GB2583941A

GB2583941A - Stiffened panel assembly

Info

Publication number: GB2583941A
Application number: GB1906796.6A
Authority: GB
Inventors: Heaysman Chris; Gaitonde Martin; Seegel Hauke
Original assignee: Airbus Operations GmbH; Airbus Operations Ltd
Current assignee: Airbus Operations GmbH; Airbus Operations Ltd
Priority date: 2019-05-14
Filing date: 2019-05-14
Publication date: 2020-11-18
Also published as: GB201906796D0

Abstract

A stiffener or stringer 8 comprises a structural part 26, a core 21, 24, 25 in the structural part, a longitudinal channel 19 in the core which extends in a length direction of the core, and a bladder 40 in the longitudinal channel. A slot 22 may be provided in the core which extends in a transverse direction from the longitudinal channel. A branch of channels 18 may be provided, which branch out from the longitudinal channel at a series of points. A method of manufacturing the part may include injecting matrix resin material 60 into the longitudinal; inflating the bladder to force at least some of the matrix material to flow out of the longitudinal channel and branch channels; and curing the matrix material so that the stiffener becomes bonded to the panel. A flexible vacuum bag 39 may be fitted over the stiffened panel assembly to form a vacuum chamber. Overflow resin may flow out of the vacuum port 37.

Description

STIFFENED PANEL ASSEMBLY FIELD OF THE INVENTION

[0001] The present invention relates to a stiffened panel assembly, and a method of manufacturing a stiffened panel assembly.

BACKGROUND OF THE INVENTION

[0002] US 2016/0339682 discloses a bladder system for curing composite parts. A flexible, inflatable bladder is placed within or inserted into the internal cavity of a cure tool prior to a cure cycle in order to react external pressures applied to a charge during a curing process, such as during an autoclave curing process.

SUMMARY OF THE INVENTION

[0003] According to a first aspect of the invention, there is provided a stiffened panel assembly comprising: a panel; and a stiffener on the panel, the stiffener comprising: a structural part, a core in the structural part, a longitudinal channel in the core which extends in a length direction of the core, and a bladder in the longitudinal channel.

[0004] The bladder may contain a liquid but more preferably it contains a gas (such as air). This has the advantage of being lighter.

[0005] The bladder may be in an inflated state or a deflated state.

[0006] The stiffener (typically the stnictural part of the stiffener) may be bonded to the panel (for instance it may be co-cured, co-bonded or co-infused to the panel).

[0007] The core may comprise a core part comprising a foam material [0008] Optionally the core comprises a core material (such as foam material), the stnictural part comprises a structural material (such as a fibrous material), and the core material has a lower density than the structural material.

[0009] Optionally the structural part comprises a fibrous material, which may be dry or impregnated with a matrix material.

[0010] The structural part may comprise a fibrous material impregnated with a matrix material which bonds the structural part to the panel (for instance the structural part and the panel may be co-cured, co-bonded or co-infused) [00H] The panel may comprise a fibrous material, which may be dry or impregnated with a matrix material.

[0012] The panel may comprise a fibrous material impregnated with a matrix material which bonds the panel to the structural part (for instance the panel and the structural part may be co-cured, co-bonded or co-infused).

[0013] In a preferred embodiment the panel and the structural part each comprise a fibrous material co-infused with a matrix material which bonds the panel to the structural part by a co-infused joint.

[0014] Optionally the structural part comprises a crown and a pair of webs, and the core is positioned between the webs. For instance the structural part may have a top-hat shape, an omega shape or a trapezoid shape.

[0015] The structural part may comprise one or more feet bonded to the panel [0016] In one embodiment the core comprises a first core part made of a first core material (such as a foam material) and a second core part made of a second core material (such as a fibrous material) different to the first core material; and the longitudinal channel and the bladder are in the first core part. The longitudinal channel may comprise a groove in the first core part for example.

