be arranged in a stack having a varying thickness along its length. It follows that the spar cap may have a tapered portion in which the thickness of the spar cap decreases. To form a tapered portion, the pultrusions are typically arranged in a staggered configuration with some pultrusions in the stack extending further into the tapered portion than others, such that ends of the pultrusions are offset from one another in the longitudinal direction. This means that the end of each pultrusion (except the furthest-extending pultrusion) is adjacent to a pultrusion that extends further into the tapered portion of the spar cap.

[0007] However, a spar cap having a tapered portion configured in this way typically experiences high loads at an interface between the end of a pultrusion and the respective adjacent, further-extending pultrusion. This is because the adjacent, further-extending pultrusion typically has a significantly greater stiffness than other materials adjacent to the tapered portion of the spar cap. This means that at the end of the respective pultrusion, the majority of the loads taken up along the length of the pultrusion are transferred to the adjacent, further-extending pultrusion at the interface between the pultrusions in the tapered portion of the spar cap. Accordingly, the end of a pultrusion may experience asymmetric, i.e. significantly imbalanced, loading in this configuration, which may be undesirable.

[0008] It is against this background that the present invention has been developed. Summary

[0009] In a first aspect of the present invention there is provided a wind turbine blade spar cap. The spar cap has an upper spar cap surface, a lower spar cap surface, and a spar cap thickness defined between the upper and lower spar cap surfaces. The spar cap has a middle portion throughout which the spar cap thickness is substantially constant, and a tapered end portion in which the spar cap thickness decreases towards an end of the spar cap. The spar cap comprises a plurality of pultrusion layers arranged in a stack. Each pultrusion layer has an upper pultrusion layer surface, a lower pultrusion layer surface, and a layer thickness defined between the respective upper and lower pultrusion layer surfaces. The stack comprises a first substack comprising a plurality of pultrusion layers and a second substack comprising a plurality of pultrusion layers. The stack further comprises an intermediate pultrusion layer comprising a tapered end section in which the layer thickness of the intermediate pultrusion layer decreases towards the end of the spar cap. The tapered end section is located in the tapered end portion of the spar cap. The intermediate pultrusion layer is sandwiched between the first and second substacks such that, in the tapered end portion of the spar cap, the tapered end section of the intermediate pultrusion layer is sandwiched between a plurality of pultrusion layers of the first substack and a plurality of pultrusion layers of the second substack.

[0010] The spar cap has a spar cap length and a spar cap width in addition to the spar cap thickness. The spar cap thickness is a dimension in a direction substantially orthogonal to each of the spar cap length and the spar cap width, and the spar cap length is a dimension in a direction substantially orthogonal to the spar cap width. The spar cap length is greater than the spar cap width, and the spar cap width is preferably greater than an average spar cap thickness over the full length of the spar cap.

[0011] Each pultrusion layer has a layer length and a layer width in addition to the layer thickness described previously. The layer thickness is a dimension in a direction substantially orthogonal to each of the layer length and the layer width, and the layer length is a dimension in a direction substantially orthogonal to the layer width. The layer length is preferably greater than the layer width, and the layer width is greater than the layer thickness. For example, each pultrusion layer may have a maximum layer thickness no greater than 0.01 m, a layer width between 0.02 m and 0.2 m, and a layer length of at least 0.5 m. A wind turbine blade including the spar cap may extend in a spanwise direction between a root end and a tip end, in a chordwise direction between a leading edge and a trailing edge, and in a thickness direction between a windward side and a leeward side of the blade. It will be appreciated that in a blade, the spar cap length and layer length extend in a direction substantially parallel to the spanwise direction of the blade, the spar cap width and layer width extend in a direction substantially parallel to the chordwise direction of the blade, and the spar cap thickness and layer thickness extend in a direction substantially parallel to the thickness direction of the blade.

[0012] It will be appreciated that references to the spar cap thickness being substantially constant throughout the middle portion of the spar cap means as constant, i.e. uniform, as possible within manufacturing tolerances of the pultrusion layers and any interlayers between the pultrusion layers.

[0013] The tapered end section of the intermediate pultrusion layer facilitates a gradual transfer of loads out of the intermediate pultrusion layer. By sandwiching the tapered end section between a plurality of pultrusion layers of the first substack and a plurality of pultrusion layers of the second substack, the spar cap is configured such that the tapered end section of the intermediate pultrusion layer experiences substantially symmetrical loading, i.e. a substantially balanced stiffness ratio between the components adjacent to the tapered end section. Accordingly, loads leaving the tapered end section of the intermediate thickness layer are evenly distributed between the sandwiching pultrusion layers of the first and second substacks. This helps to avoid stress concentrations forming at interfaces between the tapered end section and adjacent components and also helps to ensure that the tapered end section remains bonded to the adjacent pultrusion layers in use.

