Abstract
A wind turbine blade for a wind turbine is a shell structure of a fibre-reinforced composite and comprises a root region and an airfoil region. The root region has ring-shaped cross section and comprises a plurality of elongated bushings 7 with an inner thread 22 and embedded interspaced in the fibre-reinforced polymer so as to substantially follow the circumference of the root region and allow access from the outside to the inner threads. Each fastening member 7 is provided with a notch 60 in the periphery 11 thereof. A rod-shaped locking element 61 passes through the notch 60 in engagement therewith. The locking element 61 is fixedly and tightly fitting arranged in a through-going circular bore 65 extending through the wall of the root region.
Claims
1. A wind turbine blade for a wind turbine rotor comprising a hub from which the wind turbine blade extends when mounted to the hub, the wind turbine blade including a shell structure of a fibre-reinforced composite material comprising fibres embedded in a polymer matrix, the wind turbine blade extending in a longitudinal direction and having a profiled contour including a pressure side and a suction side as well as a leading edge and a trailing edge, said edges defining a chord plane therebetween, when seen in the longitudinal direction the profiled contour comprising a root region with a root end face, an airfoil region and optionally a transition region between the root region and the airfoil region, the root region having a ring-shaped cross section with an outer surface and an inner surface, the root region comprising a plurality of elongated fastening members provided with fastening means and embedded mutually spaced apart in the fibre-reinforced polymer matrix so as to substantially follow a circumference of the root region and allow access from the outside to the fastening means used for mounting the blade to the hub, the elongated fastening members each comprising an outer surface, a first end arranged at the root end face, a second end opposite the first end thereof, a first lateral face, and an opposite second lateral face, wherein at least one of the elongated fastening members comprises metal fibres, a first end thereof being firmly fixed to the fastening member and the remaining portion thereof extending outwardly from the fastening member and being embedded in the polymer matrix of the fibre-reinforced composite material, the metal fibres extending from the fastening members so as to be arranged in at least one separate layer of the fibre-reinforced composite material, wherein the remaining portion of each said metal fibre extends through, and is surrounded by, the polymer matrix, adjacent ones of the remaining portions of the metal fibres being separated from one another by a portion of the polymer matrix.
2. The wind turbine blade according to claim 1, wherein the metal fibres extend from the fastening members so as to be arranged in an at least one separate layer of the fibre-reinforced composite material.
3. The wind turbine blade according to claim 1, wherein the outwardly extending portion of the metal fibres end in a second fibre end.
4. The wind turbine blade according to claim 1, wherein the metal fibres are firmly fixed to the second end of the fastening member.
5. The wind turbine blade according to claim 1, wherein the metal fibres are firmly fixed to an outer peripheral surface of the fastening member.
6. The wind turbine blade according to claim 1, wherein the metal fibres are firmly fixed to the fastening member by casting, gluing, soldering, or brazing.
7. The wind turbine blade according to claim 1, wherein at least 50% of the fastening members are provided with firmly fixed metal fibres.
8. The wind turbine blade according to claim 7, wherein at least 60% of the fastening members are provided with firmly fixed metal fibres.
9. The wind turbine blade according to claim 8, wherein at least 70% of the fastening members are provided with firmly fixed metal fibres.
10. The wind turbine blade according to claim 9, wherein at least 80% of the fastening members are provided with firmly fixed metal fibres.
11. The wind turbine blade according to claim 10, wherein at least 90% of the fastening members are provided with firmly fixed metal fibres.
12. The wind turbine blade according to claim 11, wherein 100% of the fastening members are provided with firmly fixed metal fibres.
13. The wind turbine blade according to claim 1, wherein an E-modulus of the metal fibres is at least twice an E-modulus of glass fibres.
14. The wind turbine blade according to claim 13, wherein the E-modulus of the metal fibres is thrice the E-modulus of glass fibres.
15. The wind turbine blade according to claim 13, wherein the metal fibres comprise steel fibres.
16. The wind turbine blade according to claim 1, wherein the metal fibres have a cross section in a range between 0.04 mm and 1.0 mm.
