U.S. patent application number 16/533619 was filed with the patent office on 2019-11-28 for method of making core-stiffened structure.
This patent application is currently assigned to TEXTRON INNOVATIONS INC.. The applicant listed for this patent is TEXTRON INNOVATIONS INC.. Invention is credited to James D. Hethcock, JR., CARL A. MAY, KENNETH E. NUNN, JR..
Application Number | 20190358946 16/533619 |
Document ID | / |
Family ID | 56110301 |
Filed Date | 2019-11-28 |
United States Patent
Application |
20190358946 |
Kind Code |
A1 |
Hethcock, JR.; James D. ; et
al. |
November 28, 2019 |
Method of Making Core-Stiffened Structure
Abstract
A method of making a core-stiffened structure includes the steps
of providing a honeycomb core having an adhesive disposed on first
and second surfaces thereof, providing a first skin and a second
skin, and assembling the first skin, the second skin, and the
honeycomb core to form the core-stiffened structure. The method
further includes the steps of curing the core-stiffened structure
and inhibiting at least one of the first skin and the second skin
from protruding into at least one cell of the honeycomb core during
the step of curing the core-stiffened structure.
Inventors: |
Hethcock, JR.; James D.;
(Colleyville, TX) ; NUNN, JR.; KENNETH E.;
(Colleyville, TX) ; MAY; CARL A.; (I Mansfield,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXTRON INNOVATIONS INC. |
Providence |
RI |
US |
|
|
Assignee: |
TEXTRON INNOVATIONS INC.
Providence
RI
|
Family ID: |
56110301 |
Appl. No.: |
16/533619 |
Filed: |
August 6, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15050564 |
Feb 23, 2016 |
10369772 |
|
|
16533619 |
|
|
|
|
13521367 |
Jul 10, 2012 |
9266313 |
|
|
PCT/US2010/023357 |
Feb 5, 2010 |
|
|
|
15050564 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2250/40 20130101;
B32B 7/12 20130101; B32B 37/12 20130101; B32B 37/146 20130101; B32B
3/12 20130101; B32B 2605/18 20130101; B32B 37/1284 20130101 |
International
Class: |
B32B 37/14 20060101
B32B037/14; B32B 7/12 20060101 B32B007/12; B32B 3/12 20060101
B32B003/12 |
Claims
1. A method of making a core-stiffened structure, comprising:
providing a honeycomb core having an adhesive disposed on first and
second surfaces thereof; providing a first skin and a second skin;
assembling the first skin, the second skin, and the honeycomb core
to form the core-stiffened structure; curing the core-stiffened
structure; and inhibiting the first skin and the second skin from
protruding into at least one cell of the honeycomb core during the
step of curing the core-stiffened structure, comprising: providing
a first stabilization skin in a perforated or porous configuration;
placing the first stabilization skin between the first skin and the
first surface of the honeycomb core prior to performing the step of
curing the core-stiffened structure; providing a second
stabilization skin in a perforated or porous configuration; and
placing the second stabilization skin between the second skin and
the second surface of the honeycomb core prior to performing the
step of curing the core-stiffened structure; wherein the second
stabilization skin inhibits the second skin from protruding into
the at least one cell of the honeycomb core; and wherein the first
stabilization skin inhibits the first skin from protruding into the
at least one cell of the honeycomb core; wherein the first
stabilization skin is substantially fully cured as the
core-stiffened structure is assembled; and wherein the adhesive is
reticulated and configured to allow migration of fluid through the
first skin, the second skin, and the honeycomb core.
2. The method according to claim 1, wherein the inhibiting at least
one of the first skin and the second skin from protruding into the
cells of the honeycomb core comprises: providing a first
stabilization skin; and placing the first stabilization skin
between the first skin and the first surface of the honeycomb core
prior to performing the step of curing the core-stiffened
structure; wherein the first stabilization skin inhibits the first
skin from protruding into the at least one cell of the honeycomb
core.
3. The method according to claim 2, wherein the inhibiting at least
one of the first skin and the second skin from protruding into the
cells of the honeycomb core further comprises: providing a second
stabilization skin; and placing the second stabilization skin
between the second skin and the second surface of the honeycomb
core prior to performing the step of curing the core-stiffened
structure; wherein the second stabilization skin inhibits the
second skin from protruding into the at least one cell of the
honeycomb core.
4. The method according to claim 2, wherein the providing the first
stabilization skin comprises: providing the first stabilization
skin in a perforated or porous configuration.
5. The method according to claim 2, wherein the providing the first
stabilization skin comprises: providing the first stabilization
skin in a substantially solid form.
6. The method according to claim 2, wherein the providing the first
stabilization skin comprises: providing the first stabilization
skin in a partially cured state.
