Composite structure with steered fibres

Abstract

A composite structure comprising a body, such as an aircraft wing skin; and an opening 11 in the body, such as a manhole, the body comprises steered fibre elements 21-23 and alternating terminated fib

Description

FIELD OF THE INVENTION

[01] The present invention relates to a composite structure, and a method of manufacturing a comprise structure

[02] BACKGROUND OF THE INVENTION

[03] Citation [1] (cited below) examines stress and strain concentrations, using continuous tow steering, around a wingbox access hole. Continuous tow steering around cutouts eliminates fiber cutting, thereby precluding ply-level 3-D stress concentration, which could otherwise lead to delamination-induced damage.

[04] A first problem with Citation [1] is that the thickness of each layer varies around the access hole due to tow overlap.

[05] A second problem with Citation [1] is that the steered shape requires the adjacent tows to tessellate next to it. This would mean this pattern would have to follow either side of the access hole all the way to the forward and aft part of the lower skin. This kink in plies, whilst beneficial around the manhole, would be a stress penalty in the main region of the skin and may undo any benefit.

[06] Citation [2] (cited below) discloses an example of a continuous tow shearing process, which is an advanced tape placement technique with the ability to steer unidirectional prepreg tapes by in-plane shear deformation without the presence of tape buckling, gaps and overlaps.

[07] [Citation [1]: Continuous Tow Steering Around an Elliptical Cutout in a Composite Panel; Giovanni Zucco, Mohammad Rouhi, Vincenzo Oliveri, Enzo Cosentino, Ronan M. O’Higgins and Paul M. Weaver; AIAA Journal202159:12, pp.5117-5129; https: / / doi.org / 10.2514 / lJ060668.

[08] Citation [2]: Bohao Zhang, Byung Chui Kim, Experimental characterisation of large in-plane shear behaviour of unidirectional carbon fibre / epoxy prepreg tapes for continuous tow shearing (CTS) process, Composites Part A: Applied Science and Manufacturing, Volume 162, 2022, 107168, ISSN 13 59-83 5X. SUMMARY OF THE INVENTION

[09] A first aspect of the invention provides a composite structure comprising a body and an opening in the body, wherein the body comprises: steered fibre elements, each steered fibre element having a curved portion with a plurality of steered fibres which follow curved paths around the opening; and terminated fibre elements which alternate with the steered fibre elements, wherein each terminated fibre element comprises a plurality of terminated fibres which terminate next to the curved portion of a respective steered fibre element.

[010] Optionally each terminated fibre terminates where it meets the curved portion of a respective steered fibre element. [Oil] Optionally the terminated fibres do not follow curved paths around the opening.

[012] Optionally the steered fibre elements comprise: an outer steered fibre element; an inner steered fibre element between the opening and the outer steered fibre element; and one or more intermediate steered fibre elements between the inner and outer steered fibre elements, wherein the curved portions have a progressively increasing average radius of curvature from the inner steered fibre element to the outer steered fibre element.

[013] Optionally at least part of the curved path of at least one of the steered fibres has a radius of curvature less than 100mm or less than 70mm or less than 60mm.

[014] Optionally each steered fibre deviates away from a straight line up to a maximum angle as it passes around the opening, wherein the maximum angle of at least one of the steered fibres is more than 50 degrees or more than 60 degrees.

[015] Optionally the steered fibres and / or the terminated fibres are non-twisted.

[016] Optionally the steered fibres and / or the terminated fibres are carbon fibres.

[017] Optionally the opening is a manhole.

[018] Optionally the composite structure is an aircraft wing skin, and the opening is a manhole in the aircraft wing skin.

[019] Optionally the opening has a rounded shape, such as circular or elliptical.

[020] Optionally each terminated fibre terminates at a cut end.

[021] Optionally at least one of the terminated fibre elements has a greater in-plane width and a greater number of fibres than its respective steered element.

[022] Each steered fibre element has an in-plane width and an out-of-plane thickness. Optionally the out-of-plane thickness of each steered fibre element varies as it follows its curved path around the opening by no more than 50% or by no more than 20% or by no more than 10% or by no more than 5%.

[023] Optionally each curved portion has two points of inflection.

[024] A further aspect of the invention provides a composite structure comprising: a body; and an opening in the body, wherein the body comprises: steered fibre elements which follow curved paths around the opening; and terminated fibre elements, wherein each terminated fibre element terminates where it meets the curved path of a respective steered fibre element.

