U.S. patent application number 10/716959 was filed with the patent office on 2005-07-07 for 3-d fabrics and fabric preforms for composites having integrated systems, devices, and/or networks.
Invention is credited to Alexander, Bogdanovich, Don, Wigent.
Application Number | 20050146076 10/716959 |
Document ID | / |
Family ID | 34619916 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050146076 |
Kind Code |
A1 |
Alexander, Bogdanovich ; et
al. |
July 7, 2005 |
3-D fabrics and fabric preforms for composites having integrated
systems, devices, and/or networks
Abstract
A 3-D fabric preform for composites including a
three-dimensional engineered fiber preform formed by intersecting
yarn system components; and at least one system, device, and/or
network integrated with the preform for providing a predetermined
function, wherein the at least one system, device, and/or network
is introduced prior to formation of a composite structure including
the preform, thereby providing a 3-D fabric preform for composites.
Also, a method for forming the 3-D fabric preform for composites
including a three-dimensional engineered fiber preform formed by
intersecting yarn system components; and at least one system,
device, and/or network integrated with the preform for providing a
predetermined function, wherein the at least one system, device,
and/or network is introduced prior to formation of a composite
structure including the preform, thereby providing a 3-D fabric
preform for composites.
Inventors: |
Alexander, Bogdanovich;
(Apex, NC) ; Don, Wigent; (Greenville,
NC) |
Correspondence
Address: |
JINAN GLASGOW
300 N. GREENE ST., SUITE 1600
P.O. BOX 2974
GREENSBORO
NC
27401
US
|
Family ID: |
34619916 |
Appl. No.: |
10/716959 |
Filed: |
November 19, 2003 |
Current U.S.
Class: |
264/257 |
Current CPC
Class: |
D10B 2401/20 20130101;
D03D 1/0088 20130101; D10B 2101/12 20130101; B29C 70/88 20130101;
Y10T 442/3366 20150401; Y10T 428/24058 20150115; Y10T 442/322
20150401; Y10T 442/3325 20150401; C08L 2201/12 20130101; B29C 70/24
20130101; D03D 25/005 20130101; D10B 2401/046 20130101; Y10T
442/3195 20150401 |
Class at
Publication: |
264/257 |
International
Class: |
B27N 003/10 |
Claims
What is claimed is:
1. A 3-D fabric or preform for composites comprising: a
three-dimensional engineered fiber preform formed by intersecting
yarn system components; and at least one system, device, and/or
network integrated with the preform for providing a predetermined
function, wherein the at least one system, device, and/or network
is introduced prior to formation of a composite structure including
the preform, thereby providing a 3-D fabric preform for
composites.
2. The preform according to claim 1, wherein the at least one
system, device, and/or network is introduced at or during the
fabric-forming process.
3. The preform according to claim 1, wherein the at least one
system, device, and/or network is introduced after the
fabric-forming process, but prior to the formation of the composite
or other application of the fabric.
4. The preform according to claim 2, wherein the at least one
system, device, and/or network is integrated with the preform while
the preform is being formed on a machine.
5. The preform according to 1, wherein the at least one system,
device, and/or network is automatically integrated with the
preform.
6. The preform according to claim 1, wherein the at least one
system, device, and/or network is manually integrated with the
preform.
7. The preform according to claim 1, wherein the preform is formed
from a 3-D woven fabric.
8. The preform according to claim 1, wherein the preform is formed
from a 3-D orthogonally woven fabric.
9. The preform according to claim 1, wherein the preform is formed
from a 3-D braided fabric.
10. The preform according to claim 1, wherein the preform is formed
from a 3-D multiaxial fabric.
11. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one sensor.
12. The preform according to claim 11, wherein the at least one
sensor is selected from the group consisting of fiber optic
sensors, piezoelectric sensors, temperature sensors, pressure
sensors, piezomagnetic sensors, electrically conductive sensors,
hydraulic sensors, and combinations thereof, and combinations
thereof.
13. The preform according to claim 1, wherein the at least one
system, device, and/or network includes electrically conductive
components.
14. The preform according to claim 1, wherein the components
include electrically conductive components aimed at
telecommunication, data transmission, electromagnetic reception,
electromagnetic transmission, electromagnetic
diffusion/diffraction, electromagnetic shielding of electronic
equipment, personnel protection against electromgnetic radiation,
and other similar functions which are distinct from the functions
of sensing and actuation.
15. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one actuator.
16. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one
transducer.
17. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one diagnostic
system, device, or network.
18. The preform according to claim 17, wherein the at least one
system, device, and/or network includes at least one fabric
diagnostic system, device, or network.
19. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one magnetic
component.
20. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one component for
releasing a medication.
21. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one component for
repairing the preform.
22. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one audio
component.
23. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one video
component.
24. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one receiver
and/or transmitter components.
25. The preform according to claim 1, where the 3-D fabric or
preform is to be used for its own purpose or without being included
in further composite processes.
26. The preform according to claim 1, wherein the preform is formed
from a 3-D multiaxial woven fabric incorporating more than three
directions of fibers/tows, where at least one of them is oriented
at an angle to the direction of fabric formation.
27. The preform according to claim 1, wherein the network forms a
circuit for the transmission of fluids, electricity, or light.
28. The preform according to claim 1 wherein the network forms a
circuit for the transmission of fluids, electricity, or light and
which performs logical functions.
