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A connection between composites (10, 12) with non-compatible properties and a method of preparing of such connections are provided. The composites comprise first and second type fibres, respectively, as well as resin. The connection comprises a transition zone (52) between the composites (10, 12) ha

A connection between composites (10, 12) with non-compatible properties and a method of preparing of such connections are provided. The composites comprise first and second type fibres, respectively, as well as resin. The connection comprises a transition zone (52) between the composites (10, 12) having a layered structure. The transition zone may optionally comprise a transition member and the transition member may optionally be integrated with one or more of the composites. Examples of non-compatible properties where the present connection will be appreciated are great differences in stiffness, e.g. Young's modulus, or in coefficient of thermal expansion.

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The invention claimed is: 1. A connection for a wind turbine blade between two composites, said connection comprising: a first composite member comprising first fibres and a first resin; a second composite member comprising second fibres and a second resin, the second fibres being different than th

The invention claimed is: 1. A connection for a wind turbine blade between two composites, said connection comprising: a first composite member comprising first fibres and a first resin; a second composite member comprising second fibres and a second resin, the second fibres being different than the first fibres; and a connection between the first and the second composite members comprising a transition zone having a layered structure, wherein the transition zone comprises layers comprising the first fibres and the second fibres, each of said layers having substantially the same fibre composition as either the first composite member or the second composite member; and in a part of the transition zone, layers comprise substantially the first fibres from the first composite member extending beyond the layers of fibres comprising substantially the second fibres of the second composite member. 2. The connection according to claim 1, wherein at least one physical property of the first composite member is significantly different from that of the second composite member. 3. The connection according to claim 2, wherein the coefficient of thermal expansion of the first composite member is significantly different from the coefficient of thermal expansion of the second composite member. 4. The connection according to claim 2, wherein a Young's modulus of the first composite member is significantly different from a Young's modulus of the second composite member. 5. The connection according to claim 1, wherein the first type fibres are selected from the group consisting of carbon fibres, glass fibres, aramid fibres, synthetic fibres, bio fibres, mineral fibres, metal fibres, boron fibres and combinations of these. 6. The connection according to claim 1, wherein the second type fibres are selected from the group consisting of carbon fibres, glass fibres, aramid fibres, synthetic fibres, bio fibres, mineral fibres, metal fibres, boron fibres and combinations of these. 7. The connection according to claim 1, wherein at least one of the first resin and the second resin are based on unsaturated polyester, polyurethane, polyvinylester, epoxy, thermoplastics, or combinations of these. 8. The connection according to claim 7, wherein the first resin and the second resin have substantially the same composition. 9. The connection according to claim 1, wherein an overall plane of the interface between the transition zone and at least one of said composite members constitutes an overall angle of less than about 10° to the surface of one of said composite members. 10. The connection according to claim 1, wherein a layer in the transition zone comprises oriented fibres. 11. The connection according to claim 1, wherein the fibres are provided as prepregs, semi-pregs, woven or non-woven fabrics, mats, preforms, pre-consolidated pre-forms, individual or groups of fibres, tows, tow-pregs or a combination of these. 12. The connection according to claim 1, wherein at least one of the composite members is at least partially uncured at the time when the connection is prepared. 13. The connection according to claim 1, wherein at least one of the composite members is substantially or fully cured at the time when the connection is prepared. 14. The connection according to claim 1, wherein the transition zone comprises a transition member. 15. The connection according to claim 14, wherein said transition member is prepared directly on at least one of the composite members. 16. The connection according to claim 14, wherein said transition member is an integrated part of at least one of the composite members. 17. The connection according to claim 14, wherein said transition member is prepared in isolation from said composite members. 18. The connection according to claim 1, wherein the layers of said layered structure of the transition zone is substantially parallel to the overall plane of the interface between the transition zone and at least one of said composite members. 19. The connection according to claim 1, wherein the transition zone comprises a macro-grading in the form of a number of layers, each comprising fibres having either substantially the same fibre composition as the first composite member or substantially the same fibre composition as the second composite member. 20. The connection according to claim 1, wherein the layers of said layered structure of the transition zone are substantially parallel to a surface of at least one of the composite members. 