17. The wind turbine blade according to claim 16, wherein the range is between 0.07 and 0.75 mm.
18. The wind turbine blade according to claim 17, wherein the range is between 0.1 and 0.5 mm.
19. The wind turbine blade according to claim 1, wherein the metal fibres are fixed to the fastening member as a bundle of fibres.
20. The wind turbine blade according to claim 1, wherein the metal fibres extend outwards from the fastening members in a mutually diverging manner.
21. The wind turbine blade according to claim 1, wherein the fastening members are bushings, and the fastening means is a thread in a bore in the bushing.
22. The wind turbine blade according to claim 21, wherein the bushings comprise a uniform cross section.
23. The wind turbine blade according to claim 1, wherein the fastening members are made of metal.
24. The wind turbine blade according to claim 23, wherein the metal comprises steel.
25. The wind turbine blade according to claim 1, wherein the root region further comprises intermediate retaining means comprising metal fibres and arranged in regions between adjacent interspaced lateral surfaces of the fastening members, preferably in each region between adjacent fastening members, and preferably extending at least from the first to the second end of the fastening members when seen in the longitudinal direction of the blade.
26. The wind turbine blade according to claim 25, wherein the metal fibres comprise steel fibres.
27. The wind turbine blade according to claim 25, wherein the intermediate retaining means are in each region between adjacent fastening members and extend at least from the first to the second end of the fastening members when seen in the longitudinal direction of the blade.
28. The wind turbine blade according to claim 25, wherein the intermediate retaining means comprises a number of first layers comprising metal fibres.
29. The wind turbine blade according to claim 28, wherein the intermediate retaining means comprises a number of intermediate second layers comprising a different type of fibres than metal fibres.
30. The wind turbine blade according to claim 28, wherein the different type of fibres comprises glass and/or carbon fibres.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention is explained in greater detail below with reference to the drawings, in which
(2) FIG. 1 shows a wind turbine,
(3) FIG. 2 is a diagrammatic perspective view of a wind turbine blade according to the invention,
(4) FIG. 3 is a perspective, longitudinal, sectional view of a portion of a root region of a first embodiment of a wind turbine blade according to the invention comprising a first embodiment of fastening members provided with metal fibres,
(5) FIG. 4 shows a portion of the root region shown in FIG. 3,
(6) FIG. 5 is a diagrammatic view of a second embodiment of an elongated fastening member provided with metal fibres firmly fixed thereto,
(7) FIG. 6A shows a third embodiment of an elongated fastening member provided with metal fibres firmly fixed thereto,
(8) FIG. 6B shows a fourth embodiment of an elongated fastening member provided with metal fibres firmly fixed thereto,
(9) FIG. 7 shows a fifth embodiment of an elongated fastening member provided with metal fibres firmly fixed thereto,
(10) FIG. 8 shows a sixth embodiment of an elongated fastening member provided with metal fibres firmly fixed thereto,
(11) FIG. 9 shows in an enlarged scale a detail of FIG. 3 and discloses a fastening member in form of a bushing arranged next to a separate pre-made insert,
(12) FIG. 10 is a diagrammatic perspective view of a first embodiment of an embedding element according to the invention,
(13) FIG. 11 is a longitudinal view along the line IV-IV in FIG. 10,
(14) FIG. 12 is a longitudinal sectional view of a blank from which two embedded elements can be made, the blank being shown in a state where it has been cut to provide the two embedding elements,
(15) FIG. 13 is a schematic view of a pultrusion system for manufacturing a pultruded string from which the blank shown in FIG. 12 can be cut,
(16) FIG. 14 is a schematic view of a portion of three embedding elements according to the invention arranged so that the lateral faces thereof abut each other, and
(17) FIG. 15 is a perspective view the root of a wind turbine blade with embedding elements embedded in the root region thereof.
DETAILED DESCRIPTION OF THE INVENTION
(18) FIG. 1 illustrates a conventional, modern upwind turbine 24 according to the so-called Danish concept with a tower 36, a nacelle 25 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 23 and three blades 2 extending radially from the hub 23, each having a blade root 31 nearest the hub, and a blade tip 32 furthest from the hub 23.
