阅读说明：本技术 复合加劲件 (Composite stiffener ) 是由 张军伟 马丁·盖顿德 约舒亚·博纳文图拉 约翰·伍科克 于 2020-02-27 设计创作，主要内容包括：一种用于加劲件加固的面板的复合加劲件。该加劲件具有纵向方向和在加劲件的端部处终止的延伸尽头区域。加劲件还具有恒定截面区域,该恒定截面区域在该纵向方向上位于延伸尽头区域内侧、且具有横向于纵向方向的恒定的横截面,该恒定的横截面具有位于相邻的脚部之间的冠部。该延伸尽头区域具有横向于纵向方向的变化的横截面,该变化的横截面具有位于相邻的脚部之间的冠部且该冠部朝向加劲件的该端部减小高度从而形成斜坡。该复合加劲件包括许多由无皱褶织物层制成的覆盖层。(A composite stiffener for a panel reinforced by the stiffener. The stiffener has a longitudinal direction and an extended dead end region terminating at an end of the stiffener. The stiffener also has a constant cross-sectional area inboard of the extended dead end area in the longitudinal direction and having a constant cross-section transverse to the longitudinal direction with a crown located between adjacent feet. The extended extreme region has a varying cross-section transverse to the longitudinal direction with a crown located between adjacent feet and the crown decreasing in height towards the end of the stiffener to form a ramp. The composite stiffener includes a plurality of cover layers made of non-corrugated fabric layers.)

1. A composite stiffener for a stiffener reinforced panel, wherein the stiffener has a longitudinal direction, an extended dead end region terminating at an end of the stiffener, and a constant cross-section region inboard of the extended dead end region in the longitudinal direction and having a constant cross-section transverse to the longitudinal direction with a crown between adjacent feet, wherein the extended dead end region has a varying cross-section transverse to the longitudinal direction with a crown between adjacent feet that decreases in height towards the end of the stiffener forming a ramp, and the composite stiffener comprises a plurality of cover layers made of wrinkle-free fabric layers.

2. The composite stiffener of claim 1, wherein the extended dead-end region includes one or more woven fabric layers.

3. The composite stiffener of claim 2, wherein the one or more woven fabric layers extend from a top of the ramp to a bottom of the ramp.

4. A composite stiffener according to any preceding claim, further including a transition region between the constant cross-section area and the extended extreme area, wherein the constant cross-section area has a plurality of plies of non-crimped fabric layers sandwiched between woven fabric layers, and at least one of the plies of non-crimped fabric layers is shed in the transition region.

5. A stiffener according to claim 4, wherein all of the cover layers of wrinkle-free fabric layer in the constant cross-section area are shed in the transition area.

6. A stiffener according to claim 4 or claim 5, wherein the extended dead-end region includes the woven fabric layer and does not include a wrinkle-free fabric cover layer.

7. A stiffener according to any preceding claim, wherein the extended dead end region has a ramp portion including the ramp, and a substantially planar toe portion between the ramp and the end of the stiffener.

8. A stiffener according to any preceding claim, wherein each of the cover layers made of wrinkle-free fabric layers includes: a first layer having a 0 degree fiber orientation aligned with the longitudinal direction of the stiffener; and a second layer having a fiber orientation that is not aligned with the longitudinal direction of the stiffener.

9. A stiffener according to claim 1, wherein the extended dead-end region includes one or more of the wrinkle-free fabric cover layers.

10. A stiffener according to claim 9, wherein the cover layer has a cut-out dart in the extended end region and overlaps itself.

11. A stiffener according to any preceding claim, wherein the constant cross-sectional area has an omega-shaped cross-section.

12. A stiffener according to any preceding claim, wherein the cross-section of the constant cross-section area has a continuous layer extending through the crown and the adjacent foot.

13. A stiffener according to any preceding claim, comprising a carbon fibre composite material.

14. An aircraft structure comprising panels stiffened with stringers, the stringers being a stiffener according to any preceding claim.