7. The method according to claim 1, wherein the inhibiting at least
one of the first skin and the second skin from protruding into the
at least one cell of the honeycomb core comprises: at least
partially curing the at least one of the first skin and the second
skin prior to performing the step of assembling the first skin, the
second skin, and the honeycomb core to form the core-stiffened
structure.
8. The method according to claim 7, wherein the at least partially
curing the at least one of the first skin and the second skin
comprises: providing an insert having a geometry corresponding to
the honeycomb core; providing a first release film; disposing the
first release film between the first skin and the insert;
processing the first skin and the second skin; and removing the
insert and the first release film.
9. A method of making a core-stiffened structure, comprising:
applying a first skin to a caul and sealing thereto with a first
bagging material; applying a second skin to a tool and sealing
thereto with a second bagging material; providing a honeycomb core
between the first bagging material and the second bagging material;
providing compressive force to the honeycomb core between the caul
and the tool while at least partially curing the first and second
skin so that physical characteristics in the core are transposed
into the first and second skins; and applying adhesive to the
honeycomb core and performing a second curing cycle to directly
bond the first skin, second skin, and the honeycomb core together,
as well is complete curing of the first and second skins.
10. The method, according to claim 9, wherein the providing
compressive force to the honeycomb core comprises: providing a
vacuum enabled by a third bagging material encompassing the first
skin, the caul, the honeycomb core, and the second skin.
Specification
11. A core-stiffened assembly, comprising: a honeycomb core having
a first surface and a second surface and defining a plurality of
cells; a first skin disposed on the first surface of the honeycomb
core, the first skin terminating at a peripheral edge of the
honeycomb core; and a second skin disposed on the second surface of
the honeycomb core and extending outside of the peripheral edge of
the honeycomb core; wherein the first skin and the second are
separated so that the honeycomb core is exposed.
12. The core-stiffened assembly, according to claim 11, wherein:
the first skin includes at least one step so that a thickness of
the first skin decreases in the at least one step before
terminating at the peripheral edge of the honeycomb core.
13. The core-stiffened assembly according to claim 11, further
comprising: a thermoplastic plug disposed in at least one of the
plurality of cells for inhibiting the first skin and the second
skin from protruding into the at least one of the plurality of
cells during curing of the core-stiffened assembly.
14. The core-stiffened assembly according to claim 11, further
comprising: one of a magnetorheological fluid and a ferrofluid
disposed in at least one of the plurality of cells for inhibiting
the first skin and the second skin from protruding into the at
least one of the plurality of cells during curing of the
core-stiffened assembly.
15. The core-stiffened assembly according to claim 11, further
comprising: a first release film disposed between the first skin
and the honeycomb core; and a second release film disposed between
the second skin and the honeycomb core and between the second skin
and the first skin.
16. The core-stiffened assembly according to claim 11, further
comprising: the first skin terminating at a peripheral edge of the
honeycomb core; and the second skin extending outside of the
peripheral edge of the honeycomb core; wherein the first skin and
the second skin are separated so that the honeycomb core is
exposed.
17. The core-stiffened assembly according to claim 11, further
comprising: the first skin includes at least one step so that a
thickness of the first skin decreases in the at least one step
before terminating at the peripheral edge of the honeycomb core.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/050,564, filed 23 Feb. 2016, titled "Method of Making
Core-Stiffened Structure," which is a divisional of U.S. patent
application Ser. No. 13/521,367, filed 10 Jul. 2012, titled "Method
of Making Core-Stiffened Structure," both of which are incorporated
herein for all purposes.
1. FIELD OF THE INVENTION
[0002] The present application relates in general to the field of
core-stiffened structures.
2. DESCRIPTION OF RELATED ART
[0003] Composite structures often comprise honeycomb core disposed
between and adhesively bonded to an inner skin and an outer skin.
One example of such honeycomb core is a honeycomb core 101, shown
in FIG. 1. Generally, honeycomb core 101 includes a plurality of
cells 103 (only one labeled for clarity) defined by cell walls 105
(only one labeled for clarity). Each of the plurality of cells 103
exhibits a width W. Typically, the plurality of cells 103 have
substantially the same width W but, in some implementations, some
cells 103 of the plurality of cells 103 may have different widths W
than other cells 103 of the plurality of cells 103.
[0004] Traditionally, core-stiffened structures have been limited
to the use of honeycomb core 101 having cell widths W of less than
about 6 mm. At larger widths W, as shown in FIG. 2, cell walls 105
fail to provide sufficient support for inner skin 201 and outer
skin 203 during "curing" of the core-stiffened part, which entails
heating the assembled core-stiffened part under pressure. As a
result, portions of inner skin 201 and portions of outer skin 203
undesirably extend into cells 103 of honeycomb core 101. Thus,
while core-stiffened structures made from larger-celled honeycomb
core 101 weigh less than similar structures made from small-celled
honeycomb core 101, the manufacture of large-celled composite
structures has been limited.