(19) As evident seen from FIG. 2, the blade 2 comprises a root region 26 with a root end face 29 closest to the hub, an airfoil region 27 furthest away from the hub, and a transition area 28 between the root region 26 and the airfoil region 27. The airfoil region 27 has an ideal or almost ideal blade shape, whereas the root region 26 has a substantially circular cross section, which reduces storm loads and makes it easier and safer to mount the blade 2 to the hub 23. Preferably, the diameter of the blade root 31 is constant along the entire root region 26. The transition region 28 has a shape gradually changing from the circular shape of the root region 26 to the airfoil profile of an airfoil region 27. The width of the transition region 28 increases substantially linearly with increasing distance from the hub 23.
(20) The blade is often made of two blades halves assembled by being glued or bolted together substantially along a chord plane 35 of the blade. The blade 2 comprises a leading edge 34 facing the rotational direction of the blade 2 when the blade 2 is mounted on the hub 23 and a trailing edge 33 facing in the opposite direction of the leading edge 34. The chord plane 35 extends between the leading edge 34 and the trailing edge 33 of the blade 2. It should be noted that the chord plane does not necessarily run straight over its entire extent, since the blade may be twisted and/or curved, thus providing a 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. Due to the circular cross section, the root region 26 does not contribute to the production of the wind turbine and, in fact, it lowers the production slightly due to the wind resistance.
(21) As seen in FIGS. 3 and 4, the blade including the root region 26 is formed as a shell structure. The shell structure of the root region 26 is ring-shaped and comprises an outer surface 3 formed by an outer layer of a fibre-reinforced polymer matrix advantageously of glass fibres and/or carbon fibres and a resin, such as epoxy, polyester or vinylester, and an oppositely arranged inner surface 4 formed by an inner layer being made of the same material as the outer layer. Elongated fastening members 7 with fastening means 22 are placed between the layers 5, 6. Advantageously, the elongated fastening members 7 are bushings having a circular cross section and comprise a central bore 12 with an inner thread 22 as fastening means. The bushing 7 comprises a first end 9 and an oppositely arranged second end 10. The first end 9 of the bushing 7 is placed at the root end face 29 of the root region. The bushings 7 are arranged mutually spaced apart so as to substantially follow the circumference of the root region and allow access from the outside to the fastening means 22, i.e. the threads used for mounting the blade to the hub. Seen relative to the root region, the outer periphery 11 of the fastening members 7 comprises a radially outer surface, an opposite radially inner surface, a first lateral face, and an opposite lateral face, as shown in FIG. 5.
(22) Intermediate retaining means comprising metal fibres 13 is arranged in each region between adjacent interspaced lateral surfaces 11c, 11d of the fastening members 7, i.e. in the present example the bushings. Further, in the present embodiment the intermediate retaining means are formed of separately manufactured inserts 39. As it appears from FIG. 9, the inserts 39 comprise a first insert part 40 and a second insert part 41. The first insert part 40 essentially corresponds to the region between the lateral faces 11c, 11d of adjacent bushings 7 and is provided with opposite lateral faces 42, 43 formed complimentary to the lateral faces 11c, 11d of the adjacent bushings 7. The inserts 39 substantially extend up next to the adjacent bushings when seen in circumferential direction. Further, the first insert part 40 extends from the first end of the bushings 7 and beyond the second end thereof, as clearly seen in FIG. 9. The second insert part 41 is a wedge-shaped tapering extension of the first insert part 40. As seen in radial direction of the root region, the first insert part 40 has an extent substantially corresponding to that of the bushings.
