PULTRUDED BIBRE-REINFORCED STRIP FOR A REINFORCED STRUCTURE, SUCH AS A SPAR CAP

Abstract

A pultruded fibre-reinforced strip (50) configured to be stacked with one or more similar strips (50) to form a spar cap of a wind turbine blade (10), comprising—a core (51) comprising a plurality of first fibres embedded in a resin matrix, the plurality of first fibres being carbon fibres and/or glass fibres, and—a surface layer (52) enclosing and covering the core (51) and comprising a plurality of second fibres imbedded in the resin matrix, the majority of the plurality of second fibres having an elastic modulus less than 10 GPa.

Claims

1-37. (canceled)

38. Pultruded fibre-reinforced strip configured to be stacked with one or more similar strips to form an elongate reinforcing structure, such as a spar cap for a wind turbine blade, the pultruded strip comprising: a core comprising a plurality of first fibres embedded in a resin matrix, the plurality of first fibres being carbon fibres and/or glass fibres, and a surface layer enclosing and covering the core and comprising a plurality of second fibres embedded in the resin matrix, the majority of the plurality of second fibres having an elastic modulus less than 10 GPa, such as less than 8 GPa, such as less than 6 GPa, such as less than 4 GPa.

39. Pultruded strip according to claim 38, wherein the majority of the plurality of the first fibres are carbon fibres and/or glass fibres.

40. Pultruded strip according to claim 38, wherein the majority of the fibres of the core are carbon fibres.

41. Pultruded strip according to claim 38, wherein the fibres of the core essentially consist of carbon fibres.

42. Pultruded strip according to claim 38, wherein the second fibres of the surface layer comprises and/or essentially consist of polymeric fibres, such as polyester and/or polyethylene fibres.

43. Pultruded strip according to claim 38, wherein the majority of the second fibres of the surface layer are polymeric fibres, such as polyester and/or polyethylene fibres.

44. Pultruded strip according to claim 38, wherein the surface layer comprises a mat or a veil, such as a non-woven material comprised of uniformly distributed fibres.

45. Pultruded strip according to claim 38, wherein the surface layer is a resin rich layer.

46. Pultruded strip according to claim 45, wherein the resin rich surface layer has a volume fraction resin of 60% to 90%.

47. Pultruded strip according to claim 38, wherein the strip has a first main surface, an opposite second main surface, a first lateral face and an opposite second lateral face, defining an essentially rectangular cross section.

48. Pultruded strip according to claim 47, wherein the surface layer defined by the opposite main surfaces and the opposite lateral faces cover the subjacent surfaces of the core completely.

49. Pultruded strip according to claim 47, wherein the strip has a thickness between the opposite main surfaces of 1 mm to 20 mm such as 1.5 mm to 15 mm, such as 2 mm to 10 mm, and/or wherein the strip has a width between the opposite lateral faces of 20 mm to 400 mm, such as 20 mm to 300 mm.

50. Pultruded strip according to claim 38, wherein the resin matrix comprises polyester resin, vinyl ester resin or epoxy resin.

51. A pultrusion process for making a pultruded strip suitable to be stacked with one or more similar strips to form an elongated reinforcing structure, such as a spar cap for a wind turbine blade, the pultrusion process comprising: drawing resin impregnated fibres through a pultrusion die to form a core comprises a plurality of first fibres embedded in a resin matrix, the plurality of first fibres being carbon fibres and/or glass fibres, and to form a surface layer enclosing and covering the core and comprising a plurality of second fibres embedded in the resin matrix, the majority of the plurality of second fibres having an elastic modulus less than 10 GPa, such as less than 8 GPa, such as less than 6 GPa, such as less than 4 GPa.

52. Reinforcing structure, such as a spar cap of a wind turbine blade, comprising a stack of a plurality of pultruded strips being connected or integrated together, wherein the strips are pultruded strips according to claim 38.

53. Reinforcing structure, such as a spar cap of a wind turbine blade according to claim 52, wherein the pultruded strips are stacked on top of each other, main surface against main surface.

54. Reinforcing structure, such as a spar cap of a wind turbine blade according to claim 52, wherein the pultruded strips are stacked with an interlayer comprising fibres arranged between the main surfaces of successive pultruded strips and being embedded in a resin.

55. Reinforcing structure according to claim 15, wherein the main surfaces and optionally also the lateral surfaces of the pultruded strips are grinded surfaces.

56. A method of making an elongate reinforcement structure, such as a spar cap for a wind turbine blade comprising: providing a plurality of strips claim 38, forming a laminate by stacking the plurality of strips in a mould, infusing resin through the laminate and allow the resin to cure to form the elongated reinforcement structure, such as a spar cap, for a wind turbine blade.