[0005] Traditionally, core-stiffened composite structure has been
sealed from intrusion of moisture. Some typical core materials are
subject to moisture absorption or corrosion resulting from trapped
moisture within the core. The sealing of the core edges is done by
ramping one skin along a bevel in the core until both skins contact
each other and complete a seal around the periphery of the core.
During the cure cycle, the pressure on the ramp surface of the core
may push the core in a direction lateral to the tool. In order to
prevent such a distortion of the core, typically material is added
to the skin in the proximity of the ramp in order to stabilize the
skins from lateral distortion of the core during the cure cycle. As
such, the skin is thicker than the structural application requires
so as to prevent lateral distortion of the core during the cure
cycle.
[0006] A similar situation exists for core stiffened composite
structure where one skin is not parallel to the other skin. Such a
scenario includes the risk of the core material being pushed
laterally along the tool surface. In order to prevent such a
distortion of the core material, additional material is added to
the core material and/or to the skins in order to resist the
lateral force, and therefore resist core distortion.
[0007] There are many methods for processing honeycomb core
composite structures well known in the art; however, considerable
room for improvement remains.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The novel features believed characteristic of the
application are set forth in the appended claims. However, the
application itself, as well as a preferred mode of use, and further
objectives and advantages thereof, will best be understood by
reference to the following detailed description when read in
conjunction with the accompanying drawings, in which the leftmost
significant digit(s) in the reference numerals denote(s) the first
figure in which the respective reference numerals appear,
wherein:
[0009] FIG. 1 is a stylized, plan view of a portion of a
conventional honeycomb core;
[0010] FIG. 2 is a stylized, cross-sectional view of a portion of a
conventional, core-stiffened structure utilizing large-celled
honeycomb core;
[0011] FIG. 3 is a stylized, side, elevational view of a
core-stiffened structure according to the present application;
[0012] FIG. 4 is a stylized, cross-sectional view of a portion of
honeycomb core used in the core-stiffened structure of FIG. 3,
taken along the line 4-4 in FIG. 3;
[0013] FIG. 5, is a stylized, exploded, cross-sectional view of a
first embodiment of the core-stiffened structure of FIG. 3;
[0014] FIG. 6 is a stylized, plan view of a portion of the
honeycomb core of FIG. 4 with adhesive applied to a surface
thereof;
[0015] FIG. 7 is a stylized, cross-sectional view of the
core-stiffened structure of FIG. 5 in a configuration ready for
curing or processing;
[0016] FIGS. 8-10 are stylized, cross-sectional views of the
core-stiffened structure of FIG. 3 depicting a second illustrative
embodiment of a method for making a core-stiffened structure
according to the present application;
[0017] FIGS. 11-14 are stylized, cross-sectional views of the
core-stiffened structure of FIG. 3 depicting a third illustrative
embodiment of a method for making a core-stiffened structure
according to the present application;
[0018] FIG. 15 is a stylized, side, elevational view of a
core-stiffened structure according to and alternative embodiment of
the present application;
[0019] FIGS. 16 and 17 are stylized, cross-sectional views of the
core-stiffened structure of FIG. 3 depicting a fourth illustrative
embodiment of a method for making a core-stiffened structure
according to the present application; and
[0020] FIG. 18 is a stylized, cross-sectional view of the
core-stiffened structure of FIG. 3 depicting another illustrative
embodiment of a method for making a core-stiffened structure
according to the present application.
[0021] While the application is susceptible to various
modifications and alternative forms, specific embodiments thereof
have been shown by way of example in the drawings and are herein
described in detail. It should be understood, however, that the
description herein of specific embodiments is not intended to limit
the application to the particular forms disclosed, but on the
contrary, the application is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope
of the application as defined by the appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Illustrative embodiments of the present application are
described below. In the interest of clarity, not all features of an
actual implementation are described in this specification. It will
of course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developer's specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0023] In the specification, reference may be made to the spatial
relationships between various components and to the spatial
orientation of various aspects of components as the devices are
depicted in the attached drawings. However, as will be recognized
by those skilled in the art after a complete reading of the present
application, the devices, members, apparatuses, etc. described
herein may be positioned in any desired orientation. Thus, the use
of terms such as "above," "below," "upper," "lower," or other like
terms to describe a spatial relationship between various components
or to describe the spatial orientation of aspects of such
components should be understood to describe a relative relationship
between the components or a spatial orientation of aspects of such
components, respectively, as the device described herein may be
oriented in any desired direction.