[0014] In some preferred examples, each pultrusion layer in the stack may extend at least partially into the tapered end portion of the spar cap. For example, the tapered end portion of the spar cap may be immediately adjacent to the middle portion of the spar cap. It follows that each pultrusion layer in the stack may form at least part of the middle portion of the spar cap and at least part of the tapered end portion of the spar cap. Such a configuration helps to ensure that a requisite stiffness is maintained in the tapered end portion of the spar cap despite the intermediate pultrusion layer tapering in thickness.

[0015] In some examples, each pultrusion layer in each of the first and second substacks may extend further into the tapered end portion of the spar cap than the intermediate pultrusion layer. For example, the pultrusion layers of the first and second substacks may each extend further from the middle portion of the spar cap into the tapered end portion, than the intermediate pultrusion layer. Such a configuration means that the intermediate pultrusion layer is sandwiched between as many pultrusion layers of the first and second substacks as possible, which is particularly advantageous for transferring loads into or out of the tapered end section of the intermediate pultrusion layer in use.

[0016] In some examples, for each of the first and second substacks, the pultrusion layers may extend successively further into the tapered end portion of the spar cap with increased distance from the intermediate pultrusion layer. This means that pultrusion layers extending into the tapered end portion of the spar cap to a lesser extent are located closer to the intermediate pultrusion layer in the stack, and ends of such lesser extending pultrusion layers are therefore sandwiched between a plurality of other pultrusion layers.

[0017] In some examples, the first substack may be stacked immediately adjacent to, i.e. on top of or below, the intermediate pultrusion layer. Accordingly, the pultrusion layers of the stack may extend successively further into the tapered end portion of the spar cap going from the intermediate pultrusion layer to an outer pultrusion layer of the first substack that defines the upper or lower spar cap surface.

[0018] In some examples, the second substack may be stacked immediately adjacent to, i.e. on top of or below, the intermediate pultrusion layer. Accordingly, the pultrusion layers of the stack may extend successively further into the tapered end portion of the spar cap going from the intermediate pultrusion layer to an outer pultrusion layer of the second substack that defines the upper or lower spar cap surface.

[0019] In some examples, going from the tapered end section of the intermediate pultrusion layer to the end of the spar cap, the respective pultrusion layer that extends successively further into the tapered end portion may alternate between the first and second substacks. For example, going from the tapered end section of the intermediate pultrusion layer towards the end of the spar cap, the next-furthest extending pultrusion layer after the intermediate pultrusion layer may be part of the first substack, the next-furthest extending pultrusion layer thereafter may be part of the second substack, and such an arrangement may continue throughout the tapered end portion of the spar cap. This means that pultrusion layers extending into the tapered end portion of the spar cap to a lesser extent are located closer to the intermediate pultrusion layer in the stack, and ends of such lesser extending pultrusion layers are therefore sandwiched between as many pultrusion layers as possible. In some examples, each pultrusion layer may comprise a tapered end section in which the layer thickness decreases towards the end of the spar cap. Further, the tapered end section of each pultrusion layer may be located in the tapered end portion of the spar cap. The tapered end section of each pultrusion layer in the stack advantageously facilitates a gradual transfer of loading into or out of the respective pultrusion layer. In some examples, the tapered end sections of a plurality of different pultrusion layers may be sandwiched between other pultrusion layers in the stack. In such examples the tapered end sections may facilitate improved draping of the sandwiching pultrusion layers to conform to the respective tapered end section.

[0020] In some preferred examples, the tapered end sections of the pultrusion layers in the stack may all be offset from one another in the longitudinal direction. Such a configuration may provide the spar cap with a substantially smooth, i.e. gradually tapering, tapered end portion which may be advantageous for transferring loads into and out of the spar cap. Additionally, in some examples such a configuration may help to ensure that tapered end sections of a plurality of pultrusion layers are respectively sandwiched between thicker portions, i.e. not tapered portions, of adjacent pultrusion layers, which may be advantageous for transferring loads into and out of the respective pultrusion layer.

[0021] In some examples, the tapered end section of each pultrusion layer in the stack, except for the respective pultrusion layers of the first and second substacks defining the upper and lower spar cap surfaces, may be sandwiched between at least one pultrusion layer of the first substack and at least one pultrusion layer of the second substack. As described previously with reference to the intermediate pultrusion layer, sandwiching a tapered end section of a pultrusion layer between other pultrusion layers advantageously results in substantially symmetrical loading for transferring loads into or out of the tapered end section of the respective pultrusion layer and into the sandwiching pultrusion layers. It follows that in some preferred examples, the spar cap may comprise a plurality of pultrusion layers each having a respective tapered end section that is sandwiched between a plurality of other pultrusion layers of the first substack and a plurality of other pultrusion layers of the second substack. Sandwiching the respective tapered end sections of pultrusion layers between as many other pultrusion layers as possible is advantageous for distributing loads in use.