[0017] The core may comprise a pair of core parts (for instance a pair of battens which optionally are both made of the same material, such as a fibrous material); and the longitudinal channel and the bladder may be between the core parts. The longitudinal channel may comprise a slot or gap between the core parts for example.

[0018] In one embodiment the core comprises a filler core part made of a filler material (such as a foam material), and a pair of structural core parts made of a fibrous material, wherein the longitudinal channel and the bladder are between the structural core parts [0019] The longitudinal channel may comprise a groove, a slot, or a closed-section

passage for example.

[0020] Optionally the longitudinal channel comprises a groove with a substantially semi-circular shape when viewed in cross-section transverse to its length.

[0021] The assembly may further comprise a slot in the core which extends in a transverse direction from the longitudinal channel to the structural part of the stiffener, wherein the slot has a length which extends in the length direction of the core and a width which extends in the transverse direction.

[0022] Optionally the slot contains matrix material [0023] The slot may be between a pair of core parts.

[0024] Optionally the stiffener comprises a crown and a pair of webs, the core is positioned between the webs, and the slot extends from the longitudinal channel to the crown of the stiffener.

[0025] The assembly may further comprise branch channels which branch out from the longitudinal channel at a series of points along a length of the longitudinal channel, wherein each branch channel extends in a transverse direction from the longitudinal channel to the structural part of the stiffener. Optionally each branch channel contains matrix material.

[0026] The branch channels may be in the first core part [0027] Optionally the structural part comprises a crown and a pair of webs, the core is positioned between the webs, and each branch channel extends from the longitudinal channel to one of the webs.

[0028] According to a further aspect of the invention, there is provided an aircraft or aircraft part (such as an aircraft wing, an aircraft wing cover panel or an aircraft fuselage panel) comprising a stiffened panel assembly according to the first aspect.

[0029] According to a further aspect of the invention, there is provided a method of manufacturing a stiffened panel assembly according to the first aspect, the method comprising: injecting matrix material into the longitudinal channel so that a first portion of the matrix material flows along the longitudinal channel and then flows from the longitudinal channel into the structural part and into the panel, and a second portion of the matrix material remains in the longitudinal channel and in contact with the bladder; inflating the bladder (optionally with a gas) so that the bladder forces at least some of the second portion of the matrix material to flow out of the longitudinal channel; and curing the matrix material so that the stiffener becomes bonded to the panel [0030] Inflating the bladder may cause at least some of the matrix material to flow into the structural part and/or into the panel.

[0031] Optionally the structural part comprises a crown and a pair of webs, the core is positioned between the webs, and during the injection of matrix material at least part of the first portion of the matrix material flows along the longitudinal channel and then into the crown and webs of the structural part.

[0032] Optionally the structural part comprises a foot in contact with the panel, during the injection of matrix material at least part of the first portion of the matrix material flows along the longitudinal channel and then into the foot of the stiffener, and the foot of the stiffener becomes bonded to the panel during the curing step [0033] The matrix material may comprise a resin, such as an epoxy resin [0034] Optionally the panel assembly further comprises branch channels which branch out from the longitudinal channel at a series of points along a length of the longitudinal channel, wherein during the injection of the matrix material at least part of the first portion of the matrix material flows along the longitudinal channel and then flows from the longitudinal channel into the structural part via the branch channels [0035] Optionally the panel assembly further comprises a slot in the core, wherein the slot has a length which extends in a length direction of the core and a width which extends in a transverse direction from the longitudinal channel to the structural part of the stiffener, and the bladder forces at least some of the second portion of the matrix material to flow out of the longitudinal channel into the slot.

[0036] Inflating the bladder may cause at least some of the matrix material to flow from the branch channels and/or from the slot into the structural part and/or into the panel [0037] The bladder may force at least some of the second portion of the matrix material to flow out of the longitudinal channel into the branch channels and/or into the slot.

