Insert for forming an end connection in a uni-axial composite material

Abstract

An insert for forming an end connection in a uni-axial composite material, and an end connection comprising at least one insert, is disclosed. The insert comprises a sleeve which comprises a plurality of fibers having a multi-axial arrangement. At least a portion of the interior surface of the sleeve comprises a thread formation. A method of forming an end connection in a uni-axial composite material is also disclosed. The method comprises providing a sleeve comprising a plurality of fibers having a multi-axial arrangement and providing a thread formation on at least a portion of the interior surface of the sleeve. The sleeve is positioned and secured within the uni-axial composite material.

Claims

1. An end connection comprising: a uni-axial composite material; and at least one insert for forming an end connection in the uni-axial composite material, the at least one insert comprising a sleeve, wherein the sleeve comprises a plurality of fibres having a multi-axial arrangement, wherein at least a portion of the interior surface of the sleeve comprises a thread formation, the at least one insert being embedded within the uni-axial composite material.

2. The end connection according to claim 1 wherein the sleeve comprises at least one layer of multi-axial fibre fabric.

3. The end connection according to claim 2 wherein the sleeve comprises a plurality of layers of multi-axial fibre fabric.

4. The end connection according to claim 2 wherein the sleeve further comprises at least one helically wound fibre layer.

5. The end connection according to claim 4 wherein the sleeve comprises a plurality of helically wound fibre layers.

6. The end connection according to claim 4 wherein the or each helically wound fibre layer overlies a layer of multi-axial fibre fabric.

7. The end connection according to claim 6 wherein the fibres of the or each helically wound fibre layer are substantially aligned with a path defined by crests of the thread formation.

8. The end connection according to claim 1 wherein the sleeve comprises a fibre reinforced plastic.

9. The end connection according to claim 8 wherein the sleeve comprises a filament wound fibre composite tube.

10. The end connection according to claim 9 wherein the winding angle of 90% of the fibres is substantially equal to , where is the thread angle of the thread formation.

11. The end connection according to claim 1 wherein the fibres are embedded within a cured resin matrix.

12. The end connection according to claim 1 wherein the thread formation is integrally formed with the sleeve.

13. The end connection according to claim 12, wherein the thread formation is a cut thread formation.

14. The end connection according to claim 1 further comprising a helical thread insert located within the thread formation.

15. A wind turbine blade comprising a plurality of inserts embedded within a root of the wind turbine blade, each insert comprising a sleeve, wherein the sleeve comprises a plurality of fibres having a multi-axial arrangement, wherein at least a portion of the interior surface of the sleeve comprises a thread formation.

16. The blade according to claim 15, further comprising a helical thread insert located within the thread formation and remains in situ during operation.

17. The blade according to claim 15, wherein the sleeve comprises at least one layer of multi-axial fibre fabric.

18. The blade according to claim 17, wherein the sleeve comprises a plurality of layers of multi-axial fibre fabric.

19. The blade according to claim 17, wherein the sleeve further comprises at least one helically wound fibre layer.

20. The blade according to claim 19, wherein the sleeve comprises a plurality of helically wound fibre layers.

21. The blade according to claim 19, wherein the or each helically wound fibre layer overlies a layer of multi-axial fibre fabric.

22. The blade according to claim 21, wherein the fibres of the or each helically wound fibre layer are substantially aligned with a path defined by crests of the thread formation.

23. The blade according to claim 15, wherein the sleeve comprises a fibre reinforced plastic.

24. The blade according to claim 23, wherein the sleeve comprises a filament wound fibre composite tube.

25. The blade according to claim 24, wherein the winding angle of 90% of the fibres is substantially equal to , where is the thread angle of the thread formation.

26. The blade according to claim 15, wherein the fibres are embedded within a cured resin matrix.

27. The blade according to claim 15, wherein the thread formation is integrally formed with the sleeve.

28. The blade according to claim 27, wherein the thread formation is a cut thread formation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

(2) FIG. 1 is a schematic cross-sectional drawing of a female thread cut directly into the end of a uni-axial composite material;

(3) FIG. 2 is a schematic cross-sectional drawing of a prior art metallic insert bonded into the end of a uni-axial composite material;

(4) FIG. 3a is a schematic cross-sectional drawing of a filament wound composite tube and a schematic drawing of a female thread cutting tool before a thread cutting operation;

(5) FIG. 3b shows the components of FIG. 3a during the thread cutting operation;

(6) FIG. 3c shows the components of FIG. 3a after the thread cutting operation is complete;

(7) FIG. 4a is a schematic drawing of a threaded mandrel;

