Patent Description:
Wind turbine blades are often manufactured according to one of two constructional designs, namely a design where a thin aerodynamic shell is glued onto a spar beam, or a design where spar caps, also called main laminates, are integrated into the aerodynamic shell.

In the first design, the spar beam constitutes the load-bearing structure of the blade. The spar beam as well as the aerodynamic shell or shell parts are manufactured separately. The aerodynamic shell is often manufactured as two shell parts, typically as a pressure side shell part and a suction side shell part. The two shell parts are glued or otherwise connected to the spar beam and are further glued to each other along a leading edge and a trailing edge of the shell parts. This design has the advantage that the critical load-carrying structure may be manufactured separately and therefore easier to control. Further, this design allows for various different manufacturing methods for producing the beam, such as moulding and filament winding.

In the second design, the spar caps or main laminates are integrated into the shell and are moulded together with the aerodynamic shell. The main laminates typically comprise a high number of fibre layers compared to the remainder of the blade and may form a local thickening of the wind turbine shell, at least with respect to the number of fibre layers. Thus, the main laminate may form a fibre insertion in the blade. In this design, the main laminates constitute the load-carrying structure. The blade shells are typically designed with a first main laminate integrated in the pressure side shell part and a second main laminate integrated in the suction side shell part. The first main laminate and the second main laminate are typically connected via one or more shear webs, which for instance may be C-shaped or I-shaped. For very long blades, the blade shells further along at least a part of the longitudinal extent comprise an additional first main laminate in the pressure side shell, and an additional second main laminate in the suction side shell. These additional main laminates may also be connected via one or more shear webs. This design has the advantage that it is easier to control the aerodynamic shape of the blade via the moulding of the blade shell part.

Vacuum infusion or VARTM (vacuum assisted resin transfer moulding) is one method, which is typically employed for manufacturing composite structures, such as wind turbine blades comprising a fibre-reinforced matrix material.

During the process of filling the mould, a vacuum, said vacuum in this connection being understood as an under-pressure or negative pressure, is generated via vacuum outlets in the mould cavity, whereby liquid polymer is drawn into the mould cavity via the inlet channels in order to fill said mould cavity. From the inlet channels, the polymer disperses in all directions in the mould cavity due to the negative pressure and inter alia towards the vacuum channels. Thus, it is important to position the inlet channels and vacuum channels optimally in order to obtain a complete filling of the mould cavity. Ensuring a complete distribution of the polymer in the entire mould cavity is, however, often difficult, and accordingly this often results in so-called dry spots, i.e. areas with fibre material not being sufficiently impregnated with resin. Thus, dry spots are areas where the fibre material is not impregnated, and where there can be air pockets, which are difficult or impossible to remove by controlling the vacuum pressure and a possible overpressure at the inlet side. In vacuum infusion techniques, employing a rigid mould part and a resilient mould part in the form of a vacuum bag, the dry spots can be repaired after the process of filling the mould by puncturing the bag in the respective location and by drawing out air for example by means of a syringe needle. Liquid polymer can optionally be injected in the respective location, and this can for example be done by means of a syringe needle as well. This is a time-consuming and tiresome process. In the case of large mould parts, staff have to stand on the vacuum bag. This is not desirable, especially not when the polymer has not hardened, as it can result in deformations in the inserted fibre material and thus in a local weakening of the structure, which can cause for instance buckling effects.

In most cases, the polymer or resin applied is polyester, vinyl ester or epoxy, but may also be PUR or pDCPD, and the fibre reinforcement is most often based on glass fibres or carbon fibres or even hybrids thereof. Epoxies have advantages with respect to various properties, such as shrinkage during curing (which in some circumstances may lead to less wrinkles in the laminate), electrical properties and mechanical and fatigue strengths. Polyester and vinyl esters have the advantage that they provide better bonding properties to gelcoats. Thereby, a gelcoat may be applied to the outer surface of the shell during the manufacturing of the shell by applying a gelcoat to the mould before fibre reinforcement material is arranged in the mould. Thus, various post-moulding operations, such as painting the blade, may be avoided. Further, polyesters and vinyl esters are cheaper than epoxies and further do not require external equipment to cure the resin. Consequently, the manufacturing process may be simplified, and costs may be lowered.

