Abstract:
A method of manufacturing a wind turbine blade component in form of a shear web is described. The method comprising the steps of: a) providing a pre-manufactured shear web body having a first side and a second side as well as a first end and a second end; b) providing a first pre-formed web foot flange comprising a fibre-reinforcement material; c) arranging a first fibre layer from the first pre-formed web foot flange and to a part of the first side of the shear web body; d) arranging a second fibre layer from the first pre-formed web foot flange and to a part of the second side of the shear web body; e) supplying a resin to said first fibre layer and second fibre layer simultaneous with or subsequent to steps c) and d); and f) allowing the resin to cure so as to form the shear web.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of manufacturing a wind turbine blade component in form of a shear web body, and a shear web body manufactured according to the method. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wind turbine blades are often manufactured according to one of two constructional designs, namely a design where a thin aerodynamic shell is glued or otherwise bonded onto a spar beam, or a design where spar caps, also called main laminates, are integrated into the aerodynamic shell. 
         [0003]    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 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. 
         [0004]    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 may 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. 
         [0005]    The shear webs act to reinforce the blade structure, and prevent excessive bending or buckling. Some blade designs use shear webs formed from beam members having I- or C-shaped cross-sections, the members having a main body with load-bearing flanges extending therefrom at opposed ends of the main body. 
         [0006]    One method of manufacturing such I- or C-webs is through the provision of a sandwich panel body to which layers of fibre material are applied at the opposed ends in the shape of the desired flanges, the fibre material being infused with a resin and subsequently cured to form rigid flanges. 
         [0007]    It is well-known to manufacture such shear webs in a suitably shaped mould structure, wherein a C-web can be manufactured using a relatively simple U-shaped mould, where the sandwich panel body extends between opposed walls of the mould structure, with the flanges formed through the layup of fibre material against the said walls. 
         [0008]    Similarly, an I-web can be manufactured using a mould having a central support bounded by flexible support members on either side to define an adjustable channel between the flexible support members and the opposed mould walls. In this situation, the sandwich panel body is arranged on the central support, while the adjustable channel is arranged to receive fibre layers to form the flanges on a first side of the panel body, with the flanges on the second side of the panel body formed by the layup of fibre material against the opposed mould walls. 
         [0009]    An example of such manufacturing systems can be seen in International Patent Application Publication No. WO 2013/037466 A1. 
         [0010]    However, such systems require the provision of dedicated moulding tables for the formation of such shear webs, which can often be continuous structures in excess of 30-40 metres length, taking up considerable space in a blade factory. Also, the application, infusion and subsequent curing of the fibre layers to form the flanges of the shear webs require relatively precise alignment and working, resulting in considerable time and operational costs. 
         [0011]    Furthermore, in the case of I-web manufacture, the particular flexible profiles used can be unique to the different design of blade and the associated I-web required. This can therefore result in additional manufacturing and setup costs when it is desired to produce I-webs for use in different wind turbine blades. 
         [0012]    In addition to the above, shear webs having such resin-infused fibre-based flanges can be an area of interest for the prevention of structural faults and cracks, due to the relatively large forces transferred through said flanges. 
         [0013]    It is an object of the invention to provide an alternative system and method for the manufacture of wind turbine blade components in form of shear webs, which provides for increased ease of manufacture combined with a reduced risk of structural failure. 
       SUMMARY OF THE INVENTION 
       [0014]    Accordingly, there is provided a method of manufacturing a wind turbine blade component in form of a shear web, the method comprising the steps of:
       a) providing a pre-manufactured shear web body having a first side and a second side as well as a first end and a second end;   b) providing a first pre-formed web foot flange comprising a fibre-reinforcement material, such as glass fibres;   c) arranging a first fibre layer from the first pre-formed web foot flange and to a part of the first side of the shear web body;   d) arranging a second fibre layer from the first pre-formed web foot flange and to a part of the second side of the shear web body;   e) supplying a resin to said first fibre layer and second fibre layer simultaneously with or subsequent to steps c) and d); and   f) allowing the resin to cure so as to form the shear web.       
 
