U.S. patent application number 13/715325 was filed with the patent office on 2014-06-19 for methods for combining components of varying stages of cure.
This patent application is currently assigned to Aurora Flight Sciences Corporation. The applicant listed for this patent is AURORA FLIGHT SCIENCES CORPORATION. Invention is credited to Daniel Benjamin Cottrell.
Application Number | 20140166191 13/715325 |
Document ID | / |
Family ID | 50929566 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140166191 |
Kind Code |
A1 |
Cottrell; Daniel Benjamin |
June 19, 2014 |
METHODS FOR COMBINING COMPONENTS OF VARYING STAGES OF CURE
Abstract
The present invention provides a method of fabricating a
composite structure from components of varying stages of cure while
reducing the steps associated with the fabrication process of
infusing, curing, and bonding composite materials to form a hybrid
unitized structure. The method provides a pre-cured stiffener and a
pi-preform having a clevis and a base portion. The pre-cured
stiffener may be inserted into the clevis of the pi-preform to form
a composite structure assembly. The composite structure assembly
may be infused with a resin system at the time of cure and bonded
to a second composite structure to form a hybrid unitized
structure.
Inventors: |
Cottrell; Daniel Benjamin;
(Manassas, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AURORA FLIGHT SCIENCES CORPORATION |
Manassas |
VA |
US |
|
|
Assignee: |
Aurora Flight Sciences
Corporation
Manassas
VA
|
Family ID: |
50929566 |
Appl. No.: |
13/715325 |
Filed: |
December 14, 2012 |
Current U.S.
Class: |
156/182 |
Current CPC
Class: |
B32B 2309/02 20130101;
B32B 2315/085 20130101; B32B 37/06 20130101; B29L 2031/772
20130101; B29C 70/443 20130101; B32B 37/142 20130101; B32B 2305/28
20130101; B32B 37/24 20130101; B32B 2313/04 20130101; B29C 70/84
20130101 |
Class at
Publication: |
156/182 |
International
Class: |
B29C 70/84 20060101
B29C070/84 |
Claims
1. A method of fabricating a composite structure from components of
varying stages of cure, comprising the steps of: providing a
stiffener component; providing a dry fabric component; combining
the stiffener component and the dry fabric component to form an
assembly, wherein the stiffener component provides structural
support to the assembly; infusing the assembly with resin to yield
an infused assembly; and curing the infused assembly to yield a
cured assembly.
2. The method of claim 1, further comprising the step of bonding
the cured assembly with a component to form a hybrid unitized
structure.
3. The method of claim 1, wherein the stiffener component is
fabricated from a composite material.
4. The method of claim 1, wherein the stiffener component is (i)
L-shaped or (ii) J-shaped
5. The method of claim 1, wherein the dry fabric component is a
three-dimensional woven pi-preform, wherein said pi-preform
contains a clevis configured to receive an edge of the stiffener
component.
6. The method of claim 3, wherein the stiffener component is
fabricated from a carbon-fiber composite material.
7. The method of claim 3, wherein the stiffener component is
fabricated from a glass-fiber composite material.
8. The method of claim 1, wherein the stiffener component is
fabricated from a metal.
9. The method of claim 5, further comprising the steps of: (i)
wrapping a resin film around a first edge of said stiffener
component; and (ii) inserting the first edge of said stiffener
component into the clevis of said pi-preform.
10. The method of claim 9, further comprising the steps of: (i)
wrapping a resin film around a second edge of said stiffener
component; and (ii) inserting the second edge of said stiffener
component into the clevis of the second pi-preform.
11. The method of claim 2, wherein the component comprises Glass
Laminate Aluminum Reinforced Epoxy.
12. The method of claim 1, wherein the dry fabric component
comprises at least one of: (1) glass-fiber; (2) carbon-fiber; or
(3) para-aramid synthetic fiber.
13. A method of fabricating a composite structure from components
of varying stages of cure, comprising the steps of: providing a
pre-cured composite stiffener; providing a dry fabric component
having a base portion and a clevis configured to receive the
pre-cured composite stiffener, wherein the clevis is substantially
perpendicular to the base portion; wrapping a first film adhesive
around a first edge of said pre-cured stiffener; wrapping a first
resin film around the first edge of said pre-cured stiffener;
inserting the first edge of said pre-cured composite stiffener into
the clevis of the dry fabric component to form a composite
structure assembly; applying a second film adhesive to a surface of
the dry fabric component; applying a second resin film to the base
portion of the dry fabric component; securing the pre-cured
stiffener substantially perpendicular to the base portion of the
dry fabric component, wherein the pre-cured stiffener provides
structural support to the composite structure assembly; applying a
film adhesive to the exterior base portion of the dry fabric
component securing the pre-cured stiffener with dry fabric
component to another substrate to which it will bond; infusing the
composite structure assembly by heating the assembly to a first
temperature for a first period of time; and curing the composite
structure assembly by increasing the heat to a second temperature,
wherein the second temperature is greater than the first
temperature.