Often the composite structures comprise a core material covered with a fibre-reinforced material, such as one or more fibre-reinforced polymer layers. The core material can be used as a spacer between such layers to form a sandwich structure and is typically made of a rigid, lightweight material in order to reduce the weight of the composite structure. In order to ensure an efficient distribution of the liquid resin during the impregnation process, the core material may be provided with a resin distribution network, for instance by providing channels or grooves in the surface of the core material.

Resin transfer moulding (RTM) is a manufacturing method, which is similar to VARTM. In RTM, the liquid resin is not drawn into the mould cavity due to a vacuum generated in the mould cavity. Instead, the liquid resin is forced into the mould cavity via an overpressure at the inlet side.

Prepreg moulding is a method in which reinforcement fibres are pre-impregnated with a precatalysed resin. The resin is typically solid or near-solid at room temperature. The prepregs are arranged by hand or machine onto a mould surface, vacuum bagged and then heated to a temperature, where the resin is allowed to reflow and eventually cured. This method has the main advantage that the resin content in the fibre material is accurately set beforehand. The prepregs are easy and clean to work with and make automation and labour saving feasible. The disadvantage with prepregs is that the material cost is higher than for non-impregnated fibres. Further, the core material needs to be made of a material which is able to withstand the process temperatures needed for bringing the resin to reflow. Prepreg moulding may be used both in connection with an RTM and a VARTM process.

Further, it is possible to manufacture hollow mouldings in one piece by use of outer mould parts and a mould core. Such a method is for instance described in <CIT> and may readily be combined with RTM, VARTM and prepreg moulding.

As, for instance, blades for wind turbines have become longer and larger in the course of time and may now be more than <NUM> meters long, the impregnation time in connection with manufacturing such blades has increased, because more fibre material has to be impregnated with polymer. Furthermore, the infusion process has become more complicated, as the impregnation of large shell members, such as blades, requires control of the flow fronts to avoid dry spots, said control may e.g. include a time-related control of inlet channels and vacuum channels. This increases the time required for drawing in or injecting polymer. As a result, the polymer has to stay liquid for a longer time, normally also resulting in an increase in the curing time.

As described above in relation to the second design, the spar caps or main laminates comprise a high number of fibre layers compared to the remainder of the blade and may form a local thickening of the wind turbine shell, at least with respect to the number of fibre layers. This typically results in a tapering of the shell thickness from the spar cap region to the adjacent parts of the shell, where the number of layers is lower.

Tapering of the thickness of fibre-reinforced components is known to be challenging. Tapering involves ply drop, where one or more plies are terminated (dropped) in order to reduce the number of layers and accordingly the thickness. Ply drop is known to be a cause of delamination of the layers. This has been mitigated by applying a cover layer that covers the terminated plies. However, the process is tedious. Dropping layers requires arranging the individual layers with even higher precision, typically manually, since the termination of the ply to be dropped must take place with consistency and precision. Ply drops leave air pockets between the cover layers and the terminated layers. The higher the positioning of the ply terminations, the smaller the air pockets.

<CIT> is a relevant example of prior art in this field.

It is an object of the present invention to mitigate one or more of the issues described above concerning tapered wind turbine components such as spar caps for wind turbine blade shells.

In a first aspect, the invention provides a fibre reinforcement fabric for a wind turbine component, the fabric comprising a first plurality of fibre bundles arranged in parallel in a warp direction and stitched together, the fabric having a first outermost fibre bundle defining a first fabric edge parallel to the warp direction and a second outermost fibre bundle defining a second fabric edge opposite the first fabric edge, the fabric having a first tapered portion including the first outermost fibre bundle, wherein a thickness of the fabric in the first tapered portion is tapering from a first fabric thickness to a second fabric thickness in a direction towards the first fabric edge.

Such a fabric mitigates some of the issues related to ply-drop in a tapered fibre-reinforced composite component. As described in more detail in relation to the drawings below, ply drop inevitably leads to weaknesses due to lack of reinforcing fibre material. Accordingly, a fabric or mat is provided that is configured with an inherent tapering towards the sides/edges of the fabric (such as a "mat"). The tapering is provided by the configuration of the fibre bundles and/or the arrangement of fibre bundles changing towards the first fabric edge so as to provide the tapering to a smaller thickness (the second thickness) towards the first fabric edge.