         [0021]    Thus, it is seen that the first preformed web foot flange is attached to the shear web body by layering fibre layers from the web foot flange to the sides of the shear web, supplying the resin either by injection or as prepreg material, and then allowing the resin to cure so as to provide a permanent connection between the web foot flange and the shear web. This provides for the opportunity to manufacture the shear web body and the first web foot flange separately, which in turn allows for a more generic and modular design, where two parts can be shaped to a desired wind turbine shell shape without necessarily having to have large custom made web moulds for each wind turbine blade type. Thus, the shear web body may be simply supported in a work shop, e.g. using a plurality of simple table supports or a simple jig. 
         [0022]    Overall, it is seen that the web foot flange(s) may be joined to the pre-manufactured shear web body by laminating it onto the sides of the shear web body, e.g. via overlamination. Such lamination replaces the use of structural adhesives that could be used for providing a load-bearing joint between the web foot flanges and the shear web body. 
         [0023]    The method may advantageously also involve the step of attaching a second pre-formed web foot flange to the second end of the web body according to the same sequence, i.e. c2) arranging a first additional fibre layer from the second pre-formed web foot flange and to the first side of the shear web body; d2) arranging a second additional fibre layer from the first pre-formed web foot flange and to the second side of the shear web body; e2) supplying a resin to said first additional fibre layer and second additional fibre layer simultaneously with or subsequent to steps c2) and d2); and f2) allowing the resin to cure. 
         [0024]    In the following, various embodiments may be discussed relating to the first web foot flange and will sometimes just be referred to as the web foot flange. However, it is clear that the embodiments also may also apply to the second web foot flange, which is attached to the second end of the shear web body. 
         [0025]    According to an advantageous embodiment, a tackifier or SAERfix® fabric is supplied to the first fibre layer and the second fibre layer in order to maintain the shape prior to supplying resin to said first and second fibre layers in step e). Thus, it is ensured that the first and the second fibre layers maintain their shape so as to extend along the first side and the second side of the shear web body, respectively. If the first and the second fibre layers form part of the first pre-formed web foot flange, the tackifier ensures or at least partially ensures that the pre-formed web foot flange itself maintains its shape prior to being laminated onto the shear web body. 
         [0026]    According to another advantageous embodiment, the pre-manufactured shear web body is a sandwich panel or a sandwich-structured composite member, e.g. having skin layers of reinforcement material, such as a fibre-reinforced composite material, applied to a relatively thick light-weight core material, such as balsawood or a foamed polymer. The core material may be a low strength material, but its higher thickness provides the sandwich composite with high bending stiffness with overall low density. 
         [0027]    According to yet another advantageous embodiment, the method comprises the step of providing a forming tool adjacent at least the first end of the shear web body to form a mould cavity covering the first pre-formed web foot flange, the first fibre layer, the second fibre layer, and a part of the shear web body near the first end of the shear web body. Thus, the forming tool forms a relatively small mould cavity near the first end of the shear web body. Accordingly, only relatively small forming tools are needed instead of bulky equipment needed for manufacturing an integrally formed shear web body and web foot flange. 
         [0028]    The mould cavity is preferably an elongate or oblong cavity extending along a part or the entire shear web body. The mould cavity may be substantially web foot flange shaped. 
         [0029]    Advantageously, the forming tool comprises a first vacuum bag and possibly also a second vacuum bag. If only a first vacuum bag is used, it may cover the first web foot flange and be sealed against the first side and the second side of the shear web body. It is also possible to use two vacuum bags, e.g. a first for sealing the first fibre layer, and a second for sealing the second fibre layer. The vacuum bags may further be sealed against the pre-formed web foot flange or against a forming tool plate member supporting a base part of the pre-formed web foot flange. 
         [0030]    Alternatively, the mould cavity may be formed using a dedicated tool comprising substantially rigid parts, such as made of a metal or inflexible plastic. Preferably, such rigid parts are shaped in accordance with the desired outer shape of the web foot flange or web foot flange connection. 
         [0031]    Preferably, the method comprises the step of applying a sealant between said forming tool and said first end of said web member. The sealant may comprise a simple strip of material, possibly with adhesive properties, applied between edges of the forming tool and the surface of the web member, e.g. a silicone gel. 
         [0032]    In a particularly advantageous method, the resin in step e) is injected into the mould cavity. Advantageously, the resin is injected from a first longitudinal end of the mould cavity. The method may comprise injecting said resin at an overpressure, or at a pressure level above atmospheric pressure. Preferably, said step of injecting comprises applying a vacuum to the mould cavity. Thus, the resin is preferably supplied via vacuum infusion. The vacuum may advantageously be applied from an opposed second longitudinal end of the mould cavity. 