[025] A further aspect of the invention provides a method of manufacturing a comprise structure according to any preceding aspect, the method comprising: laying the steered fibre elements and the terminated fibre elements, wherein the steered fibre elements are laid along curved paths around the opening; and terminating the terminated fibre elements by cutting.

[026] Optionally the steered fibre elements and the terminated fibre elements are laid one after the other in an alternating sequence.

[027] Optionally each fibre element is laid in a single pass of a deposition head.

[028] Optionally the steered fibre elements and the terminated fibre elements are laid by different passes of the same deposition head.

[029] Optionally the steered fibre elements and the terminated fibre elements are each laid up in prepreg.

[030] A further aspect of the invention provides an aircraft component comprising a composite structure according to any preceding aspect.

[031] Optionally the aircraft component is a wing or a wing skin.

[032] A further aspect of the invention provides an aircraft comprising a composite structure according to any preceding aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[033] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[034] Figure 1 shows an aircraft;

[035] Figure 2 shows a Odeg layer of a wing skin in the region of a manhole;

[036] Figure 3 is an enlarged view showing fibre elements of the Odeg layer of Figure 2;

[037] Figure 4 shows a terminated fibre element with an oblique cut end;

[038] Figure 5 shows a terminated fibre element with a steered tip;

[039] Figure 6 shows a terminated fibre element which has been laid in two passes;

[040] Figure 7 shows steered fibre elements which have each been laid in two passes;

[041] Figure 8 shows a first part of a steered fibre element being laid in a first pass;

[042] Figure 9 shows a second part of the steered fibre element being laid in a second pass;

[043] Figure 10 shows a terminated fibre element being laid up;

[044] Figure 11 shows a terminated fibre element which is wider than the two adjacent steered fibre elements;

[045] Figure 12 shows a fibrous filler; and

[046] Figure 13 shows a triangular filler. DETAILED DESCRIPTION OF EMBODIMENT(S)

[047] An aircraft 1 shown in Figure 1 comprises wings 2 and a fuselage 3. Each wing 2 has a composite lower skin 4 and a composite upper skin (not visible in Figure 1).

[048] The lower skin 4 is formed from a stack of layers of carbon fibre reinforced epoxy resin. The fibres of each layer are typically unidirectional, extending in either a Odeg direction (generally along the span of the wing), in a 90deg direction (generally chordwise) or in a 45deg direction (+ / - 45 degrees).

[049] The lower skin 4 is provided with a series of manholes, which are large enough to enable access into the interior of the wing for purposes of repair or inspection. Conventionally the carbon fibres run straight, and the wing skin is machined out to form the manhole, leaving fibres that stop and start on either side of the manhole. This reduces the load carrying capability of the wing skin and means that additional weight is required to support the running loads around the manhole

[050] Figure 2 is a schematic view of a Odeg layer 20 of the lower skin 4 in the region of a manhole 11. The manhole 11 is covered by a manhole cover, which may be attached by fasteners to the lower skin 4 around the edge of the manhole 11. The manhole 11 has a rounded shape, in this case elliptical.

[051] Figure 2 shows various fibre elements 21-27 in the vicinity of the manhole 11. The fibre elements may be laid down by a deposition head as explained in more detail below. In this example the arrangement of fibre elements is symmetrical so only the fibre elements 21-27 in the top half of the figure are described below - the fibre elements in the bottom half being a mirror image. The fibre elements in the 90deg layers have a similar symmetrical arrangement, running up and down (in the chordwise direction) in the view of Figure 2. The fibre elements in the 45deg layers also have a similar arrangement, running generally at 45 degrees to the fibre elements in Figure 2. In the case of the 45deg layers, the arrangement may not have mirror symmetry, as exemplified in Figure 11 of Citation [ 1 ].

[052] The lower wing skin 4 thus provides a composite structure comprising a body (in this case the Odeg layer 20) and an opening in the body (in this case a manhole 11). The Odeg layer 20 comprises steered fibre elements 21-23; terminated fibre elements 24-26; and continuous straight elements 27. The terminated fibre elements 24-26 may alternate with the steered fibre elements 21-23.