The first plurality of fibre bundles consists of dry fibres. That is, the fibre bundles have not been impregnated with a resin. As a result, the tapered fabric is still pliable both in the warp direction and in the direction from the first fabric edge to the second fabric edge, similar to a textile fabric. This allows personnel to easily drape the fabric in the desired shape, flat or curved. The use of dry fibres also allows the fibre bundles to be easily stitched together, as the stitching needle can easily penetrate either through individual fibre bundles or between adjacent fibre bundles. This also means that the stitches can be provided in the exact pattern desired. Thus, in some embodiments, the first plurality of fibre bundles is stitched together at least via stitches going through one or more individual fibre bundles in the first plurality of fibre bundles.

The weight of the fabric is also lower compared to a combination of fabric and resin, which is another advantage both for transport purposes and for laying up fibre material.

Furthermore, dry fibre bundles can change shape when subjected to pressure, for instance during resin infusion, which results in a stronger composite.

In some embodiments, the first plurality of fibre bundles is stitched together with one or more fibre bundles impregnated with resin. In some cases, this can reduce the risk of dry spots remaining even after resin infusion. Such embodiments are particularly useful for wind turbine components in which part of the component is flat and a neighbouring part needs the drapability provided by the first plurality of fibre bundles.

In some embodiments, the first plurality of fibre bundles comprises a second plurality of fibre bundles arranged in a first layer and a third plurality of fibre bundles arranged in a second layer on the first layer, wherein the second layer is terminated before the first fabric edge. Stitching together multiple layers in a single fabric but terminating one of the layers before terminating the other layer (which then defines the edge of the fabric) provides a robust fabric that is easier to manage. Layer termination is currently done manually, which means arranging a known fabric to terminate at the desired point. This is prone to imprecision, and it is time consuming to arrange the terminating layer precisely to meet tolerances.

In some embodiments, the first tapered portion comprises one or more fibre bundles having a first cross-sectional area and one or more fibre bundles having a second cross-sectional area smaller than the first cross-sectional area, arranged such as to provide the tapering of the thickness in the first tapered portion. Using fibre bundles with different cross-sectional areas can further mitigate the issues discussed above, as it provides the possibility to taper the thickness of the fabric more gradually. A ratio between the second cross-sectional area and the first cross-sectional area is preferably at most <NUM> %, such as at most <NUM> %, such as at most <NUM> %, such as in the range <NUM> % to <NUM> %, such as in the range <NUM> % to <NUM> %. In some embodiments, the tapered portion comprises at least two bundles for which the ratio is <NUM> %, such as a fibre bundle with <NUM> tex and a fibre bundle with <NUM> tex. Other values can be chosen that give the same ratio. In some embodiments, the tapered portion comprises at least two bundles for which the ratio is <NUM> %, such as a fibre bundle with <NUM> tex and a fibre bundle with <NUM> tex.

In some embodiments, the tapered portion comprises at least a fibre bundle with <NUM> tex, a fibre bundle with <NUM> tex and a fibre bundle with <NUM> tex.

In some embodiments, the tapering is provided by a combination of terminating a layer and providing one or more fibre bundles having a first cross-sectional area and one or more fibre bundles having a second cross-sectional area smaller than the first cross-sectional area. This provides further granularity in tapering the thickness of a fabric.

In some embodiments, the fabric has a second tapered portion including the second outermost fibre bundle, and a thickness of the fabric in the second tapered portion is tapering from a third fabric thickness to a fourth fabric thickness in a direction towards the second fabric edge. In some embodiments, the fourth fabric thickness is equal to the second fabric thickness. In other words, the edges of the fabric have the same thickness. In some embodiments, the tapering in the second tapered portion towards the second fabric edge is identical to the tapering in the first tapered section towards the first fabric edge. This is typically used to provide a symmetric shape, although in some embodiments the tapering at the two edges is similar only near the edges. Such fabrics can provide a more advanced tapering. However, in some embodiments, the fabric has a reflectional symmetry seen in a direction along the warp direction. Thus, the thickness behaves identically towards the two edges from a central point in a weft direction. In some embodiments, a thickness across the fabric in the weft direction is uniform and has a constant thickness across at least <NUM> %, such as across at least <NUM> % of a width of the fabric, the width being the distance between the first fabric edge and the second fabric edge. In some embodiments, the tapering towards one or both edges occurs over a weft-wise distance of at least <NUM>, such as in the range <NUM>-<NUM>, such as in the range <NUM>-<NUM>. This depends in part on the fibre bundle size, but such tapering distance can significantly mitigate ply drop issues. In some embodiments, the tapering occurs over a distance of at least <NUM>, such as at least <NUM>. In some embodiments, the width is in the range <NUM>-<NUM>, such as in the range <NUM>-<NUM>, such as in the range <NUM>-<NUM>.