[0038] Optionally the method further comprises fitting a flexible vacuum bag over the stiffened panel assembly to form a vacuum chamber, and during the injection of the matrix material applying a vacuum to the vacuum chamber which draws the matrix material along the longitudinal channel, into the structural part and into the panel.

[0039] The bladder may be removed from the longitudinal channel after the matrix material has cured, but more preferably the bladder is not removed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the invention will now be described with reference to the accompanying drawings, in which: [0041] Figure 1 shows an aircraft; [0042] Figure 2 is a schematic view of the wing box of one of the wings; [0043] Figure 3 shows a pair of foam core parts on a panel; [0044] Figure 4 shows a pair of battens laid onto each of the foam core parts, [0045] Figure 5 shows a panel assembly comprises a pair of stiffeners on a panel, and also showing the positions of the resin inlet ports; [0046] Figure 6 is a plan view of part of the assembly of Figure 5; [0047] Figure 7 is a cross-section across one of the stiffeners taken along line A-A in Figure 6 at an initial stage of the infusion process; [0048] Figure 8 shows a later stage in the infusion process after the panel assembly has been fully infused; [0049] Figure 9 shows the panel assembly after the bladder has been inflated; [0050] Figure 10 is a cross-section across an alternative panel assembly at an initial stage of the infusion process, [0051] Figure 11 shows a later stage in the infusion process after the panel assembly has been fully infused, and [0052] Figure 12 shows the panel assembly after the bladder has been inflated. DETAILED DESCRIPTION OF EMBODIMENT(S) [0053] Figure 1 shows an aircraft 1 with port and starboard wings 2 and 3. Each wing has a cantilevered structure with a length extending in a span-wise direction from a root to a tip, the root being joined to an aircraft fuselage 4. The wings 2, 3 are similar in construction, so only the starboard wing 3 will be described in detail with reference to Figure 2. The main structural element of the wing is a wing box formed by upper and lower covers and front and rear spars 6, 7. The upper cover 5a of each wing box is visible in the plan view of Figure 1 and the lower cover 5b of the starboard wing box is shown from above in Figure 2.

[0054] The covers 5a, 5b and spars 6, 7 are made of carbon fibre reinforced polymer (CFRP) laminate components. Each cover also has an inner surface carrying a series of stiffeners 8 extending in a spanwise direction. Each cover carries a large number of stiffeners 8, only five of which are shown in Figure 2, and only two of which are shown in Figures 3-5. In the case of aircraft wings, such stiffeners are commonly referred to as stringers, but the term "stiffeners" will be used below.

[0055] The wing box also has a plurality of transverse ribs, each rib being joined to the covers 5a, 5b and the spars 6, 7. The ribs include an inner most inboard rib 10 located at the root of the wing box, and a number of further ribs spaced apart from the inner most rib along the length of the wing box. The wing box is divided into two fuel tanks; an inboard wing fuel tank bounded by an inboard rib 10, a mid-span rib 11, the covers and the spars 6, 7. An outboard wing fuel tank is bound by the mid span rib 11, an outboard rib 12 at the tip of the wing box, the covers and the spars 6, 7. The inboard rib 10 is an attachment rib which forms the root of the wing box and is joined to a centre wing box 20 within the body of the fuselage 4. Baffle ribs 13 (shown in dash lines) form internal baffles within the fuel tanks which divide the fuel tanks into bays. The ribs 10, 11, 12 are sealed to prevent the flow of fuel out of the two fuel tanks, but the baffle ribs 13 are not sealed so that fuel can flow across between the bays. As seen in Figure 2, the stiffeners 8 stop short of the inboard rib 10 and the outboard rib 12, but pass through the baffle ribs 13 and the mid span rib 11 [0056] Figure 5 shows part of a stiffened panel assembly 28 which forms part of the upper or lower cover of one of the wings 2,3 The panel assembly 28 comprises stiffeners 8 carried on a panel 16 [0057] As shown in Figure 7, each stiffener 8 comprises a structural part 26, and a core 21, 24, 25 in the structural part 26. The structural part 26 comprises a layer of fibre-reinforced composite material such as carbon fibre reinforced polymer (CFRP). The structural part 26 is formed into a trapezoidal shape in cross section that includes a foot 36, a pair of webs 34, and a crown 33 The core includes a foam core part 21 made of a filler material such as foam, and a pair of battens 24, 25 made of a fibre-reinforced composite material such as carbon fibre reinforced polymer (CFRP). The filler material has a lower density than the fibre-reinforced composite material of the battens 24, 25 [0058] The foot 36 is bonded to the inner surface of the panel 16 by a co-infused joint. The crown 33 and the battens 24, 25 are spaced away from the neutral bending axis of the panel assembly at the apex of the stiffener 8 to enhance its bending stiffness [0059] As shown in Figures 3 and 5, the foam core part 21 and the stiffener 8 each have a length in a length direction L, a width in a width direction W (transverse to the length direction L) and a height in a height direction H (transverse to the length direction L). As shown in Figure 3, the foam core part 21 has a longitudinal channel 19 which extends in the length direction L along the full length of the foam core part 21. The longitudinal channel 19 is a groove in the upper face of the foam core part 21 with a semi-circular shape in cross-section.