14. A method of fabricating a composite structure from components
of varying stages of cure, comprising the steps of: providing a
pre-cured composite stiffener; providing a dry fabric component
having a base portion and a clevis configured to receive the
pre-cured composite stiffener, wherein the clevis is substantially
perpendicular to the base portion; wrapping a first resin film
around a first edge of said pre-cured stiffener; inserting the
first edge of said pre-cured composite stiffener into the clevis of
the dry fabric component to form a composite structure assembly;
applying a second resin film to a surface of the dry fabric
component; securing the pre-cured stiffener substantially
perpendicular to the base portion of the dry fabric component,
wherein the pre-cured stiffener provides structural support to the
composite structure assembly; infusing the composite structure
assembly; and curing the composite structure assembly.
15. The method of claim 14, further comprising the steps of bonding
composite structure assembly with a component to form a hybrid
unitized structure.
16. The method of claim 14, wherein the dry fabric component
comprises at least one of: (1) glass-fiber; (2) carbon-fiber; or
(3) para-aramid synthetic fiber.
17. The method of claim 14, further comprising the steps of: (i)
wrapping a resin film around a second edge of said stiffener
component; and (ii) inserting the second edge of said stiffener
component into the clevis of the second pi-preform.
18. The method of claim 15, wherein the component comprises Glass
Laminate
19. The method of claim 14, wherein the second resin film has a
weight that is different than the third resin film.
20. A method of fabricating a composite structure from components
of varying stages of cure, comprising the steps of: providing a
pre-cured composite stiffener; providing a dry fabric component
having a base portion and a clevis configured to receive the
pre-cured composite stiffener, wherein the clevis is substantially
perpendicular to the base portion; wrapping a first resin film
around a first edge of said pre-cured stiffener; inserting the
first edge of said pre-cured composite stiffener into the clevis of
the dry fabric component to form a composite structure assembly;
applying a second resin film to a surface of the dry fabric
component; securing the pre-cured stiffener substantially
perpendicular to the base portion of the dry fabric component,
wherein the pre-cured stiffener provides structural support to the
composite structure assembly; infusing the composite structure
assembly by heating the assembly to a first temperature for a first
period of time; and curing the composite structure assembly by
increasing the heat to a second temperature, wherein the second
temperature is greater than the first temperature.
21. The method of claim 20, wherein (i) the first temperature is
between 150 and 200 degrees Fahrenheit, (ii) the second temperature
is between 200 and 300 degrees Fahrenheit, (iii) the first period
of time is between 10 and 25 minutes, and (iv) the second period of
time is between 250 and 350 minutes.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to composite
materials. More particularly, the invention relates to methods for
combining components of varying stages of cure and for creating
unitized hybrid composite structures.
BACKGROUND INFORMATION
[0002] Over recent years, composite materials have become an
increasingly desirable material for aircraft structures. Composite
materials typically comprise strands of fibers (e.g., glass- and/or
carbon-fiber) mixed with a resin. For example, many commercially
produced composites use a polymer matrix material as the resin. In
fact, there are many different polymers available, depending upon
the starting raw ingredients. The more common polymer may include,
for example, polyester, vinyl ester, epoxy, phenolic, polyimide,
polyamide, polypropylene, and PEEK. During fabrication, fibers may
be often wound, or woven, into a sheet of material and then
impregnated (e.g., infused) with a resin. Once the fibers have been
impregnated with a resin, the composite material may then be formed
into the desired shape and cured until properly hardened.
[0003] Composite materials have an advantage of being extremely
lightweight and having high strength. As a result, they are useful
in, among other things, aircraft applications. Additionally,
composite structures may be molded into desired shapes and
configurations, thus eliminating the time and cost associated with
fabricating shapes using traditional methods and materials. While
many parts manufactured using composite materials could also be
made from metal, a metallic part of the same strength and stiffness
would be significantly heavier.
[0004] An example composite material is fiberglass, which consists
of a matrix of glass-fiber, impregnated with a polymer resin. The
glass-fiber provides tensile strength, but is flexible (like
cloth). To provide rigidity, resin is used to lock the glass-fibers
in place, thus resulting in a strong, relatively lightweight
material that may be cut, drilled and otherwise manipulated while
being resistant to moisture and chemicals.
[0005] An example group of composite materials includes
carbon-based composites, which are strong and light
fiber-reinforced polymers that contain carbon-fibers instead of
glass-fiber. Examples of such carbon-based composites include
carbon-fiber-reinforced polymers or carbon-fiber-reinforced
plastics (CFRP or CRP). The polymer used to lock the carbon-fiber
in place is typically an epoxy, but other polymers, such as
polyester, vinyl ester or nylon, are sometimes used. Carbon-based
composites may also contain fibers such as, for example,
para-aramid synthetic fiber-reinforced polymers (e.g.,
Kevlar.RTM.), nickel, titanium, glass-fiber, as well as
carbon-fiber and carbon nanotubes. Due to their strength and
lightweight construction, carbon composites have many applications
in both the aerospace and automotive fields.