In some embodiments, the fabric comprises three or more layers. A fabric with three layers simplifies the layup process significantly.

In some embodiments, the fabric has a rotational symmetry seen in a direction along the warp direction.

In some embodiments, the first plurality of fibre bundles comprises a plurality of glass fibre rovings, i.e. bundles of glass filaments.

In some embodiments, the first plurality of fibre bundles consists of a plurality of glass fibre rovings, i.e. bundles of glass filaments.

In some embodiments, the first plurality of fibre bundles comprises carbon fibre tows, i.e. bundles of carbon filaments.

In some embodiments, the first plurality of fibre bundles consists of carbon fibre tows, i.e. bundles of carbon filaments.

Glass fibre bundles and carbon fibre tows can also be included in the same fabric.

In some embodiments, some or all of the first plurality of fibre bundles have a tex value in the range <NUM>-<NUM>, such as in the range <NUM>-<NUM>, such as in the range <NUM>-<NUM>.

A second aspect of the invention provides a spar cap for a wind turbine blade. The spar cap comprises one or more fibre fabrics. For instance, the spar cap comprises a plurality of fibre layers including at least one fabric in accordance with an embodiment of the first aspect of the invention.

A third aspect of the invention provides a wind turbine blade comprising one or more fibre fabrics in accordance with an embodiment of the first aspect of the invention. In some embodiments, the wind turbine blade comprises a spar cap in accordance with an embodiment of the second aspect of the invention.

A fourth aspect of the invention provides a method of laying up fibre material in a mould for manufacturing a wind turbine blade shell part. The method comprises:.

In some embodiments, the method further comprises arranging a vacuum bag on the mould and evacuating air from the laid up material, and infusing resin in between individual fibres in one or more of the first plurality of fibre bundles, such as in every fibre bundle of the first plurality of fibre bundles, and curing the resin. The fabric that was pliable before infusion now forms part of a highstrength fibre-reinforced composite component.

In some embodiments, an ambient temperature at the mould during laying up of the first plurality of fibre layers and/or a maximum temperature of the layup surface of the mould during laying up of the first plurality of fibre layers do not exceed <NUM> degrees Celsius.

In some embodiments, the maximum temperature of the layup surface of the mould during laying up of the first plurality of fibre layers does not exceed <NUM> degrees Celsius independent of the ambient temperature at the mould.

This prevents premanufactured fibre-reinforced composite parts or fabrics impregnated with resin from expanding or contracting or shifting significantly in the mould relative to dry fibre before resin infusion. A stronger fibre-reinforced wind turbine blade shell part is thereby obtained.

The invention is explained in detail below with reference to the embodiments shown in the drawings.

Embodiments of the invention will be described in more detail in the following with reference to the accompanying drawings. Like reference numerals may refer to like elements throughout. The drawings show selected ways of implementing the present invention and are not to be construed as being limiting.

<FIG> illustrates a conventional modern upwind wind turbine <NUM> according to the so-called "Danish concept" with a tower <NUM>, a nacelle <NUM> and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub <NUM> and three blades <NUM> extending radially from the hub <NUM>, each having a blade root <NUM> nearest the hub and a blade tip <NUM> farthest from the hub <NUM>.

<FIG> shows a schematic view of a wind turbine blade <NUM>. The wind turbine blade <NUM> has the shape of a conventional wind turbine blade and comprises a root region <NUM> closest to the hub, a profiled or an airfoil region <NUM> farthest away from the hub and a transition region <NUM> between the root region <NUM> and the airfoil region <NUM>. The outermost point of the blade <NUM> is the tip end <NUM>, opposite the root end <NUM> that attaches to the wind turbine hub <NUM>.

The airfoil region <NUM> (also called the profiled region) of the wind turbine has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region <NUM> due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade <NUM> to the hub. The diameter (or the chord) of the root region <NUM> may be constant along the entire root region <NUM>. The width of the chord decreases with increasing distance from the hub.

A shoulder <NUM> of the blade <NUM> is defined as the position where the blade <NUM> has its largest chord length. <FIG> also illustrates the longitudinal extent LB and also represents the longitudinal axis of the blade.