(23) As seen in FIG. 9, the intermediate retaining means formed of the separately manufactured and pre-formed insert 39 comprises a number of first layers 16 comprising metal fibres and intermediate second layers 37 comprising a second fibre material 38 differing from the metal fibres. The first layers 16 comprising metal fibres 13 may be formed of mats comprising metal fibres. The metal fibres are preferably of a material having an E-modulus of at least twice, preferably thrice the E-modulus of glass fibres. A preferred material for the metal fibres is steel. The steel fibres or steel filaments may also be formed into steel wires having a cross-sectional dimension in the range between 0.04 mm and 1.0 mm, or in the range between 0.07 mm and 0.75 mm in the range between 0.1 mm and 0.5 mm. The second layers 37 comprising a different type of fibres than metal fibres preferably comprise glass and/or carbon fibres. The layers 37 may be formed of fibre mats. During manufacture of the inserts 39 the layers comprising the metal fibres and the layers comprising a second type of fibres differing from the metal fibres are embedded in a suitable resin such as polyester, epoxy or vinylester. One of the suitable methods for manufacturing the inserts 39 is pultrusion, whereby elongated fibre-reinforced products having a uniform cross section may be produced.
(24) As seen in FIG. 3, a wedge-shaped element 17 is arranged behind each bushing 7 as seen in the longitudinal direction of the blade. A first end 18 of the element 17 is arranged in abutment with the second end of the bushing 7, and a second end 19 of the element 17 is tapered. The wedge-shaped elements 17 are made of balsawood or a hard polymer foam or another similar material. In a longitudinal sectional view, the bushing 7 and the abutting wedge-shaped element 17 have a shape corresponding to the shape of the insert 39 so that the wall thickness of the root region decreases gradually in the longitudinal direction of the blade.
(25) As shown in FIGS. 3-4, the bushings 7 are provided with metal fibres 13 having a first fibre end 201 and an opposite second fibre end 202. The first fibre end 201 of the metal fibres is firmly fixed to the second end 10 of the bushing 7, especially the end face of the bushing 7. A portion 203 of the metal fibres extends outwardly from said end face. As mentioned, the metal fibre 13 may be fixed to the end face of the bushings 7 and/or close thereto at the outer surface 11 of the bushings 7.
(26) As shown in FIG. 4, the fibres 13 extend from the second end 10 of the bushing 7 in a fan-shaped manner so that the distance between the second fibre ends 202 of adjacent fibres exceeds the distance between the first ends 201 of adjacent fibres. The outwardly extending portions 203 of the metal fibres 13 are embedded in the polymer matrix of the fibre-reinforced composite material of the root region. In addition to the metal fibres 13 the fibre-reinforced composite material of the root region comprises additional fibres, which also may be metal fibres and/or fibres other than metal fibres such as carbon and/or glass fibres. Preferably, the metal fibres are steel fibres and may be firmly fixed to the bushings 7 by welding, casting, gluing, soldering or brazing depending on the considered most suitable method and further depending on the material of the fibres and the bushings 7. The metal fibres may, however, also be firmly fixed to the bushings 7 by mechanical means. As an example, the first fibre end of the metal fibres 13 may be firmly clamped between portions of the bushings 7 such as in a compressed opening in the bushing 7.
(27) FIG. 5 shows a second embodiment of the bushing 7 comprising metal fibres 13 firmly fixed to the outer periphery 11 of the bushing 7. The outer periphery of the bushing 7 is corrugated so as to increase the surface area thereof.
(28) FIG. 6A shows a third embodiment of a bushing 7 provided with outwardly extending metal fibres 13. The metal fibres 13 are arranged in unidirectional fibre bundles 204. Each bundle 204 is firmly fixed to the second end 10 of the bushing 7. The bundle 204 is fixed to the second end 10 in separate circular rows. A first circular row is placed near the periphery of the second end 10 and a second circular row is placed inwardly of the first row. The bushing 7 and the fibre bundles 204 are embedded in the polymer matrix of the fibre-reinforced composite material of the root region. Additional fibres, such as steel fibres or fibres of a different material than metal, are preferably placed in the area between the bundles 204. The fibre bundles 204 are firmly fixed to the bushings 7 as explained above.
(29) FIG. 6B shows a fourth embodiment of a bushing 7 comprising metal fibres 13. The metal fibres 13 are arranged unidirectionally and each of the fibres is separately firmly fixed to the bushing 7.