[0060] The foam core part 21 also has branch channels 18 which extend in the width direction W from the longitudinal channel 19, and are spaced apart at regular intervals along the longitudinal channel 19. These branch channels 18 are grooves in the upper face of the foam core part 21, in fluid communication with the longitudinal channel 19.

[0061] The battens 24, 25 contact the crown 33 at the apex of the stiffener and are positioned between the webs 34. As seen most clearly in Figure 4, one of the battens 25 has tabs 23 which are spaced apart along the length of the batten 25 and contact the side of the other batten 24 at an interface 23a [0062] Between the tabs 23, the battens 24, 25 are spaced apart to form slots 22. As shown in Figure 7, each slot 22 extends in the height direction H from the longitudinal channel 19 to the structural part 26 of the stiffener. As shown in Figure 4 each slot 22 also has a length which extends in the length direction L between the tabs 23, and a width which extends in the width direction W. [0063] The structural layer 26 may be formed as a single tubular part by braiding carbon fibre over the core parts 21, 24, 25. Alternatively the structural layer 26 may be formed into its trapezoidal shape by wrapping dry-fibre fabric round the core parts 21, 24, 25 and then joining together the butting edges to form a butt-joint. In this example the structural layer 26 has a trapezoidal shape with a single foot 36 bonded to the panel 16, but in an alternative embodiment the structural layer 26 may have an omega shape with a pair of outward-facing feet which are bonded to the panel 16.

[0064] The panel assembly 28 is laid up predominantly as dry-fibre, then infused with resin by the process shown in Figures 7-9. During the infusion process the panel 16 is carried on an infusion tool 70.

[0065] A flexible bladder 40 is laid into the longitudinal channel 19 in a deflated state as shown in Figure 7, before the battens 24, 25 are laid on top of the foam core part 21. A flexible vacuum bag 39 is laid over the panel assembly 28 and sealed to the infusion tool 70 by a seal 38 to form a vacuum chamber 50 between the vacuum bag 39 and the infusion tool 70. A vacuum is applied to the vacuum chamber via a vacuum port 37 as epoxy resin is injected via inlet ports 41 at the end of each stiffener 8. During the injection of resin the vacuum continues to be applied to the vacuum chamber 50 which draws the resin along the longitudinal channel 19, into the structural part 26 and into the panel 16.

[0066] Initially the vacuum draws the resin along the longitudinal channel 19 of each stiffener. Figure 7 shows a stage in the infusion process when the longitudinal channel 19 has been partially filled with resin 60.

