U.S. patent application number 13/431706 was filed with the patent office on 2012-08-02 for sandwich structure having arrestment feature and method of making the same.
This patent application is currently assigned to The Boeing Company. Invention is credited to John H. Fogarty, Haozhong Gu, Kevin M. Retz, Terry D. Richardson, Charles R. Saff.
Application Number | 20120193016 13/431706 |
Document ID | / |
Family ID | 43064534 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120193016 |
Kind Code |
A1 |
Saff; Charles R. ; et
al. |
August 2, 2012 |
Sandwich Structure Having Arrestment Feature and Method of Making
the Same
Abstract
A composite sandwich structure comprises a core sandwiched
between composite laminate facesheets. The core includes a
plurality of core sections spliced together at joints that
incorporate integral features for arresting the propagation of
irregularities in the facesheets.
Inventors: |
Saff; Charles R.; (St.
Peters, MO) ; Fogarty; John H.; (St. Louis, MO)
; Gu; Haozhong; (Chesterfield, MO) ; Richardson;
Terry D.; (Dardenne Prairie, MO) ; Retz; Kevin
M.; (Bothell, WA) |
Assignee: |
The Boeing Company
Chicago
IL
|
Family ID: |
43064534 |
Appl. No.: |
13/431706 |
Filed: |
March 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12631029 |
Dec 4, 2009 |
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13431706 |
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Current U.S.
Class: |
156/182 ;
156/185; 156/300 |
Current CPC
Class: |
Y10T 428/24777 20150115;
Y10T 428/239 20150115; Y10T 428/249923 20150401; B29C 66/122
20130101; Y10T 29/49622 20150115; Y10T 428/24752 20150115; B29C
66/118 20130101; B32B 2250/03 20130101; Y10T 156/1093 20150115;
Y10T 29/49982 20150115; B32B 3/18 20130101; B32B 3/14 20130101;
B32B 2307/718 20130101; B29C 66/01 20130101; B29C 66/114 20130101;
B29C 66/128 20130101; B29C 66/112 20130101; Y10T 156/10 20150115;
B29C 66/1122 20130101; B23B 3/04 20130101; B29C 66/05 20130101;
B29C 66/10 20130101; B32B 3/06 20130101; B32B 2605/18 20130101;
B29C 65/00 20130101; B29C 66/11 20130101; B32B 3/04 20130101; Y10T
428/24174 20150115; B32B 3/12 20130101; B29C 66/1182 20130101; B29C
66/1142 20130101; Y10T 156/1002 20150115; Y10T 156/1034
20150115 |
Class at
Publication: |
156/182 ;
156/185; 156/300 |
International
Class: |
B32B 37/02 20060101
B32B037/02; B32B 37/12 20060101 B32B037/12 |
Claims
1-16. (canceled)
17. A method of making a composite sandwich structure, comprising:
producing a core by forming joints between a plurality of core
segments; sandwiching the core between first and second facesheets,
including joining the core to each of the facesheets; and, forming
an arrestment feature between the core and at least one of the
facesheets along each of the joints.
18. The method of claim 17, wherein forming an arrestment feature
includes placing a composite wrap on each of the core segments
along each of the joints.
19. The method of claim 17, wherein placing the composite wrap on
each of the core segments along each of the joints includes forming
the wrap over at least portions of each of three sides of each of
the core segments.
20. The method of claim 19, wherein forming an arrestment feature
includes placing a composite strap between the composite wrap and
the at least one of the facesheets.
21. The method of claim 19, wherein forming an arrestment feature
includes applying a layer of adhesive between the wraps on adjacent
facesheets of the core segments.
22. (canceled)
23. A method of making a composite sandwich structure for an
aircraft, comprising: providing a plurality of core segments;
wrapping three sides of each of the core segments along the edges
of the core segments with a fiber reinforced composite resin wrap;
assembling the wrapped core segments into a core, including forming
joints between the core segments by arranging the core segments in
edge-to-edge relationship and abutting the wraps on adjacent ones
of the core segments; introducing a layer of adhesive between the
wraps along each of the joints; forming a plurality of composite
tear straps; placing one of the tear straps over the wraps along
each of the joints; assembling the structure including sandwiching
the core, the wraps and the tear straps between first and second
facesheets; and, curing the assembled structure.
24. (canceled)
25. The method of claim 19, wherein the composite wrap comprises a
fiber reinforced resin material.
Description
TECHNICAL FIELD
[0001] This disclosure generally relates to composite structures,
and deals more particularly with a composite sandwich structure
having a segmented core and an integral arrestment feature.