The blade is typically made from a pressure side shell part <NUM> and a suction side shell part <NUM> that are glued to each other along bond lines at the leading edge <NUM> and the trailing edge <NUM> of the blade <NUM>.

<FIG> shows a schematic view of a cross-section of the blade along the line I-I shown in <FIG>. As previously mentioned, the blade <NUM> comprises a pressure side shell part <NUM> and a suction side shell part <NUM>. The pressure side shell part <NUM> comprises a spar cap <NUM>, also called a main laminate, which constitutes a load-bearing part of the pressure side shell part <NUM>. The spar cap <NUM> comprises a plurality of fibre layers <NUM> mainly comprising unidirectional fibres aligned along the longitudinal direction of the blade in order to provide stiffness to the blade. The suction side shell part <NUM> also comprises a spar cap <NUM> comprising a plurality of fibre layers <NUM>. The pressure side shell part <NUM> may also comprise a sandwich core material <NUM> typically made of balsawood or foamed polymer and sandwiched between a number of fibre-reinforced skin layers. The sandwich core material <NUM> is used to provide stiffness to the shell in order to ensure that the shell substantially maintains its aerodynamic profile during rotation of the blade. Similarly, the suction side shell part <NUM> may also comprise a sandwich core material <NUM>.

The spar cap <NUM> of the pressure side shell part <NUM> and the spar cap <NUM> of the suction side shell part <NUM> are connected via a first shear web <NUM> and a second shear web <NUM>. The shear webs <NUM>, <NUM> are in the shown embodiment shaped as substantially I-shaped webs. The first shear web <NUM> comprises a shear web body and two web foot flanges. The shear web body comprises a sandwich core material <NUM>, such as balsawood or foamed polymer, covered by a number of skin layers <NUM> made of a number of fibre layers. The second shear web <NUM> has a similar design with a shear web body and two web foot flanges, the shear web body comprising a sandwich core material <NUM> covered by a number of skin layers <NUM> made of a number of fibre layers. The sandwich core material <NUM>, <NUM> of the two shear webs <NUM>, <NUM> may be chamfered near the flanges in order to transfer loads from the webs <NUM>, <NUM> to the main laminates <NUM>, <NUM> without the risk of failure and fractures in the joints between the shear web body and web foot flange. However, such a design will normally lead to resin rich areas in the joint areas between the legs and the flanges. Further, such resin rich area may comprise burned resin due to high exothermic peeks during the curing process of the resin, which in turn may lead to mechanical weak points.

In order to compensate for this, a number of filler ropes <NUM> comprising glass fibres may be arranged at these joint areas. Further, such ropes <NUM> will also facilitate transferring loads from the skin layers of the shear web body to the flanges. However, according to the invention, alternative constructional designs are possible.

The blade shells <NUM>, <NUM> may comprise further fibre reinforcement at the leading edge and the trailing edge. Typically, the shell parts <NUM>, <NUM> are bonded to each other via glue flanges in which additional filler ropes may be used (not shown). Additionally, very long blades may comprise sectional parts with additional spar caps, which are connected via one or more additional shear webs.

The indicated portion <NUM> illustrates a portion of the spar cap <NUM> at a transition from the thicker spar cap <NUM> to a thinner portion of the shell <NUM> not reinforced with a spar cap.

<FIG> schematically illustrates a ply-drop in a three-layer layup in the portion <NUM>. The drop of a ply results in a reduction in the thickness towards the right side of the portion <NUM>. Fabric <NUM> represents an outermost layer. Fabric <NUM> is a middle layer that is terminated. Fabric <NUM> is an innermost layer that covers fabric <NUM> (at least in portion <NUM>) and part of fabric <NUM> (at least in portion <NUM>). Even though it provides the desired reduction of thickness in the component from a first thickness <NUM> to a second thickness <NUM>, the termination (drop) of the fabric <NUM> leaves behind a cavity <NUM> free of fibre material that fabric <NUM> is not able to fill. Such a cavity may at best be filled with resin during infusion of resin; at worst, an air pocket within the infused component is left behind that will have to be manually repaired by filling it with resin after curing. In either case, the portion <NUM> will have a lower strength than the surrounding portions.