57. A wind turbine blade comprising a reinforcing structure, such as a spar cap, according to claim 52.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0055] Embodiments of the invention will be described in more detail in the following with regard to the accompanying figures. The figures show one way of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0056] FIG. 1 is a schematic view illustrating an exemplary wind turbine.

[0057] FIG. 2 is a schematic view illustrating an exemplary wind turbine blade.

[0058] FIG. 3 is a schematic view illustrating a cross-section of an exemplary wind turbine blade.

[0059] FIG. 4 is a schematic cross-sectional view of a pultruded strip of fibre-reinforced resin composite material.

[0060] FIG. 5 is a schematic cross-sectional view illustrating a spar cap for a wind turbine blade comprising two laterally adjacent arranged stacks of pultruded strips as shown in FIG. 4 stacked with interlayers comprising fibre material between the succeeding strips.

[0061] FIG. 6 is a schematic cross-sectional view illustrating a spar cap for a wind turbine blade comprising two laterally adjacent arranged stacks of pultruded strips as shown in FIG. 4 stacked without interlayers between the succeeding strips.

DETAILED DESCRIPTION

[0062] FIG. 1 illustrates a conventional modern upwind wind turbine 2 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 blade having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The invention is not limited to use in wind turbines of this type.

[0063] FIG. 2 shows a schematic view of an exemplary wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade with a root end 17 and a tip end 15 and comprises a root region 30 closest to the hub, a profiled or airfoil region 34, 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.

[0064] The airfoil region 34 (also called the profiled region) preferably has an ideal shape with respect to generating hub rotation, 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 of the root region 30 may be constant along the entire root area 30. The transition region 32 present in the wind turbine blade 10 in this example has a transitional profile gradually changing from the circular 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 in an outward direction 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.

[0065] It should be noted that different sections of the blade normally do not have a common plane, since the blade may be twisted and/or curved (i.e. pre-bent) along a direction from the root region to the tip, this being most often the case, for instance to more or less compensate for the local velocity of the blade being dependent on the distance from the hub.

[0066] The wind turbine blade 10 comprises a blade shell which may for instance comprise two blade shell parts, a first blade shell part 24 and a second blade shell part 26, for instance made at least partly of fibre-reinforced polymer. The first blade shell part 24 may for instance be part of a pressure side or upwind blade part. The second blade shell part 26 may for instance be part of a suction side or downwind blade part. The first blade shell part 24 and the second blade shell part 26 are typically joined, such as glued together, along bond lines or glue joints 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Typically, the root ends of the blade shell parts 24, 26 have a semi-circular or semi-oval outer cross-sectional shape that, when the first and second shell parts are joined, forms the root region, such as a circular or oval root region.

[0067] FIG. 3 is a schematic diagram illustrating a cross-sectional view of the exemplary wind turbine blade 10, corresponding to line A-A in FIG. 2. The wind turbine blade 10 comprises shear webs 40, a first spar cap 44 that is part of the pressure side 24 of the blade 10, and a second spar cap 46 that is part of the suction side 26 of the blade 10. The spar caps provide structural strength to the blade and typically extend along the blade in a spanwise direction. Typically, spar caps will extend over 60-95% of the blade length. The trailing edge 20 and leading edge 18 are also indicated in FIG. 3.

[0068] FIG. 4 discloses a schematic cross-sectional view of an exemplary pultruded strip 50 of fibre-reinforced resin composite material. The pultruded fibre-reinforced strip 50 is configured to be stacked with one and more similar strips to form a spar cap for a wind turbine blade and comprises a core 51 and a surface layer 52 enclosing and covering the core 51. In the embodiment shown, the strip 50 has an essentially rectangular cross-section and comprises a first main surface 53, an opposite second main surface 54, a first lateral face 55 and an opposite second lateral face 56. The thickness of the strip between the opposite main surfaces can e.g. be 1 mm to 10 mm, the width of the strip between the opposite lateral faces can e.g. be 20 mm to 400 mm and the length of the strip can e.g. be 10 m to 200 m.

[0069] The core 51 comprises a plurality of first fibres embedded in a resin matrix. The first fibres can comprise carbon fibres and/or glass fibres. At present, it is preferred that the majority of the fibres of the core 51 are carbon fibres or that the core essentially consist of carbon fibre. The core can be provided by biaxial fibre mats, monoaxial fibre mats, rovings, weaved fibre mats, chopped strand mats, non-woven mats of continuous strands, etc. and/or combinations thereof.