[0024] There is a need for an improved method for processing a
honeycomb core-stiffened structure and the core-stiffened structure
thereof. Therefore, it is an object of the present application to
provide an improved method for processing a honeycomb
core-stiffened structure and a core-stiffened structure
thereof.
[0025] This and other objects are achieved by providing a method of
making a core-stiffened structure. The method includes the steps of
providing a honeycomb core having an adhesive disposed on first and
second surfaces thereof, providing a first skin and a second skin,
and assembling the first skin, the second skin, and the honeycomb
core to form the core-stiffened structure. The method further
includes the steps of curing the core-stiffened structure and
inhibiting at least one of the first skin and the second skin from
protruding into at least one cell of the honeycomb core during the
step of curing the composite structure.
[0026] In another aspect, the present application provides a
core-stiffened structure, including a honeycomb core having first
and second surfaces, a first stabilization skin adhesively bonded
to the first surface of the core, and in some embodiments, a second
stabilization skin adhesively bonded to the second surface of the
core. The core-stiffened structure further includes a first skin
adhesively bonded to the first stabilization skin a second skin
adhesively bonded to the first skin and the second stabilization
skin, when the second stabilization skin is used.
[0027] In yet another aspect of the present application, a
core-stiffened structure assembly is provided. The structure
assembly includes a honeycomb core having a first surface and a
second surface and defining a plurality of cells and passages
extending between the plurality of cells and a first skin disposed
on the first surface of the honeycomb core. The core-stiffened
structure assembly further includes a second skin disposed on the
second surface of the honeycomb core and a soluble plug disposed in
at least one of the plurality of cells .for inhibiting the first
skin and the second skin from protruding into the at least one of
the plurality of cells during curing of the core-stiffened
structure assembly.
[0028] In another aspect of the present application, a
core-stiffened structure assembly is provided. The core-stiffened
structure assembly includes a honeycomb core having a first surface
and a second surface and defining a plurality of cells and passages
extending between the plurality of cells and a first skin disposed
on the first surface of the honeycomb core. The core-stiffened
structure assembly further includes a second skin disposed on the
second surface of the honeycomb core. Further, a plug that can be
dissolved by chemical reaction is disposed in at least one of the
plurality of cells for inhibiting at least one of the first skin
and the second skin from protruding into the at least one of the
plurality of cells during curing of the core-stiffened structure
assembly.
[0029] In another aspect, the present application provides a
core-stiffened structure assembly. The core-stiffened structure
assembly includes a honeycomb core having a first surface and a
second surface and defining a plurality of cells and passages
extending between the plurality of cells and a first skin disposed
on the first surface of the honeycomb core. The core-stiffened
structure assembly further includes a second skin disposed on the
second surface of the honeycomb core and a thermoplastic plug
disposed in at least one of the plurality of cells for inhibiting
the first skin and the second skin from protruding into the at
least one of the plurality of cells during curing of the
core-stiffened structure assembly.
[0030] In yet another aspect of the present application, a
core-stiffened structure assembly is provided. The core-stiffened
structure assembly includes a honeycomb core having a first surface
and a second surface and defining a plurality of cells and passages
extending between the plurality of cells and a first skin disposed
on the first surface of the honeycomb core. The core-stiffened
structure assembly further includes a second skin disposed on the
second surface of the honeycomb core and one of a
magnetorheological fluid and a ferrofluid, disposed in at least one
of the plurality of cells for inhibiting at least one of the first
skin and the second skin from protruding into the at least one of
the plurality of cells during curing of the composite assembly.
[0031] In another aspect of the present application, a
core-stiffened structure assembly is provided. The core-stiffened
structure assembly includes a core, or optionally an insert having
a geometry corresponding to a honeycomb core, a first skin, and a
first release film disposed between the first skin and the insert
or core. The core-stiffened structure assembly further includes a
second skin and a second release film disposed between the second
skin and the insert or core and between the second skin and the
first skin.
[0032] In another aspect of the present application, a
core-stiffened structure assembly is provided. The core-stiffened
structure assembly includes honeycomb core having a first surface
and a second surface and defining a plurality of cells and a first
skin disposed on the first surface of the honeycomb core and a
second skin disposed on the second surface. The first and second
skin are not sealed together, instead, either the first or second
skin terminates at the edge of the honeycomb core. Any moisture can
drain or dry out through venting of the edges or through the skin,
if the skin is breathable. The skin that terminates at the edge of
the honeycomb core is tailored to prevent overloading of the core
material near the core termination edge by progressively dropping
off plies in the skin before reaching the edge.