[053] Each steered fibre element 21-23 has a curved portion with a plurality of steered fibres 21’, 22’ which follow curved paths around the opening 11. For example, the inner steered fibre element 21 closest to the manhole 11 has a curved portion 28, and each other steered fibre element 22, 23 has a similar curved potion, albeit with a progressively reducing degree of curvature.

[054] Each curved portion 28 (and typically also each steered fibre within the curved portion) has two points of inflection as it passes around the opening 11. Optionally each curved portion deviates away from a straight line as it passes around the opening 11, then returns to the straight line after it has passed around the opening 11.

[055] Each fibre element 21-27 comprises a plurality of unidirectional non-twisted carbon fibres, impregnated by an epoxy resin matrix. Figure 3 is an enlarged view of part of the fibre elements 21, 22, 24. In this example, each fibre element 21, 22, 24 is a tape comprising unidirectional non-twisted carbon fibres 21’, 22’, 24’. These fibres may be grouped with other fibres to form tows, or they may be in any other form. Figure 3 illustrates the edge of the tape in bold lines, and exemplary fibres 21’, 22’, 24’ in thinner lines. Note that there may be a large number of fibres per tape, and only three fibres are shown per tape in Figure 3 for illustrative purposes.

[056] In other embodiments of the invention, each fibre element 21-27 may comprise dry fibres (i.e. fibres which are not impregnated by an epoxy resin matrix).

[057] Note that the fibre elements 21-27 are illustrated schematically in Figure 2, with the lines not touching each other. In practice it is preferred that the adjacent fibre elements abut each other to tessellate the layer 20 with minimal overlaps or voids. Figure 3 is thus a more realistic representation, although it can also be considered as schematic.

[058] Each steered fibre 21’, 22’ may extend continuously along the full length of the wing skin 4, or at least along the full length of the portion of the wing skin 4 shown in Figure 2, including the curved portions 28.

[059] Each terminated fibre element 24-26 comprises a plurality of terminated fibres which terminate next to the curved portion of a respective steered fibre element at a cut end. For example, the terminated fibre element 24 shown in Figure 3 comprises a plurality of terminated fibres 24’ which terminate next to the curved portion 28 of the inner steered fibre element 21 at a cut end 29.

[060] In the example of Figure 2, each terminated fibre terminates where it meets the curved portion of a respective steered fibre element. For example, each terminated fibre 24’ of the terminated fibre element 24 terminates where it meets the curved portion 28 of the steered fibre element 21 as shown in Figure 3. Similarly, each terminated fibre of the terminated fibre element 25 terminates where it meets the curved portion of the steered fibre element 22, and so on.

[061] Each termination leaves a void 30 which may become filled with resin during the curing process. One way of reducing the size of the void 30 is to cut the terminated fibre elements at an oblique angle as shown in Figure 4. In this example, one or all of the terminated fibre elements 24-26 terminates at a face which extends at an oblique angle to a direction of the terminated fibres, an example of such an oblique face 40 being shown in Figure 4 for the terminated fibre element 24.

[062] In the case of Figure 4 the terminated fibre element 24 is cut at an oblique angle such that it is longer on the side which the steered fibre elements 21, 22 are steered towards.

[063] In the case of Figure 4 the oblique face 40 is cut in a straight line, but in other examples the oblique face 40 may be cut along a curved line.

[064] In the example of Figure 2, the terminated fibre elements 24-26 (and their associated terminated fibres) are substantially straight up to their cut ends, and do not follow curved paths around the opening 11. In the alternative example of Figure 5, a modified terminated fibre element 24 is shown with a curved tip 22b which curves slightly before terminating next to the curved portion 28 of the steered fibre element 21.

[065] Hence in Figure 5 the terminated fibres 24’ do not terminate at the point where they meet the curved portion 28 of the steered fibre element 21 as in Figure 3, but rather they follow the path of the curved portion 28 for a small distance before terminating.

[066] In the case of Figure 5, the curved tip 22b is terminated at a cut end where the cut is perpendicular to a direction of the terminated fibres. In other embodiments the curved tip 22b may be cut at an oblique angle similar to the oblique face 40 of Figure 4.

[067] Each fibre element 21-27 may be laid in a single pass of a deposition head, or in multiple passes of a deposition head. Figure 6 gives an example of a terminated fibre element 24 which is laid in two passes: a first pass which deposits a first collection of terminated fibres 24a which terminate next to the curved portion 28 of the steered fibre element 21 without following a curved path around the opening; and a second pass which deposits a second collection of terminated fibres 24b with a curved tip. The curved tip curves slightly before terminating next to the curved portion 28 of the steered fibre element 21.