[0067] As the infusion process continues, the resin fills the longitudinal channel 19 and then overflows from the longitudinal channel 19 into the porous dry-fibre structural layer 26 via the branch channels 18 and the slots 22. The resin also flows into the porous dry-fibre panel 16. Once the vacuum chamber 50 is filled with resin, it overflows out of the vacuum port 37. At the end of the infusion process as shown in Figure 8, a first portion of the resin (including the resin 60 shown in Figure 7) has flowed along the longitudinal channel 19 and then flowed from the longitudinal channel 19 into the structural part 26 and into the panel 16. A second portion 61 of the resin remains in the longitudinal channel 19 as shown in Figure 8 in contact with the bladder 40. A third portion 62 of the resin fills the branch channels 18 and a fourth portion 63 fills the slots 22 [0068] The purpose of the channel 19 is to aid in the infusion process and reduce the requirement to have external resin flow channels in the infusion tool 70.

[0069] The bladder 40 is then inflated with air as shown in Figure 9 This inflation of the bladder pushes the second portion 61 of resin into the branch channels 18 and/or into the slots 22, which in turn pushes the third and fourth portions 62, 63 of resin out of the branch channels 18 and the slots 22 into the structural part 26. As the bladder 40 inflates, more resin overflows from the vacuum port 37 as shown in Figure 9 [0070] Once the bladder 40 has been fully inflated as in Figure 9, the panel assembly is fully impregnated with resin and the bladder 40 is full of air 65. The bladder 40 is not removed, but there is an overall weight saving because the weight of the bladder 40 is less than the weight of the second portion 61 of the resin which it has displaced from the longitudinal channel 19.

[0071] The panel assembly is then heated to cure the epoxy resin so that the stiffeners become bonded to the panel 16. The cured epoxy resin forms co-infused joints between the feet 36 of the stiffeners and the panel 16; and co-bonded joints between the structural part 26 and the core parts 21, 24,25 of each stiffener.

[0072] An alternative embodiment of the present invention is shown in Figures 10-12. The panel assembly is similar to the panel assembly shown in Figures 7-9 and the same reference numbers will be used to indicate equivalent components In this embodiment, the foam core part 21 is replaced by a foam core part 32 with no channels In Figures 3-9 there are multiple slots 22 separated by tabs 23, but in the case of Figures 10-12 there are no tabs 23 so a single slot runs continuously along the full length of the stiffener between the battens 24, 25 and contains a bladder 40a shown in Figure 10 in its deflated state.

[0073] Figure 10 shows a stage in the infusion process when the slot has been filled with resin 60a. As the infusion process continues, the resin overflows from the slot into the porous dry-fibre structural layer 26. The resin also flows into the porous dry-fibre panel 16. Once the vacuum chamber is filled with resin, it overflows out of the vacuum port 37. At the end of the infusion process as shown in Figure 11, a first portion of the resin (including the resin 60a shown in Figure 10) has flowed along the slot and then flowed from the slot into the structural part 26 and into the panel 16. A second portion 61a of the resin remains in the slot as shown in Figure 11 in contact with the bladder 40a.

[0074] The bladder 40a is then inflated with air as shown in Figure 12 This inflation of the bladder pushes the second portion 61a of resin out of the slot and into the structural part 26. As the bladder 40a inflates, more resin overflows from the vacuum port 37 as shown in Figure 12.

[0075] Once the bladder 40a has been fully inflated as in Figure 12, the panel assembly is fully saturated with resin and the bladder 40a is full of air. The panel assembly is then heated to cure the epoxy resin so that the stiffeners become bonded to the panel 16.

[0076] 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.