         [0033]    In one embodiment, the pre-manufactured shear web body in step a) is arranged in a substantially vertical position, and wherein the first pre-formed web foot flange is arranged at the first end and below the shear web body. Thus, the resin may be supplied while the web foot flange and the shear web body are arranged in a substantially vertical configuration, and where the first fibre layer and the second fibre layer extend substantially vertically along the first side and the second side of the shear web body, respectively. This may compensate for build-up of air pockets in the laminate and creep of the fibre layers due to gravity. 
         [0034]    The second pre-formed web foot flange may be arranged at the second end and above the shear web body and be infused in a similar manner. Alternatively, the shear web body may be turned 180 degrees and the second pre-formed web foot flange be attached to the shear web body in a subsequent infusion step, where it is arranged below the shear web body. 
         [0035]    In another particularly advantageous embodiment, the first web foot flange comprises a base part having a first side and a second side, a first projection part projecting from the first side of the base part and a second projection part projecting from the second side of the base part so that a recess is formed between the first projecting part and the second projecting part. The first end of the shear web body may thus be arranged in the recess formed between the two projecting parts. The first end of the shear web body may be chamfered or bevelled. The recess may have a complimentary shape. A fibre layer may be arranged in the recess between the pre-formed web foot flange and the shear web body. The complimentary shapes may be shaped so that the angle between the web foot flange and the shear web body is pre-defined. The end of the shear web body and/or the cavity of the web foot flange may for instance be shaped via milling or a similar operation. 
         [0036]    The fibre layer may be wrapped around the first end of the shear web body. Accordingly, the first fibre layer and the second fibre layer may be formed by a single fibre layer wrapped around the end and between the two bodies. 
         [0037]    The first and the second projecting parts both comprise a first side part and a second side part. The first side part may be concave, and the second side may also be concave. Thus, the projections provide a smooth transition to the shear web body. The side parts of the projecting parts may also be defined as inner side parts (being the sides which face towards the shear web body, and outer side parts (being the sides which face away from the shear web body. 
         [0038]    In one embodiment, the recess formed has a part circular cross-section with a first radius or curvature. In a second embodiment, the first end of the shear web body is rounded having a second radius of curvature. The second radius may be substantially equal to or slightly smaller than the first radius. Thereby, the two parts may be connected in a spherical joint like connection, and the first end of the shear web body may be angled arbitrarily and still fit the recess. Thereby, the angle between the shear web body and the web foot flange may more easily be varied in order to fit the aerodynamic shell part of the wind turbine blade. 
         [0039]    In one embodiment, the recess has a measure of arc of 90-180 degrees, or 120-160 degrees, e.g. around 140 degrees. The measure of arc may be relatively high if only a small variable angle between the web foot flange and the shear web body is needed. 
         [0040]    The first radius may advantageously be 10-100 mm, or 10-50 mm, e.g. around 20 mm. The shear web body may advantageously have a thickness of approximate 20-200 mm, or 20-100 mm, e.g. around 30 or 40 mm. The first radius and the shear web body thickness may also vary in the longitudinal direction. The shear web body may for instance be thicker near the blade root than near the tip, and the first radius may vary accordingly. 
         [0041]    The first fibre layer and the second fibre layer may advantageously comprise a multiaxial fibre layer, such as a biaxial, triaxial or quadaxial fibre layer. Thus, the fibre layers comprise multiaxially arranged fibres, whereby loads can be transferred in several directions and thereby take up both longitudinal forces and transverse forces. It is also possible to use fibre layers having randomly oriented reinforcement fibres. 
         [0042]    The resin may advantageously be polyester, vinylester or epoxy. The polyester may advantageously be chemically compatible with the resin matrix of the pre-manufactured shear web body. 
         [0043]    The first fibre layer and the second fibre layer are advantageously made from glass fibres. However, the reinforcement fibres could also be carbon fibres, plant fibres, nylon, aramid or another suitable reinforcement fibre. 
         [0044]    The first fibre layer and the second fibre layer may also be prepreg material, e.g. UV curing prepregs. 
         [0045]    The pre-formed web foot flange may advantageously form an I-shaped foot with the shear web body, once it has been attached to the shear web body. The web foot flange may advantageously have a substantially flat base part. 
         [0046]    The first fibre layer and the second fibre layer may advantageously extend along 5-20 cm of the first side and the second side of the shear web body, respectively. 
         [0047]    In one particularly advantageous embodiment, the first pre-formed web foot flange is a pre-cured composite body. Thus, the pre-cured composite body may be a pre-manufactured body, e.g. formed in a separate mould prior to being attached to the first end of the shear web body. The pre-cured body may still have a degree of flexibility so that the angle between the web foot flange and the shear web may be varied or twisted in the longitudinal direction in order to accommodate the shape of the aerodynamic shell. 