[068] The terminated fibre element 24 in Figure 6 has twice the width of the terminated fibre element 24 in Figure 5, but in other embodiments the collections of terminated fibres 24a, 24b may be half-width so the overall width of the terminated fibre element is the same.

[069] Figures 7-10 give an example of how the steered fibre elements 21, 22 could be laid in two passes. In a first pass, shown in Figure 8, a deposition head 60 lays a first strip 21a of steered fibres. In a second pass, shown in Figure 9, the deposition head 60 lays a second strip 21b of steered fibres next to the first strip. The pair of adjacent strips together provide a single steered fibre element 21 shown in Figure 7. The steered fibre element 22 is laid up in a similar way from two adjacent strips 22a, 22b as shown in Figure 7.

[070] In Figure 10, the terminated fibre element 24 is laid by a different (wider) deposition head 61 which can deposit the terminated fibre element 24 in a single pass.

[071] Figure 11 gives an example in which the terminated fibre element 24 has a greater in-plane width W (and hence a greater number of fibres) than its respective steered element 21. This increased width W may be achieved by using a wider deposition head, or by depositing the terminated fibre element 24 in multiple passes.

[072] The reverse of Figure 11 is also possible: i.e. the terminated fibre element 24 may have a lower in-plane width W (and hence a smaller number of fibres) than its respective steered element 21.

[073] Returning to Figure 2: the steered fibre elements 21-23 comprise an outer steered fibre element 23; an inner steered fibre element 21 between the opening 11 and the outer steered fibre element 23; and an intermediate steered fibre element 22 between the inner and outer steered fibre elements. In this case there is only a single intermediate steered fibre element 22, but in other embodiments there may be more than one.

[074] The curved portions 28 have a progressively increasing average radius of curvature from the inner steered fibre element 21 to the outer steered fibre element 23. In other words, the curved portions 28 become progressively less curved. This enables the next fibre element to be a continuous straight element 27 which passes the manhole 11 without needing to deviate in any way. Hence the pattern of steered fibre elements 21-23 does not need to follow either side of the manhole 11 all the way to the forward and aft part of the lower skin 4.

[075] At least part of the curved path of at least one of the steered fibres may have a radius of curvature less than 100mm or less than 70mm or less than 60mm. For example, the steered fibres 21’ of the inner steered fibre element 21 may have such a low radius of curvature in the highly curved region shown in Figure 3.

[076] A low radius of curvature is particularly important for the inner steered fibre element 21 because it will reduce the size of the triangular void 50 shown in Figure 2 at the edge of the manhole 11 between the inner steered fibre element 21 and the adjacent steered fibre element 40 on the other half of the manhole.

[077] Optionally the triangular void 40 could be filled with a fibrous filler element 35 shown in Figure 12, or a triangular filler 41 shown in Figure 13.

[078] The curved paths of the steered fibres each deviate away from a straight line up to a maximum angle as they pass around the manhole 11. The maximum angle of at least one of the curved paths may be more than 50 degrees or more than 60 degrees. For example, the steered fibres 21’ of the inner steered fibre element 21 may have a maximum angle of more than 60 degrees in the highly curved region shown in Figure 3.

[079] As noted above, the steered fibre elements 21-23 are laid along curved paths around the opening 11, and the terminated fibre elements 24-26 are terminated (typically by cutting). Different deposition methods will now be described.

[080] In the examples below the fibre elements 21-27 are each laid up in prepreg (i.e., fibres impregnated with an uncured or partially cured matrix material such as an epoxy resin) but in other embodiments some (or all) of the fibre elements 21-27 may be laid up as dry fibre.

[081] Laying up a wide prepreg tape (eg 1 or 2 inch wide) along a path with in-plane curvature (as in Figure 2) can cause fibres on the inside of the curve to buckle. One solution to this problem is to use a continuous tow shearing process as described in Citation [2], Each steered fibre element has an in-plane width and an out-of-plane thickness. A problem with continuous tow shearing processes is that they may cause the out-of-plane thickness of the steered fibre element to vary as it follows its curved path around the opening. Such variation is undesirable because it means that different length fasteners may be required around the periphery of the opening, and in the case of a manhole cover or window it can cause difficulties in providing a tight seal between the window / manhole cover and the structure.

