Abstract:
A modular fibre reinforced plastic flange for a structural composite beam which comprises a body formed of a plurality of elongate elements arranged in an array, wherein the dimensions of the body are substantially determined by the number and arrangement of the elongate elements in the array, and a skin member at least partially surrounding the array. Also, a structural composite beam comprising the modular fibre reinforced plastic flange and a shear web connected to the skin member of the modular flange. A method of making the modular flange and beams, and a kit of parts for making the modular flange are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/663,296, filed on Oct. 29, 2012, and entitled “A MODULAR STRUCTURAL COMPOSITE BEAM,” which is a continuation of Patent Cooperation Treaty International Patent Application PCT/GB2011/000661, filed Apr. 28, 2011, and entitled “A MODULAR STRUCTURAL COMPOSITE BEAM,” which is incorporated by reference herein in its entirety, and which claims priority to Great Britain Patent Application 1007336.9, filed on Apr. 30, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a modular structural composite beam. In particular, the present invention relates to a modular structural composite beam for use in a wind turbine blade. 
         [0004]    2. Description of the Related Art 
         [0005]    Large wind turbine blades (&gt;35 m in length) are typically constructed by forming a strengthening and stiffening cantilever beam or box spar inside an aerodynamic fairing. The current approach to manufacturing wind turbine blades is to produce each blade either as two half shells with a separate beam, or as two half shells with an integral beam. In both cases, the two half shells are bonded together along their edges to form the complete blade. 
         [0006]    The structural beam comprises flanges at either end which are connected to one another by one, or more commonly two, shear webs. The flanges are made from predominantly unidirectional fibre reinforced plastic and the shear webs consist of predominantly multi-axial (+/−45°) fibre reinforced plastic. 
         [0007]    It is well known in the art to make the beam by moulding the flanges within the half shells of the aerodynamic fairing and then bonding the flanges together with the shear webs when the aerodynamic fairings are joined together. Alternatively the beam is made by moulding a separate beam on a separate tool and then bonding the beam into the aerodynamic fairings when they are joined together. 
         [0008]    These methods each have a number of shortcomings. Firstly, if the unidirectional flange of the beam is moulded within the fairing it is difficult to accurately control the quality of the flange material. This typically results in poor mechanical properties from the flange material leading, in turn, to increased mass required for engineering safety and therefore increased cost. 
         [0009]    If the beam is made separately by moulding on a separate tool some of the above shortcomings may be avoided. However, the cost of the separate tool adds to the overall cost of the component. 
         [0010]    In either case, if a new design or a slight variation in design is required, completely new tools need to be made thereby increasing prototyping time and cost also increasing the cost introducing new models. Similarly, if the use of automation is considered, the cost of automation will be high since then it must be capable of dealing with a number of different beam designs and geometries. 
       SUMMARY OF THE INVENTION 
       [0011]    A design for a modular wind turbine blade is described in the applicant&#39;s published International patent application WO 2009/034291. This application discloses a wind turbine blade which comprises a plurality of standardised component parts which allow for greater design flexibility, for the blade as a whole, than traditional manufacture techniques. However, it only provides limited options for modification of the structural beam design. It is an aim of the present invention to provide a modular structural composite beam which provides improved design flexibility and quality and which can be used as part of a traditional wind turbine blade, as part of a modular wind turbine blade, or in other structural applications such as bridges. 
         [0012]    Accordingly, in a first aspect the present invention provides a modular fibre reinforced plastic flange for a structural composite beam comprising: a body formed of a plurality of elongate elements arranged in an array such that the longitudinal axes of the elongate elements are substantially parallel to one another, wherein the dimensions of the body are substantially determined by the number and arrangement of the elongate elements in the array; and a skin member at least partially surrounding a plurality of the elongate elements in the array. 
         [0013]    By constructing the body of the flange from a plurality of elongate elements with an outer skin the design of the flange can be readily varied by varying the size and configuration of the array of elongate elements and skin member. The provision of a skin member also provides improved shear load performance. 
         [0014]    In a preferred embodiment the skin member fully surrounds the array of elongate elements to provide additional support and structural integrity. 
         [0015]    The skin member preferably comprises first and second skin elements, the first skin element having a concave form and the second skin element being arranged to fit within the first skin element. This arrangement allows the body to be placed in the first skin element before the second skin element is fitted to complete the skin member. In this way the thickness of the body can be varied with little, or no, variation the dimensions of the skin member. 
         [0016]    Preferably the skin member comprises a socket to receive, in use, a shear web. This provides a convenient method of attaching the flange to the shear web and transferring loads between the flange and shear web. 
         [0017]    In a preferred embodiment at least two of the elongate elements comprise different materials. This allows the mechanical properties of the flange to be readily varied. 
         [0018]    In order to further improve the shear load performance, at least one reinforcement layer is preferably at least partially located within the array of elongate elements. 