[0070] The surface layer 52 defined by the opposite main surfaces and the opposite lateral faces covers and encloses the subjacent surfaces of the core 51 completely. The surface layer 52 comprises a plurality of second fibres imbedded in the resin matrix. A majority of the plurality of the second fibres of the surface layer has an elastic modulus less than 10, 8, 6 or 4 GPa. At present the preferred fibres are polymeric fibres, such as e.g. polyester and/or polyethylene fibres. The surface layer can comprise a non-woven fibre material comprising or essentially consisting of uniformly distributed continuous strands. Further, the surface layer can essentially consist of polymeric fibres, such as polyester and/or polyethylene fibres.

[0071] FIG. 5 is a schematic cross-sectional view illustrating an exemplary spar cap 57 for a wind turbine blade comprising two laterally adjacent arranged stacks 58 of pultruded strips 50 as shown in FIG. 4 stacked with interlayers 59 comprising fibre material between succeeding strips 50. The main surfaces and optionally also the lateral surfaces of the pultruded strips can be grinded surfaces in order to control the roughness and the cleanness to ensure proper bonding to an infusion resin. The fibre material of the interlayers can be a resin-infusion promoting fibre layer promoting infusion of a resin in the interlayers 59. The infusion of the resin in the interlayers 59 can be carried out after the stacks of pultruded strips 50 and interlayers 59 have been arranged on a skin layer of fibres in a mould part for moulding a wind turbine blade half shell. The infusion of resin in the interlayers 59 takes place at the same time as infusion of the shell of the blade half part. Alternatively, the infusion of the interlayers 59 can be carried out in a separate spar cap mould. Subsequently, the moulded spar cap 57 is arranged on the skin layer of fibres in a mould part for moulding a wind turbine blade half shell and the skin layer and additional fibre layers are infused with a resin.

[0072] The surface layer 52 defining the main surfaces 53, 54 of the pultruded strips 50 provides after infusion of the resin a bond of high fracture toughness between the pultruded strips 50 and adjacent interlayers 59. Additionally, the surface layer 52 defining of the lateral faces 55, 56 of the pultruded strips 50 provides at least a sufficient fracture toughness in the connections between the adjacent lateral surfaces 55, 56 of the pultruded strips 50 of the two laterally adjacent arranged stacks 58.

[0073] The infused resin can be the same resin as the resin matrix of the pultruded strips 50.

[0074] FIG. 6 is a schematic cross-sectional view illustrating an exemplary spar cap 157 for a wind turbine blade comprising two laterally adjacent arranged stacks 158 of pultruded strips as shown in FIG. 4 stacked without interlayers between succeeding strips 50.

[0075] The stacks 158 of pultruded strips 50 can be arranged on a skin layer of fibres in a mould part for moulding a wind turbine blade half shell. Thereafter infusion of a resin is carried out on the skin layer and additional fibre layers of the blade shell half part such as fibre layers covering the stacks 158. Thereby, resin will enter between adjacent surfaces 53, 54 and 55, 56 of the adjacent arranged pultruded strips 50 and provide a connection between the adjacent surfaces and thereby the adjacent strips 50. The surface layers 52 of the pultruded strips 50 provide an improvement of the fracture toughness of the mentioned connections. Alternatively, the surface layers 52 of the pultruded strips 50 can be uncured or semi-cured when the pultruded strips are stacked, thereby improving the connection between adjacent surfaces of the strips.

[0076] Alternatively, the stacks of pultruded strips 50 can be arranged in a spar cap mould and adjacent surfaces 53, 54 and 55, 56 of the strips 50 be mutually bonded by infusion of a resin between the adjacent surfaces of the strips. Alternatively, the pultruded strips 50 can be uncured or semi-cured when stacked. After curing of the resin of the pultruded strips 50 the formed spar cap 157 can be arranged on the fibre skin layer arranged on the moulding face of a wind turbine blade half shell mould. The shell is thereafter infused with a resin as described above.

[0077] The infused resin can be the same resin as the resin matrix of the pultruded strips 50.

LIST OF REFERENCES

[0078] 2 wind turbine [0079] 4 tower [0080] 6 nacelle [0081] 8 hub [0082] 10 blade [0083] 14 blade tip [0084] 15 tip end [0085] 16 blade root [0086] 17 root end [0087] 18 leading edge [0088] 20 trailing edge [0089] 24 first blade shell part (pressure side) [0090] 26 second blade shell part (suction side) [0091] 28 bond lines/glue joints [0092] 30 root region [0093] 32 transition region [0094] 34 airfoil region [0095] 40 shear web [0096] 44 first spar cap [0097] 46 second spar cap [0098] 50 pultruded strip [0099] 51 core [0100] 52 surface layer [0101] 53 first main surface [0102] 54 second main surface [0103] 55 first lateral face [0104] 56 second lateral face [0105] 57, 157 spar cap [0106] 58,158 stack [0107] 59 interlayer