[0022] In some examples, each pultrusion layer in the stack may comprise a substantially constant layer thickness throughout the middle portion of the spar cap. Such a configuration may provide substantially evenly distributed load-bearing performance along the respective pultrusion layer, minimising the risk of stress concentrations forming in a respective pultrusion layer in use. Further, such a configuration may facilitate a simple manufacturing process because it may be easier to arrange the pultrusion layers in the stack in examples where each pultrusion layer has a substantially constant layer thickness throughout the respective portion that forms the middle portion of the spar cap.

[0023] It will be appreciated that references to the layer thickness of each pultrusion layer in the stack being substantially the same throughout the middle portion of the spar cap means as constant, i.e. uniform as possible within manufacturing tolerances of the pultrusion layers.

[0024] In some examples, the layer thickness of each pultrusion layer in the stack may be substantially the same throughout the middle portion of the spar cap. Accordingly, throughout the middle portion of the spar cap, the layer thickness of every pultrusion layer may be substantially the same, in some examples. Each of the pultrusion layers being the same thickness throughout the middle portion may be advantageous for the structural performance of the spar cap. In particular, this means that each of the pultrusion layers in the stack may be a load-bearing pultrusion layer, and the load-bearing capacity of the spar cap may therefore be evenly distributed between the pultrusion layers in the middle portion of the spar cap. Sandwiching the tapered end section of the intermediate pultrusion layer between a plurality of pultrusion layers of the first substack and a plurality of pultrusion layers of the second substack which are all are substantially the same thickness in the middle portion, i.e. between two load-bearing pultrusion layers of each substack, may facilitates an advantageous transfer of loading from the intermediate pultrusion layer to the pultrusion layers of the first and second substacks in the tapered end portion of the spar cap.

[0025] In some examples, each of the pultrusion layers in the stack may comprise a maximum layer thickness located within the middle portion of the spar cap. The middle portion of the spar cap may experience the highest loading in use. Accordingly in some examples it may be advantageous to provide the maximum layer thickness of each pultrusion layer in the middle portion of the spar cap to provide the requisite stiffness in the middle portion in use. It follows that in some examples each pultrusion layer may comprise a maximum layer thickness that is substantially constant throughout the middle portion of the spar cap.

[0026] In some examples, each pultrusion layer in the first and second substacks may comprise a portion of maximum layer thickness that extends from the middle portion of the spar cap into the tapered end portion of the spar cap. Accordingly, despite the spar cap thickness tapering in the tapered end portion as a result of the tapered end section of the intermediate pultrusion layer, the pultrusion layers in the first and second substacks may each maintain a substantially constant maximum layer thickness for at least a portion of the tapered end portion of the spar cap.

[0027] It follows that in some preferred examples, the tapered end section of the intermediate pultrusion layer may be sandwiched between respective portions of maximum layer thickness of a plurality of pultrusion layers of each of the first and second substacks. Such a configuration means that the tapered end section of the intermediate pultrusion layer may experience substantially symmetrical loading, i.e. a substantially balanced stiffness ratio between the components adjacent to the tapered end section, such that loads leaving the tapered end section of the intermediate thickness layer are evenly distributed between the sandwiching pultrusion layers.

[0028] In some examples, the tapered end section of the intermediate pultrusion layer may comprise a non-uniform rate of taper. The non-uniform rate of taper may facilitate advantageous draping of the pultrusion layers sandwiching the tapered end section. The longitudinal stiffness of the sandwiching pultrusion layers can result in these layers being resistant to abrupt changes in direction, such that they may not follow sharp contours closely. By providing the tapered end section of the intermediate pultrusion layer with a non-uniform rate of taper, the tapered end section is configured to allow the relatively stiff sandwiching pultrusion layers of the first and second substacks to more closely follow the contour of the tapered end section. Advantageously this maintains a relatively compact stack in the spar cap, and helps to avoid the formation of resin rich areas during manufacture of the spar cap, or a wind turbine blade comprising the spar cap integrated therein, in areas where the sandwiching pultrusion layers may have otherwise “overshot” or not closely followed the contour of the tapered end section of the intermediate pultrusion layer.

[0029] In some examples, the intermediate pultrusion layer may comprise (i) a middle thickness band; (ii) an upper thickness band between the middle thickness band and the upper pultrusion layer surface; and (iii) a lower thickness band between the middle thickness band and the lower pultrusion layer surface. In some examples, the upper and / or lower thickness band of the intermediate pultrusion layer may have a thickness of between 5% to 25% of the layer thickness, and the middle thickness band may have a thickness of between 50% to 90% of the layer thickness. Each of these thickness bands may have a tapered end within the tapered end portion of the spar cap. Such a configuration means that the intermediate pultrusion layer is tapered throughout its whole thickness, in the tapered end section. This may be beneficial both for gradual load transfer into and out of the intermediate pultrusion layer, and for draping the sandwiching pultrusion layers adjacent to the tapered end section of the intermediate pultrusion layer.