         [0019]    In a second aspect, the present invention provides a structural composite beam comprising: a modular flange according to the first aspect of the invention; and a shear web connected to the skin member of the modular flange. In this way an improved and more versatile structural composite beam is provided. 
         [0020]    The shear web preferably comprises a structural core located between two composite material layers to provide further structural integrity. The composite material layers are preferably multiaxial composite material. The shear web is advantageous as it can be assembled into the flange as an ‘open’ sandwich panel as the panel is terminated by the socket of the skin member. This means that the shear web(s) can be made in a continuous production process as opposed to a discrete moulding process (which would otherwise be required to ‘close’ the ends of the sandwich panel), thereby reducing production costs and increasing flexibility. 
         [0021]    In a third aspect, the present invention provides a method of forming a modular fibre reinforced plastic flange for a structural composite beam comprising: forming a body from a plurality of elongate elements arranged in an array such that the longitudinal axes of the elongate elements are substantially parallel to one another, wherein the dimensions of the body are substantially determined by the number and arrangement of the elongate elements in the array; and connecting a skin member to the body such that the skin member at least partially surrounds a plurality of the elongate elements in the array. 
         [0022]    The method preferably further comprises: selecting a number and arrangement of elongate elements to define the dimensions of the body; and selecting a skin member which is sized to substantially fit the dimensions of the body. In this way flanges of varying dimensions and mechanical properties can be readily formed from standardised components without the need to re-tool. 
         [0023]    Preferably the skin member comprises first and second skin elements, the first skin element having a concave form and the second skin element being arranged to fit within the first skin element; the method further comprising: locating the body within the first skin element; and locating the second skin element within the first skin element to form a skin member which fully surrounds the body. 
         [0024]    In a fourth aspect, the present invention provides a method of forming a structural composite beam comprising: using the method of the third aspect of the invention; and connecting at least one shear web to the skin member of the modular flange. 
         [0025]    Preferably in the method of the third aspect of the invention, or in the method of the fourth aspect of the invention each component part of the modular flange or structural composite beam is made in a continuous production process. This reduces production costs and improves quality since continuous production processes are less time and labour intensive and more repeatable thereby reducing waste. 
         [0026]    Before the methods of the third or fourth aspects of the invention are carried out, the elongate elements and skin member of the modular flange, and the at least one shear web of the structural composite beam, are preferably in a cured or semi-cured state and exhibit their final form. Thus, the shape and dimensions of the elongate elements, skin member and shear webs are substantially fixed before the modular flange or structural composite beam is assembled. In addition, the principal mechanical properties of the elongate elements, skin member and shear webs are substantially fixed before the modular flange or structural composite beam is assembled. 
         [0027]    In a fifth aspect, the present invention provides a kit of parts for forming modular fibre reinforced plastic flanges comprising: a plurality of elongate elements suitable for forming a body comprising a plurality of elongate elements arranged in an array wherein the longitudinal axes of the elongate elements are substantially parallel to one another; and a plurality of skin members, wherein the plurality of skin members are sized to correspond to predetermined multiples of elongate elements. The kit thereby provides means for producing flanges of varying sizes and mechanical properties. 
         [0028]    The elongate elements and skin members of the kit of parts are preferably in a cured or semi-cured state and exhibit their final form. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    An example of the present invention will now be described with reference to the following drawings in which: 
           [0030]      FIG. 1  shows an exploded schematic view of part of a modular structural composite beam; 
           [0031]      FIG. 2  shows a schematic sectional view of a modular fibre reinforced plastic flange and separate webs; 
           [0032]      FIG. 3  shows a schematic sectional view of part of an assembled modular structural composite beam; 
           [0033]      FIG. 4  shows a schematic sectional view of part of an alternative assembled modular structural composite beam; and 
           [0034]      FIG. 5  shows a schematic sectional view of part of a further alternative assembled modular structural composite beam. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]      FIG. 1  shows an exploded schematic view of a section of a modular structural composite beam  10 . The beam  10  comprises first  20  and second  30  skin elements and a plurality of elongate elements  40 . In addition, the beam  10  comprises two shear webs  50  each comprising a structural core  52  and outer skin layers  54 . 
         [0036]    The structural cores  52  may be made of any suitable material including PVC, PET, balsa wood or STYROFOAM or other structural core material widely known and used in the art. The outer skin layers  54  comprise predominantly multiaxial (±45°) fibre reinforced plastic. The outer skin layers  54  are attached to the cores  52  by an adhesive such as a structural adhesive (such as epoxy, polyurethane, acrylic, silicone) or with a resin such as a polyester, vinylester, epoxy or other structural thermosetting or thermoplasic resin. 
         [0037]    The elongate elements  40  comprise predominantly uniaxial fibre reinforced plastic. The elongate elements are typically ‘preformed’ unidirectional composite materials such as pulltrusions or semi-cured prepreg or intermediate types of materials such that they exhibit their final shape or form before the flange  5  (see  FIG. 2 ) is formed. As shown in  FIG. 1 , the elongate elements  40  are arranged in an array, in this case a three by three array, to form a body  42  which forms the main load bearing component of the flange  5 . The elongate elements  40  are adhered together to form the body  42  either by structural adhesive or by laminating together with structural resin using a process such as hand laminating, vacuum infusion, vacuum consolidation or similar laminating processes used in the art. 