21. The connection according to claim 1, wherein the transition zone is integrated at least partially with the first composite member, and interlaced layers comprising fibres having substantially the same fibre composition as a second composite member extend from within said first composite member to beyond said first composite member or vice versa from a second composite member. 22. The connection according to claim 21, wherein the interlaced layers comprise fibres of a first composite member overlaying fibres of the second composite member to define an overlay distance, the overlay distance being greater than a maximum shear stress zone defined as an end of a respective fibre which when overlayed by a respective end of an adjacent fibre in the transition zone is subjected to shear stress above an average level of shear stress to which a fibre is subjected. 23. The connection according to claim 21, wherein a distance between ends of the fibre layers comprising fibres having substantially the composition of the second composite member within the first composite member is larger than an end portion of a respective fibre which is subjected to shear stress above an average shear stress of a remaining portion of the fibre. 24. The connection according to claim 1, wherein the transition zone comprises layers comprising fibres extending from the first composite member into the second composite member and/or layers comprising fibres extending from the second composite member into the first composite member. 25. A connection according to claim 1, wherein the first fibres are carbon-fibres and the second type fibres are glass-fibres or vice versa. 26. A transition member having an area enhanced for connecting to a first composite member and an area enhanced for connecting to a second composite member, said transition member comprising two layers or sheets comprising fibres, one of the layers comprising fibres substantially the same as fibres comprising the first composite member and another of the layers comprising fibres having substantially the same fibres comprising the second composite member, wherein the two layers are partially interlaced, and the fibres comprising the first composite member are different than the fibres comprising the second composite member. 27. A connection for connecting two relatively incompatible composite members, the connection comprising: a first composite member comprising first fibres and a first resin, a second composite member comprising second fibres and a second resin, the first composite member and the second composite member possessing different physical properties, wherein said connection comprises a transition zone having a layered structure, wherein the transition zone comprises layers comprising fibres, each of said layers having substantially the same fibre composition as either the first composite member or the second composite member, and in a part of the transition zone, layers comprising fibres having substantially the same fibre composition as one of the composite members extend beyond the layers of fibres comprising substantially the same fibre composition as the other composite member. 28. The connection according to claim 1, wherein the first composite member comprises a mainly carbon-fibre reinforced part for forming a spar for a wind turbine blade and the second composite member comprises a mainly glass-fibre reinforced part of the spar for a wind turbine blade. 29. The connection of claim 27, wherein the different physical properties comprises a coefficient of thermal expansion and/or Young's modulus. 30. The connection of claim 3, wherein the difference in coefficient of thermal expansion is more than 3×10-6° C-1. 31. The connection of claim 4, wherein the difference in Young's modulus is larger than 25% of either the Young's modulus of the first composite member or the Young's modulus of the second composite member, whichever one has a lower value. 32. The connection of claim 5, wherein the first fibres are carbon-fibres. 33. The connection of claim 6, wherein the second fibres are glass-fibres. 34. The connection according to claim 9, wherein the overall angle is less than about 2° to the surface of one of said composite members. 35. The connection according to claim 10, wherein the transition zone comprises unidirectional fibres or biaxial fibres. 36. The connection of claim 17, wherein the transition member is pre-consolidated prior to connecting to said composite members. 37. The connection according to claim 19, wherein a first side of a stack of the layers of fibres is connected to the first composite member and a second side of the stack is connected to the second composite member. 38. The connection of claim 22, wherein the overlay distance of the interlace is greater than two times the extent of the end-condition of the interfacial stress between fibre layers comprising fibres having substantially the same fibre composition as the first composite member and fibre layers comprising fibres having substantially the same fibre composition as the second composite member. 39. The connection according to claim 23, wherein the distance is two times end portion. 40. The connection according to claim 25, wherein the first resin and the second resin are epoxy-based. 41. The connection for a wind turbine blade of claim 1, wherein the first fibres are composed of a composition which is different than a composition which composes the second fibres. 42. The transition member of claim 26, wherein fibres which compromise the first composite member are composed of a composition which is different than a composition which composes the fibres of the second composite member.