[0030] In some examples, the tapered end of the upper thickness band may have a lower rate of taper than the tapered end of the middle thickness band. Additionally or alternatively, in some examples, the tapered end of the lower thickness band may have a lower rate of taper than the tapered end of the middle thickness band. A lower rate of taper for the tapered end of the upper and / or lower thickness band may improve draping of the sandwiching pultrusion layers because reducing the gradient in a portion where the contour of the intermediate pultrusion layer changes direction allows the sandwiching pultrusion layers to conform more closely to the contour of the intermediate pultrusion layer. In some preferred examples, the tapered end of the upper thickness band and the tapered end of the lower thickness band may both have a lower rate of taper than the tapered end of the intermediate thickness band.

[0031] In some examples, the tapered end of the upper thickness band may define a curved taper. Additionally or alternatively, in some examples the tapered end of the lower thickness band may define a curved taper. A curved taper substantially eliminates abrupt direction changes in the contour of the tapered end section of the intermediate pultrusion layer. It follows that a curved taper in the upper and / or lower thickness band of the intermediate pultrusion layer therefore advantageously helps the sandwiching pultrusion layers to conform to the contour of the intermediate pultrusion layer, thereby further reducing the possibility of resin rich areas forming between the pultrusion layers during manufacture of the spar cap, or a wind turbine blade comprising the spar cap integrated therein. In some preferred examples both the tapered end of the upper thickness band and the tapered end of the lower thickness band may define a curved taper.

[0032] In some examples wherein the tapered end of the upper and / or lower thickness band defines a curved taper, the radius of curvature of the respective tapered end may be substantially constant throughout the tapered end of the respective thickness band. Such a configuration may be relatively simple to manufacture. Alternatively, in some other examples wherein the tapered end of the upper and / or lower thickness band defines a curved taper, the radius of curvature of the respective tapered end may vary throughout said tapered end of the respective thickness band. For example, the radius of curvature of the tapered end of the respective thickness band may increase with increased distance from the middle thickness band. Accordingly, the respective upper and / or lower thickness band may have a smaller radius of curvature near to the tapered end of the middle thickness band, and a relatively larger radius of curvature near to the respective upper or lower pultrusion layer surface. The contour of the tapered end section of the intermediate pultrusion layer may therefore be steeper nearer to the middle thickness band and shallower nearer to upper and / or lower pultrusion layer surface. A shallower gradient may help to guide the sandwiching pultrusion layers to conform more closely to the tapered end section of the intermediate pultrusion layer.

[0033] In some examples, the tapered end of the middle thickness band may define a substantially linear taper. The contour of the tapered end section of the intermediate pultrusion layer may not change direction in the middle thickness band, and the sandwiching pultrusion layers may therefore still conform sufficiently well to the linear taper of the middle thickness band. Further, a substantially linear taper may be easier and faster to manufacture than a curved taper, in some examples.

[0034] In some examples, the tapered ends of the upper, lower and middle thickness bands of the intermediate pultrusion layer may together define a generally S-shaped or Z-shaped profile in the tapered end section of the intermediate pultrusion layer. A generally S-shaped or Z-shaped profile in the tapered end section may be particularly advantageous for draping the sandwiching pultrusion layers over the tapered end section of the intermediate pultrusion layer. In an example of an S-shaped profile, where the tapered ends of the upper and lower thickness bands each define a curved taper, it will be appreciated that the tapered end of the upper thickness band is preferably tapered, i.e. curved, in an opposed sense to the tapered end of the lower thickness band.

[0035] In some examples, the tapered end section of the intermediate pultrusion may extend over a longitudinal length of more than 0.3 m, preferably more than 0.4 m, and more preferably more than 0.5 m. The intermediate pultrusion layer may have a maximum layer thickness of between 1 mm and 10 mm, preferably between 2.5 mm and 7.5 mm, and more preferably between 4 mm and 6 mm, such as 5 mm in some examples. Accordingly the tapered end section may have a relatively large aspect ratio when viewed in cross-section, such that the intermediate pultrusion layer tapers in thickness over a substantial longitudinal distance with a relatively low average gradient. The tapered end portion of the spar cap may extend over a longitudinal length of more than 2.5 m, preferably more than 5 m, and more preferably more than 7.5 m. In some examples in which each of the pultrusion layers in the stack comprises a tapered end section each tapered end section of each pultrusion layer may comprise a non-uniform rate of taper. The respective tapered end sections may be configured in the same way with a non-uniform rate of taper as described previously with reference to the tapered end section of the intermediate pultrusion layer. Accordingly, it will be appreciated that the benefits described previously in relation to examples of the intermediate pultrusion layer having a tapered end section with a non-uniform rate of taper apply equally to other pultrusion layers in the stack having a non-uniform rate of taper in their respective tapered end sections.