BACKGROUND
[0002] One type of composite structure used in a variety of
applications comprises a core sandwiched between a pair of
composite facesheets, sometimes referred to as a sandwich
structure. Where the core includes multiple core details, such as
multiple core segments joined together, the structure may be
referred to as a "core blanket". The core in these structures may
be formed of any of various materials including, but not limited to
honeycombs, foams and balsa, to name only a few. The facesheets may
be formed from multiple laminated plies of a fiber reinforced
resin.
[0003] Inconsistencies may sometimes occur within localized areas
of the facesheets of these sandwich structures. For example, a
facesheet may contain a void, a dent or a porosity that may occur
at the time the facesheet is manufactured or later during the
service life of the sandwich structure. For instance, a facesheet
impacted by an object may cause a localized disbond or crack
occurring in one or more plies of the facesheet. Unless arrested, a
disbond or crack may spread or propagate to areas outside of the
local impact area.
[0004] One solution to the problem involves the inclusion of
substructures within the sandwich to limit the propagation of
inconsistencies, however substructures may be relatively expensive
to manufacture and assemble, and may add additional weight to the
sandwich structure. In addition, known substructure solutions are
specifically designed to either limit propagation of disbands or
cracks, but may not limit both. It may be possible to combine
multiple substructure designs in order to arrest the propagation of
both disbonds and cracks, however the use of multiple substructures
may lead to an overall composite structure design that exceeds
target weight specifications. Another solution to the problem is to
limit the operating strain applied to the sandwich structure, and
perform periodic visual checks on the integrity of the structure,
however this approach may not be practical in some applications
where the operating strains placed on the sandwich structure cannot
be limited, and/or predicted.
[0005] Accordingly, there is a need for a sandwich structure having
a lightweight but robust core capable of reducing or arresting the
propagation of irregularities that may occur in the structure,
particularly as a result of object impacts.
SUMMARY
[0006] According to the disclosed embodiments, a sandwich structure
comprises a lightweight, segmented core which may reduce or arrest
the propagation of irregularities that may occur in the structure,
such as those resulting from an object impact on facesheets during
service. The structure includes an arrestment feature that may be
easily and inexpensively integrated into the core along joints
where the core segments are spliced together. In addition to
arresting the propagation of inconsistencies, the arrestment
feature may improve the strength of the core, as well as both its
fracture and structural toughness and the overall load carrying
ability of the sandwich structure.
[0007] According to one disclosed embodiment, a composite sandwich
structure is provided comprising a core including a plurality of
core segments sandwiched between the facesheets. Arrestment means
are provided between the core and each of the facesheets for
arresting the propagation of an inconsistency in the facesheets.
The arrestment means may include a composite wrap that covers edges
of the core segments includes a portion sandwiched between the core
and each of the facesheets. The arrestment means may further
include a composite strap overlying joints between the core
segments, as well as a layer of adhesive that joins the wraps along
the joints.
[0008] According to another disclosed embodiment, a composite
sandwich structure having integral arrestment comprises a segmented
core sandwiched between and joined to first and second multi-ply,
composite facesheets. The core includes a plurality of core
segments that are spliced together along joints between their
mutual edges. The sandwich structure further comprises composite
wraps and composite straps. The wraps cover the edges of each of
the core segments along the joints and may have a C-shaped cross
section. The wraps on the adjacent core sections form a
back-to-back C-shape along each of the joints. The composite straps
respectively cover the joints and are sandwiched between each of
the wraps and one of the facesheets. Each of the wraps may cover
three adjacent sides of one of the core segments. Adjacent ones of
the wraps may be joined together with a layer of adhesive. The
wraps and the straps may comprise a fiber reinforced resin.
[0009] According to another embodiment, a method is provided of
making a composite sandwich structure. The method comprises
producing a core by forming joints between a plurality of core
segments, and sandwiching the core between first and second
facesheets, including joining the core to each of the facesheets.
The method further comprises forming an arrestment feature between
the core and at least one of the facesheets along each of the
joints. Forming the arrestment feature may include placing a
composite wrap on each of the core segments along each of the
joints. Forming the arrestment feature may further include placing
a composite strap between the wrap and at least one of the
facesheets.
[0010] The disclosed embodiments satisfy the need for a composite
sandwich structure and a method of producing the same that may
overcome the limitations of existing sandwich structures while
providing a segmented core that may exhibit improved strength, and
which includes an integral arrestment feature that may limit the
propagation of irregularities in the facesheets.
BRIEF DESCRIPTION OF THE ILLUSTRATIONS
[0011] FIG. 1 is an illustration of a functional block diagram of a
composite sandwich structure having an integral arrestment
feature.
