Method of forming a structural connection between a spar cap and a fairing for a wind turbine blade
A method of forming a structural connection between a spar cap 14 and an aerodynamic fairing 12 . A composite comprising an uncured matrix and a compressible solid is applied between the spar cap and fairing and is then compressed and cured to adhere the fairing to the spar cap. The cured matrix composite has a void volume of at least 20%. The high void volume means that as the fairing is compressed into place and compresses the composite, it has space in which to deform so as not to place undue stress on the fairing and to produce a lightweight connection.
1. A method of forming a structural connection between a spar cap and an aerodynamic fairing for a wind turbine blade, the method comprising:
applying a composite between the spar cap and the fairing, the composite comprising an uncured matrix and a compressible solid;
compressing the compressible solid so that composite substantially occupies a space between the spar cap and the fairing;
curing the uncured matrix to maintain the compressible solid in its compressed state with the composite having a void volume of at least 20%, the void volume absent of the matrix and the compressible solid; and
adhering the fairing to the spar cap as the matrix is cured.
2. A method according to claim 1 , wherein the void volume is at least 30%.
3. A method according to claim 1 , wherein the adhering of the fairing to the spar cap is carried out by the matrix.
4. A method according to claim 1 , wherein the matrix comprises an epoxy resin.
5. A method according to claim 1 , wherein the matrix comprises a structural adhesive.
6. A method according to claim 1 , further comprising providing an additional adhesive, wherein the adhering of the fairing to the spar cap is carried out at least in part by the additional adhesive.
7. A method according to claim 1 , wherein the matrix is non-foaming.
8. A method according to claim 1 , wherein the compressible solid is deformed by compression.
9. A method according to claim 8 , wherein the compressible solid is approximately 20% thicker than the space between the spar cap and the fairing when the compressible solid is in an uncompressed state.
10. A method according to claim 8 , wherein the compressible solid comprises a first porous layer facing the fairing and a second porous layer facing the spar cap, the first and second porous layers being separated by a third layer which has a greater thickness and a lower density than the first and second layers.
11. A method according to claim 10 , wherein the first and second layers are woven fibrous layers.
12. A method according to claim 10 , wherein the third layer is formed of fibers which are woven or stitched between the first and second layers.
13. A method according to claim 10 , wherein the solid is impregnated with the matrix prior to the step of applying the composite between the spar cap and the fairing.
14. A method according to claim 1 , wherein the blade is at least 45 meters in length.
15. A wind turbine blade comprising:
a spar with at least one spar cap;
a fairing positioned over the spar cap; and
a composite which substantially fills a space between the spar cap and the fairing,
wherein the composite comprises a cured matrix, a compressed solid and a void volume of at least 20%, the void volume absent of the matrix and the compressible solid.
16. A wind turbine blade according to claim 15 , wherein the void volume is of at least 30%.
17. A wind turbine blade according to claim 15 , wherein the compressible solid comprises a first porous layer facing the fairing and a second porous layer facing the spar cap, the first and second porous layers being separated by a third layer which has a greater thickness and a lower density than the first and second layers.
18. A wind turbine blade according to claim 17 , wherein the first and second layers are woven fibrous layers.
19. A wind turbine blade according to claim 17 , wherein the third layer is formed of fibres which are woven or stitched between the first and second layers.
20. A wind turbine blade according to claim 15 , wherein the composite is arranged to adhere the spar cap to the fairing.
21. A wind turbine blade according to claim 15 , further comprising an additional adhesive arranged to at least partially adhere the spar cap to the fairing.
22. A wind turbine comprising a wind turbine blade according to claim 15 .