         [0038]    The first and second skin elements  20 ,  30  each comprise predominantly multiaxial fibre reinforced plastic. The first skin element  20  has a U-shaped concave form and the second skin element  30  comprises projections  32  which define sockets  34  at each outer edge of the second skin element  30 . The sockets  34  are sized to receive the edges  56  of the shear webs  50 . 
         [0039]    As shown in  FIG. 2 , in the assembled flange  5  the second skin element  30  fits within the first skin element  20 . Together the two skin elements  20 ,  30  form skin member  60  which fully surrounds the body  42 . In this example, ‘fully surrounds’ means that the skin member  60  encircles the body  42  but does not cover the ends of the body  42 . 
         [0040]    As is also shown in  FIG. 2 , the first and second skin elements  20 ,  30  are sized to fit the body  42 . The dimensions of the body  42  are defined by the number and arrangement of elongate elements in the array. In the example shown in  FIG. 2 , the body  42  comprises a three by three array such that the depth of the body  42  is substantially the same as three times the depth of the elongate elements  40 , and the width of the body  42  is substantially the same as three times the width of the elongate elements  40 . 
         [0041]      FIG. 3  shows the flange  5  assembled together with the shear webs  50 . The shear webs fit into the sockets  34  and are attached by means of an adhesive such as a structural epoxy adhesive. As shown, location of the shear webs  50  in the sockets  34  ‘closes’ the ends of the shear webs  50 . In  FIG. 3  only the upper section of a box beam  10  is shown. It will be appreciated that another flange  5  can be attached to the lower side of the shear webs  50  to form the complete box beam  10 . In addition, the shear webs  50  can be of various depths to vary the depth of the box beam  10 . This depth can be varied along the length of the beam to account, for example, for the taper of a wind turbine blade. 
         [0042]      FIG. 4  shows an alternative configuration of an upper section of a modular structural composite beam  100 . In this case the beam  100  is an I-beam comprising only one shear web  50  located in a central socket  134  of second skin member  130 . The elongate elements  40 ,  140  which form the body  142  of the flange  105  comprise different fibre reinforced plastic materials such that elongate elements  40  may comprise, for example, glass fibre reinforce plastic, and elongate elements  140  may comprise, for example, carbon fibre reinforced plastic. The arrangement of the different material elongate elements  40 ,  140  shown is  FIG. 4  is an example only and any other arrangement may be selected depending of the mechanical properties desired. 
         [0043]    The beam  100  further comprises reinforcement layers  144  located between the layers of elongate elements  40 ,  140  in the body  42 . These reinforcement layers comprise predominantly multiaxial (□±45°) fibre reinforced plastic and provide additional shear strength to the flange  105 . Reinforcement layers  144  may be included in any of the modular structural composite beam configurations described herein. 
         [0044]      FIG. 5  shows a further alternative configuration of an upper section of a modular structural composite beam  200 . elongate elements  40  and the skin member  260  comprises only a single skin element  220  which partially surrounds elongate elements  40   a,    40   b  and  40   c  of the array. 
         [0045]    It will be appreciated that any number of elongate elements  40 ,  140  may be included in the array which forms the body  42 ,  142 ,  242 , and any number of different fibre reinforced plastic materials in any desired arrangement may be selected for the elongate elements. In this way the mechanical properties of the flange  5 ,  105 ,  205  may be varied as desired. 
         [0046]    Referring again to  FIG. 2 , if the width of the body  42  stays the same (three elongate elements wide) but the depth changes (for example, two elongate elements deep) the same skin elements  20 ,  30  can be used since the difference in depth is accommodated by the fact that the second skin element  30  fits into the first skin element  20  until it reaches the body  42 . If desired, the sides  22  of the first skin element  20  may be trimmed to remove the overlap with the projections  32  of the second skin element  30 . Alternatively, a greater depth body  42  (for example, four or more elongate elements deep) can be accommodated by the variable depth capability provided by the interaction of the first and second skin elements  20 ,  30 . In this case the projections  32  of the second skin element  30  may optionally be trimmed to remove the overlap with the sides  22  of the first skin element  20 . 
         [0047]    If the width of the body  42  varies (for example, two elongate elements wide) it is desirable to provide skin elements  20 ,  30  of a suitable size to fit the width of the body  42 . The elongate elements  40  preferably have standard dimensions so that a set of standardised sizes of skin elements  20 ,  30  can be provided to fit various different arrays of elongate elements. 
         [0048]    The fibre reinforced plastic components described above are typically glass fibre reinforced plastics or carbon fibre reinforced plastics as are well known in the art. However any other suitable fibre reinforced plastic material may be used.