[0006] Another example composite material is Glass Laminate
Aluminum Reinforced Epoxy (GLARE). GLARE typically comprises
several thin layers of aluminum interspersed with layers of
glass-fiber "pre-preg" (i.e., "pre-impregnated" composite fibers
where a material, such as epoxy is already present), bonded
together with a matrix such as epoxy. Initially, pre-preg is
flexible and sticky, but becomes hard and stiff once it has been
heated (i.e., during the curing process). Although GLARE utilizes
standard metallic materials such as aluminum, its manufacturing
process, inspection and repair are more representative of other
composite materials.
[0007] However, as recognized by U.S. Pat. No. 7,681,835 to Simpson
et al., a drawback to certain composite materials is the actual
assembly, or joining, of the composite materials. Unlike more
traditional materials (e.g., metals), different considerations must
be made for assembling composite materials. For example, placing
holes in composite materials for attachment of fasteners severs the
strands of fibers within the material and creates weak points
within the material. While forming holes in the composite material
by displacing the strands of the uncured fibers prevents severing
of the fibers, this process is time-consuming and often
impractical. Another alternative for assembling composite materials
is the use of high-strength epoxies. Epoxies have an advantage of
limiting the number of manufacturing steps. However, the
distribution of the epoxy and the placement of the parts together
can require expensive machines and numerous jigs (e.g., tooling).
Moreover, such structures routinely involve multiple sets of tools,
are very labor intensive, require several cure cycles and can
require B-staged material with set expiration dates.
[0008] Therefore, there is a need in the art, for an improved
method of combining, or joining, composite components of varying
stages of cure that alleviates the aforementioned drawbacks.
SUMMARY
[0009] The present disclosure endeavors to provide methods for
creating a unitized hybrid composite structure. The present
disclosure also endeavors to provide a system and method for
combining composite components of varying stages of cure and
components of either similar or dissimilar materials.
[0010] According to a first aspect, a method of fabricating a
composite structure from components of varying stages of cure
comprises the steps of: providing a stiffener component; providing
a dry fabric component; combining the stiffener component and the
dry fabric component to form an assembly, wherein the stiffener
component provides structural support to the assembly; infusing the
assembly with resin to yield an infused assembly; and curing the
infused assembly to yield a cured assembly.
[0011] According to a second aspect, a method of fabricating a
composite structure from components of varying stages of cure
comprises the steps of: providing a pre-cured composite stiffener;
providing a dry fabric component having a base portion and a clevis
configured to receive the pre-cured composite stiffener, wherein
the clevis is substantially perpendicular to the base portion;
wrapping a first resin film around a first edge of said pre-cured
stiffener; inserting the first edge of said pre-cured composite
stiffener into the clevis of the dry fabric component to form a
composite structure assembly; applying a second resin film to a
surface of the dry fabric component; securing the pre-cured
stiffener substantially perpendicular to the base portion of the
dry fabric component, wherein the pre-cured stiffener provides
structural support to the composite structure assembly; infusing
the composite structure assembly; and curing the composite
structure assembly.
[0012] According to a third aspect, a method of fabricating a
composite structure from components of varying stages of cure
comprises the steps of: providing a pre-cured composite stiffener;
providing a dry fabric component having a base portion and a clevis
configured to receive the pre-cured composite stiffener, wherein
the clevis is substantially perpendicular to the base portion;
wrapping a first resin film around a first edge of said pre-cured
stiffener; inserting the first edge of said pre-cured composite
stiffener into the clevis of the dry fabric component to form a
composite structure assembly; applying a second resin film to a
surface of the dry fabric component; securing the pre-cured
stiffener substantially perpendicular to the base portion of the
dry fabric component, wherein the pre-cured stiffener provides
structural support to the composite structure assembly; infusing
the composite structure assembly by heating the assembly to a first
temperature for a first period of time; and curing the composite
structure assembly by increasing the heat to a second temperature,
wherein the second temperature is greater than the first
temperature.
[0013] According to a fourth aspect, a method of fabricating a
composite structure from components of varying stages of cure
comprises the steps of: providing a pre-cured composite stiffener;
providing a dry fabric component having a base portion and a clevis
configured to receive the pre-cured composite stiffener, wherein
the clevis is substantially perpendicular to the base portion;
wrapping a first film adhesive around a first edge of said
pre-cured stiffener; wrapping a first resin film around the first
edge of said pre-cured stiffener; inserting the first edge of said
pre-cured composite stiffener into the clevis of the dry fabric
component to form a composite structure assembly; applying a second
film adhesive to a surface of the dry fabric component; applying a
second resin film to the base portion of the dry fabric component;
securing the pre-cured stiffener substantially perpendicular to the
base portion of the dry fabric component, wherein the pre-cured
stiffener provides structural support to the composite structure
assembly; applying a film adhesive to the exterior base portion of
the dry fabric component securing the pre-cured stiffener with dry
fabric component to another substrate to which it will bond;
infusing the composite structure assembly by heating the assembly
to a first temperature for a first period of time; and curing the
composite structure assembly by increasing the heat to a second
temperature, wherein the second temperature is greater than the
first temperature.
[0014] In certain aspects, the method may further comprise the step
of bonding the cured assembly with a component to form a hybrid
unitized structure.
[0015] In certain aspects, the stiffener component is fabricated
from a composite material, a carbon-fiber composite material and/or
metal.
