U.S. patent application number 17/646251 was filed with the patent office on 2022-04-21 for composite stiffener.
The applicant listed for this patent is AIRBUS OPERATIONS LIMITED. Invention is credited to Joshua BONAVENTURA, Martin GAITONDE, John Norman WOOLCOCK, Junwei ZHANG.
Application Number | 20220118727 17/646251 |
Document ID | / |
Family ID | 1000006062627 |
Filed Date | 2022-04-21 |
United States Patent
Application |
20220118727 |
Kind Code |
A1 |
ZHANG; Junwei ; et
al. |
April 21, 2022 |
COMPOSITE STIFFENER
Abstract
A composite stiffener for a stiffener reinforced panel is
disclosed. The stiffener has a longitudinal direction and a run-out
region which terminates at an end of the stiffener. The stiffener
also has a constant section region inboard of the run-out region in
the longitudinal direction and having a constant cross section
transverse to the longitudinal direction with a crown between
adjacent foot portions. The run-out region has a changing cross
section transverse to the longitudinal direction with a crown
between adjacent foot portions and the crown reduces in height
towards the end of the stiffener forming a ramp. The composite
stiffener comprises a number of blankets of non-crimp fabric
layers.
Inventors: |
ZHANG; Junwei; (Bristol,
GB) ; GAITONDE; Martin; (Bristol, GB) ;
BONAVENTURA; Joshua; (Bristol, GB) ; WOOLCOCK; John
Norman; (Bristol, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AIRBUS OPERATIONS LIMITED |
Bristol |
|
GB |
|
|
Family ID: |
1000006062627 |
Appl. No.: |
17/646251 |
Filed: |
December 28, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16798860 |
Feb 24, 2020 |
11241851 |
|
|
17646251 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29L 2031/3085 20130101;
B32B 5/024 20130101; B29D 99/001 20130101; B29D 99/0014 20130101;
B29C 70/462 20130101; B29D 99/0003 20130101; B32B 2262/106
20130101; B32B 7/03 20190101; B29B 11/16 20130101 |
International
Class: |
B29D 99/00 20060101
B29D099/00; B32B 7/03 20060101 B32B007/03; B29B 11/16 20060101
B29B011/16; B29C 70/46 20060101 B29C070/46; B32B 5/02 20060101
B32B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2019 |
GB |
1902778.8 |
Claims
1. A method of manufacturing a stiffener, comprising laying up a
plurality of blankets of non-crimp fabric layers and a plurality of
woven fabric layers as dry fabrics on a mould tool and co-infusing
the dry fabrics with resin followed by co-curing to form the
stiffener.
2. A method according to claim 1, wherein the stiffener has a
longitudinal direction with a run-out region at which terminates at
an end of the stiffener, and a constant section region inboard of
run-out region longitudinal direction and having a constant cross
section transverse to the longitudinal direction with a crown
between adjacent foot portions, wherein the run-out region has a
changing cross section transverse to the longitudinal direction
with a crown between adjacent foot portions and the crown reduces
in height towards the end of the stiffener forming a ramp, the
composite stiffener comprises a plurality of blankets of non-crimp
fabric layers, and a transition region between the constant section
region and the run-out region, wherein the method comprises laying
up a plurality of blankets of non-crimp fabric layers sandwiched
between woven fabric layers in the constant section region, and
cutting at least one of the blankets of non-crimp fabric layers so
that the blanket is terminated in the transition region.
3. A method according to claim 2, wherein the run-out region
comprises one or more woven fabric layers.
4. A method according to claim 3, wherein the one or more woven
fabric layers extends from a top of the ramp to the bottom of the
ramp.
5. A method according to claim 2, further comprising cutting all of
the blankets of non-crimp fabric layers so that all of the blankets
are terminated in the transition region.
6. A method according to claim 2, wherein the run-out region
includes the woven fabric layers and no non-crimp fabric
blankets.