15. A method of manufacturing a stiffener comprising laying a plurality of cover layers made of wrinkle-free fabric layers and a plurality of woven fabric layers as dry fabric on a mold, and co-injecting the dry fabric with a resin, followed by co-curing to form the stiffener.

16. The method of claim 15, wherein the stiffener has: a longitudinal direction; an extended dead end region at an end of the stiffener; a constant cross-sectional area inboard of the ends in the longitudinal direction and having a cross-section with a crown between adjacent feet, wherein the extended dead end area has a varying cross-section with a crown between adjacent feet that decreases in height toward the ends of the stiffener to form a ramp; and a transition region between the constant cross-sectional area and the extended extreme end area, wherein the method comprises laying down a plurality of cover layers made of wrinkle-free fabric layers sandwiched between woven fabric layers in the constant cross-sectional area, and cutting at least one of the cover layers made of wrinkle-free fabric layers to peel off the cover layer in the transition region.

17. The method of claim 15 or 16, further comprising cutting all of the cover layers made of wrinkle-free fabric layers to cause all of the cover layers to fall off in the transition region.

18. The method of any of claims 15-17, wherein the extended dead-end region includes the woven fabric layer and does not include a wrinkle-free fabric cover layer.

19. The method of any of claims 15 to 18, further comprising: laying the plurality of woven fabric layers on the portion of the mould defining the shape of the ramp in the extended end region, followed by the step of co-curing without an intermediate step of cutting the woven fabric layers laid on the mould.

Technical Field

The present invention relates to a composite stiffener for a stiffener reinforced panel and a method of manufacturing the stiffener.

Background

Stiffeners are typically attached to or integral with the panel to provide reinforcement to the panel. For example, a stringer is an elongate stiffening member that may be attached to a skin or cover of an aircraft wing and extend in a generally span-wise direction. The same basic layout can be seen in the vertical and horizontal planes of stability. Similar structures can also be found in aircraft fuselages, in which the stiffeners extend in the longitudinal direction of the aircraft. The stiffeners provide the necessary reinforcement to withstand the aerodynamic and structural loads experienced by the aircraft during flight and on the ground.

In the region where the stringer terminates, the cross-section of the stringer changes to facilitate the transfer of loads from the stringer to the panel. The height of the stringer (perpendicular to the plane of the panel) generally decreases towards a terminal end known as an extended dead end region.

Stringer run-outs can result in areas of complex geometry for the fabrication of composite stringers. Manufacturing problems such as wrinkling may occur in the area of these complex geometries. Different fibre layer materials will be more or less adapted to these areas due to their different drapability. Wrinkles and other manufacturing defects, such as bubbles and fiber dislocations, may introduce local stress points and thus reduce the overall performance of the stringer. Simplifying the manufacturing process to minimize cutting of the fiber layers and cutting of the cured composite stringer to define the geometry may reduce manufacturing costs and time.

Disclosure of Invention

A first aspect of the invention provides a composite stiffener for a stiffener reinforced panel, wherein the stiffener has a longitudinal direction, an extended dead end region terminating at an end of the stiffener and a constant cross-section region inboard of the extended dead end region in the longitudinal direction and having a constant cross-section transverse to the longitudinal direction with a crown between adjacent feet, wherein the extended dead end region has a varying cross-section transverse to the longitudinal direction with a crown between adjacent feet and the crown reduces in height towards the end of the stiffener forming a ramp, and the composite stiffener comprises a plurality of plies of non-corrugated fabric layers.

Stringers having a crown between adjacent feet may be referred to as "omega" or "top hat" or "hardhat" shaped stringers, for example. A web may extend between each foot and the crown. The fabric layer may extend continuously from a lateral edge of one foot and up through one web to the crown and down through the other web to a lateral edge of the foot on the other side of the crown.