[0016] In certain aspects, the dry fabric component may be a
three-dimensional, woven pi-preform, wherein said pi-preform
contains a clevis configured to receive an edge of the stiffener
component.
[0017] In certain aspects, the method may further comprise the
steps of: (i) wrapping a resin film around a first edge of said
stiffener component; and (ii) inserting the first edge of said
stiffener component into the clevis of said pi-preform.
[0018] In certain aspects, the method may further comprise the
steps of: (i) wrapping a resin film around a second edge of said
stiffener component; and (ii) inserting the second edge of said
stiffener component into the clevis of the second pi-preform.
[0019] In certain aspects, the component comprises Glass Laminate
Aluminum Reinforced Epoxy.
[0020] In certain aspects, the dry fabric component comprises at
least one of: (1) glass-fiber; (2) carbon-fiber; or (3) para-aramid
synthetic fiber.
[0021] In certain aspects, the stiffener component is (i) L-shaped
or (ii) J-shaped.
[0022] In certain aspects, (i) the first temperature is between 150
and 200 degrees Fahrenheit, (ii) the second temperature is between
200 and 300 degrees Fahrenheit, (iii) the first period of time is
between 10 and 25 minutes, and (iv) the second period of time is
between 240 and 360 minutes.
[0023] In certain aspects, (i) the first temperature is about 175
degrees Fahrenheit, (ii) the second temperature is about 250
degrees Fahrenheit, (iii) the first period of time is between 15
and 20 minutes, and (iv) the second period of time is between 290
and 310 minutes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] These and other advantages of the present invention will be
readily understood with reference to the following specifications
and attached drawings wherein:
[0025] FIG. 1 illustrates a cross sectional view of an L-shaped
stiffener with a pi-preform sandwiched between two different
mandrel halves;
[0026] FIGS. 2a through 1i illustrate a first example infusion and
cure process using a pre-cured stiffener and a pi-preform;
[0027] FIGS. 3a through 3f illustrate a second example infusion and
cure process using a pre-cured stiffener and a pi-preform;
[0028] FIGS. 4a through 4h illustrate cross-sectional views of
example stiffener shapes and configurations;
[0029] FIG. 5 illustrates a first example unitized hybrid structure
wherein a plurality of pi-preform stiffener assemblies are used to
provide rigidity and strength;
[0030] FIGS. 6a through 6c illustrate a second example unitized
hybrid structure;
[0031] FIGS. 7a and 7b illustrate a third example unitized hybrid
structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Preferred embodiments of the present invention will be
described hereinbelow with reference to the accompanying drawings.
In the following description, certain well-known functions or
constructions are not described in detail since they would obscure
the invention in unnecessary detail. For this application, the
following terms and definitions shall apply:
[0033] As used herein, the term "composite material" refers to
material made from two or more constituent materials with different
physical or chemical properties, including resin-fiber composites.
Examples of such composite materials include fiberglass,
carbon-fiber-reinforced polymers ("carbon-fiber"), Glass Laminate
Aluminum Reinforced Epoxies (GLARE), para-aramid synthetic
fiber-reinforced polymers (e.g., Kevlar.RTM.) and any other
composite material known in the art of manufacturing aircraft,
watercraft and land craft.
[0034] As used herein, the term "composite component" refers to an
article fabricated from a composite material.
[0035] As used herein, the terms "cure" and "curing" refer to the
process of transforming an initially liquid resin into its final
rigid solid form.
[0036] As used herein, the terms "bond" and "bonding" refer to the
process of joining two or more components, including, but not
limited to, composite components.
[0037] As disclosed herein, it is an objective of the present
invention to provide systems and methods for combining
non-composite components and/or composite components of varying
stages of cure. That is, structures that would normally require
several cure steps or independent fabrications may instead be more
efficiently fabricated. A consolidated infusion and cure cycle
streamline the fabrication process by merging multiple steps into a
single step, thereby reducing tooling, fabrication time, complexity
of tools, oven run time, and potential contamination of individual
components by consolidating processes. Moreover, a consolidated
infusion and cure cycle extends the shelf life of components (e.g.,
expensive dry fiber components, such as three-dimensional woven
pi-preforms) by not infusing (i.e., impregnating) them with resin
until the time of cure, thus reducing overall costs and preventing
damage to B-staged parts (e.g., parts that have undergone a partial
cure).
[0038] Accordingly, a dry fiber component, such as a dry,
three-dimensional woven fiberglass pi-preform, can be infused while
simultaneously curing and bonding said dry pi-preform to other
structures, such as previously cured composite structures. While a
dry three-dimensional woven fiberglass pi-preform is described and
illustrated, numerous other dry fiber components may be used, which
may be of varying shapes and sizes, such as multi-spoked
three-dimensional woven shapes (e.g., having multiple devises).
[0039] Previously cured structures, which include, but are not
limited to, pre-cured stiffeners, can also function as tooling,
thus eliminating the time and expense attributed to the additional
tooling steps that would normally be required by the process. While
a pre-cured carbon-fiber stiffener is described and illustrated in
the various figures, other materials are contemplated and may be
used in lieu of, or in conjunction with, carbon-fiber. Such
materials include, for example, polymers, other composites, metals,
plastics, nano-materials, and ceramics.