[0033] The present application provides significant advantages,
including: (1) providing a means for utilizing a large-celled
honeycomb core in core-stiffened sandwich structures; (2) providing
a means for inhibiting face sheets or skins from protruding into
cells of a honeycomb core during curing of a core-stiffened
sandwich structure; (3) reducing the tendency of lateral movement
of honeycomb core during manufacture; and (4) simplifying edge
details in some embodiments of the core-stiffened structures.
[0034] The present application represents a method of making
honeycomb core-stiffened composite structures comprising
large-celled hoheycomb core. For the purposes of this disclosure,
the term "honeycomb core" means a core material comprising a
plurality of interconnected cell walls that define a plurality of
cells. While many honeycomb core materials define hexagonal cells,
the scope of the present application encompasses core materials
that define cells of other shapes, such as square, rectangular, and
the like. It should be appreciated that honeycomb can be of a
variety of materials, including but not limited to, composite
materials and metals. Core can be of any shape and can attach to
adjacent skins at angles ranging from perpendicular to parallel.
Moreover, the term "large-celled honeycomb core" means, for the
purposes of this disclosure, honeycomb core defining cells having a
width dimension of more than about 6 mm.
[0035] FIG. 3 depicts an illustrative embodiment of one particular
core-stiffened structure 301 according to the present application.
Core-stiffened structure 301 comprises an inner skin 303, an outer
skin 305, and a honeycomb core 401 (shown in FIG. 4) disposed
between and adhesively bonded to inner skin 303 and outer skin 305.
It should be noted that inner skin 303 and outer skin 305
preferably comprise a plurality of reinforcing fibers disposed in a
polymeric matrix. As shown in FIG. 4, honeycomb core 401 comprises
a plurality of cells 403 (only one labeled for clarity) defined by
a plurality of interconnected cell walls 405 (only one labeled for
clarity). The present application is particularly useful when using
honeycomb core 401 having cells 403 that exhibit a width W that is
greater than about 6 mm.
[0036] FIG. 5 depicts a first illustrative embodiment of a method
for making core-stiffened structure 301 according to the present
application. In the illustrated embodiment, an inner stabilization
skin 501 is placed against an inner side 503 of honeycomb core 401
and a lower stabilization skin 505 is placed against an outer side
507 of honeycomb core 401. It should be appreciated that in some
embodiments only one stabilization skin may be required. For
example, if outer skin 305 is thick enough, then lower
stabilization skin 505 is not required to prevent outer skin 305
from deforming into cells 403 of honeycomb core 401. It should be
noted that an adhesive (not shown in FIG. 5) is applied to inner
surface 503 of honeycomb core 401 and to outer surface 507 of
honeycomb core 401. Preferably, the adhesive is applied in a
reticulating process, resulting in adhesive 601 substantially
covering cell walls 405 at inner surface 503 and outer surface 507
of honeycomb core 401, as shown in FIG. 6. The adhesive, such as
adhesive 601, bonds inner stabilization skin 501 and outer
stabilization skin 505 to honeycomb core 401.
[0037] Referring again to FIG. 5, inner stabilization skin 501 and
outer stabilization skin 503 are very thin, such as one or two
plies of fiber-reinforced composite material. Stabilization skins
501 and 503 may be perforated, porous, or substantially solid
without passages extending therethrough. It should be noted that
inner stabilization skin 501 and outer stabilization skin 505 may
be substantially fully "cured," i.e., the polymeric matrix is
substantially fully cross-linked, if the polymeric matrix comprises
a thermosetting polymer, or the polymeric matrix is in a hardened
state, if the polymeric matrix comprises a thermoplastic polymer.
Alternatively, if the polymeric matrix of inner stabilization skin
501 and outer stabilization skin 505 is a thermosetting polymer,
inner stabilization skin 501 and outer stabilization skin 505 may
be only cured to an extent such that inner stabilization skin 501
and outer stabilization skin 505 do not substantially deform into
cells 403 of honeycomb core 401 during processing. In such an
embodiment, adhesive may not be required between inner
stabilization skin 501 and inner skin 303, as well as between outer
stabilization skin and outer skin 305.
[0038] Still referring to FIG. 5, outer skin 305 is placed in
contact with outer stabilization skin 505 and inner skin 303 is
placed in contact with inner stabilization skin 501. In the
illustrated embodiment, inner skin 303 contacts outer skin 305 in
areas where inner skin 303 does not contact inner stabilization
skin 501 and outer skin 305 does not contact outer stabilization
skin 505. Adhesive may be used between inner stabilization skin 501
and inner skin 303, as well as between outer stabilization skin 505
and outer skin 305.