Non-crimped fabrics (NCFs) are typically provided as "cover layers" comprising two or possibly more fibrous layers. Each fibrous layer may be unidirectional. The fibrous layers are bonded together, for example by stitching, to form the cover layer. The fibrous layers in the cover layer typically have different fiber orientations. A cover layer comprising two fiber layers with different unidirectional fiber orientations is called biaxial NCF. Triaxial and quadcoptral fabrics are also available.

An advantage of NCF cover is that it can make laying faster because the multiple fabric layers in the cover are stitched together so that they can be laid as one piece. However, NCF cover layers suffer from relatively poor drapability compared to, for example, woven or unidirectional fabrics, due to the different fibre orientation of the layers in the cover layer and the stitching between the layers. The lower the number of layers in the overlay, the better the drape, and therefore biaxial NCF overlays may be preferred for drape performance. NCF overlay with 0 degree fiber layers aligned with the longitudinal direction of the stiffener provides excellent load bearing performance in the main load direction.

The specific geometry of the extended extreme region of an omega shaped stiffener, with a slope in the crown of the stiffener in the extended extreme region, presents challenges to using NCF materials in the stiffener. The inventors have discovered a method of using NCF material in stiffeners that achieves cost-effective manufacturing without cutting the fiber material in the stiffener once laid out before resin infusion.

In a first example, the stiffener comprises both NCF cover layers and woven fibre layers, in the extended extreme areas that are difficult to form, the NCF cover layers are shed (dropped off) leaving only the woven fibre layers. The woven fibre layers provide several advantages in that they provide better drapability and the absence of a 0 degree fibre layer in the extended end region provides better force-bearing performance.

The extended termination area may include one or more woven fabric layers.

The one or more woven fabric layers may extend from the top of the ramp to the bottom of the ramp.

The composite stiffener may also include a transition region between the constant cross-sectional area and the extended termination area. The constant cross-sectional area may have a plurality of cover layers of non-crimped fabric layers sandwiched between knitted fabric layers. At least one of the cover layers made of non-crimped fabric layers can be detached in the transition region. The woven fibre layer also provides good damage tolerance. It is therefore advantageous to provide the woven fibre layers as outer layers (top and bottom) of the lay-up.

All cover layers made of wrinkle-free fabric layers in the constant cross-sectional area can be detached in the transition area.

The extended terminal area may include a woven fabric layer and not include a wrinkle-free fabric cover layer.

In a second example, the stiffener includes NCF plies, at least one of which extends to the end of the stiffener and is cut to form darts, so that the NCF plies can hang down to form the shape of the extended dead end region. The use of only NCF overlays in the layup provides economy, but takes additional time to form darts.

The extended dead end region may include one or more non-crimped textile cover layers. The cover layer may have a cut-out dart in the extended area and overlap itself.

The extended termination area may have a ramp portion including a ramp and a generally planar toe portion between the ramp and the end of the stiffener.

Each of the cover layers made of non-pleated fabric layers may include: a first layer having a 0 degree fiber orientation aligned with the longitudinal direction of the stiffener; and a second layer having a fiber orientation that is not aligned with the longitudinal direction of the stiffener.

The constant cross-sectional area may have an omega-shaped cross-section.

The cross-section of the constant cross-sectional area may have a continuous layer extending through the crown and the adjacent foot.

The stiffener may comprise a carbon fiber composite material.

Another aspect of the invention provides an aircraft structure comprising a panel stiffened with stringers, the stringers being stiffeners according to the first aspect.

Another aspect of the invention provides a method of manufacturing a stiffener, the method comprising laying a plurality of cover layers made of wrinkle-free fabric layers and a plurality of woven fabric layers as a dry fabric on a mold, and co-injecting the dry fabric with a resin and then co-curing to form the stiffener. The stiffener may be a stiffener according to the first aspect.

The method can comprise the following steps: laying a plurality of covering layers made of wrinkle-free fabric layers sandwiched between woven fabric layers in a constant cross-sectional area, and cutting at least one of the covering layers made of wrinkle-free fabric layers so that the covering layer comes off in a transition area.