[0040] Moreover, using a dry fiber component, such as a dry
three-dimensional woven fiberglass pi-preform, provides the
additional function of creating a barrier between the stiffener and
composite structure. For example, a glass-fiber pi-preform may
provide a barrier between an aluminum GLARE component and a
carbon-fiber stiffener, thus reducing, or eliminating, the risk of
corrosion that can result when such materials make contact with
each other. Specifically, in cases where GLARE and a carbon-fiber
are used, the barrier deters galvanic corrosion. Similarly, a
glass-fiber pi-preform may act as an insulator and/or isolator
between the carbon fiber and aluminum surface of the GLARE. More
specifically, in cases were electrical power and/or signals may be
carried through the conductive carbon fiber structure, the
fiber-glass prevents shorting to the aluminum of the GLARE by
acting as an electrical insulator and/or isolator.
[0041] Using prior methods, such infusion processes would have
required a separate set of tooling to: (i) orient and retain the
pi-preforms; and (ii) allow sufficient saturation of the fibers
without destroying the geometry. This tooling is often used only
for infusion and is therefore unnecessary after the infusion
process is complete. Indeed, using prior processes to manufacture a
component having a glass-fiber pi-preform and carbon-fiber
stiffener would have required substantially more steps, time and
expense. For example, a single-piece pi-preform with carbon-fiber
stiffener would have been made by (1) curing the carbon-fiber
stiffener, (2) infusing the pi-preform, (3) curing the pi-preform,
and (4) then finally bonding the carbon-fiber stiffener to the
glass-fiber pi-preform. Moreover, during that process, unique
tooling would have been required to infuse the pi-preform.
Furthermore, after infusion, infused preforms (e.g., pi-preforms)
would be much harder to handle due to the added stiffness and
tackiness of the resin. Finally, infusion was typically done per
order which also meant that pi-preforms were delivered with an
expiration date based on the resin.
[0042] The present system and method overcomes these deficiencies
by consolidating several of the manufacturing processes to increase
the speed and efficiency of fabrication while reducing the
necessary tooling required for the finished product. For example, a
carbon-fiber stiffener may be pre-cured and configured to function
as a backbone and/or support during a consolidated infusion, cure
and bond process. With the assistance of mandrels that can be used
during other phases of manufacturing, pre-cured carbon-fiber
stiffeners may be bonded with a dry fiber component (e.g., a
pi-preform) to function as part of the tooling used during
infusion, thereby providing a seamless transition from infusion to
cure. In essence, the present method effectively consolidates what
would normally require at least two curing steps, one of which
includes a separate infusion step, and a bonding step into only two
curing steps, therefore eliminating at least one iteration of
infusion and tooling, while also decreasing the overall fabrication
time and cost. It is generally advantageous to eliminate these more
traditional secondary bonding steps because they require more prep
work on components before assembly as well as more tolerance on
individual parts/tools for assembly and/or differing adhesives,
which could negatively affect the final properties of the unitized
structure. In addition, simultaneously curing a multi element
component as one unit reduces the amount of extra/scrap material
that often results when components are separately cured and
bonded/assembled. For example, using prior techniques, bonding two
cured components would likely require that the components be
trimmed to the exact shape needed before using additional tooling
to jig the components into place and then bond them together. This
step is omitted using a consolidated infusion and cure cycle as
disclosed herein.
[0043] In the consolidated infusion and cure cycle, resin film may
be applied directly to the dry fiber component and stiffener. With
the assistance of a mandrel, additional pressure may be provided
during the consolidated infusion and cure cycle of the component
fabrication. By controlling the oven temperature, the consolidated
infusion and cure cycle allows for resin to flow into the dry fiber
component (infusion/impregnation) and then cures the impregnated
fiber component by increasing the temperature while simultaneously
bonding the impregnated fiber component with the stiffener. This
consolidated infusion and cure cycle saves time (e.g., requiring
fewer cure cycles and fabrication steps) and reduces tooling (e.g.,
eliminates infusion tooling and reduces cure tooling), and reduces
wasted material (dry components are infused at time of fabrication
rather than when initially manufactured for which they are given an
expiration date) which reduces the overall cost of production for a
component.
[0044] A consolidated infusion and cure cycle may be accomplished
using, for example, resin film and film adhesive in addition to a
dry fiber component, such as a three-dimensional woven fiberglass
pi-preform, and pre-cured composite stiffeners, such as
carbon-fiber stiffeners. To achieve a desired resin content by
weight, different resin film weights may be applied along certain
faces of the pi-preform. Moreover, film adhesive may be applied to
the portion of the carbon-fiber stiffener residing inside the
clevis of the pi-preform to aid in adhesion/bonding to one and
other during cure. Opposed to a film adhesive, which typically has
a carrier lattice imbedded in the adhesive sheet, allowing it to
act slightly more like a fabric, a resin film need not have an
embedded carrier and is a free-form sheet of a tacky semi-fluid
resin film.