[082] Preferably the out-of-plane thickness of each steered fibre element 21-23 varies as it follows its curved path around the manhole 11 by no more than 50% or by no more than 20% or by no more than 10% or by no more than 5%.

[083] Hence it may be preferred to use a more traditional “fibre placement” approach in which a relatively narrow tape of prepreg fibres (for instance 6mm wide or narrower) is used to form at least the steered fibre elements 21-23. This reduces the risk of buckling and reduces variation of out-of-plane thickness, in return for a slower deposition rate. In continuous tow shearing there may be a change of thickness of the layer, but in tow steering the thickness of the layer remains unchanged but it may buckle to create wrinkles in the layer. Preferably any wrinkles in a layer are no more than 5% of the thickness of the layer.

[084] If the tape is very narrow, then optionally each steered fibre element could be laid in a series of passes, as in Figures 8 and 9, to make the steered fibre element wider.

[085] At the deposition head, the prepreg tape may be unrolled and applied with heat and pressure. An example of a suitable deposition head is given in Figure 1(a) of Citation [2], in which the deposition head has a tape guide roller, compaction shoe and gripping shoe. Other types of deposition head are well known to a skilled person so will not be described in detail here. The deposition head may incorporate a blade to cut the terminated fibre elements at a required angle - for instance at a right angle as in Figures 3 and 5 or at an oblique angle as in Figure 4.

[086] The steered fibre elements 21-23 and the terminated fibre elements 24-26 could have the same widths, or different widths. For example, each terminated fibre element 24-26 could be laid as a single pass of a 2inch wide tape from a wide deposition head 61 as in Figure 10, and each steered fibre element 21-23 could be laid as two passes of 6mm wide strips from a narrow deposition head 60 as in Figures 8 and 9 (giving a total thickness of 12mm per steered fibre element). Alternatively, the steered fibre elements 21-23 and the terminated fibre elements 24-25 may be laid by different passes of the same deposition head.

[087] Optionally the steered fibre elements 21-23 are laid before any of the terminated fibre elements 24-26 are laid. More typically the fibre elements 21-26 are laid one after the other in an alternating sequence: 21, 24, 22, 25, 23, 26, 27 etc.

[088] Typically the terminated fibre elements on opposite sides of the manhole 11 are laid up in the same pass of a deposition head. For example, the terminated fibre element 24 on the left side of the manhole may be laid up in the same pass as the opposite terminated fibre element on the right side of the manhole 11. After this pair of terminated fibre elements has been deposited from left to right, the deposition head may deposit the next steered fibre element 22 from right to left, and so on.

[089] The fibre elements 21-27 are typically each laid up in prepreg, although they may be laid up as dry fibres and subsequently impregnated (for instance by resin infusion). Once all layers of the wing skin 4 have been laid up, the wing skin is cured under heat and pressure to cure the epoxy resin matrix and provide the finished composite structure.

[090] The present invention is particularly useful for a manhole in an aircraft wing skin, as described in Figures 1-13, because aircraft wing skins are exposed to high load in flight and the skin thickness at the edge of the manhole should be tightly controlled so as to avoid variations in the aerodynamic surface of the wing which might increase drag. However, in other embodiments of the present invention the opening may be an opening for a window in the fuselage 3, a cut-out in a composite wing rib within the wing 2, or an opening in any other composite structure of an aircraft, a ship, or any other article.

[091] In summary, the embodiments described above provide a composite structure comprising a body 20 and an opening 11 in the body. The body 20 comprises steered fibre elements 21-23 which follow curved paths around the opening 11 and terminated fibre elements 24-26. Each terminated fibre element 24-28 terminates next to the curved path 28 of a respective steered fibre element.

[092] In step 1, the fibres closest to the centre of the manhole 11 are steered around the manhole 11. In step 2, the next fibres to be laid down run straight until they hit the steered fibres. At this point they are terminated. In step 3, the next steered fibres laid down follow the same pattern, but at a slightly shallower angle around the manhole 11 due to the offset provided by the terminated fibres. In step 4, another straight fibre is laid outside of that in step 3, and this terminates once it hits the steered fibres of step 3. The above pattern is then repeated, getting further away from the centre of the manhole 11 each time. As this goes further, the angle of the fibres steered around the manhole 11 reduces until they are almost straight. At this point a continuous straight fibre element 27 runs all the way along the outside. From this continuous straight fibre element 27, any subsequent fibres laid down in the majority of the wing skin 4 are now straight.