<FIG> schematically illustrates the same portion <NUM>, but with fibre bundles. Fabric <NUM> comprises bundles <NUM> stitched together as represented by stitched line <NUM>. A real stitching extends vertically in between or through individual bundles <NUM>, but these are left out to increase the visibility of the features. Fabric <NUM> comprises individual bundles <NUM> stitched together by stitching <NUM>. Fabric <NUM> comprises individual bundles <NUM> stitched together by stitching <NUM>. Each fabric is a unidirectional fibre fabric, the bundles of which extend along the longitudinal axis of the spar cap <NUM> (<FIG>). It is noted that in an actual layup, the bundles <NUM>, <NUM>, <NUM> may have an oval shape, even before being pressed together by a vacuum. For simplicity, they are illustrated with a circular cross-section.

In case fabrics of the same type is used for the different layers <NUM>, <NUM>, <NUM>, the cross-sectional area of the rovings <NUM>, <NUM>, and <NUM> will be identical, being the same type of rovings.

A unidirectional fabric <NUM> is illustrated in a perspective view in <FIG>. Fibre bundles <NUM> like those in <FIG> are held together in the fabric by stitchings <NUM>. The fibre bundles <NUM> are typically referred to as rovings or tows. Sometimes, the term roving is used to refer to glass bundles and tow is used to refer to carbon bundles. For simplicity, the term roving will be used in the remainder of the description to refer to any kind of fibre filament bundle. The filaments may for instance be made of glass filaments or carbon filaments or a combination. Other materials can be used, such as polyester.

In some cases, a unidirectional fabric will have a backing layer that modifies the properties. For simplicity, such a backing layer is not included in the drawings.

<FIG> illustrates the unidirectional fabric seen in a top view, also schematically showing the stitching <NUM> holding the rovings together. Usually, the stitching is more complex in order to give the fabric certain mechanical properties and to hold the backing layer in place.

<FIG> illustrates an embodiment of a fabric <NUM> in accordance with an embodiment of the invention. The fabric <NUM> comprises rovings <NUM> similar to those shown in <FIG> as part of known fabric <NUM>. However, a smaller, but in this embodiment crucial, roving <NUM> at a first fabric edge <NUM> of the fabric <NUM> has a smaller cross-section. Roving <NUM> is the outermost roving (fibre bundle) <NUM> that defines the first fabric edge <NUM>. Stitching <NUM> holds the rovings <NUM> and <NUM> together as a single, individual fabric that can be manufactured, handled, and laid up individually as part of a fibre layup for a fibre-reinforced composite component, such as a spar cap in particular or another composite element in general.

Roving <NUM> is at the same time the outermost roving that defines the first fabric edge.

The second fabric edge <NUM> of the fabric <NUM> opposite the first fabric edge <NUM> is illustrated as having the same thickness as rovings <NUM> to illustrate that fabrics can be tailored at one edge only, if so needed. An example below illustrates tailoring at both edges.

The fabric <NUM> can be manufactured similarly to known unidirectional fabrics. However, instead of using rovings having the same cross-section, rovings with smaller cross-sections are provided where the thickness is to be different, such as towards the first fabric edge <NUM>. Known stitching methods can be used when stitching together the rovings <NUM> and smaller roving <NUM> of different sizes. The illustration of the stitching is schematic. Stitching is usually an elastic material that will adapt its shape to the rovings, once stitched through or between rovings.

<FIG> illustrates a spar cap portion <NUM> that results instead of the portion <NUM> shown in <FIG> when using fabric <NUM> instead of the fabric of fabric <NUM> as in <FIG>. The outer layer is made of the same fabric <NUM> as the layup in <FIG> and the innermost layer is made of the same fabric <NUM> as the layup in <FIG>. As seen from <FIG>, the smaller roving <NUM> having a smaller cross-section causes a reduction of the size of the cavity when a ply is dropped. As seen when comparing Fig. <NUM> to Fig. <NUM>, the size of the resulting cavity <NUM> is smaller than the size of the cavity <NUM> when using known fabric <NUM>. However, the same thickness reduction is achieved, going from the first thickness <NUM> down to the second thickness <NUM>. However, the cavity <NUM> that causes a degree of weakness is smaller, and that translates into a resulting strength of the component that is higher compared to the layup shown in <FIG>.

The embodiment <NUM> in <FIG>, used to form the spar cap portion <NUM> in <FIG>, mitigates the effect of dropping a ply, but the issue of aligning the termination (the edge) of the ply to-be-dropped is unmitigated.