(30) FIG. 7 shows a fifth embodiment of a bushing 7 comprising metal fibres 13. The metal fibres 13 are firmly fixed to the second end 10 in bundles 204 and are arranged multidirectionally. As shown, layers of a second fibre material 38 different from metal fibres are arranged between the fibre bundles 204 extending from the second end 10 of the bushing 7 so as to substantially form a fan. However, as shown, some of the metal fibres 13 may cross and pass through the layers of the second fibre material 38 different from metal fibres. As mentioned above, the bushings 7, the metal fibres 13 and the second fibre material 38 are embedded in the polymer matrix of the fibre-reinforced composite material of the root region. Preferably, the layers of the second fibre material 38 are made of glass and/or carbon fibres.
(31) FIG. 8 shows a sixth embodiment of an elongated bushing 7 provided with metal fibres 13. The metal fibres 13 are arranged in separate layers 205 of metal fibres 13, said layers being in form of fibre bundles, fibre mats or fibre strips. A first end of the fibres bundles, mats or strips is firmly fixed to the second end 10 of the bushing 7. Between layers 205 of metal fibres 13, a layer 206 of a second fibre material different from metal is arranged. The layers 205 of metal fibres and the layer 206 of a second fibre material are embedded in the polymer matrix of the fibre-reinforced composite material of the root region.
(32) The metal fibres, filaments or wire may have a cross-sectional dimension in the range between 0.04 mm and 1.0 mm, or in the range between 0.07 mm and 0.75 mm, or in the range between 0.1 mm and 0.5 mm. In some of the embodiments of the longitudinal fastening members, such as the bushing 7, the metal fibres may be formed into fibre mats, strips or bundles which may be unidirectional mats, strips or bundles, multidirectional mats, strips or bundles, woven mats or strips, or mats or strips comprising chopped fibres. Additionally, the metal fibres, filaments or wires may be incorporated into mats, strips or bundles comprising a different type of fibres than metal fibres, such as carbon fibres and/or glass fibres, i.e. the metal fibres may be incorporated into so-called hybrid mats, strips or bundles.
(33) The percentage by volume of metal fibres in the mats, strips or bundles may be 20, 30, 40, 50, 60, 70, 80 90 or 100, the remaining fibres being a different type of fibres, preferably glass and/or carbon fibres. Correspondingly, the percentage by volume of metal fibres in the root region, where metal fibres are provided, may be 20, 30, 40, 50, 60, 70, 80 90 or 100, the remaining fibres being a different type of fibres, preferably glass and/or carbon fibres.
(34) The embodiment of the embedding element 1.sup.2 according to the invention shown in FIGS. 10 and 11 is elongated and has a first end 3.sup.2 and an opposite second end 4.sup.2, a first longitudinal lateral face 5.sup.2 and an opposite second longitudinal lateral face 6.sup.2. Further, the embedding element has an upper face 7.sup.2 and a lower face 8.sup.2 interconnecting the longitudinal lateral face 5.sup.2, 6.sup.2. The first longitudinal lateral face 5.sup.2 extends substantially convexly in a cross-sectional view of the embedding element and the second longitudinal lateral face 6.sup.2 extends substantially correspondingly concavely in a cross-sectional view of the embedding element 1.sup.2. The upper face 7.sup.2 and the lower face 8.sup.2 are essentially parallel at least over about half the length thereof. Over a remaining portion 22.sup.2 of the length of the upper face 7.sup.2, the upper surface taper gradually towards the lower face 8.sup.2 so as to form a wedge shaped embedding element 1.sup.2.
(35) The embedding element 1.sup.2 is formed of a fibre-reinforced composite material 9.sup.2 comprising fibres embedded in a polymer matrix. The fibres may be glass fibres and/or carbon fibre and/or metal fibres, such as preferably steel or iron fibres and the polymer matrix may be a resin such a polyester, epoxy or vinylester.