         [0048]    The pre-cured composite body is attached to the shear web body by applying the first and the second fibre layer overlapping the two bodies, supplying resin and finally letting the resin cure or harden. Accordingly, it is seen that the two parts are attached to each other via an overlamination as opposed to a structural adhesive or glue joint. 
         [0049]    Further, the pre-cured body may act as a part of the forming tool that forms the mould cavity. 
         [0050]    In one embodiment, the pre-cured composite structure is a pultruded or extruded body. Thus, the web foot flange may be pre-manufactured with a uniform cross-sectional shape according to known pultrusion or extrusion processes and cut to the desired length. The pre-manufactured web foot flange may then be bent into the desired angle relative to the shear web body so as to accommodate the shape of the aerodynamic shell. 
         [0051]    The pre-cured web foot flange may be attached to the shear web body by use of a fibre layer between the inner side parts of the projecting parts and fibre layers arranged so as to cover a part of the base part, the outer side parts of the projecting parts, and the sides of the shear web body. 
         [0052]    In a second particularly advantageous embodiment, the first pre-formed web foot flange is a sewn or weaved fibre body. Accordingly, the sewn or weaved fibre body may be pre-formed into an approximate desired shape. The first fibre layer and the second fibre layer may be integrally formed with the web foot flange. The fibre body may be manufactured as a continuous body and then cut to the desired length. Accordingly, this embodiment also provides a flexible method of manufacturing a wind turbine blade shear web. 
         [0053]    If the pre-formed web foot flange is formed by use of the sewn fibre body, it may be necessary to provide a forming tool having a primary base plate member, which defines a primary surface or base of the finished web foot flange, and thereby the side that is later attached to the inner side of the aerodynamic blade shell. The base plate member may have to be angled in accordance with the desired angle between the web foot flange and the shear web body. However, the forming tool is still much smaller than a mould needed to manufacture an integrally formed shear web whereby the manufacture is much more flexible than existing methods of manufacturing shear webs. 
         [0054]    The sewn fibre body may advantageously comprise dry reinforcement fibres, i.e. reinforcement fibres that have not yet been impregnated by a resin. Accordingly, a mould cavity may be formed by a forming tool surrounding the pre-formed body and sealed against the sides of the shear web body, after which a resin is injected into the cavity and finally cured in order to form the shear web. The sewn fibre body may alternatively comprise a prepreg material, optionally being a UV-curing prepreg material. In this embodiment, the formed mould cavity is substantially flange-shaped. 
         [0055]    In one embodiment, the shear web body has a length of at least 30 metres. Accordingly, it is seen that the invention is directed towards the manufacture of very large shear webs, e.g. for wind turbine blades having a blade length of at least 40 metres. The shear web body may also be sectionised, e.g. by connecting pre-manufactured panels having a length between 8 and 12 metres. The web bodies may be connected to each other via an over-lamination at the seams. This may be carried out at the same time as the web foot flange is attached to the panels. 
         [0056]    The web foot flange advantageously has substantially the same length as the shear web body. However, the web foot flange may also be sectionised or modular. The individual web foot flanges may for instance have a length of 1-10 metres. 
         [0057]    As the profile of the wind turbine blade has a particular curvature, the base part or primary surface of the flange of the shear web may require arrangement at a specific angle relative to the web body. This angle may vary along the length of the component, dependent on the longitudinal profile of the blade. Accordingly, the forming tool may be made of a relatively flexible material to allow for variations in the angling of the tool along the length of the web member, and/or a plurality of forming tools may be used arranged at different angles relative to the web member along the length of the web member. 
         [0058]    Preferably, said step of angling comprises arranging the web foot flange at an angle of between −20 to +20 degrees to the first end of said web member. Accordingly a primary plate member for forming the mould cavity may be similarly angled at an angle of between −20 to +20 degrees to the first end of said web member. It is also possible to vary said angles between −30 and 30 degrees. 
         [0059]    The web foot flange may advantageously be formed with a shaped surface for attachment to the blade shell part, such as a rippled, hatched or scored surface profile. The shaped surface may be part of the pre-cured web foot flange, or the primary plate member of the forming tool may be configured to provide the shaped surface. The provision of a shaped or treated flange surface at the end of the component can provide a surface which provides an improved adhesive bond between components. 
         [0060]    The invention further provides a shear web manufactured according to the aforementioned method. Accordingly, the invention provides a wind turbine component in form of a shear web comprising:
       a pre-manufactured shear web body having a first end and a second end as well as a first side and a second side, and at least   a first pre-formed web foot flange, wherein   the first pre-formed web foot flange is attached to the shear web body via
           a first fibre layer extending from the first pre-formed web foot flange and to a part of the first side of the shear web body, and   a second fibre layer extending from the first pre-formed web foot flange and to a part of the second side of the shear web body, wherein   the first fibre layer and the second fibre layer are embedded in a cured resin matrix.   
               