[0039] It should be noted that, in a preferred embodiment, outer
skin 305 is first placed onto a mold or tool 701 (shown in FIG. 7).
It should be noted, however, that one or more other plies or
layers, such as a breather ply, may be disposed between outer skin
305 and tool 701. Outer stabilization skin 505 is then located on
and placed onto outer skin 305. Honeycomb core 401, with adhesive
applied to inner surface 503 and outer surface 507 of honeycomb
core 401, is then placed onto outer stabilization skin 505, such
that outer surface 507 is adjacent outer stabilization skin 505.
Inner stabilization skin 501 is then placed onto honeycomb core
401, such that inner surface 501 of honeycomb core 401 is adjacent
inner stabilization skin 501. Inner skin 303 is then placed on
inner stabilization skin 501, extending onto outer skin 305.
[0040] FIG. 7 depicts assembled core-stiffened structure 301 on
tool 701. Bagging material 703 extends over core-stiffened
structure 301 and onto tool 701. A vacuum is generated between
bagging material 703 and tool 701 during processing or curing to
consolidate components of core-stiffened structure 301 and to
extract gases from core-stiffened structure 301 during processing.
Core-stiffened structure 301 is then processed or cured using heat
and, preferably, pressure, to form a consolidated core-stiffened
structure 301.
[0041] While stabilization skins 501 and 505 are depicted as
extending only to the edges of honeycomb core 401, the scope of the
present application is not so limited. Rather, as inner
stabilization skin 501 and/or outer stabilization skin 505 may, in
certain embodiments, extend beyond the edges of honeycomb core
401.
[0042] FIGS. 8-10 depict a second illustrative embodiment of a
method for making core-stiffened structure 301 according to the
present application. In the illustrated embodiment, cell walls 405
of honeycomb core 401 define openings 801 extending between cells
403. Rather than using stabilization skins 501 and 505, a support
plug 803 is placed in each of the plurality of cells 403. Adhesive
601 is depicted in reticulated form so as to provide a fillet of
adhesive between inner surface 503 and inner skin 303, and between
outer surface 507 and outer skin 305. Plugs 803 extend from inner
surface 503 to outer surface 507 of honeycomb core 401. Plugs 803
support inner skin 303 and outer skin 305 in areas between cell
walls 405, thus inhibiting inner skin 303 and outer skin 305 from
protruding into cells 403 during processing or curing. It is
preferred that plugs 803 are configured so as to be removable after
processing or curing; however, plugs 803 may also be permanent and
reside within core 401 during the life of core-stiffened structure
301.
[0043] Openings 801 are to introduce fluid flow within core 401.
The fluid flow could be gas or liquid. Flow through core 401 can be
utilized to introduce heat for manufacturing purposes, to utilize
the volume contained in the core to store a liquid such as fuel, or
to introduce a washout fluid to dissolve or chemically react to the
solid material of plugs 803. Furthermore, flow through core may be
used to transfer heat in order to provide ice prevention. In
addition, flow through core may be used to transfer heat in order
to change heat signature during service of structure 301. Flow
through the core may also be used for pressure relief for a
gradient, or to build up pressure in the volume within core 401. In
an alternative embodiment, openings through at least one of the
inner skin 303 or outer skin 305 provide fluid flow, in lieu of or
in addition to, openings 801 through core 401.
[0044] In one embodiment, plugs 803 comprise a soluble material. In
a preferred embodiment, a solvent, such as water, is flushed
through honeycomb core 401, as indicated by arrows 901, via
openings 801 to erode and remove plugs 803 after core-stiffened
structure 301 has been processed or cured, as shown in FIGS. 9 and
10. In such an embodiment, plugs 803 may comprise, for example, a
eutectic salt, sodium silicate-bonded sand, polyvinyl
alcohol-bonded ceramic microspheres, or the like. Alternatively,
plugs 803 may comprise a thermoplastic material that is melted and
evacuated from honeycomb core 401 via openings 801. In other
embodiments, plugs 803 may comprise a magnetorheological fluid, a
ferrofluid, Or the like, which become solid or semi-solid in the
presence of a magnetic field and which become liquid when the
magnetic field is removed. Alternatively, plugs 803 may comprise a
clay, such as bentonite, which is removed from honeycomb core 401
via openings 801 by vibrating core-stiffened structure 301.
Moreover, plugs 803 may take on the form of a plurality of beads
disposed in each of the plurality of cells 403, such that the beads
are small enough to pass through openings 801 after core-stiffened
structure 301 is processed or cured. Moreover, plugs 803 may be
configured to be physically compromised through a chemical
reaction, and thus evacuated from core 401 in a solid, liquid, or
gaseous state. It is preferred that plugs 803 are configured so as
to be removable after processing or curing; however, plugs 803 may
also be permanent and reside within core 401 during the life of
core-stiffened structure 301.