7. A method according to claim 2, wherein the run-out region has a
ramped portion including the ramp, and a substantially planar toe
portion between the ramp and the end of the stiffener.
8. A method according to claim 2, wherein each of the blankets of
non-crimp fabric layers include a first layer having a 0-degree
fibre orientation aligned with the stiffener longitudinal direction
and a second layer having a fibre orientation not aligned with the
stiffener longitudinal direction.
9. A method according to claim 2, wherein the run-out region
includes one or more of the non-crimp fabric blankets.
10. A method according to claim 9, wherein the blanket has a dart
cut out and overlaps itself in the run-out region.
11. A method according to claim 2, wherein the constant section
region has an omega section.
12. A method according to claim 2, wherein the constant section
region has a cross section with continuous layers extending through
the crown and the adjacent foot portions.
13. A method according to claim 2, wherein the stiffener comprises
carbon fibre composite material.
14. A method according to claim 1, further comprising laying up the
plurality of woven fabric layers on a portion of the mould tool to
define the shape of the ramp in the run-out region followed by the
co-curing step without an intermediate step of cutting the woven
fabric layers laid up on the mould tool.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional application of U.S. patent
application Ser. No. 16/798,860, filed Feb. 24, 2020, now allowed,
which claims priority to United Kingdom patent application GB
1902778.8, filed Mar. 1, 2019, the entire contents of each of which
are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a composite stiffener for a
stiffener reinforced panel, and a method of manufacturing a
stiffener.
BACKGROUND OF THE INVENTION
[0003] Stiffeners are often attached to or integral with a panel to
provide reinforcement to the panel. For example, stringers are
elongated stiffening members that may be attached to a skin or
cover of an aircraft wing and extend in a generally spanwise
direction. The same basic layout is found in the vertical and
horizontal stabilizers. A similar structure is also found in an
aircraft fuselage, where the stiffeners extend in the longitudinal
aircraft direction. The stiffeners provide the necessary
reinforcement to withstand the aerodynamic and structural loads
experienced by the aircraft during flight and whilst on the
ground.
[0004] In areas where the stringers terminate, the cross section of
the stringer changes in order to facilitate the load transfer from
the stringer to the panel. The height of the stringer
(perpendicular to the plane of the panel) is typically decreased
towards the termination, known as a run out region.
[0005] Stringer runouts can result in areas of complex geometry for
the manufacture of composite stringers. Manufacturing issues, such
as wrinkling, can occur in these regions of complex geometry.
Different fibre layer materials may be more or less suitable in
these regions due to their different drapeability. Wrinkles and
other manufacturing defects, such as voids and fibre misalignments,
have the potential to provide localised stress points and therefore
reduce the overall performance of the stringer. Simplifying the
manufacturing process to minimise cutting of the fibre layers and
cutting of the cured composite stringer to define the geometry
reduces the cost and time to manufacture.
SUMMARY OF THE INVENTION
[0006] A first aspect of the invention provides a composite
stiffener for a stiffener reinforced panel, wherein the stiffener
has a longitudinal direction and a run-out region which terminates
at an end of the stiffener, and a constant section region inboard
of the run-out region in the longitudinal direction and having a
constant cross section transverse to the longitudinal direction
with a crown between adjacent foot portions, wherein the run-out
region has a changing cross section transverse to the longitudinal
direction with a crown between adjacent foot portions and the crown
reduces in height towards the end of the stiffener forming a ramp,
and the composite stiffener comprises a plurality of blankets of
non-crimp fabric layers.
[0007] The stringer with a crown between adjacent foot portions may
be known as an `omega`, or `top hat`, or `bowler hat` shaped
stringer, for example. A web may extend between each foot portion
and the crown. The fabric layers may run continuously from the
lateral edge of one foot portion and up through one web to the
crown and down though the other web to the lateral edge of the foot
on the other side of the crown.