[0036] In some examples, the layer thickness of each pultrusion layer may be the same except for the respective tapered end section of each respective pultrusion layer. Such a configuration may be particularly simple and cost effective to manufacture because each of the pultrusion layers can be formed of pultrusions from the same stock material and / or manufactured using the same pultrusion apparatus.

[0037] In some examples each pultrusion layer may comprise a single pultrusion. For example, the entire length of each pultrusion layer may be formed of a respective single pultrusion. This may be advantageous for the structural performance of the spar cap because such a configuration eliminates the risk of stress concentrations forming at a join between pultrusions in a pultrusion layer. In this configuration the loads are taken up and transferred along the entire length of the respective pultrusion layer by a single pultrusion. It should be understood that the spar cap may comprise a plurality of stacks arranged side by side. Accordingly, it should be understood that in examples where each pultrusion layer in a stack comprises a single pultrusion, the spar cap may comprise a plurality of pultrusions arranged side by side in adjacent stacks, which each respectively form a pultrusion layer of the respective stack.

[0038] In some examples the spar cap may comprise a layer of fibrous reinforcing material and / or polymer resin between each of the pultrusion layers in the stack. For example, the inclusion of one or more layers of fibrous reinforcing material arranged between each of the pultrusion layers in the stack may aid resin infusion between the pultrusion layers during manufacture of the spar cap, or a wind turbine blade comprising the spar cap, when integrating or bonding the pultrusion layers together. As such, this may minimise the risk of defects such as dry spots forming between the pultrusion layers, thereby increasing the longevity and load bearing capacity of the spar cap. In some examples, the tapered end portion of the spar cap may define an outboard end of the spar cap. Accordingly, the spar cap thickness may decrease towards an outboard end of the spar cap. In some examples, the spar cap may comprise a tapered end portion as described herein defining an inboard end of the spar cap. For example, the spar cap thickness may decrease towards an inboard end of the spar cap. It follows that the configuration of pultrusion layers in the tapered end portion of the spar cap may be applicable to either the outboard end or the inboard end of the spar cap, or both, in some examples.

[0039] In some examples, the outboard end of the spar cap may be defined by a tapered end portion as described herein, and an inboard end of the spar cap may be defined by an inboard chamfered portion. The spar cap thickness may decrease towards an inboard end of the spar cap defined by the inboard chamfered portion in such an example. The pultrusion layers may extend successively further into the chamfered inboard portion, going from the pultrusion layer that defines one of the upper spar cap surface or the lower spar cap surface to the pultrusion layer that defines the other of the upper spar cap surface or the lower spar cap surface. Such a configuration may be easier and faster to assemble when manufacturing the spar cap or a blade comprising the spar cap.

[0040] In another aspect of the present invention there is provided a wind turbine blade comprising a spar cap according to any of the examples described herein.

[0041] Brief description of the drawings

[0042] Examples of the present invention will now be described by way of non-limiting example only, with reference to the accompanying figures, in which:

[0043] Figure 1 is a schematic exploded view of a wind turbine blade comprising a spar cap;

[0044] Figure 2 is a schematic side view of the spar cap showing a plurality of pultrusion layers arranged in a stack;

[0045] Figure 3 is an enlarged view of a tapered end portion of the spar cap;

[0046] Figure 4 is a schematic exploded view of the spar cap showing the pultrusion layers of the stack; and

[0047] Figure 5 is a schematic side view of an example of an intermediate pultrusion layer of the spar cap. Detailed description

[0048] Figure 1 shows a schematic exploded view of an example of a wind turbine blade 10. The blade 10 may comprise a first half shell 12a and a second half shell 12b which each extend in a spanwise direction (S) from an inboard end 14 of the blade 10 to an outboard end 16. The first and second half shells 12a, 12b may be joined together to form a blade shell 18 which defines an aerodynamic contour and is configured to capture energy from wind incident on the blade 10 in use.

[0049] The blade shell 18 may be supported by a longitudinally-extending spar structure. For example, the spar structure may include a shear web 20 arranged between longitudinally- extending spar caps 22 configured to take up bending loads experienced by the blade 10 in use. Whilst the example of a wind turbine blade 10 shown in Figure 1 comprises a single spar structure, it should be appreciated that in some examples the blade 10 may comprise a plurality of spar structures. Similarly, whilst the example shown in Figures 1 comprise a single spar cap 22 associated with each half shell 12a, 12b, in some other examples the blade 10 may comprise a plurality of spar caps 22 associated with each half shell 12a, 12b. In some examples each spar cap 22 may be embedded within a respective half shell 12a, 12b, for example by integrating the spar cap 22 with a plurality of laminate layers during manufacture of the half shell 12a, 12b. In some other examples, the spar caps 22 may be bonded to an interior surface of the respective half shell 12a, 12b.