[0077] 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

CLAIMS1. A stiffened panel assembly comprising: a panel; and a stiffener on the panel, the stiffener comprising: a structural part, a core in the structural part, a longitudinal channel in the core which extends in a length direction of the core, and a bladder in the longitudinal channel.
2. A stiffened panel assembly according to claim I wherein the structural part comprises one or more feet bonded to the panel.
3 A stiffened panel assembly according to any preceding claim wherein the core comprises a core material, the structural part comprises a structural material, and the core material has a lower density than the structural material
4. A stiffened panel assembly according to any preceding claim wherein the panel and the structural part each comprise a fibrous material co-infused with a matrix material which bonds the panel to the structural part.
5. A stiffened panel assembly according to any preceding claim wherein the structural part comprises a crown and a pair of webs, and the core is positioned between the webs.
6. A stiffened panel assembly according to any preceding claim wherein the structural part comprises a fibrous material
7 A stiffened panel assembly according to any preceding claim wherein the core comprises a first core part made of a first core material and a second core part made of a second core material different to the first core material; and the longitudinal channel and the bladder are in the first core part.
8. A stiffened panel assembly according to claim 7 wherein the longitudinal channel comprises a groove in the first core part.
9. A stiffened panel assembly according to any preceding claim wherein the core comprises a first core part made of a filler material, and a pair of structural core parts made of a fibre-reinforced composite material; and the bladder is between the pair of structural core parts.
10. A stiffened panel assembly according to any preceding claim further comprising a slot in the core which extends in a transverse direction from the longitudinal channel to the structural part of the stiffener, wherein the slot has a length which extends in the length direction of the core and a width which extends in the transverse direction
11 A stiffened panel assembly according to any preceding claim further comprising branch channels which branch out from the longitudinal channel at a series of points along a length of the longitudinal channel, wherein each branch channel extends in a transverse direction from the longitudinal channel to the structural part of the stiffener.
12. A stiffened panel assembly according to claim 11 wherein the structural part comprises a crown and a pair of webs, the core is positioned between the webs, and each branch channel extends from the longitudinal channel to one of the webs.
13. An aircraft or aircraft part comprising a stiffened panel assembly according to any preceding claim.
14. A method of manufacturing a stiffened panel assembly according to claim 1, the method comprising: injecting matrix material into the longitudinal channel so that a first portion of the matrix material flows along the longitudinal channel and then flows from the longitudinal channel into the structural part and into the panel, and a second portion of the matrix material remains in the longitudinal channel and in contact with the bladder; inflating the bladder so that the bladder forces at least some of the second portion of the matrix material to flow out of the longitudinal channel; and curing the matrix material so that the stiffener becomes bonded to the panel
15. A method according to claim 14 wherein inflating the bladder causes at least some of the matrix material to flow into the structural part or into the panel.
16. A method according to claim 14 or 15 wherein the structural part comprises a crown and a pair of webs, the core is positioned between the webs, and during the injection of the matrix material at least part of the first portion of the matrix material flows along the longitudinal channel and then into the crown and webs of the structural part.
17. A method according to claim 14, 15 or 16 wherein the structural part comprises a foot in contact with the panel, during the injection of the matrix material at least part of the first portion of the matrix material flows along the longitudinal channel and then into the foot of the stiffener, and the foot of the stiffener becomes bonded to the panel during the curing step.
18. A method according to any of claims 14 to 17 wherein the panel assembly further comprises branch channels which branch out from the longitudinal channel at a series of points along a length of the longitudinal channel, and during the injection of matrix material at least part of the first portion of the matrix material flows along the longitudinal channel and then flows from the longitudinal channel into the structural part via the branch channels.
19. A method according to any of claims 14 to 18 wherein the panel assembly further comprises a slot in the core, the slot has a length which extends in a length direction of the core and a width which extends in a transverse direction from the longitudinal channel to the stmctural part of the stiffener, and the bladder forces at least some of the second portion of the matrix material to flow out of the longitudinal channel into the slot.
20. A method according to any of claims 14 to 19 further comprising fitting a flexible vacuum bag over the stiffened panel assembly to form a vacuum chamber, and during the injection of the matrix material applying a vacuum to the vacuum chamber which draws the matrix material along the longitudinal channel, into the structural part and into the panel.