 
         [0067]    Overall, it is seen that the web foot flange(s) may be joined to the pre-manufactured shear web body by laminating it onto the shear web body, e.g. via overlamination. Such, lamination replaces the use of structural adhesives that could be used for providing a load-bearing joint between the web foot flanges and the shear web body. 
         [0068]    Preferably, the first pre-formed web foot flange is attached to the pre-manufactured shear web by one or more overlaminations comprising the first fibre layer and the second layer, whereby the use of a structural adhesive may be avoided. 
         [0069]    The invention further provides a wind turbine blade comprising a shear web according to any of the aforementioned embodiments, the shear web being connected between a pressure side and a suction side of the wind turbine blade. 
         [0070]    The wind turbine blade may comprise a first spar cap attached to or integrally formed with a pressure side shell part and a second spar cap attached to or integrally formed with a suction side shell part. The shear web may be connected between the two spar caps, e.g. with the first web foot flange attached to the first spar cap and the second web foot flange attached to the second spar cap. 
         [0071]    The invention additionally provides a wind turbine comprising at least one, and advantageously two or three, such wind turbine blades. 
     
    
     
       DESCRIPTION OF THE INVENTION 
         [0072]    The invention is explained in detail below with reference to an embodiment shown in the drawings, in which 
           [0073]      FIG. 1  shows a wind turbine, 
           [0074]      FIG. 2  shows a schematic view of a wind turbine blade, 
           [0075]      FIG. 3  shows a schematic view of a cross-section of a wind turbine blade, 
           [0076]      FIG. 4  shows a first embodiment of a pre-cured web foot flange according to the invention, 
           [0077]      FIG. 5  shows a second embodiment of a pre-cured web foot flange according to the invention, 
           [0078]      FIG. 6  illustrates a first embodiment of a manufacturing method according to the invention for manufacturing a shear web, and 
           [0079]      FIG. 7  illustrates a second embodiment of a manufacturing method according to the invention for manufacturing a shear web. 
       
    
    