[0008] Non-crimp fabrics (NCF) are typically provided as `blankets`
comprising two, or possibly more, fibre layers. Each fibre layer
may be unidirectional. The fibre layers are joined together, e.g.
by stitching, to form the blanket. The fibre layers in a blanket
typically have different fibre orientations. A blanket comprising
two fibre layers of different unidirectional fibre orientations is
known as a biaxial NCF. Triaxial and quadraxial fabrics are also
available.
[0009] NCF blankets are advantageous in that they enable a faster
layup because the multiple fabric layers in the blankets are
stitched together so they can be laid down as one. However NCF
blankets suffer the problem that they can have relatively poor
drapeability, compared to woven or unidirectional fabrics for
example, due to the different fibre orientations of the layers in
the blanket and the stitching between the layers. The fewer the
number of layers in the blanket the better the drapeability, so a
biaxial NCF blanket may be preferred for draping performance. NCF
blankets with a 0 degree fibre layer aligned with the stiffener
longitudinal direction provide excellent load carrying performance
in the primary load direction.
[0010] The particular geometry of the run out region of an omega
shaped stiffener with a ramp in the crown of the stiffener in the
run out region presents a challenge to the use of NCF material in
the stiffener. The inventors have found ways to achieve cost
effective manufacturing using NCF material in the stiffener without
having to resort to cutting the fibre material of the stiffener
once laid up prior to resin infusion.
[0011] In a first example, the stiffener includes both NCF blankets
and woven fibre layers with the NCF blankets being dropped off
leaving only the woven fibre layers in the more difficult to form
run out region. The woven fibre layers provide several advantages
in that they provide better drapeability and there are no 0 degree
fibre layers in the run out region which provides better stress
performance.
[0012] The run-out region may comprise one or more woven fabric
layers.
[0013] The one or more woven fabric layers may extend from a top of
the ramp to a bottom of the ramp.
[0014] The composite stiffener may further comprise a transition
region between the constant section region and the run-out region.
The constant section region may have a plurality of blankets of
non-crimp fabric layers sandwiched between woven fabric layers. At
least one of the blankets of non-crimp fabric layers may be dropped
off in the transition region. The woven fibre layers also provide
good damage tolerance. It is therefore advantageous to provide the
woven fibre layers as the outer layers (top and bottom) of the
layup.
[0015] All of the blankets of non-crimp fabric layers in the
constant section region may be dropped off in the transition
region.
[0016] The run-out region may include the woven fabric layers and
no non-crimp fabric blankets.
[0017] In a second example, the stiffener includes NCF blankets, at
least one of which extends to the end of the stiffener and which is
cut to form darts so that the NCF blankets can be draped to form to
the shape of the run out region. The use of only NCF blankets in
the layup provides economies but at the expense of additional time
to form the darts.
[0018] The run-out region may include one or more of the non-crimp
fabric blankets. The blanket may have a dart cut out and overlap
itself in the run-out region.
[0019] The run-out region may have a ramped portion including the
ramp, and a substantially planar toe portion between the ramp and
the end of the stiffener.
[0020] Each of the blankets of non-crimp fabric layers may include
a first layer having a 0 degree fibre orientation aligned with the
stiffener longitudinal direction and a second layer having a fibre
orientation not aligned with the stiffener longitudinal
direction.
[0021] The constant section region may have an omega section.
[0022] The constant section region may have a cross section with
continuous layers extending through the crown and the adjacent foot
portions.
[0023] The stiffener may comprise carbon fibre composite
material.
[0024] A further aspect of the invention provides an aircraft
structure including a panel reinforced with a stringer which is a
stiffener according to the first aspect.
[0025] A further aspect of the invention provides a method of
manufacturing a stiffener, comprising laying up a plurality of
blankets of non-crimp fabric layers and a plurality of woven fabric
layers as dry fabrics on a mould tool and co-infusing the dry
fabrics with resin followed by co-curing to form the stiffener. The
stiffener may be in accordance with the first aspect.