The method may further comprise cutting all cover layers made of wrinkle-free fabric layers such that all cover layers are detached in the transition region.

The extended terminal area may include a woven fabric layer and not include a wrinkle-free fabric cover layer.

The method may further comprise the intermediate step of laying a plurality of layers of knitted fabric on the portion of the mould defining the shape of the ramp extending in the end region, followed by a co-curing step without cutting the layers of knitted fabric laid on the mould.

Drawings

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

FIG. 1 is a plan view of an aircraft;

FIG. 2 is a schematic plan view of an aircraft wing box;

FIG. 3 is a schematic cross-sectional view of an aircraft wing box;

FIG. 4 is a cross-sectional view of a stringer-stiffened panel;

FIG. 5 is a three-dimensional view of a stringer (stiffener);

FIG. 6 is a transverse cross-sectional view through a constant cross-section area of a stringer;

FIG. 7 is a longitudinal cross-sectional view through a stringer showing a constant cross-section area, an extended dead end area and a transition area;

FIG. 8 is a schematic representation of a NCF biaxial overlay;

FIG. 9 is a schematic illustration of a stringer lay-up in which the NCF blanket is sandwiched between woven fibre plies;

FIG. 10 is a cross-sectional view of a layup being laid on a mold; and

figure 11 is a schematic view of an NCF overlay with darts cut out.

Detailed Description

Fig. 1 shows an aircraft 1 with a left wing 2 and a right wing 3. Each wing has a cantilevered structure with a length extending in a spanwise direction from a wing root to a wing tip, the wing root being joined to an aircraft fuselage 4. The wings 2, 3 are similar in construction and therefore only the right wing 3 will be described in detail with reference to fig. 2 and 3. The aircraft 1 shown is a conventional transonic jet passenger aircraft, but it should be understood that the present description may refer to a variety of aircraft, including military aircraft, civilian aircraft, general aviation aircraft, jet aircraft, propeller aircraft, high wing aircraft, low wing aircraft, and the like.

The main structural elements of the wing are the wing box formed by the upper and lower covers 5, 6 and the front and rear spars 7, 8 shown in the cross-sectional view of figure 3. Both the caps 5, 6 and the spars 7, 8 are Carbon Fibre Reinforced Polymer (CFRP) laminate components. Each cover has an aerodynamic surface (the upper surface of the upper cover 5 and the lower surface of the lower cover 6) on which air flows during flight of the aircraft. Each cover also has an inner surface with "stringers" or stiffeners thereon. Each cap carries about 30 to 40 stiffeners and therefore only 5 are shown in figure 2 for clarity. The stringer is designated 40.

As shown in fig. 3, each spar has a C-shaped cross-section with upper and lower spar flanges each bonded to an inner surface of a respective one of the caps 5, 6, and a spar web extending between the spar flanges. One or more of the caps 5, 6 may be integral with the spars 7, 8 to form an omega-shaped or "u" -shaped or "n" -shaped wing box component.

The wing box also has a plurality of transverse ribs 13, each bonded to the caps 5, 6 and spars 7, 8. These ribs include an inboard rib 10 at the root of the wing box and a plurality of further ribs 13 spaced from the innermost rib along the length of the wing box. There are a number of such ribs 13 on the wing, only 10 of which are shown in figure 2 for clarity.

The wing box may be divided into a plurality of fuel tanks, such as an inboard fuel tank bounded by inboard rib 10, mid-span rib 13a in solid lines, caps 5, 6 and spars 7, 8; and an outboard fuel tank defined by the mid-span rib 13a, outboard ribs 12 at the tips of the wing box sections, caps 5, 6 and spars 7, 8.

The inboard rib 10 is an attachment rib that forms the root of the wing box and is joined to a central wing box 20 within the body of the fuselage 4. As can be seen in fig. 2, the stiffener 40 stops near the inner 10 and outer 12 ribs but passes through the rib 13.