[0050] Each spar cap 22 is configured to provide structural support to the blade shell 18 along its length. A spar cap thickness T defined between an upper spar cap surface 24 and a lower spar cap surface 26 (shown more clearly in Figure 2) of each spar cap 22 therefore varies along the length of the respective spar cap 22 in accordance with the stiffness requirements throughout different portions of the blade 10. The spar caps 22 each include a middle portion 28 throughout which the spar cap thickness T is substantially constant, and a tapered end portion 30 in which the spar cap thickness T decreases towards an end 32 of the spar cap 22. In the example shown in Figure 1 , the end 32 of the spar cap 22 is an outboard end of the spar cap 22. The spar cap 22, and in particular the tapered end portion 30 of the spar cap 22, will now be described in more detail with reference to the remaining figures.

[0051] Referring initially to Figure 2, which shows a schematic side view of a spar cap 22, the spar cap 22 comprises a plurality of pultrusion layers 34, i.e. layers of pultrusions, arranged in a stack 36. Pultrusions are longitudinally-extending strips or rods formed of a fibre reinforced composite material. For example, the pultrusions may be formed of carbon fibre reinforced plastic (CFRP) in some examples. As shown in Figure 2, in some examples each pultrusion layer 34 in the stack 36 may comprise a single pultrusion forming the full length of the respective pultrusion layer 34.

[0052] The individual pultrusion layers 34 are shown more clearly in the enlarged view of Figure 3 and the schematic exploded view of Figure 4. Referring therefore additionally to Figures 3 and 4, each pultrusion layer 34 has an upper pultrusion layer surface 38 and a lower pultrusion layer surface 40. It follows that a layer thickness t of each pultrusion layer 34 is defined between the respective upper and lower pultrusion layer surfaces 38, 40.

[0053] In some examples, the layer thickness t of each pultrusion layer 34 in the stack 36 may be substantially the same throughout the middle portion 28 of the spar cap 22. For example, the layer thickness t of each pultrusion layer 34 may be substantially constant, i.e. uniform, and the same as the layer thickness t of each other pultrusion layer 34, throughout the middle portion 28 of the spar cap 22. The middle portion 28 may therefore be configured as the main load-bearing portion of the spar cap 22. It follows that in some examples, each of the pultrusion layers 34 in the stack 36 may therefore comprise a maximum layer thickness t located within the middle portion 28 of the spar cap 22.

[0054] Referring to each of Figures 2, 3 and 4, the pultrusion layers 34 in the stack 36 may be grouped into a first substack 42 comprising a plurality of pultrusion layers 34 and a second substack 44 comprising a plurality of pultrusion layers 34. The stack 36 further comprises an intermediate pultrusion layer 34i sandwiched between the first and second substacks 42, 44.

[0055] The layer thickness t of the intermediate pultrusion layer 34i decreases towards the end 32 of the spar cap 22 to form a tapered end section 46 of the intermediate pultrusion layer 34i which is located in the tapered end portion 30 of the spar cap 22. Accordingly, the tapered end section 46 of the intermediate pultrusion layer 34i may contribute to forming the tapered end portion 30 of the spar cap 22, in some examples.

[0056] In the tapered end portion 30 of the spar cap 22, the tapered end section 46 of the intermediate pultrusion layer 34i is sandwiched between a plurality of pultrusion layers 34 of the first substack 42 and a plurality of pultrusion layers 34 of the second substack 44. This means that loads taken up by the intermediate pultrusion layer 34i in use can be gradually transferred from the tapered end section 46 to the sandwiching pultrusion layers 34 of the first and second substacks 42, 44. Sandwiching the tapered end section 46 of the intermediate pultrusion layer 34i between the first and second substacks 42, 44 advantageously facilitate substantially symmetrical loading at the tapered end section 46 of the intermediate layer 34i in use. Accordingly, when loads are transferred out of the tapered end section 46 of the intermediate pultrusion layer 34i, these loads are shared substantially evenly between the sandwiching pultrusion layers 34 of the first and second substacks 42, 44.

[0057] As shown most clearly in Figures 3 and 4, each pultrusion layer 34 in each of the first and second substacks 42, 44 may extend further into the tapered end portion 30 of the spar cap 22 from the middle portion 28 of the spar cap 22, than the intermediate pultrusion layer 34i. For example, with reference to the first substack 42, each of the pultrusion layers 34 may extend successively further into the tapered end portion 30 of the spar cap 22 with increased distance from the intermediate pultrusion layer 34i. As shown in Figure 4, the second substack 44 may also be configured such that each successive pultrusion layer 34 extends further into the tapered end portion 30 with increased distance from the intermediate pultrusion layer 34i.