[0012] FIG. 2 is an illustration of a perspective view of a
sandwich structure having a segmented core and an integral
arrestment feature.
[0013] FIG. 3 is an illustration of a sectional view taken along
the line 3-3 in FIG. 2.
[0014] FIG. 4 is an illustration of the area designated as "A" in
FIG. 3.
[0015] FIG. 5 is an illustration of a flow diagram showing the
steps of a method of producing a sandwich structure having an
integral arrestment feature.
[0016] FIGS. 6A-6F are illustrations useful in explaining a method
of producing the sandwich structure illustrated in FIGS. 1-4.
[0017] FIG. 7 is an illustration of a sectional view of an edge of
one of the core segments in which recesses have been formed.
[0018] FIG. 8 is an illustration of an exploded sectional view
showing an alternate method of producing the sandwich
structure.
[0019] FIG. 9 is an illustration of a sectional view of a portion
of a sandwich structure showing an alternate form of the arrestment
feature.
[0020] FIG. 10 is an illustration similar to FIG. 9 but showing
another embodiment of the arrestment feature.
[0021] FIG. 11 is an illustration of a flow diagram of aircraft
production and service methodology.
[0022] FIG. 12 is an illustration of a block diagram of an
aircraft.
DETAILED DESCRIPTION
[0023] Referring first to FIGS. 1 and 2, the disclosed embodiments
relate to a composite sandwich structure 20 comprising a segmented
core 22 sandwiched between and affixed to first and second
facesheets 24, 26. The core 22 includes a plurality of core
segments 28 spliced together along their mutual edges 37 to form
joints 30. In the illustrated embodiment, the joints 30 extend
substantially orthogonal, however other geometries are possible.
Also, while the sandwich structure 20 is shown as being
substantially planar, it may include curves or contours (not shown)
to suit the particular application.
[0024] The sandwich structure 20 includes an arrestment feature 25
along the joints 30, which is disposed between both adjacent ones
of the core segments 28, and between the facesheets 24, 26. As will
be discussed below in more detail, the arrestment feature 25 may
function to arrest the propagation of one or more localized
inconsistencies (not shown) in the sandwich structure 20, such as a
disbond or crack in either of the facesheets 24, 26 resulting from,
for example and without limitation, an object (not shown) impacting
an outer surface 26a of one of the facesheets 26. As used herein
"inconsistent area", "inconsistency" and "inconsistencies" refer to
a localized area in the composite sandwich 20 that may be outside
of designed tolerances. The inconsistency may comprise, for example
and without limitation, a void, a dent, a crack or a porosity that
may occur at the time the composite sandwich structure 20 is
manufactured or later during the service life of the sandwich
structure 20. Additionally, the arrestment feature 25 may provide
the core 22 with additional strength and/or form alternate load
paths through the sandwich structure 20.
[0025] Referring now also to FIGS. 3 and 4, the arrestment feature
25 may comprise a pair of composite wraps 32, a pair of composite
tear straps 34, and a layer 36 of adhesive between adjacent ones of
the wraps 32. Each of the wraps 32 is generally C-shaped in cross
section, and includes three legs 32a, 32b and 32c respectively
covering three sides 33 of each of the core sections 28, along the
outer edges 37 of the core section 28. Depending on the
application, the wraps 32 may have cross sectional shapes other
than a C-shape. The C-shaped wraps 32 are arranged in back-to-back
relationship and are joined together by the adhesive layer 36 which
extends substantially through the entire thickness of the core 22.
In the illustrated embodiment, each of the core segments 28
includes a recess 35 in the outer faces 33a thereof. Legs 32b, 32c
of each of the wraps 32 are received within the recesses 35 so that
the facesheets 24, 26 lie substantially flat over the outer faces
33a of the core segments 28.
[0026] As best seen in FIG. 4, each of the legs 32b, 32c includes
an outwardly tapered or inclined section 40, and an outer end 42
that extends substantially parallel to and engages a corresponding
facesheet 24, 26. The outer ends of the legs 32b, 32c are
sandwiched between the core section 28 and one of facesheets 24,
26, each of which may comprise multiple laminated composite plies
38.
[0027] The composite tear straps 34 extend along the joint 30 and
are sandwiched between one of the facesheets 24, 26 and legs 32b,
32c of the wraps 32. As best seen in FIG. 4, each of the straps 34
lies within one of the recesses 35 to allow the facesheets 24, 26
to lie substantially flat. As will be discussed below, in other
embodiments, the core segments 28 may not be provided with recesses
35, in which case the facesheets 24, 26 may include slightly raised
areas (not shown) where the facesheets 24, 26 cover the wraps 32
and straps 34. The tear straps 34 may function to arrest the
propagation of irregularities such as cracks in the structure 20 in
the through-the-thickness direction of the structure 20.