[0045] While plugs 803 are illustrated in FIGS. 8 and 9 as
substantially filling cells 403 of honeycomb core 401, the scope of
the present application is not so limited. Rather, plugs 803 may
not fully extend between cell walls 405, as long as sufficient
support is provided to inner skin 303 and outer skin 305 to inhibit
inner skin 303 and outer skin 305 from protruding into cells 403 of
honeycomb core 401 during processing or curing. For example, plugs
803 may exhibit a plurality of legs extending from a central focal
point or line. Preferably, plugs 803 not only exhibit strength to
prevent skins from compressing, but also exhibit strength in the
lateral direction to prevent lateral deformation of core 401 during
processing. Plugs 803 may also exhibit opposing caps supported by
an thin axial member such that the caps provide maximum support of
inner skin 303 and outer skin 305 while the thin axial member.
Preferably, a gap between the caps and the cell walls of core 401
allow space for fillets of adhesive between skins 303 and 305 and
core 401.
[0046] FIGS. 11-14 depict a third illustrative embodiment of a
method for making core-stiffened structure 301. In the illustrated
embodiment, processing or curing of core-stiffened structure 301 is
accomplished in two steps. In the first step, an insert 1101
corresponding to the geometry of honeycomb core 401 (best shown in
FIG. 13) is placed between inner skin 303 and outer skin 305. An
inner release film 1103 is disposed between insert 1101 and inner
skin 303 and an outer release film 1105 is disposed between insert
1101 and outer skin 305. Release film 1103 and 1105 comprise, in
one embodiment, "peel-ply" material. As shown in FIG. 12, bagging
material 1201 is placed over inner skin 303, extending onto tool
701. Inner skin 303 and outer skin 305 are then at least partially
cured or processed to achieve at least a semi-rigid state.
[0047] Referring now to FIG. 13, inner skin 303 is separated from
outer skin 305 and insert 1101 is replaced with honeycomb core 401,
having adhesive on inner surface 503 and outer surface 505, as
discussed herein. An adhesive layer 1301 is disposed between inner
skin 303 and outer skin 305 in areas where inner skin 303 and outer
skin 305 abut. FIG. 14 depicts core-stiffened structure 301
assembled and ready for curing or processing, with a bagging
material 1401 extending over inner skin 303 and onto tool 701.
Core-stiffened structure 301 is then processed, preferably with
heat and, in some situations pressure, to adhesively bond inner
skin 303 to outer skin 305 and honeycomb core 401 and to adhesively
bond outer skin 305 to honeycomb core 401.
[0048] FIG. 15 depicts another illustrative embodiment of one
particular core-stiffened structure 301 according to the present
application. Core-stiffened structure 301 comprises an inner skin
303, an outer skin 305, and a honeycomb core 401 (shown in FIG. 4)
disposed between and adhesively bonded to inner skin 303 and outer
skin 305. It should be noted that inner skin 303 and outer skin 305
preferably comprise a plurality of reinforcing fibers disposed in a
polymeric matrix. As shown in FIG. 4, honeycomb core 401 comprises
a plurality of cells 403 (only one labeled for clarity) defined by
a plurality of interconnected cell walls 405 (only one labeled for
clarity). Inner skin 303 and outer skin 305 are not sealed
together; instead, inner skin 303 terminates at a peripheral edge
1503 of the honeycomb core 401. Any moisture can drain or dry out
through peripheral edge 1503 of the honeycomb core 401. If either
inner skin 303 or outer skin 305 is breathable, then moisture
within honeycomb core 401 can also drain or dry out through
breathable skin 303 or 305. Preferably, inner skin 303 does not
abruptly terminate at peripheral edge 1503 of the honeycomb core
401; instead inner skin 303 steps down via steps 1501 by
progressively dropping off at least one ply in inner skin 303
before reaching peripheral edge 1503. The progressive dropping off
in plies of inner skin 303 is tailored to prevent overloading of
the honeycomb core 401 near the core peripheral edge 1503. It
should be appreciated that the dropping of plies is exemplified in
steps 1501 shown in FIG. 15; however, steps 1501 may take on a wide
variety of configurations depending upon the thickness of inner
skin 1501 as well as the predicted loading of core-stiffened
structure 301.
[0049] Core-stiffened structure 301 illustrated in FIG. 15 can be
manufactured by the methods of manufacture disclosed herein.