       [0080]      FIG. 1  illustrates a conventional modern upwind wind turbine according to the so-called “Danish concept” with a tower  4 , a nacelle  6  and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub  8  and three blades  10  extending radially from the hub  8 , each having a blade root  16  nearest the hub and a blade tip  14  farthest from the hub  8 . The rotor has a radius denoted R. 
         [0081]      FIG. 2  shows a schematic view of a wind turbine blade  10 . The wind turbine blade  10  has the shape of a conventional wind turbine blade and comprises a root region  30  closest to the hub, a profiled or an airfoil region  34  farthest away from the hub and a transition region  32  between the root region  30  and the airfoil region  34 . The blade  10  comprises a leading edge  18  facing the direction of rotation of the blade  10 , when the blade is mounted on the hub, and a trailing edge  20  facing the opposite direction of the leading edge  18 . 
         [0082]    The airfoil region  34  (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region  30  due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade  10  to the hub. The diameter (or the chord) of the root region  30  may be constant along the entire root area  30 . The transition region  32  has a transitional profile gradually changing from the circular or elliptical shape of the root region  30  to the airfoil profile of the airfoil region  34 . The chord length of the transition region  32  typically increases with increasing distance r from the hub. The airfoil region  34  has an airfoil profile with a chord extending between the leading edge  18  and the trailing edge  20  of the blade  10 . The width of the chord decreases with increasing distance r from the hub. 
         [0083]    A shoulder  40  of the blade  10  is defined as the position, where the blade  10  has its largest chord length. The shoulder  40  is typically provided at the boundary between the transition region  32  and the airfoil region  34 . 
         [0084]    It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub. 
         [0085]    The blade is typically made from a pressure side shell part  36  and a suction side shell part  38  that are glued to each other along bond lines at the leading edge  18  and the trailing edge of the blade  20 . 
         [0086]      FIG. 3  shows a schematic view of a cross section of the blade along the line I-I shown in  FIG. 2 . As previously mentioned, the blade  10  comprises a pressure side shell part  36  and a suction side shell part  38 . The pressure side shell part  36  comprises a spar cap  41 , also called a main laminate, which constitutes a load bearing part of the pressure side shell part  36 . The spar cap  41  comprises a plurality of fibre layers  42  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  38  also comprises a spar cap  45  comprising a plurality of fibre layers  46 . The pressure side shell part  38  may also comprise a sandwich core material  43  typically made of balsawood or foamed polymer and sandwiched between a number of fibre-reinforced skin layers. The sandwich core material  43  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  38  may also comprise a sandwich core material  47 . 
         [0087]    The spar cap  41  of the pressure side shell part  36  and the spar cap  45  of the suction side shell part  38  are connected via a first shear web  50  and a second shear web  55 . The shear webs  50 ,  55  are in the shown embodiment shaped as I-shaped webs. However, other configurations, such as C-shaped webs may also be utilised. The first shear web  50  comprises a shear web body and two web foot flanges. The shear web body comprises a sandwich core material  51 , such as balsawood or foamed polymer, covered by a number of skin layers  52 . The second shear web  55  has a similar design with a shear web body and two web foot flanges, the shear web body comprising a sandwich core material  56  covered by a number of skin layers  57 . The sandwich core material  51 ,  56  of the two shear webs  50 ,  55  is chamfered near the flanges in order to transfer loads from the webs  50 ,  55  to the main laminates  41 ,  45  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. 
         [0088]    In order to compensate for this, a number of filler ropes  60  comprising glass fibres are normally arranged at these joint areas. Further, such ropes  60  will also facilitate transferring loads from the skin layers of the leg to the flanges. However, according to the invention, the web foot flanges and the shear web body are manufactured separately, and the web foot flanges are then laminated onto the ends of the shear web body. 
         [0089]    The blade shells  36 ,  38  may comprise further fibre-reinforcement at the leading edge and the trailing edge. Typically, the shell parts  36 ,  38  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. 
         [0090]      FIG. 4  shows a first embodiment of a pre-cured web foot flange  70  according to the invention. The web foot flange  70  comprises a base part having a first side for mounting to the inner side of the wind turbine blade shell and an opposed, second side from which a first projection  73  and a second projection  76  extend. The two projections  73 ,  76  form a recess, which can take up an end of a shear web body. 
         [0091]    The pre-cured web foot flange may be formed by a number of outer fibre layers  71  and a number of inner fibre layers  72 . A filler material  60 ′ made of fibre reinforcement material is arranged so as to provide the projections  73 ,  76 . The filler material  60 ′ may for instance be ropes comprising reinforcement fibres, such as glass fibres. In the shown embodiment, the filler material  60 ′ is shown as found. However, the filler material  60 ′ may also be shaped in accordance with the desired web foot flange shape, in particular to shape the two projections  73 ,  76 . The first projection comprises an inner side  74  facing the recess and an outer side  75  facing away from the recess. Similarly, the second projection  76  also comprises an inner side  77  facing towards the recess, and an outer side  78  facing away from the recess. The inner sides  74 ,  77  of the projections may be rounded and have a first curvature radius R 1 . The entire recess may advantageously follow a circle, e.g. along a measure of arc being approximately 140 degrees. The outer sides  75 ,  78  may also be rounded having an outer radius of curvature R o , which will provide a smooth transition and thereby also a gradual load transition between the flange and the shear web body. 
         [0092]    The pre-cured web foot flange  70  may be moulded in a separate mould. Alternatively, the pre-cured web foot flange may be formed by known pultrusion or extrusion techniques. 
         [0093]      FIG. 5  shows a second embodiment of a pre-cured web foot flange  170  according to the invention. In this embodiment the projections are formed by a pre-shaped filler material  160 . The pre-shaped filler material  160  may for instance be a pultruded or extruded body. In this embodiment, the filler  160  is shaped as a triangular. However, the sides of the pre-shaped filler  160  may also be slightly rounded to provide a rounded shape to the recess of the web foot flange. Similar to the first embodiment, the filler material  170  is covered by a number of outer fibre layers  171  and a number of inner fibre layers  172 . As with the first embodiment, the pre-cured web foot flange  170  may be moulded with the pultruded or extruded filler material  170  in a separate mould. Alternatively, the entire body may be formed by extrusion or pultrusion. 
         [0094]      FIG. 6  illustrates a first embodiment of a manufacturing method according to the invention for manufacturing a shear web. In the shown embodiment a first pre-cured web foot flange  270  is laminated onto a first end  253  of a shear web body  250 . The pre-cured web foot flange  270  may e.g. be formed like the two embodiments shown in  FIGS. 4 and 5 . 
         [0095]    The shear web body  250  is pre-manufactured and comprises a sandwich core material  251 , such as balsawood or foamed polymer, covered by a number of fibre skin layers  252 . The shear web body  250  is an elongated body that—when mounted in the wind turbine blade shell—extends in the longitudinal direction of the wind turbine blade and may have a length of 30 metres or more. The shear web body comprises a first side  254  and a second side  258  as well as a first end  253  and a (not shown) second end. 