(8) FIG. 4b shows the threaded mandrel of FIG. 4a with a cross-sectional schematic representation an insert according to the present invention during fabrication;

(9) FIG. 4c shows a cross-sectional schematic drawing of the insert of FIG. 4b when removed from the threaded mandrel;

(10) FIG. 5a is a drawing of the first stages of fabrication of an insert in accordance with the present invention;

(11) FIG. 5b is a drawing of the second stage of fabrication of the insert of FIG. 5a;

(12) FIG. 5c is a drawing of the later stages of fabrication of the insert of FIG. 5a;

(13) FIG. 5d is a drawing of the completed insert of FIG. 5a;

(14) FIG. 6 is a schematic cross-sectional drawing of an insert according to the present invention bonded into the end of a uni-axial composite material; and

(15) FIG. 7 is a schematic cross-sectional drawing of the insert of FIG. 6 with a thread insert;

(16) FIG. 8 is a drawing of a wind turbine blade with inserts embedded within a root of the wind turbine blade.

(17) FIGS. 3a to 3c schematically illustrate a first method of fabricating an insert according to the present invention. FIG. 3a shows a filament wound fibre composite tube 10 and a thread cutting tool 12. The winding angle of the majority of the fibres 20 of the tube 10 is approximately equal to (5E), where is the thread angle of the thread cutting tool 12. Ideally, the filament wound fibre composite tube 10 has 90% of its fibres wound at . However, a tube having between 75% to 95% of its fibres wound at may also be used.

DETAILED DESCRIPTION

(18) For clarity, the winding angle of the fibres 20 is the acute angle that the fibres 20 make with the major axis 11 of the tube 10 when the tube 10 is viewed from the side (FIG. 3a). Similarly, the thread angle of the thread cutting tool 12 is the acute angle that the threads 17 make with the major axis 13 of the thread cutting tool 12 when the thread cutting tool is viewed from the side (FIG. 3a). For the purposes of clarity in the Figures, only fibres 20 having a winding angle of approximately are illustrated in FIG. 3a. However, it will be understood that the tube 10 comprises fibres 20 having a winding angle of approximately .

(19) In one example, the tube 10 may comprise standard e-glass and epoxy resin. However, any other suitable fibre composite material may be used such as e-glass and polyester or vinylester resin or carbon or aramid fibres.

(20) FIG. 3b shows the filament wound fibre composite tube 10 during a thread tapping process. During the thread tapping process the thread cutting tool 12 is screwed into the tube 10 to cut a thread formation 25 in the interior surface of the tube 10. The thread cutting tool 12 is then removed (FIG. 3c). The resulting component is a threaded insert 30 which comprises sleeve 35, formed from the tube 10, having thread formation 25 on its interior surface. The threads 26 of the thread formation have a thread angle which is equal to the thread angle of the thread cutting tool 12 and which is therefore approximately equal to the winding angle of the fibres 20. In use, the insert 30 is bonded into the uni-axial material of the root end of a wind blade as will be described in greater detail below.

(21) FIGS. 4a to 4c schematically illustrate the general principal of a second, alternative, method of fabricating an insert in accordance with the present invention. FIG. 4a shows a threaded mandrel 112 onto which layers 120 of fibres are positioned (FIG. 4b) to build up a sleeve 135. Because the mandrel 112 has a threaded formation 117 on its outer surface, the sleeve 135, which is built up on the threaded mandrel 112, also has a thread formation 125 on its interior surface. In a preferred method of fabrication, described in greater detail below with reference to FIGS. 5a to 5d, layers 220 of multi-axial fibre fabric are positioned on the mandrel and a uni-axial fibre tow 221 is wound over each layer of multi-axial fibre fabric in order to pull the multi-axial fibre fabric into the thread form on the mandrel. However, other methods, discussed below, of building up a sleeve 135 on a threaded mandrel may be used without departing from the present invention.

(22) Once the sleeve 135 has been built up, by any appropriate means, on the threaded mandrel 112 it can be infused with resin, cured and removed from the threaded mandrel 112 to form a pre-cured insert 130. Alternatively the sleeve 135 may be supplied and installed whilst still mounted on the threaded mandrel without any resin having been infused. In this case the insert 130 is infused with resin and cured whilst in-situ as will be described in greater detail below.

(23) FIGS. 5a to 5c show a preferred method of fabricating an insert in accordance with the present invention. As shown in FIG. 5a, in a first process step a layer 220a of low tex (typically 3-24 k) multi-axial fibre fabric is positioned over a threaded mandrel 212. The multi-axial fibre fabric is preferably a fibre braid. However, a sheet fabric, or helically wound tape may also be used.