However, because core 401 is left exposed about peripheral edge
1503, the method of manufacture illustrated in FIGS. 8-10 is
particularly well suited for manufacturing the embodiment of
core-stiffened structure 301 shown in FIG. 15. The embodiment shown
in FIG. 15 is configured to survive in high strain environment
while being extremely light due to the lack of ramps between inner
skin 303 and outer skin 305.
[0050] FIGS. 16 and 17 depict another illustrative embodiment
method for making core-stiffened structure 301 according to the
present application. In the illustrated embodiment, processing or
curing of core-stiffened structure 301 is preferably accomplished
using out-of-autoclave materials that do not require an autoclave
to provide high temperature and pressure. The illustrated
embodiment involves two primary steps. In the first step, inner
skin 303 is laid against a caul 1601 and sealed thereto with
bagging material 1201A. Similarly, outer skin 305 is laid against
tool 701 and sealed thereto with bagging material 1201B. Honeycomb
core 401 which is to be used in core-stiffened structure 301 is
sandwiched between bagging materials 1201A and 1201B. Next, a
subsequent bagging material 1201C is placed in sealing contact with
tool 701 so as to enclose caul 1601, inner skin 303, core 401, and
outer skin 305. In an alternative embodiment, tool 701 is
completely enclosed by bagging material 1201. In another
alternative embodiment, bagging material 1201C is omitted while
pressure from caul 1601 is used to provide pressure between inner
skin 303, core 401, and outer skin 305. Inner skin 303 and outer
skin 305 are allowed to cure while a separate vacuum is pulled on
inner skin 303, outer skin 305, and on the assembly via bagging
materials 1201A, 1201B, and 1201C. The vacuum on inner skin 303 and
outer skin 305 prevents inner skin 303 and outer skin 305 from
sagging and deforming into the cells of core 401. During the curing
process, any physical deformations in core 401 are transposed into
inner skin 303 and outer skin 305 which provides for improved
structural characteristics within core-stiffened structure 301. At
this point in the process, core is not bonded to inner skin 301 and
outer skin 305 due to lack of adhesive and the barrier provided by
bagging material 1201A and 1201B.
[0051] The second step involves bonding core 401 to inner skin 303
and outer skin 305. Bagging materials 1201A and 1201B are removed.
In addition, adhesive 601 is applied to core 401, preferably
through a reticulating process. Adhesive may also be applied
directly between inner skin 303 and outer skin 305. During this
second step of the process, bagging material 1201 is preferably
used to apply pressure to the final curing step for core-stiffened
structure 301. However, caul 1601 may be used in lieu of, or in
addition to, bagging material 1201. It should be appreciated that
the embodiment of core-stiffened structure 301 shown in FIG. 15 may
also be manufactured using the method disclosed herein regarding
FIGS. 16 and 17.
[0052] FIG. 18 depicts another illustrative embodiment method for
making core-stiffened structure 301 according to the present
application. In the illustrated embodiment, processing or curing of
core-stiffened structure 301 is preferably accomplished using
out-of-autoclave materials that do not require an autoclave to
provide high temperature and pressure. Outer skin 305 is placed
against tool 701. Core 401 is placed against outer skin. Adhesive
is used to bond inner skin 303 and outer skin 305 to core 401.
Cells 403 within core 401 are substantially filled with a plurality
of flexible spherical balls, the spherical balls being filled with
a gas. Inner skin 303 is placed against core 401. Bagging material
1201 is used to create a vacuum seal between the assembly and tool
701. Core 401, spherical balls, inner skin 303 and outer skin 305
are subjected to vacuum and heat, thereby causing the spherical
balls to expand, thereby preventing inner skin 303 and outer skin
305 from sagging into cells 403 of core 401. After curing,
temperature and pressure are decreased, thereby causing the volume
of the spherical balls to decrease. It is then preferred that the
spherical balls are shaken out of core 401 through openings in cell
walls of core 401. Spherical balls may also be removed by other
means, such as being dissolved by water. In an alternative
embodiment, a foam is applied into cells 403 in lieu of the
spherical balls. The foam expands, similar to the spherical balls,
when exposed to at least one of vacuum and heat in order to prevent
inner skin 303 and outer skin 305 from sagging or deforming in core
401 during curing.
[0053] While the methods disclosed herein are useful in making
composite structures comprising conventional honeycomb core
materials, they are particularly useful in making composite
structures that include honeycomb core comprising reinforcing
fibers disposed in a polymeric matrix.
[0054] The particular embodiments disclosed above are illustrative
only, as the application may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope and spirit of the application. Accordingly, the
protection sought herein is as set forth in the claims below. It is
apparent that an application with significant advantages has been
described and illustrated. Although the present application is
shown in a limited number of forms, it is not limited to just these
forms, but is amenable to various changes and modifications without
departing from the spirit thereof.
* * * * *