[0026] The method may comprise laying up a plurality of blankets of
non-crimp fabric layers sandwiched between woven fabric layers in
the constant section region, and cutting at least one of the
blankets of non-crimp fabric layers so that the blanket is dropped
off in the transition region.
[0027] The method may further comprise cutting all of the blankets
of non-crimp fabric layers so that all of the blankets are dropped
off in the transition region.
[0028] The run-out region may include the woven fabric layers and
no non-crimp fabric blankets.
[0029] The method may further comprise laying up the plurality of
woven fabric layers on a portion of the mould tool to define the
shape of the ramp in the run-out region followed by the co-curing
step without an intermediate step of cutting the woven fabric
layers laid up on the mould tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Embodiments of the invention will now be described with
reference to the accompanying drawings, in which:
[0031] FIG. 1 is a plan view of an aircraft;
[0032] FIG. 2 is a schematic plan view of an aircraft wing box;
[0033] FIG. 3 is a schematic section view of an aircraft wing
box;
[0034] FIG. 4 is a cut away view of a stringer reinforced
panel;
[0035] FIG. 5 is a three dimensional view of a stringer
(stiffener);
[0036] FIG. 6 is a transverse section view through the constant
section region of the stringer;
[0037] FIG. 7 is a longitudinal section view through the stringer
showing the constant section region, the run out region and the
transition region;
[0038] FIG. 8 is a schematic view of an NCF biaxial blanket;
[0039] FIG. 9 is a schematic view of the stringer layup with NCF
blankets sandwiched between woven fibre layers;
[0040] FIG. 10 is a section view of the layup being laid up on a
mould tool; and
[0041] FIG. 11 is a schematic view of an NCF blanket with darts cut
out.
DETAILED DESCRIPTION
[0042] FIG. 1 shows an aircraft 1 with port and starboard wings 2,
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 that only the starboard wing 3 will be described in
detail with reference to FIGS. 2 and 3. The aircraft 1 shown is a
conventional transonic jet passenger transport aircraft, but it
will be appreciated that this description can relate to a wide
variety of aircraft including military, civilian, general aviation,
jet, prop, high wing, low wing, etc.
[0043] The main structural element of the wing is a wing box formed
by upper and lower covers 5, 6 and front and rear spars 7, 8 shown
in cross section in FIG. 3. The covers 5, 6 and spars 7, 8 are each
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) over which air
flows during flight of the aircraft. Each cover also has an inner
surface carrying `stringers` or stiffeners. Each cover carries of
the order of 30 to 40 stiffeners, so for the purposes of clarity
only 5 are shown in FIG. 2. The stringers are labelled 40.
[0044] As shown in FIG. 3, each spar has a C-shaped cross section
with upper and lower spar flanges each joined to the inner surface
of a respective one of the covers 5, 6 and a spar web extending
between the spar flanges. One or more of the covers 5, 6 may be
integrated with the spars 7, 8 to form an omega or `u` or `n`
shaped wing box component.
[0045] The wing box also has a plurality of transverse ribs 13,
each rib being joined to the covers 5, 6 and the spars 7, 8. The
ribs include an inboard rib 10 located at the root of the wing box,
and a number of further ribs 13 spaced apart from the innermost rib
along the length of the wing box. The wing has a large number of
such ribs 13 and for the purposes of clarity only 10 are shown in
FIG. 2.
[0046] The wing boxes may be divided into a plurality of fuel
tanks, such as an inboard fuel tank bounded by the inboard rib 10,
a mid-span rib 13a indicated in solid line, the covers 5, 6 and the
spars 7, 8; and an outboard fuel tank bounded by the mid-span rib
13a, an outboard rib 12 at the tip of the wing box, the covers 5, 6
and the spars 7, 8.