[093] The main benefit is the weight saving coming from the optimisation of the fibres to the shapes required. Another benefit is that it reduces wastage as fibres are not laid down across the manhole 11 that are then machined out and thrown away.

[094] Tow steering has a low deposition rate but a high degree of optimisation capability. Conventional automated tape laying is the opposite. The present invention allows these two methods to be used alongside each other, providing a highly optimised design around manholes, or other openings, and a higher deposition rate in the main section of the wing skin.

[095] Where the word 'or' appears this is to be construed to mean 'and / or' such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination.

[096] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A composite structure comprising a body and an opening in the body, wherein the body comprises:steered fibre elements, each steered fibre element having a curved portion with a plurality of steered fibres which follow curved paths around the opening; andterminated fibre elements which alternate with the steered fibre elements, wherein each terminated fibre element comprises a plurality of terminated fibres which terminate next to the curved portion of a respective steered fibre element.

2. A composite structure according to claim 1, wherein each terminated fibre terminates where it meets the curved portion of a respective steered fibre element.

3. A composite structure according to any preceding claim, wherein the terminated fibres do not follow curved paths around the opening.

4. A composite structure according to any preceding claim, wherein the steered fibre elements comprise: an outer steered fibre element; an inner steered fibre element between the opening and the outer steered fibre element; and one or more intermediate steered fibre elements between the inner and outer steered fibre elements, wherein the curved portions have a progressively increasing average radius of curvature from the inner steered fibre element to the outer steered fibre element.

5. A composite structure according to any preceding claim, wherein at least part of the curved path of at least one of the steered fibres has a radius of curvature less than 100mm or less than 70mm or less than 60mm.

6. A composite structure according to any preceding claim, wherein each steered fibre deviates away from a straight line up to a maximum angle as it passes around the opening, wherein the maximum angle of at least one of the steered fibres is more than 50 degrees or more than 60 degrees.

7. A composite structure according to any preceding claim, wherein the steered fibres and / or the terminated fibres are non-twisted.

8. A composite structure according to any preceding claim, wherein the steered fibres and / or the terminated fibres are carbon fibres.

9. A composite structure according to any preceding claim, wherein the opening is a manhole.

10. A composite structure according to claim 9, wherein the composite structure is an aircraft wing skin, and the opening is a manhole in the aircraft wing skin.

11. A composite structure according to any preceding claim, wherein the opening has a rounded shape, such as circular or elliptical.

12. A composite structure according to any preceding claim, wherein each terminated fibre terminates at a cut end.

13. A composite structure according to any preceding claim, wherein at least one of the terminated fibre elements has a greater in-plane width and a greater number of fibres than its respective steered element.

14. A composite structure according to any preceding claim, wherein each steered fibre element has an in-plane width and an out-of-plane thickness, and the out-of-plane thickness of each steered fibre element varies as it follows its curved path around the opening by no more than 50% or by no more than 20% or by no more than 10% or by no more than 5%.

15. A composite structure according to any preceding claim, wherein each curved portion has two points of inflection.

16. A composite structure comprising: a body; and an opening in the body, wherein the body comprises: steered fibre elements which follow curved paths around the opening; and terminated fibre elements, wherein each terminated fibre element terminates where it meets the curved path of a respective steered fibre element.

17. A method of manufacturing a comprise structure according to any preceding claim, the method comprising: laying the steered fibre elements and the terminated fibre elements, wherein the steered fibre elements are laid along curved paths around the opening; and terminating the terminated fibre elements by cutting.

18. A method according to claim 17, wherein the steered fibre elements and the terminated fibre elements are laid one after the other in an alternating sequence.

19. A method according to claim 17 or 18, wherein each fibre element is laid in a single pass of a deposition head.

20. A method according to any of claims 17 to 19, wherein the steered fibre elements and the terminated fibre elements are laid by different passes of the same deposition head.

21. A method according to any of claims 17 to 20, wherein the steered fibre elements and the terminated fibre elements are each laid up in prepreg.

22. An aircraft component comprising a composite structure according to any of claims 1 to 16.

23. An aircraft component according to claim 22, wherein the aircraft component is a wing or a wing skin.

24. An aircraft comprising a composite structure according to any of claims 1 to 16.

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