Figure 4 shows a schematic cross-sectional view of a stringer 40 attached to an upper wing cover 5, and in particular shows the region where the stringer 40 terminates. The stringers are in a longitudinal direction generally aligned with the spanwise direction of the wing and have an "omega" shaped cross-sectional shape. The stringer 40 has a generally constant cross-section transverse to the longitudinal direction and an extended dead end region 41 terminating at the end of the stringer 40.

The stringer 40 is shown in more detail with reference to figures 5 to 7. The constant cross-section area 42 of the stringer 40 is located inboard of (i.e. away from) the terminal end region 41 in the longitudinal direction x. The constant section area 42 has a constant cross-section transverse to the longitudinal direction x with a crown 43 located between adjacent feet 44a, 44 b. The crown is joined to the feet 44a, 44b by respective webs 45a, 45 b. The webs 45a, 45b are substantially in an upright direction z perpendicular to the plane x-y of the upper flap 5, so that the webs 45a, 45b are substantially parallel to the longitudinal direction x in the constant cross-section area 42 of the stringer 40.

The extended extreme area 41 has a varying cross-section transverse to the longitudinal direction x, which also has a crown 43 located between adjacent feet 44a, 44 b. In the extended dead end region 41, the crown 43 decreases in height toward the toe 46 at the end of the stiffener 40 to form a ramp 47. The extended terminal end region 41 has a substantially "omega" shape similar to the medial constant cross-section region 42, but the height of the crown 43 above the feet 44a, 44b decreases generally linearly from the top 48 of the ramp to the bottom 49 of the ramp. There is a transition region 50 between the top 48 of the ramp and the constant cross-sectional area 42, which transition region 50 will be described in more detail with reference to fig. 7.

Turning first to fig. 6, which shows a cross-section through the constant cross-section area 42, it can be seen that the stiffener comprises a stack of fibre layers including a lowermost woven fabric layer 51, an uppermost woven fabric layer 52 and a plurality of cover layers 53 of non-crimped fabric (NCF) between the lowermost woven fabric layer 51 and the uppermost woven fabric layer 52.

Fig. 7 shows a cross-section through the stiffener 40 in the xz-plane along the central longitudinal axis x of the stiffener 40. In the constant cross-section area 42, it can be seen that the plurality of cover layers 53 made of non-crimped fabric layers are sandwiched between the knitted fabric layers 51, 52. The knitted fabric layers 51, 52 are continuous across the constant cross-section area 42, the transition area 50, the extended end area 41 and the toe 46. A cover layer 53 made of a wrinkle-free fabric layer ends in the transition region 50. Preferably, the individual cover layers 53 made of non-crimped fabric layers terminate in a staggered manner along the longitudinal direction x. Thus, the height of the stack of covering layers 53 made of non-crimped fabric layers decreases towards this end of the stiffener, forming a taper towards this end of the stringer in the crown 43, webs 45a, 45b and feet 44a, 44 b. In the transition region 50, all the covering layers 53 made of the wrinkle-free fabric layer end, so that in the extended end region 41 only the woven fabric layers 51, 52 remain at the top 48 of the ramp 47.

Fig. 8 shows an exploded view of one of the wrinkle-free fabric cover layers 53, which includes a first layer 53a having a fiber orientation of 0 ° and a second layer 53b having a fiber orientation of 45 °. The first layer 53a and the second layer 53b are bonded together, for example by stitching, as generally indicated by the dashed line 53 c. In this example, the 0 ° fiber orientation is aligned with the longitudinal axis x of the stiffener 40.

In the constant cross-sectional area 42 of the stiffener 40, having multiple layers with 0 ° fiber orientation may be beneficial to provide the stiffener 40 with longitudinal bending stiffness. However, in the extended extreme region 41, this bending stiffness is generally undesirable, as the purpose of the extended extreme region 41 is to provide flexibility to transition the stiffener load into the panel to which the stiffener is attached, e.g. the upper or lower wing covers 5, 6.