[0045] Fabrication of the stiffeners, both blade (i.e.,
substantially flat) and other configurations, such as those
depicted in FIGS. 2a through 2g, may be fabricated using shaping
tools, molds and pre-preg composite layup techniques known to those
of ordinary skill in the art. The stiffener used to provide support
for the infusion, cure, or bonding of additional components should
not be limited to composite materials such as carbon-fiber, but
could be manufactured from any material that provides the required
stiffness to the assembly at the time of infuse, cure, and/or bond.
The dry fiber component, including three-dimensional woven
fiberglass pi-preforms, may be fabricated from, for example,
S-Glass and infused with resin. S-Glass is generally used for
polymer matrix composites that require improved mechanical
properties compared to E-glass-based composites. This is often the
case when the material is operated under more extreme conditions.
FIG. 1 provides a cross-sectional view of an example pi-preform 102
and L-shaped stiffener 104 sandwiched between two mandrel halves
106a, 106b. U.S. Patent Publication No. 2009/0247034 to Goering
discloses additional example pi-preforms.
[0046] A consolidated infusion and cure cycle enables users to
produce infused and fully-cured pi-preforms on an as-needed basis.
This is advantageous because, while the resin film itself has a
finite lifespan and will eventually expire, it is a small fraction
of the cost of dry fiber components, such as three-dimensional
woven pi-preforms. By infusing the pi-preforms as needed, remaining
dry fiber components may be stored indefinitely until needed and
only require an in-date (i.e., not expired) batch of resin film at
the time of cure. This consolidated infusion and cure cycle may
also be applied to other pre-manufactured dry composite materials
of any number of shapes.
[0047] To provide an overview, the present invention may be
illustrated by the following example, which is provided to aid in
the understanding of the invention and is not to be construed as a
limitation thereof.
Example 1
[0048] FIGS. 2a through 2i illustrate a first example consolidated
dry fiber component infusion and cure process using a composite
stiffener. Specifically, as illustrated, a pre-cured L-shaped
stiffener 202 may be fused with a dry fiber component, such as
pi-preform 208. FIG. 2a illustrates a first step wherein the bottom
edge portion (e.g., about 0.5 inches) of a pre-cured stiffener 202
is wrapped with a film adhesive 204. FIG. 2b illustrates a second
step wherein a resin film 206 is wrapped around the bottom edge
portion of the pre-cured stiffener 202 (i.e., on the film adhesive
204) to form a stiffener subassembly 232. The film adhesive 204 can
function to create a superior bond between the pi-preform 208 and
the stiffener 202. FIG. 2c illustrates a third step wherein the
wrapped edge of the stiffener subassembly 232 is inserted into an
open clevis 234 of a pi-preform 208.
[0049] FIG. 2d illustrates a fourth step wherein a resin film 210
is applied to the top and bottom of the pi-preform 208's base. The
weight of the resin film 210 may be adjusted to achieve a desired
resin weight content of the final cured product. FIG. 2e
illustrates a fifth step wherein a second resin film 212 is applied
to the exterior of the pi-preform 208's clevis. As illustrated, the
first and second resin films 210, 212, which may be of different
weights, are added to the various faces of the pi-preform 208.
Specifically, the resin film 212 may be applied to the vertical
faces of the pi-preform 208 while the resin film 210 is applied to
all horizontal faces. Depending on the application, the various
film weights may be tailored to provide a specific percent resin
weight of the final cured composite. Accordingly, this specific
percent resin weight may vary from application to application, but
may fall within, for example, the 30-40% resin content weight
range. To ensure that the complete pi-preform 208 is fully
saturated with resin, and to aid in ease of fabrication, resin film
may be overlapped in each of the exterior corners where the clevis
meets the base of the pi-preform during dry pi-preform layup.
[0050] FIG. 2f illustrates a sixth step wherein a peel ply 214 is
applied to the pi-preform 208's base. The peel ply 214 provides a
prepared bonding surface during later manufacturing. It may be
preferable to cut the peel ply 214 larger (e.g., about 0.25 inches
larger) than the base of the pi-preform 208, thereby aiding in
applying the peel ply by requiring decreased accuracy while still
covering the intended area. However, superfluous peel ply should be
minimized as it can absorb additional resin, thus affecting the
final resin percent by weight of the cured product. While a
pi-preform 208 is illustrated, depending on the application, the
stiffener assembly 232 may be inserted in, or bonded with, other
dry fiber components and therefore should not be limited to the
illustrated pi-preform type.
[0051] The rigidity of the stiffeners 202 may be increased by
implementing geometric features (e.g., "L", "J", "Hat", etc.) or
increasing the thickness of the stiffeners. An advantage of
employing a L-shaped stiffener 202, or other geometric shape, is
that tooling is not required. Specially, additional tooling, which
is often used to provide stiffness/straightness along the
stiffener's length, may be omitted, thereby eliminating any
associated set-up time and expense. Mandrels may be used to
perpendicularly orient the stiffener to the dry pi-preform while
providing uniform pressure during infusion/cure but may not be
required. For example, as FIG. 2i illustrates, a mandrel half 222
may be configured on each side of the pi-preform 208's clevis. The
mandrels 222, may be used to apply pressure to the pi-preform
stiffener assembly to ensure resin flows into the crevices and
corners of the pi-preform 208 during infusion. The mandrels 222 may
be used for infusion, cure, and bonding of the pi-preform
components and bonded joints. These mandrels can assist in
providing additional support for the composite structures as well
as applying uniform pressure. The mandrels 222 may also be used to
apply uniform pressure along the faces of the pi-preform and into
the corners. To prevent unwanted adhesion, the stiffeners 202 may
be covered in a release film between the laminates and the mandrels
222.