[0028] Wraps 32 and tear straps 34 may each comprise a composite
ply laminate such as, without limitation, a fiberglass reinforced
epoxy resin which may be in the form of a unidirectional tape. The
straps 34 may include ply drop offs 34a which conform to the
tapered section 40 of the wrap 32. The outer end 42 of each of the
wraps 32 extends a distance "D" beyond the outer edges 34b of each
of the straps 34, so that the ends 42 of each of the wraps 32 are
joined directly to the innermost ply 38a of one of the facesheets
24, 26. The extension of the wrap ends 32 past the tear straps 34
may aid in guiding the propagation of possible disbonds along a
desired path that leads to arrestment.
[0029] From the forgoing, it can be appreciated that both the wraps
32 and the straps 34 are affixed directly to the facesheets 24, and
that the core segments 28 are secured to the facesheets 24 through
both the wraps 32 and the straps 34. Moreover, as best seen in FIG.
3, adjacent ones of the core sections 28 are spliced together by
both the adhesive layer 36 which joins adjacent ones of the wraps
32, and by the straps 34 which extend between and are joined to
adjacent ones of the wraps 32.
[0030] Reference is now made to FIG. 5 and FIGS. 6A-6F which
illustrate the steps of making a composite sandwich structure such
as that shown in FIGS. 1-4. Beginning at step 44 (FIG. 5) the
desired number of core segments 28 are provided which may each
comprise, as previously described, any of various materials and
constructions, including, but not limited to honeycombs, foams and
balsa as well as a combination of these and other materials. At
step 46, the peripheral edges 37 (FIGS. 3 and 4) of each of the
core segments 28 may be machined, as desired to form the recesses
35 in the core segments 28.
[0031] Next, as shown at step 48 in FIG. 5 and in FIG. 6A, a layer
62 of adhesive may optionally be applied to the outer sides 33 of
each of the core segments 28 in order to aid in holding the wraps
32 in place during subsequent processing steps. At step 50 (FIG. 5)
a strip 64 (FIG. 6A) of composite material is folded over the outer
edges 37 of each of the core segments 28, so as to cover three
sides 33 of the core segment 28, as shown in FIG. 6C. As previously
noted, the layers 62 of adhesive may assist in holding the wrap 32
in its folded state covering all three sides 33 during subsequent
processing steps.
[0032] Next, as shown at step 52 in FIG. 5, a layer of suitable
adhesive 36 is applied to the wrapped edges 37 of the core segments
28, and particularly to the legs 32a of each wrap 32. At step 54,
core segments 28 are assembled to form the configuration shown in
FIG. 2 by bringing the edges 37 of the core segments 38 into
abutment with each other. FIGS. 6D and 6E illustrate the wrapped
core segments 28 after completion of step 52. It should be noted
here, that because the wraps 32 and the straps 34 are integrated
into the core 22 in an uncured state, the assembled structure 20
may be formed before curing into curved or contoured parts if
desired.
[0033] Next, as shown at step 56 in FIG. 5, the straps 34 are
placed over adjoining wraps 32, overlying the joints 30, as shown
in FIG. 6F. At step 58 in FIG. 5, the facesheets 24, 26 may be
applied over the assembled core segments 28, also shown in FIG. 6F.
Finally, at step 60 in FIG. 5, the constituent parts of the
assembled sandwich structure 20 may be co-cured to form an
integrated structure. The production process described above, and
particularly the assembly process, may be carried out by hand labor
or may be partly or fully automated by machines (not shown).
[0034] In the embodiment illustrated in FIGS. 6A-6F a recess 35 has
not been formed in the core segments 28. Thus, in this embodiment,
the facesheets 24, 26 may be slightly raised in the area of the
joints 30. As previously mentioned, however, and as shown in FIG.
7, it may be possible to form recesses 35 in the core segments 28
to accommodate the combined thickness of the wraps 32 and the
straps 34 by machining the outer faces 33a of the core segments 28
along the outer edges 37 to a depth "d", where "d" is substantially
equal to the combined thickness of the straps 34 and the legs 32b
of the wraps 32 (see FIG. 4).
[0035] FIG. 8 illustrates a sandwich structure 20 similar to that
described above, but which may be made by an alternate embodiment
of the disclosed method. In this embodiment, the arrestment feature
25 comprises a pair of wraps 32, a pair of straps 34 and a layer of
adhesive 36, that are preassembled prior to assembly of the core
segments 28 and the facesheets 24, 26. In this embodiment, the
arrestment feature 25, which is similar in cross sectional shape to
the arrestment feature 25 previously described, may be
pre-assembled as an uncured layup, using prepreg. The pre-assembled
feature 25 may then be installed between the core segments 28 as
the core segments 28 are being assembled into the core 22.