[0047] 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. As can be seen in FIG. 2, the stiffeners 40
stop short of the inboard rib 10 and the outboard rib 12, but pass
through the ribs 13.
[0048] FIG. 4 shows a schematic cut-away view of the stringers 40
attached to the upper-wing cover 5, and in particular show the area
in which the stringers 40 terminate. The stringers have a
longitudinal direction generally aligned with the wing's span-wise
direction and an "Omega" cross-sectional shape. The stringers 40
have a generally constant cross section transverse to the
longitudinal direction, and a run-out region 41 which terminates at
an end of the stringer 40.
[0049] The stringer 40 is shown in more detail with reference to
FIGS. 5 to 7. The constant section region 42 of the stringer 40
lies inboard (i.e. away from) the run-out region 41 in the
longitudinal direction, x. The constant section region 42 has the
constant cross section transverse to the longitudinal direction, x,
with a crown 43 between adjacent foot portions 44a, 44b. The crown
is joined to the foot portions 44a, 44b by respective webs 45a,
45b. The webs 45a, 45b are generally upstanding, z, perpendicular
to the plane, x-y, of the upper-wing cover 5 and therefore
generally parallel in the longitudinal direction, x, in the
constant section region 42 of the stringer 40.
[0050] The run-out region 41 has a changing cross section
transverse to the longitudinal direction, x, also with a crown 43
between the adjacent foot portions 44, a, 44b. In the run-out
region 41 the crown 43 reduces in height towards the toe portion 46
at the end of the stiffener 40 forming a ramp 47. The run out
region 41 has a similar basic "omega" shape as the inboard constant
section region 42 but the height of the crown 43 above the foot
portions 44a, 44b decreases substantially linearly from a top 48 of
the ramp to a bottom 49 of the ramp. Between the top 48 of the ramp
and the constant section region 42 there is a transition region 50
which will be described in more detail with reference to FIG.
7.
[0051] Turning first to FIG. 6, which shows a cross section through
the constant section region 42 it can be seen that the stiffener
comprises a laminate stack of fibre layers comprising a lowermost
woven fabric layer 51, an uppermost woven fabric layer 52 and a
plurality of blankets 53 of non-crimp fabric (NCF) layers between
the lowermost woven fabric layer 51 and the uppermost woven fabric
layer 52.
[0052] 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 section region 42 the plurality of blankets 53
of non-crimp fabric layers can be seen sandwiched between the woven
fabric layers 51, 52. The woven fabric layers 51, 52 are continuous
through the constant section region 42, the transition region 50,
the run-out region 41 and the toe portion 46. In the transition
region 50 the blankets 53 of non-crimp fabric layers are
terminated. Preferably, the blankets 53 of non-crimp fabric layers
are terminated in a staggered fashion along the longitudinal
direction, x. The height of the stack of blankets 53 of non-crimp
fabric layers therefore reduces towards the end of the stiffener
forming a taper in the crown 43, the webs 45a, 45b and the foot
portions 44a, 44b towards the end of the stringer. In the
transition region 50 all of the blankets 53 of non-crimp fabric
layers are terminated leaving only the woven fabric layers 51, 52
at the top 48 of the ramp 47 in the run-out region 41.
[0053] FIG. 8 shows an exploded view of one of the non-crimp fabric
blankets 53 and which comprises a first layer 53a having a
0.degree. fibre orientation, and a second layer 53b having a
45.degree. fibre orientation. The first and second layers 53a, 53b
are joined together, e.g. by stitching, as generally indicated by
the broken lines 53c. In this example, the 0.degree. fibre
orientation is aligned with the longitudinal axis, x, of the
stiffener 40.
[0054] In the constant section region 42 of the stiffener 40,
having a plurality of layers having a 0.degree. fibre orientation
may be advantageous to provide longitudinal bending stiffness for
the stiffener 40. However, in the run-out region 41 this bending
stiffness is generally undesirable as the purpose of the run-out
region 41 is to provide flexibility to transition the stiffener
load into the panel to which it is attached, e.g. the upper or
lower wing covers 5, 6.