(36) In the fibre-reinforced composite material 9.sup.2 of the embedding element 1.sup.2, an elongated fastening element 10.sup.2 is embedded. The elongated fastening element 10.sup.2 has an outer surface 11.sup.2, a first end 12.sup.2 and an opposite second end 13.sup.2. Additionally, the elongated fastening element 10.sup.2 is provided with an inner longitudinal bore 14.sup.2 extending from the first end 12.sup.2 thereof and being provided with an inner thread 15.sup.2.
(37) In the embodiment shown in FIGS. 10 and 11, the elongated fastening element 10.sup.2 has a substantially circular cylindrical shape, the outer surface 11.sup.2 thereof being however corrugated.
(38) The elongated fastening element 10.sup.2 is provided with metal fibres 16.sup.2, preferably formed by iron or steel. A first end 17.sup.2 of the metal fibres 16.sup.2 is firmly fixed to the second end 13.sup.2 of the fastening element 1.sup.2 and a portion 18.sup.2 extends essentially axially outwardly from said second end and ends in a second end 19.sup.2 of the metal fibres 16.sup.2.
(39) As described below with reference to FIGS. 12 and 13, the embedding element 1.sup.2 may be manufactured by pultrusion in a pultrusion system 40.sup.2. Pairs 20.sup.2, 20.sup.2 of fastening elements are formed by connecting opposite ends of metal fibres 16.sup.2 to second ends 13.sup.2, 13.sup.2 of two fastening elements 10.sup.2, 10.sup.2 facing each other as shown in FIG. 13. Further, a rod 21.sup.2 of preferably a fibre-reinforced polymer may with its opposite ends be fastened to the second ends 13.sup.2, 13.sup.2 of the fastening elements 10.sup.2, 10.sup.2 facing each other. Thereby, the pairs 20.sup.2, 20.sup.2 of fastening elements have at least a certain ridigity. Thereafter pairs 20.sup.2, 20.sup.2 of fastening elements are mutually connected by means of threaded rods 30.sup.2 preferably made of plastic threaded into the inner thread 15.sup.2 in the inner longitudinal bore 14.sup.2 in the first ends 12.sup.2, 12.sup.2 of juxtaposed pairs of fastening elements 10.sup.2, 10.sup.2, whereby a string 37.sup.2 of fastening elements has been formed.
(40) The string 37.sup.2 of fastening elements is as illustrated in FIG. 13 introduced into the pultrusion system 40.sup.2, comprising a receiving section 41.sup.2 together with webs or bundles of fibre-reinforced materials such as webs or bundles of glass fibres and/or carbon fibres and/or metal/fibres. The webs or bundles of fibres are designated with the reference number 42.sup.2 and 43.sup.2. From the receiving section 41.sup.2 a string 44.sup.2 comprising the string 37.sup.2 of fastening elements and the fibre webs or bundles 42.sup.2, 43.sup.2 is introduced into a resin applicator and resin heating and curing apparatus 45.sup.2 with a resin reservoir 46.sup.2, to supply resin thereto. The string 44.sup.2 that has been saturated with resin in the resin applicator and resin heating and curing apparatus 45.sup.2 leaves said apparatus through a nozzle 46.sup.2 from which a pultruded string 47.sup.2 extends having a cross-section of the embedding element 1.sup.2 in the not-tapered portion thereof. The pultruded string 47.sup.2 is extracted from the nozzle by means of a pulling device 48.sup.2. On the downstream side of the pulling device 48.sup.2, a cutting device 49.sup.2 is arranged. The cutting device 49.sup.2 cuts the pultruded string between to fastening elements 10.sup.2, i.e. the area where the fastening elements 10.sup.2, 10.sup.2 are connected first end 10.sup.2 against first end 10.sup.2 by means of the threaded rod 30.sup.2. Thereby, a blank 50.sup.2 comprising two embedding elements 10.sup.2, 10.sup.2 is provided.
(41) FIG. 12 illustrates how this blank 50.sup.2 is cut through along an inclined cutting line 51.sup.2 extending between the upper and lower face thereof. Thereby, two identical embedding elements 10.sup.2, 10.sup.2, are provided, the cut along the inclined cutting line 51.sup.2 providing the tapering portion 22.sup.2of the upper face 7.sup.2 of the embedding elements.