<FIG> illustrates a further embodiment of a fabric <NUM> in accordance with an embodiment of the invention. The fabric <NUM> comprises an array of rovings <NUM> forming a first layer <NUM>' similar to the individual fabric <NUM> shown in <FIG>. In addition, an array of further rovings <NUM> forms a second layer <NUM>' similar to the individual fabric <NUM> shown in <FIG>. In fabric <NUM>, all rovings are stitched together in a single stitching <NUM>. More than a single stitching may be used.

In this example, rovings <NUM> are identical to rovings <NUM> because the purpose of fabric <NUM> in this illustration is to mimic, to a certain extent, the known fabrics <NUM> and <NUM> shown in <FIG>, while at the same time mitigating the ply-drop issues related to use of known fabrics such as <NUM> and <NUM>.

As seen from <FIG>, a tapering is obtained in part by terminating the second layer <NUM>' before the first fabric edge <NUM>, which edge is therefore defined by an outermost roving <NUM> in the first layer <NUM>'.

To further refine the tapering, two smaller rovings <NUM> and <NUM> similar to smaller roving <NUM> in <FIG> are part of the fabric <NUM> and, importantly, are stitched into the fabric as part of the single fabric. In this example, the rovings towards the first fabric edge <NUM> of the fabric <NUM> have the same thickness as those in <FIG>, thereby mimicking the fabric <NUM> shown in <FIG>.

For simplicity, the stitchings have been generally shown as surrounding the fibre bundles in the drawings. However, stitchings may also pass through one or more of the fibre bundles, as shown in roving <NUM> in <FIG>. This is possible because the fibre bundles are not solidified. This makes the stitching process simpler.

The second fabric edge <NUM> is formed, for the purpose of the example only, by rovings in both layers, in this case left-most rovings of type <NUM> and <NUM> identical to those used in the fabrics <NUM> and <NUM> shown in <FIG>. However, in the fabric <NUM>, they are instead stitched together into an individual fabric that can be handled and used independently as a single unit. As a result of the combination of multiple layers, a tapering of the fabric <NUM> is achieved towards the first fabric edge <NUM>. Further, the rovings <NUM> and <NUM>, having a smaller cross-section, contribute to the tapering towards the first fabric edge <NUM>. Finally, as seen in <FIG>, the top layer <NUM>' ends before the first fabric edge <NUM>, which results in a further tapering of the fabric as it is only made up of a single layer of rovings near the first fabric edge <NUM>.

<FIG> illustrates a spar cap portion <NUM> that results when fabric <NUM> is used instead of the two fabrics <NUM> and <NUM> as in <FIG> or even the improved fabric <NUM> is used instead of fabric <NUM>, as shown in <FIG>. The fabric <NUM> from <FIG> takes the place of two known layers, such as fabrics <NUM> and <NUM> in <FIG>, or the place of the fabrics <NUM> together with the improved fabric embodiment <NUM> used in the spar cap portion <NUM> shown in <FIG>. Thus, in effect, when laying up the structure corresponding to section <NUM> shown in <FIG>, only two fabrics are used: the fabric <NUM> in accordance with an embodiment of the invention and the fabric <NUM> also used in the example in <FIG>, where it illustrates the problem associated with ply drop.

By tailoring the fabric in the way illustrated by fabric <NUM> in <FIG>, fewer layers must be handled, which in turn simplifies the layup process.

Furthermore, as shown in <FIG>, the cavity <NUM> resulting when fabric <NUM> is used together with fabric <NUM> is further reduced compared to using the already-improved fabric <NUM> shown in <FIG>. Again, a tapering from a first thickness <NUM> down to a second thickness <NUM> is achieved, but the cavity <NUM> that causes weakness is smaller compared to the cavities shown in <FIG> and <FIG>, and this translates into a higher strength of the resulting component compared to the spar cap portion in <FIG> and into an even higher strength than the spar cap portion in <FIG> having a cavity resulting from termination of a known uniform unidirectional fabric <NUM>.

<FIG> illustrates the spar cap portion <NUM> in the same way that <FIG> illustrates the section <NUM> obtained without a tapered fabric. As can be seen from <FIG>, the single fabric <NUM> replaces the two fabrics <NUM> and <NUM>. Fabric <NUM> is still used as a cover layer. In <FIG>, the additional portion <NUM> schematically illustrates a portion that rovings <NUM> and <NUM> add in the spar cap portion, whereby the resulting cavity <NUM> is smaller than can be obtained with a known uniform unidirectional fabric such as fabric <NUM> in <FIG>.