[0058] In some preferred examples, the stack 36 may be arranged such that the next-furthest extending pultrusion layer 34 is located in a different substack 42, 44 to the previous- furthest extending pultrusion layer 34. With reference to Figure 4 for example, going from the tapered end section 46 of the intermediate pultrusion layer 34i to the end 32 of the spar cap 22, the respective pultrusion layer 34 that extends successively further into the tapered end portion 30 alternates between the first and second substacks 42, 44. From the intermediate pultrusion layer 34i, the next-furthest extending pultrusion layer 34 is in the first substack 42, thereafter the next-furthest extending pultrusion layer 34 is in the second substack 44, and thereafter the next-furthest extending pultrusion layer 34 is in the first substack 42, and so on until the end 32 of the spar cap 22. In such a configuration the lesser-extending pultrusion layers 34 are located nearer to the middle of the stack 36 and are sandwiched between as many other pultrusion layers 34 as possible. Such a configuration may therefore provide particularly beneficial additional advantages for the spar cap in terms of transferring loads into and out of each of the pultrusion layers 34 in use.

[0059] Referring still to Figures 2 to 4, in some examples each of the pultrusion layers 34 in the first and second substacks 42, 44 may comprise a portion of maximum layer thickness t that extends from the middle portion 28 of the spar cap 22 into the tapered end portion 30. Accordingly, as shown most clearly in Figure 3, the tapered end section 46 of the intermediate pultrusion layer 34i may be sandwiched between respective portions of maximum layer thickness t of a plurality of pultrusion layers 34 of each of the first and second substacks 42, 44.

[0060] To provide the requisite stiffness to the blade 10 in use, the pultrusion layers 34 may each have a significant longitudinal stiffness, which may result from the pultrusion layers 34 comprising a high percentage of longitudinally-extending fibres (not shown). However, in some examples the stiffness of the pultrusion layers 34 may make said pultrusion layers 34 somewhat resistant to bending. In some examples the pultrusion layers 34 of the first and / or second substacks 42, 44 may therefore be somewhat resistant to conforming to the contour of the tapered end section 46 of the intermediate pultrusion layer 34i. This is particularly applicable to examples where the tapered end section 46 is sandwiched between portions of maximum layer thickness t of the pultrusion layers 34 of the first and second substacks 42, 44.

[0061] As shown in the enlarged view of Figure 5, the tapered end section 46 of the intermediate pultrusion layer 34i may therefore comprise a non-uniform rate of taper, in some examples. The tapered end section 46 may be shaped to allow the relatively stiff sandwiching pultrusions 34 of the first and second substacks 42, 44 to better conform to the contour of the intermediate pultrusion layer 34i.

[0062] The intermediate pultrusion layer 34i may comprise a middle thickness band 48a, an upper thickness band 48b between the middle thickness band 48a and the upper pultrusion layer surface 38, and a lower thickness band 48c between the middle thickness band 48a and the lower pultrusion layer surface 40. In some preferred examples, each of the thickness bands 48a, 48b, 48c may have a respective tapered end 50a, 50b, 50c within the tapered end portion 30 of the spar cap 22.

[0063] The non-uniform rate of taper of the tapered end section 46 of the intermediate pultrusion layer 34i may result from the tapered end 50b of the upper thickness band 48b and the tapered end 50c of the lower thickness band 48c having a lower rate of taper than the tapered end 50a of the middle thickness band 48a. The lower rate of taper may help to guide the sandwiching pultrusion layers 34 into changing direction around the tapered end section 46 of the intermediate pultrusion layer 34i. In some examples, as shown in Figure 5, the tapered ends 50b, 50c of the upper and lower thickness bands 48b, 48c may each define a curved taper. Accordingly, the tapered ends 50a, 50b, 50c of the middle, upper, and lower thickness bands 48a, 48b, 48c may together define a generally S-shaped profile in the tapered end section 46 of the intermediate pultrusion layer 34i, in some examples.

[0064] Finally, referring back to Figure 4, in some examples each pultrusion layer 34 in the stack 36 may have a tapered end section 46 located in the tapered end portion 30 of the spar cap 22. Except for the respective tapered end section 46 of each pultrusion layer 34, the layer thickness t of each pultrusion layer 34 may be the same. The layer thickness t of each pultrusion layer 34 may decrease towards the end 32 of the spar cap 22 to form the respective tapered end section 46. It should be understood that the tapered end section 46 of each pultrusion layer 34 in the first and second substacks 42, 44 may be configured in substantially the same way as the tapered end section 46 of the intermediate pultrusion layer 34i described previously, and additional description of examples of configurations of the respective tapered end sections 46 will not be repeated here for conciseness.

[0065] In some examples where each pultrusion layer 34 comprises a respective tapered end section 46, the tapered end section 46 of each pultrusion layer 34, except for the respective pultrusion layers 34 defining the upper and lower spar cap surfaces 24, 26, may be sandwiched between at least one pultrusion layer 34 of the first substack 42 and at least one pultrusion layer 34 of the second substack 44. As described previously with reference to the intermediate pultrusion layer 34i, sandwiching a tapered end section 46 of a pultrusion layer 34 between other pultrusion layers 34 advantageously results in substantially symmetrical loading when transferring loads into or out of the tapered end section 46 of the respective pultrusion layer 34 and into the sandwiching pultrusion layers 34 of the first and second substacks 42, 44.