(42) As shown in FIG. 14, several embedding elements 1.sup.2 may be arranged in parallel to allow the convex lateral faces 5.sup.2 to engage the concave lateral faces 6 and such that the first ends 3.sup.2 of the embedding elements 1.sup.2 are placed in a common plane. Due to the concave and convex lateral faces the embedding elements 1.sup.2 may form a curve, such as a circle in a plane perpendicular to the longitudinal axis of the embedding elements 1.sup.2.
(43) FIG. 15 illustrates the root region 26.sup.2, the transition region 28.sup.2 and a portion of the airfoil region 27.sup.2 of a wind turbine blade made of a fibre composite material, and wherein embedding elements 1.sup.2 according to the invention have been embedded in the root along the circumference thereof, such as to allow access to the threaded holes 14.sup.2, 15.sup.2 of the embedding elements 1.sup.2 from the root end face 29.sup.2 of the blade root. The embedding element 1.sup.2 has been arranged in the manner disclosed in FIG. 14, wherein the first lateral face of each embedding element engage the second lateral face of the juxtaposed embedding element. The fibre-reinforced composite material of the root region, wherein the embedding elements 1 are embedded comprises fibres embedded in a polymer matrix. The fibres are preferably glass and/or carbon and/or metal fibres preferably steel fibres and the polymer may be a resin such as polyester, epoxy and vinylester.
LIST OF REFERENCE NUMERALS
(44) 2 Wind turbine blade 3 Outer surface of root 4 Inner surface of root 5 Outer layer 6 Inner layer 7 Elongated fastening member (bushing) 9 First end of fastening member 10 Second end of fastening member 11 Outer periphery of fastening member 12 Central bore 13 Metal fibres 16 First layer comprising metal fibres 17 Wedge-shaped element 18 First end of element 19 Second end of element 22 Fastening means (inner threads) 23 Hub 24 Wind turbine 25 Nacelle 26 Root region 27 Airfoil region 28 Transition region 29 Root end face 31 Blade root 32 Blade tip 33 Trailing edge 34 Leading edge 35 Chord plane 36 Tower 37 Second layers 38 Second fibre material 39 Insert 40 First insert part 41 Second insert part 42 Lateral face of insert 43 Lateral face of insert 46.sup.2 Resin reservoir 201 First fibre end 202 Second fibre end 203 Outwardly extending portion of metal fibres 204 Metal fibre bundle 205 Separate layer of metal fibres 206 Layer of a second fibre material 1.sup.2 Embedding element 3.sup.2 First end of embedding element 4.sup.2 Second end of embedding element 5.sup.2 First longitudinal lateral face 6.sup.2 Second longitudinal lateral face 7.sup.2 Upper face 8.sup.2 Lower face 9.sup.2 Fibre-reinforced composite material of the embedding element 10.sup.2 Elongated fastening element 11.sup.2 Outer surface of elongated fastening element 12.sup.2, 12.sup.2 First end of fastening element 13.sup.2, 13.sup.2 Second end of fastening element 14.sup.2 Longitudinal bore 15.sup.2 Inner thread 16.sup.2 Metal fibres 17.sup.2 First end of metal fibres 18.sup.2 Portion of metal fibres 19.sup.2 Second end of metal fibres 20.sup.2 ,20.sup.2 Pairs of fastening elements 21.sup.2 Rod 22.sup.2 Tapering portion of upper face 30.sup.2 Threaded rod made of plastic 37.sup.2 String of fastening elements 40.sup.2 Pultrusion system 41.sup.2 Receiving section 42.sup.2 Webs of fibres 43.sup.2 Bundles of fibres 44.sup.2 String 45.sup.2 Resin applicator heating and curing apparatus 46.sup.2 Nozzle 47.sup.2 Pultruded string 48.sup.2 Pulling device 49.sup.2 Cutting device 50.sup.2 Blank 51.sup.2 Inclined cutting line