In a further embodiment, known fabric <NUM> is stitched together with the rovings of fabric <NUM>, preferably in a single stitching, i.e. not by stitching fabric <NUM> together with fabric <NUM>, but by stitching together all the rovings of fabric <NUM> and fabric <NUM> in one stitching process. However, further stitching can be used. In both cases, the end result is a single fabric that can be manufactured and handled individually, further simplifying layup and mitigating the issues associated with cavities resulting from ply drop of known fabrics.

<FIG> illustrates another fabric <NUM> in accordance with an embodiment of the invention. In this embodiment, the tapering is towards both edges <NUM> and <NUM> of the fabric.

The tapering in the fabric <NUM> in <FIG> is more advanced than in fabrics <NUM> and <NUM> shown in <FIG> and <FIG>. Tapering is achieved by a combination of tapering the number of layers and using rovings with different sizes, illustrated by rovings <NUM> and <NUM>. For this example, rovings <NUM> are shown as identical to rovings <NUM>, <NUM>, and <NUM> from <FIG> and <FIG>. The rovings may have been stitched together in a single stitching, or more.

As seen in <FIG>, the use of only two different roving sizes can create a relatively smooth tapering of the thickness. Towards the middle of the fabric, the thickness is provided by two layers of rovings of the type <NUM>. In the direction towards the edges <NUM> and <NUM>, tapering is provided by using a smaller roving <NUM> together with a larger roving <NUM>; then two smaller rovings <NUM>; then a single larger roving <NUM>; and finally, a single smaller roving <NUM>. An outermost roving <NUM> defines the first fabric edge, and a second outermost roving <NUM> defines the second fabric edge opposite the first fabric edge. The thickness of the fabric is constant in a central weft-wise portion and tapers from a first thickness <NUM> to a second thickness <NUM> towards both the first fabric edge <NUM> and towards the second fabric edge <NUM>. The tapering is the same in both directions and is obtained using the same arrangement of rovings seen in an outward direction from the weft-wise centre of the fabric. The fabric <NUM> is therefore symmetric seen along the warp direction (as in the figure).

More elaborate fabrics can be made. For instance, additional roving sizes can be used and/or smaller rovings in larger numbers could be used to provide an even smoother tapering.

<FIG> illustrates use of the fabric <NUM> for manufacturing a spar cap <NUM> in combination with outer skin layers <NUM>. The outer skin layers <NUM> typically comprise multiple fibre fabric layers of various directionality. These are shown as a single element. Similarly, spar caps may comprise fibre material with different directionalities, including unidirectional fibre fabrics. For simplicity, the example in <FIG> illustrates unidirectional fabric only in the spar cap <NUM>. Spar caps typically comprise many layers, not just three as shown in <FIG>, but for simplicity, the example illustrates three layers.

The spar cap <NUM> is made up of a known unidirectional fabric <NUM> such as the fabric <NUM> in <FIG>, made of uniform rovings, and the fabric <NUM> in accordance with the embodiment shown in <FIG>. Fabric <NUM> is placed on the outer skin layers <NUM>, and fabric <NUM> is placed onto the fabric <NUM>. This results in a three-layer structure <NUM> that tapers smoothly towards the sides, forming a smooth termination of the spar cap towards the outer skin layers <NUM>.

Claim 1:
A fibre reinforcement fabric (<NUM>) for a wind turbine component, the fabric comprising a first plurality of fibre bundles (<NUM>, <NUM>) arranged in parallel in a warp direction and stitched together, the fabric having a first outermost fibre bundle (<NUM>, <NUM>, <NUM>) defining a first fabric edge (<NUM>, <NUM>, <NUM>) parallel to the warp direction and a second outermost fibre bundle (<NUM>) defining a second fabric edge (<NUM>, <NUM>, <NUM>) opposite the first fabric edge, the fabric having a first tapered portion including the first outermost fibre bundle (<NUM>, <NUM>, <NUM>), wherein a thickness of the fabric in the first tapered portion is tapering from a first fabric thickness (<NUM>, <NUM>, <NUM>) to a second fabric thickness (<NUM>, <NUM>, <NUM>) in a direction towards the first fabric edge (<NUM>, <NUM>, <NUM>).