The plurality of cover layers 53 made of non-crimped fabric layers may be arranged in a stack to achieve a substantially balanced lay-up. To this end, some cover layers 53 may comprise biaxial NCF cover layers with a 0 °/45 ° fiber orientation, while other cover layers 53 made of NCF fabric may have a 0 °/135 ° fiber orientation. In a preferred embodiment, the number of biaxial 0 °/45 ° fiber oriented NCF plies is equal to the number of 0 °/135 ° fiber oriented NCF plies. The different NCF overlays having 0 °/45 ° fiber orientation and 0 °/135 ° fiber orientation may alternate throughout the stack and have mirror image plies on both sides of the mid-plane throughout the stack of NCF overlays 53.

By terminating the NCF cover layer 53 in the transition region 50 so as to leave only the woven fabric layers 51, 52 in the extended extreme region 41, the force performance in the extended extreme region of the stiffener can be optimized. In addition, the knitted fabric layers 51, 52 will generally have better drape properties than the NCF cover layer 53, and therefore the complex shape of the extended termination area 41 can be formed without any savings in knitted fabric layers 51, 52. The woven fabric may be, for example, a 5-harness (harness) fabric, but any other suitable woven fabric may be used. Good drape performance and the lack of the need to incorporate woven fabric layers 51, 52 helps to improve the manufacturability of the stiffener and the quality of the final composite stiffener 40.

Fig. 10 schematically illustrates a method of manufacturing a stiffener 40, wherein a dry or semi-prepreg carbon fiber material layer is laid on a mold 60. The uppermost woven fibre fabric layer 52 is first placed on the mould 60, followed by the plurality of NCF cover layers 53 and finally the lowermost woven fibre fabric layer 51. The dry or semi-prepreg layer is then impregnated with a suitable resin and cured in a conventional manner. Once cured, the stiffener 40 may be removed from the mold 60.

The mold 60 has a shape that follows the outer molding surface of the finished stiffener 40, including the transition region 50 and the extended dead end region 41, so that the finished stiffener 40 can be removed from the mold 60 after curing without any cutting or machining of the fiber fabric layer during lay-up on the mold 60 or after removing the cured composite stiffener 40 from the mold 60. By avoiding these cutting steps, the manufacturability of the stiffener 40 is significantly improved.

In an alternative embodiment, the stiffener 40 may include an NCF coating 53 in the extended dead end region, but no change is made to the overall shape of the stiffener 40 as described previously. Since the NCF cover layer 53 is not as drapable as woven fabric, darts 70 may need to be cut into the NCF cover layer 53 as shown in fig. 11.

When the NCF cover 53 with the dart 70 is laid on the mould 60, the edges of the cover 53 on both sides of the dart 70 are brought together and overlap slightly. The presence of dart 70 provides sufficient formability for NCF cover layer 53 to follow the shape of mold 60 in extended extreme region 41.

In the case where the NCF cover 53 is omitted, then only the NCF cover 53 may be used in the lay-up of the stiffener 40 and the woven fabric layers 51, 52 may be omitted. Alternatively, the woven fibre fabric layers 51, 52 may remain. When NCF overlays with darts 70 are used in the extended extreme area 41, some of the NCF overlays 53 present in the constant cross-section area 42 may be peeled off in the transition area 50. In other words, the extended terminal end region 41 may have a smaller number of NCF overlays 53 than the constant cross-sectional region 42. While the presence of the NCF overlay 53 in the extended dead-end region 41 may not be most preferred because it may be desirable to cut the dart 70 from the overlay 53 in advance before laying the overlay 53 on the mold 60, this arrangement is advantageous because no further cutting of the cured stiffener 40 is required after removing the cured stiffener 40 from the mold 60.

Where the word "or" is present, this is to be understood as meaning "and/or" such that the items referred to are not necessarily mutually exclusive, but may be used in any suitable combination.

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