         [0096]    The first end  253  of the shear web body may be rounded or chamfered, e.g. having a second radius R 2 . The second radius R 2  may substantially match or be smaller than the first radius of curvature R 1  of the recess, so that the recess of the web foot flange  270  may take up the first end  253  of the shear web body  250  and so that the web foot flange  270  may be angled in relation to the shear web body. It is also possible to use an additional piece, e.g. having a semi-circular profile, in order to form the rounded or chamfered part. The piece may for instance be made of a foamed polymer or balsawood. 
         [0097]    In one example, the shear web body has a thickness of 32 mm, whereby the second radius R 2  may be 16 mm. Further, the first radius of curvature is 17 mm. 
         [0098]    A fibre layer  280  is arranged between the recess of the web foot flange  270  and the first end  253  of the shear web body  250 . The fibre layer  280  is wrapped around the first end  253  of the shear web body  250  and extends along a part of the first side  254  of the shear web body and along a part of the second side  258  of the shear web body. Further, a number of first fibre layers  281  are arranged along the surface of the web foot flange  270  along the outer side of the first projection  273  and further along the first side  254  of the shear web body  250 . Similarly, a number of second fibre layers  282  are arranged along the surface of the web foot flange  270  along the outer side of the second projection  276  and further along the second side  258  of the shear web body  250 . 
         [0099]    The first fibre layers  281  are covered by a first vacuum bag  290  and are sealed via a first sealant  291  to the web foot flange  270  and a second sealant  292  to the first side  254  of the shear web body  250 . Similarly, the second fibre layers  280  are covered by a second vacuum bag  295  and are sealed via a first sealant  296  to the web foot flange  270  and a second sealant  297  to the second side  258  of the shear web body  250 . The sealants  291 ,  292 ,  296 ,  297  may for instance be tacky tape or silicone. Thereby, a longitudinally extending mould cavity is formed between the first vacuum bag  290 , the second vacuum bag  295 , the web foot flange  270  and the shear web body  250 . One end of the mould cavity is connected to a vacuum pump and the other end is connected to a resin source. Once the vacuum pump has evacuated the mould cavity, a valve to the resin source is opened and resin is injected into the mould cavity. Finally, the resin is cured so that a laminate bonding is formed between the web foot flange  270  and the first end  253  of the shear web body  250 . 
         [0100]    In an alternative embodiment, only a single vacuum bag is used which is wrapped around the bottom of the web foot flange  270 , whereby the first sealants  291 ,  296  may be omitted. 
         [0101]    The fibre layers  280 ,  281 ,  282  may also comprise a prepreg material. However, additional resin may advantageously be infused into the mould cavity as described above. 
         [0102]    The pre-cured web foot flange  270  is relatively flexible. Thereby, it can be varied or twisted in the longitudinal direction so that the angle relative to the shear web body may be varied in order to accommodate the shape of the wind turbine blade shell. Alternatively, the web foot flange may be sectionised and provided as individual parts extending along separate parts of the shear web body  250 . The attachment method may be carried out by a relatively simple jig setup that holds the pre-manufactured shear web body  250  and the first web foot flange  270 . In the shown embodiment, the shear web body  250  and the web foot flange are attached to each other in a setup, where shear web body is arranged in a substantially vertical orientation. Thereby, the resin may be injected from a lower part and flow upwards, which may compensate for air pockets forming and creep of the fibre layers due to gravity. The fibre layers  280 ,  281 ,  282  may advantageously be provided with a tackifier or a SAERfix® fabric in order for the fibre layers to maintain their shape during layup. It is also contemplated that the pre-cured web foot flange may be laminated onto the blade shell first and then laminated onto the shear web body. 
         [0103]    The fibre layers  280 ,  281 ,  282  extend along a length d along the sides  254 ,  258  of the shear web body. The length may for instance be 10-15 cm. 
         [0104]    The second web foot flange may be attached to the second end of the shear web body through a similar attachment method. The shear web body may advantageously be turned 180 degrees and the second web foot flange be attached to the second end of the shear web body in a setup, where the second web foot flange is arranged below the shear web body  250 . Alternatively, the second web foot flange may be arranged above the shear web body without having to turn the shear web body  250 . 
         [0105]    While the attachment method has been described in a setup, where the shear web body is arranged in a vertical orientation, it is recognised that the web foot flanges may also be attached to the shear web body in a setup, where the shear web body is arranged in a horizontal orientation, e.g. by arranging the shear web body on a simple work table. 
         [0106]      FIG. 7  illustrates a second embodiment of a manufacturing method according to the invention for manufacturing a shear web, in which similar reference numerals refer to like parts of the first embodiment shown in  FIG. 6 . Therefore, only the differences between the two embodiments are described. 
         [0107]    The second embodiment differs from the first embodiment in that the web foot flange  370  is not pre-cured. Instead the web foot flange is pre-formed as a sewn or weaved fibre body, advantageously comprising dry reinforcement fibres. In this embodiment, the fibre layers that are laminated onto the sides  354 ,  358  of the shear web body  350  are integrally formed as part of the two projections  373 ,  376  of the web foot flange  370 . 
         [0108]    Since the pre-formed web foot flange  370  only maintains a rough shape for the final flange, it is necessary to utilise a forming tool in order to define the angle of the base part of the web foot flange  370  relative to the shear web body  350 . Accordingly, a primary base plate  398  is utilised to define the angle of the base part of the web foot flange  370  relative to the shear web body  398 . The first vacuum bag  390  is sealed to the base plate  398  via a first sealant and to the first side  354  of the shear web body  350  via a second sealant  392 . Similarly, the second vacuum bag  395  is sealed to the base plate  398  via a first sealant  396  and to the second side  358  of the shear web body  350 . The fibre material of the pre-formed web foot flange  370  may be provided with a tackifier or a SAERfix® fabric in order for the fibre layers to maintain their shape during layup. Alternatively, additional fibre layers comprising e.g. a tackifier or a SAERfix® fabric may be arranged to cover the projections  373 ,  376  in order to maintain n the shape. 
         [0109]    The mould cavity formed between the vacuum bags  390 ,  395 , the shear web body  350  and the base plate  398  may be connected to a vacuum pump and a resin source similar to the first embodiment in order to inject resin into the mould cavity and impregnate the fibre material of the pre-formed web foot flange  370 . Finally, the resin is cured so that a laminate bonding is formed between the web foot flange  370  and the first end  353  of the shear web body  350 . 
         [0110]    The reinforcement fibres used in the web foot flanges according to the first and the second embodiment are advantageously glass fibres. The same applies to the additional fibre layers used for laminating the web foot flange onto the shear web body. However, other applicable reinforcement fibre types could also be used. 
         [0111]    In the shown embodiments, the ends of the shear web body have been described as rounded. However, it is also possible to use other shapes, such as chamfered or bevelled ends. However, it is advantageous that a large laminate bonding surface is formed between the ends of the shear web body and the recess of the web foot flange in order to provide a stronger mechanical attachment. 
       LIST OF REFERENCE NUMERALS 
       [0112]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 2 
                 wind turbine 
               