[0052] FIG. 2h illustrates a cut-away side view of a final
assembly. FIG. 2i illustrates a pi-preform stiffener assembly in a
traditional vacuum bagging assembly 224. For example, the vacuum
bagging assembly 224 may comprise a plurality of vacuum ports 226,
a reader port 228, and a breather fabric 230, which may be laid
down around the pi-preform stiffener assembly as well as with paths
to the vacuum ports 226. The final assembly may then be bagged and
put under vacuum to apply pressure during the infusion/cure
processes. The vacuum bag may then be placed into an oven which
heats the material, causing the resin in the resin film and/or
pre-preg to change from sticky and soft to hard and stiff.
Providing pleats in the bag can enable uniform distribution of the
vacuum pressure along the mandrels 222 and into the pi-preform
stiffener assembly. The use of breather fabric 230 around the
perimeter of the pi-preform stiffener assembly allows air pathways
to the vacuum ports 226 to create as much pressure as possible on
and around the part without allowing the back to choke off sections
of the layup.
[0053] Depending on the size and shape of the manufactured
component, the cure cycle may be tuned to allow full infusion of
the resin prior to cure. Specifically, the oven temperature and
time for infusion may be set to a specific temperature at which
point the resin retains a fluid state allowing it to saturate the
dry material. This temperature may differ depending on the
resin/epoxy matrix being used; and the time required for it to
fully permeate the dry fibers may also vary. In one case, where the
resin may cure around 250 degrees, the infusion temperature may be
around 175 degrees. Where the cure time may be 250-360 minutes the
infusion time may be 10-25 minutes. The stiffeners 202 may be cured
on flat plate aluminum to provide a smooth, flat base to the
pi-preform, however, due to the benefit of the use of dry fiber
components being infused during the curing, this process can be
employed on any type of surface of varying curvature (for example
the skins and leading edge of the interior of a wing). Once the
component is fully infused and saturated with the resin matrix, the
temperature can then be increased to a point at which curing will
occur. Once cured, the oven may be decreased to ambient
temperature. Therefore, an advantage of using the methods described
herein is that the composite assembly may essentially be
simultaneously infused and cured. That is, unlike prior methods,
the composite assembly may go from infusion to cure by simply
increasing the temperature of the oven, thus eliminating
unnecessary tooling and the costs usually associated with the
transition from infusion to cure.
Example 2
[0054] The process of Example 2 is substantially the same as the
process of Example 1. However, in certain situations stiffeners
302, such as the blade-shaped stiffener illustrated in FIG. 3a, may
be employed in lieu of stiffeners having geometric shapes.
Unfortunately, such blade-shaped stiffeners may not be sufficiently
stiff to keep the stiffener structure straight along the length of
the assembly. For example, where a blade-shaped stiffener is too
thin and/or must span a greater distance. Thus, unlike Example 1,
tooling angles 316 may be further employed to keep the blade-shaped
stiffeners 302 vertical while the lengthwise clamps 318, which may
be attached (e.g., bolted) to the angles 316, can keep the whole
assembly straight along its length. Specifically, as illustrated in
FIGS. 3c and 3d, a clamp 318 may be configured to span the length
of the to-be-cured components to keep the blade-shaped stiffener
302 substantially straight along its length. The various tooling
may be fabricated from materials known in the art, such as
aluminum. For example, FIG. 3c illustrates a step wherein tooling
angles 316 are used to clamp the ends of the overhanging stiffener
302 to keep it vertically straight. In other words, tooling angles
316 may be used to position the blade-shaped stiffener 302
vertically inside its clevis 234, keeping it substantially
perpendicular to the pi-preform 208's base. As with Example 1, the
size, shape and length of the blade-shaped stiffener 302 may be
increased or decreased to fulfill a particular application.
[0055] While FIGS. 2a through 2i and 3a through 3f illustrate two
example stiffener shapes (i.e., "L" 202 and "Blade" 302), the
above-described methods may be applied to stiffeners of various
shapes, forms and sizes. For example, FIGS. 4a through 4h provide a
plurality of cross-sectional views of example stiffener shapes and
configurations. Specifically, FIG. 4a illustrates the
above-mentioned blade-shaped stiffener. FIGS. 4b and 4c illustrate
J-shaped and L-shaped stiffeners, respectively. As noted above, by
increasing geometry (e.g., providing additional bends or curves in
the stiffener), rigidity can be increased thereby eliminating the
need to use additional tooling. Additionally, while the
blade-shaped, the L-shaped and the J-shaped stiffeners of FIGS. 4a
through 4c have a single contact point and thus use only a single
pi-preform 208, additional pi-preforms 208 may be implemented to
facilitate additional shapes having multiple contact points, thus
further increasing strength and/or rigidity. For example, the
stiffener may be bent into a narrow or wide U-shape and connected
to a substrate using two pi-preforms 208. This is exemplified in
FIGS. 4d, 4e, 4f, 4g and 4h, which illustrate hat-shape, wide
hat-shape, hemispherical-shape, vertical bracket and a corner
bracket configurations, respectively. In addition, as illustrated
in FIGS. 4g and 4h, a stiffener may be configured to connect
parallel or perpendicular surfaces, which may be advantageous in
applications such as airfoil fabrication.