[0066] Many modifications may be made to the examples described above without departing from the scope of the present invention as defined in the accompanying claims. For example, the tapered end portion 30 of the spar cap 22 has been described herein with reference to examples in which the tapered end portion 30 defines an outboard end 32 of the spar cap 22. However, it should also be understood that in some other examples, an inboard end of the spar cap 22 may be defined by a tapered end portion 30 as described herein.

[0067] Finally, it will be appreciated that features described in relation to each of the examples above may be readily combined with features described with reference to other examples without departing from the scope of the invention as defined by the following claims.

Claims

CLAIMS:1 . A wind turbine blade spar cap having an upper spar cap surface, a lower spar cap surface, a spar cap thickness defined between the upper and lower spar cap surfaces, a middle portion throughout which the spar cap thickness is substantially constant, and a tapered end portion in which the spar cap thickness decreases towards an end of the spar cap; wherein the spar cap comprises a plurality of pultrusion layers arranged in a stack, each pultrusion layer having an upper pultrusion layer surface, a lower pultrusion layer surface, and a layer thickness defined between the respective upper and lower pultrusion layer surfaces; wherein the stack comprises a first substack comprising a plurality of pultrusion layers and a second substack comprising a plurality of pultrusion layers; wherein the stack further comprises an intermediate pultrusion layer comprising a tapered end section in which the layer thickness of the intermediate pultrusion layer decreases towards the end of the spar cap, the tapered end section being located in the tapered end portion of the spar cap; wherein the intermediate pultrusion layer is sandwiched between the first and second substacks such that, in the tapered end portion of the spar cap, the tapered end section of the intermediate pultrusion layer is sandwiched between a plurality of pultrusion layers of the first substack and a plurality of pultrusion layers of the second substack.

2. The spar cap of Claim 1 , wherein each pultrusion layer in each of the first and second substacks extends further into the tapered end portion of the spar cap than the intermediate pultrusion layer.

3. The spar cap of Claim 1 or Claim 2, wherein for each of the first and second substacks, the pultrusion layers extend successively further into the tapered end portion of the spar cap with increased distance from the intermediate pultrusion layer.

4. The spar cap of Claim 3, wherein, going from the tapered end section of the intermediate pultrusion layer to the end of the spar cap, the respective pultrusion layer that extends successively further into the tapered end portion alternates between the first and second substacks.

5. The spar cap of any preceding claim, wherein each pultrusion layer comprises a tapered end section in which the layer thickness decreases towards the end of the spar cap, the tapered end section of each pultrusion layer being located in the tapered end portion of the spar cap.

6. The spar cap of Claim 5, wherein, except for the pultrusion layers of the first and second substacks defining the upper and lower spar cap surfaces, the tapered end section of each pultrusion layer in the stack is sandwiched between at least one pultrusion layer of the first substack and at least one pultrusion layer of the second substack.

7. The spar cap of any preceding claim, wherein each pultrusion layer in the stack comprises a substantially constant layer thickness throughout the middle portion of the spar cap.

8. The spar cap of any preceding claim, wherein, the layer thickness of each pultrusion layer in the stack is substantially the same throughout the middle portion of the spar cap.

9. The spar cap of any preceding claim, wherein each of the pultrusion layers in the stack comprises a maximum layer thickness located within the middle portion of the spar cap.

10. The spar cap of Claim 9, wherein each pultrusion layer in the first and second substacks comprises a portion of maximum layer thickness that extends from the middle portion of the spar cap into the tapered end portion of the spar cap.

11. The spar cap of Claim 10, wherein the tapered end section of the intermediate pultrusion layer is sandwiched between respective portions of maximum layer thickness of a plurality of pultrusion layers of each of the first and second substacks.

12. The spar cap of any preceding claim, wherein the tapered end section of the intermediate pultrusion layer comprises a non-uniform rate of taper.

13. The spar cap of Claim 12, wherein the intermediate pultrusion layer comprises (i) a middle thickness band; (ii) an upper thickness band between the middle thickness band and the upper pultrusion layer surface; and (iii) a lower thickness band between the middlethickness band and the lower pultrusion layer surface, each of the thickness bands having a tapered end within the tapered end portion of the spar cap.

14. The spar cap of Claim 13, wherein the tapered end of the upper thickness band and / or the tapered end of the lower thickness band has a lower rate of taper than the tapered end of the middle thickness band.

15. The spar cap of Claim 13 or Claim 14 wherein the tapered end of the upper thickness band and / or the tapered end of the lower thickness band defines a curved taper.

16. A wind turbine blade comprising the spar cap of any preceding claim.

Images