               
                 4 
                 tower 
               
               
                 6 
                 nacelle 
               
               
                 8 
                 hub 
               
               
                 10 
                 blade 
               
               
                 14 
                 blade tip 
               
               
                 16 
                 blade root 
               
               
                 18 
                 leading edge 
               
               
                 20 
                 trailing edge 
               
               
                 22 
                 pitch axis 
               
               
                 30 
                 root region 
               
               
                 32 
                 transition region 
               
               
                 34 
                 airfoil region 
               
               
                 36 
                 pressure side shell 
               
               
                 38 
                 suction side shell 
               
               
                 40 
                 shoulder 
               
               
                 41 
                 main laminate/spar cap of pressure side 
               
               
                 42 
                 fibre layers 
               
               
                 43 
                 sandwich core material 
               
               
                 45 
                 main laminate/spar cap of suction side 
               
               
                 46 
                 fibre layers 
               
               
                 47 
                 sandwich core material 
               
               
                 50 
                 first shear web 
               
               
                 51 
                 sandwich core material of first shear web 
               
               
                 52 
                 skin layer(s) 
               
               
                 253, 353 
                 First end of shear web body 
               
               
                 254, 354 
                 First side of shear web body 
               
               
                 55 
                 second shear web 
               
               
                 56 
                 sandwich core material of second shear web 
               
               
                 57 
                 skin layer(s) 
               
               
                 258, 358 
                 Second side of shear web body 
               
               
                 60, 60′, 160 
                 Filler 
               
               
                 70, 170, 270, 370 
                 First web foot flange 
               
               
                 71, 171 
                 Fibre layer(s) 
               
               
                 72, 172 
                 Fibre layer(s) 
               
               
                 73, 373 
                 First projection 
               
               
                 74 
                 Inner side of first projection 
               
               
                 75 
                 Outer side of first projection 
               
               
                 76, 376 
                 First projection 
               
               
                 77 
                 Inner side of first projection 
               
               
                 78 
                 Outer side of first projection 
               
               
                 280 
                 Fibre layer(s) 
               
               
                 281 
                 Fibre layer(s) 
               
               
                 282 
                 Fibre layer(s) 
               
               
                 290, 390 
                 Forming tool/vacuum bag 
               
               
                 291, 391 
                 Sealant 
               
               
                 292, 392 
                 Sealant 
               
               
                 295, 395 
                 Forming tool/vacuum bag 
               
               
                 296, 396 
                 Sealant 
               
               
                 297, 397 
                 Sealant 
               
               
                 398 
                 Base plate of forming tool 
               
               
                 d 
                 Length of fibre layer connection 
               
               
                 R 0   
                 Radius of curvature of outer side of projection 
               
               
                 R 1   
                 Radius of curvature of inner side of projection 
               
               
                 R 2   
                 Radius of curvature of shear web body end 
               
               
                 θ 
                 Measure of arc