Following assembly of the core 22, the facesheets 24, 26 may be
applied to the core 22, and the assembled structure 20 may then be
cured. In other embodiments, depending upon the application,
arrestment feature 25 may be pre-cured, in which case it may be
joined to the core segments 28 and facesheets 24, 26 with a bonding
adhesive that is cured along with the core segments 28 and
facesheets 24, 26.
[0036] In some embodiments, it may be not be necessary to use both
the wraps 32 and the straps 34. For example, as shown in FIG. 9, in
an alternate embodiment of the sandwich structure 20a, it may be
possible to achieve adequate arrestment through the use of tear
straps 34 which are sandwiched between the core segments 28 and the
facesheets 24, 26, overlying the joints 30. In this example, the
straps 34 are recessed into the core segments 28, and the layer of
adhesive 36 joins adjoining core segments 28 along the joint
30.
[0037] FIG. 10 illustrates another embodiment of a sandwich
structure 20b in which the desired arrestment may be achieved
through the use of wraps 32 joined together by the layer 36 of
adhesive. In this example, adjacent core segments 28 are joined
together through the wraps 32 and adhesive 36, while the entire
lengths of the outer legs 32b, 32c of the wraps 32 are joined to
the facesheets 24, 26. The back-to-back wraps 32 form an integral
part of the core 22 which both reinforces the joints 30 and forms a
periodic reinforcement between the core 22 and the facesheets 24,
26 that may aid in reducing propagation of inconsistencies such as
disbonds in the facesheets 24, 26.
[0038] Embodiments of the disclosure may find use in a variety of
potential applications, particularly in the transportation
industry, including for example, aerospace, marine and automotive
applications. Thus, referring now to FIGS. 11 and 12, embodiments
of the disclosure may be used in the context of an aircraft
manufacturing and service method 68 as shown in FIG. 11 and an
aircraft 70 as shown in FIG. 12. During pre-production, exemplary
method 68 may include specification and design 72 of the aircraft
70 and material procurement 74, during which the disclosed sandwich
structure 20 may be specified for use in the aircraft 70. During
production, component and subassembly manufacturing 76 and system
integration 78 of the aircraft 70 takes place. The disclosed method
may be used during processes 76, 78 to manufacture and assemble
components that incorporate the disclosed sandwich structure 20.
Thereafter, the aircraft 70 may go through certification and
delivery 80 in order to be placed in service 82. While in service
by a customer, the aircraft 70 is scheduled for routine maintenance
and service 84 (which may also include modification,
reconfiguration, refurbishment, and so on). The disclosed method
may be used to produce sandwich structures that are installed on
the aircraft as part of the maintenance and service 84.
[0039] Each of the processes of method 68 may be performed or
carried out by a system integrator, a third party, and/or an
operator (e.g., a customer). For the purposes of this description,
a system integrator may include without limitation any number of
aircraft manufacturers and major-system subcontractors; a third
party may include without limitation any number of vendors,
subcontractors, and suppliers; and an operator may be an airline,
leasing company, military entity, service organization, and so
on.
[0040] As shown in FIG. 12, the aircraft 70 produced by exemplary
method 68 may include an airframe 86 with a plurality of systems 94
and an interior 90. Examples of high-level systems 94 include one
or more of a propulsion system 92, an electrical system 94, a
hydraulic system 96, and an environmental system 98. Any number of
other systems may be included. Although an aerospace example is
shown, the principles of the disclosure may be applied to other
industries, such as the marine, automotive and construction
industries.
[0041] Systems and methods embodied herein may be employed during
any one or more of the stages of the production and service method
68. For example, components or subassemblies using the disclosed
sandwich structure corresponding to production process 76 may be
fabricated or manufactured in a manner similar to components or
subassemblies produced while the aircraft 70 is in service. Also,
one or more of the disclosed embodiments may be utilized during the
production stages 76 and 78, for example, by substantially
expediting assembly of or reducing the cost of an aircraft 70.
Similarly, one or more of the embodiments, or a combination thereof
may be utilized while the aircraft 70 is in service, for example
and without limitation, to maintenance and service 184.
[0042] Although the embodiments of this disclosure have been
described with respect to certain exemplary embodiments, it is to
be understood that the specific embodiments are for purposes of
illustration and not limitation, as other variations will occur to
those of skill in the art.
* * * * *