(24) In a second process step, a uni-axial low tex fibre tow, comprising a plurality of uni-axial fibres, is wound over the multi-axial fibre fabric layer 220a to form a helically wound fibre layer 221a. As can be seen in FIG. 5a, the uni-axial fibre tow is wound onto the mandrel 212 so that it lies within the grooves of the thread formation on the mandrel. This pulls the layer 220a of multi-axial fibre fabric into the thread formation and helps to ensure that the thread formation on the finished insert is a true mould of the thread formation in the threaded mandrel 212. Thus the fibres of the helically wound fibre layer are substantially aligned with a path defined by the crests 127 (FIG. 4c) of the thread formation on the interior surface of the sleeve 235. As can be seen from FIG. 5a, the helically wound fibre layer 221a is not continuous in the axial direction such that it does not totally cover the multi-axial fibre fabric layer below.

(25) FIG. 5b shows a third process step in which a second layer 220b of multi-axial fibre fabric is positioned over the mandrel 212. In a fourth process step, shown in FIG. 5c, an optional guide thread 222 is wound over the second layer 220b of multi-axial fibre fabric in order to pull the second layer 220b of multi-axial fibre fabric into the form of the threaded mandrel 212. The guide thread 222 is then over-wound by a second helically wound fibre layer 221b. This process is repeated 4 or 5 times until the threads of the threaded mandrel 212 are completely filled by the fibre laminate structure which form a sleeve 235. In one example, the sleeve 235 is impregnated with resin and cured before being removed from the threaded mandrel, by unscrewing, to produce a pre-cured insert 230 (FIG. 5d). In an alternative example, described below, the insert 230 is supplied and installed whilst still mounted on the threaded mandrel without any resin having been infused.

(26) As mentioned above, the preferred method of building up the sleeve 135, 235 of the insert 130, 230 on a threaded mandrel is as described with reference to FIGS. 5a to 5c. However, other methods of building up a fibre sleeve on a threaded mandrel may also be used. For example, only one layer of multi-axial fibre fabric may be used, said layer being overlaid with layers of wound uni-axial fibres and/or filament wound layers. Alternatively, the sleeve may be built up only of multi-axial fibre layers. In such a case a vacuum bag, or external female mandrel, may be used to ensure that the fibre layers properly lie within the thread formation of the threaded mandrel.

(27) In a further alternative method, a fibre composite tube made up of layers of multi-axial fibre fabric, wound uni-axial fibre and filament wound fibres, or any combination thereof, laid-up on a plane cylindrical mandrel. In this case the sleeve is infused with resin and cured before being removed from the mandrel and threaded with a thread cutting tool such as is shown in FIGS. 3a to 3c.

(28) The pre-cured inserts, when made by any method, may be installed into the uni-axial composite material of the root of a wind blade (see FIG. 8) in two ways. In the first method a hole is drilled in the root end and the insert is bonded into the hole with adhesive. In an alternative method, the pre-cured insert may be positioned in the uni-axial material of the root during lay-up. The root is then infused with resin and cured to secure the insert in place.

(29) For inserts comprising no resin, the insert is positioned in the uni-axial material of the root during lay-up whilst still supported on the mandrel. The root and insert are then infused with resin together in the same process step and cured. The mandrel may then be removed.

(30) FIG. 6 illustrates an insert, when made/installed by any method, positioned in a uni-axial composite material. As shown, the insert is installed so that its major axis 11 is substantially parallel to the direction of the uni-axial fibres.

(31) In practice, it is preferable that the thread of the insert be re-useable to allow connecting bolts to be installed/removed a number of times for service and maintenance. In order to improve the re-usability of the inserts, a metallic thread insert 300 (FIG. 7) is located within the thread formation on the interior surface of the sleeve. The thread insert 300 initially has a diameter which is slightly larger than the thread formation in the composite insert so that when it is screwed into the thread formation the insert is compressed and held in place by an interference fit.

(32) It is not necessary for the whole of the interior surface of the insert to comprise a thread formation. In one example (not shown) the thread formation exists only at one end of the insert. Such an embodiment may be useful when it is desired to increase the bond area provided on the external surface of the insert.

(33) Although the insert of the present invention has been described with reference to installation within the uni-axial material of the root of a wind blade, it will be appreciated that the insert may also be used in other areas of technology where bolted connections need to be made. Similarly, it will be understood that the insert may be installed in non-uni-axial composite materials or other types of material.

(34) While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.