[0055] The plurality of blankets 53 of non-crimp fabric layers may
be arranged in a stack to achieve a generally balanced layup. To
that end, some of the blankets 53 may comprise biaxial NCF blankets
having 0/45 fibre orientations, and others of the blankets 53 of
NCF fabrics may have 0/135 fibre orientations. In a preferred
embodiment the number of biaxial 0/45 NCF blankets equals the
number of 0/135 NCF blankets. The different NCF blankets having
0/45 and 0/135 fibre orientations may be alternated through the
stack and with a mirror layup either side of a mid-plane through
the stack of NCF blankets 53.
[0056] By terminating the NCF blankets 53 in the transition region
50 so as to leave only the woven fabric layers 51, 52 in the
run-out region 41, the stress performance in the run-out region of
the stiffener can be optimised. As well, the woven fabric layers
51, 52 typically will have better drape performance than the NCF
blankets 53 and so can form to the complex shape of the run-out
region 41 without requiring any darting of the woven fabric layers
51, 52. The woven fabric may be, e.g. a 5 harness fabric although
any other suitable woven fabric may be used. The good drape
performance and lack of requirement for darting of the woven fibre
fabric layers 51, 52 helps to improve manufacturability and also
the quality of the final composite stiffener 40.
[0057] FIG. 10 illustrates schematically a method of manufacturing
the stiffener 40, in which the layers of dry or semi-preg carbon
fibre material are laid upon a mould tool 60. The uppermost woven
fibre fabric layer 52 is laid first on the mould tool 60 followed
by the plurality of NCF blankets 53 and finally the lowermost woven
fibre fabric layer 51. The dry or semi-preg layers are then infused
with a suitable resin and cured in a conventional manner. Once
cured the stiffener 40 can be removed from the mould tool 60.
[0058] The mould tool 60 has a shape conforming to the outer-mould
surface of the completed stiffener 40, including the transition
region 50 and the run-out region 41, such that after curing the
completed stiffener 40 may be removed from the mould tool 60
without the need for any cutting or machining of the fibre fabric
layers either during the layup on the mould tool, or after removing
the cured composite stiffener 40 from the mould tool 60. By
avoiding these cutting steps the manufacturability of the stiffener
40 is significantly improved.
[0059] In an alternative embodiment the stiffener 40 may include
NCF blankets 53 in the run-out region but without any change to the
overall shape of the stiffener 40 previously described. Since the
NCF blanket 53 is less drapeable than the woven fibre fabric, as
shown in FIG. 11 darts 70 may need to be cut in the NCF blanket
53.
[0060] When the NCF blanket 53 with the darts 70 is laid upon the
mould tool 60 the edges of the blanket 53 either side of the dart
70 are brought together and are slightly overlapping. The presence
of the darts 70 provides sufficient formability to the NCF blankets
53 to conform to the shape of the mould 60 in the run-out region
41.
[0061] Where NCF blankets 53 are darted then only NCF blankets 53
may be used in the layup of the stiffener 40 and the woven fibre
fabric layers 51, 52 may dispensed with. Alternatively, the woven
fibre fabric layers 51, 52 may be retained. When NCF blankets with
darts 70 are used in the run-out region 41 some of the NCF blankets
53 present in the constant section region 42 may be dropped off in
the transition region 50. In other words, the run-out region 41 may
have a fewer number of NCF blankets 53 as compared with the
constant section region 42. Although the presence of the NCF
blankets 53 in the run-out region 41 may be less preferable since
the darts 70 may need to be cut out from the blankets 53 prior to
layup on the mould tool 60, such an arrangement is still
advantageous as no further cutting of the cured stiffener 40 is
required after the removal from the mould tool 60.
[0062] 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.
[0063] 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.
* * * * *