[0056] One or more pi-preform stiffener assemblies may be used to
provide rigidity and strength to composite components, such as
those fabricated from GLARE. Thus, pi-preform stiffener assemblies
may be bonded to a bonding surface using paste adhesive. To enhance
bond strength, a composite material bonding surface may be scuffed
using an abrasive pad, and then wiped with, for example, acetone.
Once prepared, the composite material bonding surface may sit for a
period of time (e.g., about one hour) prior to bonding to ensure
that, for example, all fluid has fully evaporated. Any peel ply
applied to the base (i.e., underside) of the pi-preform stiffener
assembly should be removed just before bonding, thus preserving the
surface until bonding. When bonding the components, paste adhesive
should be mixed thoroughly and applied to each component of the
bond (e.g., the bonding surface and the pi-preform stiffener
assembly). The GLARE surface may be wetted out with a very thin
layer of adhesive, while adhesive may simultaneously be applied to
the base of the pi-preform stiffener. An adhesive spreader may be
used to uniformly spread the adhesive. Glass beads premixed into
the adhesive help to control bond line thickness. The silicone
mandrels used during cure of the stiffeners may also be used to
apply uniform pressure during the bond. The pi-preform stiffener
assembly and GLARE bonding surface may be left to cure at room
temperature under vacuum (typically at 25-27 in Hg) for up to 24
hours. Heat may be applied in some cases to accelerate curing of
the adhesive.
[0057] During the curing process, mandrels, like those used during
cure of the pi-preform stiffeners, may be used to apply uniform
pressure from the vacuum. The only addition to this procedure may
be to add flash tape placed approximately 0.25'' from the edge of
the pi-preform base. This flash tape could later be removed once
the adhesive cured; taking with it any additional squeeze-out from
the bond leaving a precise edge along the length of the bonded
parts, while still allowing the paste adhesive to feather from the
discrete edge of the pi-preform stiffener down to the GLARE.
[0058] FIG. 5 illustrates an example unitized hybrid structure
wherein one or more pi-preform stiffener assemblies 502 are used to
provide rigidity and strength to a composite hatch of the
Aircraft's access panel 500. The composite hatch panel 500 may
comprise a composite material such as, for example, GLARE. To
stiffen the panel, pi-preform stiffener assemblies 502, which may
be approximately 1.0'' wide by 0.5'' tall with a four-ply L-shaped
stiffener, may be bonded spanning the hatch panel. As one of skill
in the art would recognize, the size of the pi-preform stiffener
assemblies 502 may be adjusted for a particular purpose. The
L-shaped stiffener may be made from, for example, four-ply
(45/0/0/45) cloth carbon-fiber pre-preg.
[0059] FIGS. 6a through 6c illustrate a second example unitized
hybrid structure 600. More specifically, FIGS. 6a through 6c
illustrate an airfoil 600 having a GLARE substrate 602 to which
other components are bonded to form a hybrid unitized structure.
For example, a stiffener 604 may be bonded with the GLARE substrate
602 using a pi-preform 606. For this type of application, the
stiffener 604 may be substantially planar with a center portion
removed to reduce weight and enable wires, cables and the like to
be run along the length of the component. However, to increase
strength, the stiffener 604 may be fabricated one or more diagonal
straight portions, thereby forming a truss. The stiffener 604 may
be fabricated using techniques known in the art to achieve a
desired shape or size.
[0060] FIGS. 7a and 7b illustrate a third example of a unitized
hybrid structure 700. More specifically, FIGS. 7a and 7b illustrate
a second airfoil 700 having a GLARE substrate 702 to which other
components are bonded to form hybrid a unitized structure. For
example, a stiffener 704 with a 708 core may be bonded with the
GLARE substrate 602 using a pi-preform 606. Like the stiffener 604
of FIGS. 6a through 6c, the stiffener 704 is substantially planar.
However, to provide further stiffness, the stiffener 704 may
comprise a core 708. Example cores may include, for example,
hexagonal-celled core of various materials or foam core.
Specifically, the core 708 can provide additional rigidity during
infusion, cure and bond, as well as additional strength and
stiffness to the final assembly.
[0061] While the present invention has been described with respect
to what are presently considered to be the preferred embodiments,
it is to be understood that the invention is not limited to the
disclosed embodiments. To the contrary, the invention is intended
to cover various modifications and equivalent arrangements included
within the spirit and scope of the appended claims. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
[0062] All United States and foreign patent documents, all
articles, brochures, and all other published documents discussed
above are hereby incorporated by reference into the Detailed
Description of the Preferred Embodiment.
* * * * *