29. The preform according to claim 1, wherein the preform is formed
from/as a 3-D warp-knitted fabric.
30. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one optical
fiber.
31. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one piezoelectric
fiber or other piezoelectric object substantially extended in one
direction.
32. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one shape memory
alloy fiber or other shape memory alloy object substantially
extended in one direction.
33. The preform according to claim 1, wherein the at least one
system, device, and/or network includes at least one tubular,
hollow, or microchannel fiber, rod, or filament.
34. A method for forming a 3-D preform for composites comprising
the steps of: providing yarn system component for forming a
three-dimensional engineered fiber preform formed by intersecting
textile system components; and providing at least one system,
device, and/or network integrated with the preform for providing a
predetermined function, wherein the at least one system, device,
and/or network is introduced prior to formation of a composite
structure including the preform, thereby providing a 3-D fabric
preform for composites.
35. The method according to claim 34, further including the steps
of: introducing device/network materials to the textile processing
system supply for integration with the preform in at least one
fiber or pathway of the network materials; producing the preform
via a textile processing system; thereby producing a 3-D fabric
having integrated networks/devices therein.
36. The method according to claim 35, wherein the at least one
fiber or pathway of the network materials, device and/or sensors is
a substantially straight pathway.
37. The method according to claim 35 wherein the at least one fiber
or pathway is flexible.
38. The method according to claim 35 wherein the at least one fiber
or pathway is rigid.
39. A polymer matrix composite material which is manufactured with
the utilization of the preform according to claim 1 using any
suitable room temperature or elevated temperature composite
fabrication technique.
40. A ceramic matrix, metal matrix and/or carbon matrix composite
material which is manufactured with the utilization of the preform
according to claim 1 using any suitable processing technique, with
the selection of the system, device, and/or network able to
maintain its functionality in a respective high temperature
processing and/or in-service environment.
Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] The present invention relates generally to fabric materials
and, more particularly, to fabric preforms used for composites
further including sensors, devices, and/or networks.
[0003] (2) Description of the Prior Art
[0004] Composites are materials formed from a plurality of
components combined to form an integral structure. Typically,
fabrics referred to as preforms are used within a composite
structure provide a supporting framework for the composite, with a
resinous material added thereto for filling interstitial regions
and for providing a more amorphous component for transforming an
otherwise non-stiff fabric preform into a rigid component for
further shaping, machining, or other processing. The name
"fiberglass" is a common slang term for one such composite
material, but many other composite materials employ fabrics as
preforms, including metal matrix, and carbon or ceramic matrix
composites.
[0005] Prior art composites are known to employ sensors, devices,
and/or networks for the purpose of sensing fatigue, failure,
changing conditions, and the like and are generally refered to as
"Smart Structures", or "Smart Materials"; however, in all cases
known at the time of the present invention, any such sensors,
devices, and/or networks were added or incorporated into the
composite at or after the formation of the composite itself, i.e.,
they have not been included in the fabric preform prior to
composite formation in any case. Further, such sensors, devices,
and/or networks were added or incorporated into three-dimensional
fabrics.
[0006] "Smart Structures" instrumented with a variety of sensing
and/or actuation systems and devices have been one of the major
focuses of science and engineering in the last two decades. They
continue attracting great interest, which is primarily motivated by
the fast growing capabilities of modern microelectronics and new
structural materials which, in combination, enable development of
the miniature, fully integrated in the structural material,
multifunctional in-situ diagnostic and real-time control means.
Typically, a smart structure, which is commonly associated with a
vehiclular, civil, marine, or other critical structural member,
contains multiple attached or embedded sensor and/or actuator
elements and some hardware and software for collecting, analyzing
and storing information regarding the strain, temperature, damage,
cracks, delamination, and other parameters characterizing
structural integrity of the airframe. For smart structures to be
relied on for mission or flight critical decision, the above flight
critical characteristics must be continuously monitored, and
structural integrity should be assessed in real time. Accomplishing
this very complex task requires, in the first place, to reliably
integrate and interrogate a large number of individual sensors
distributed over the structure, as well as the means to receive
data from them.
[0007] Various three-dimensional fabrics are often used as
reinforcement of composite materials and as such are referred to as
preforms. These fabrics may utilize both flexible and rigid
elements ranging from staple cotton yarn to solid ceramic wires or
rods, and may be usefully employed in both their fabric states, or
further processed as within composites, and as such no major
distinction is made here between the terms "fabric" and "preform",
whether extremely flexible as with a fine insulation fabric or
rigid as with a structural wire grid formed with rigid rods. The
plurality of controllably isolated or joined fiber or tow layers
formed in 3-D fabrics provide particularly valuable opportunities,
well beyond that of 2-D fabrics, for the development of elaborate
functional systems, circuits, or networks as is so often done with
multi-layer integrated circuits or multi-layer hydraulic manifolds.
The very regular, inherently periodic nature of 3-D orthogonally
woven and other 3-D fabrics, which are mentioned here as examples,
allows them to perform functions similar to those of 3-D grids,
arrays or networks. Examples of such functions include phased array
emission/detection, shielding or refraction or diffraction of a
known wavelength, damage and delamination detection, resin flow and
cure rate control, acoustic emission signal sensing, active control
of shapes, vibration suppression, supply or transmission of fluids
to mention a few.
[0008] Optical fibers and sensing devices associated with them are
one desirable means for producing smart structures. Optical fibers
are available in small diameter; they are flexible, relatively
light, relatively strong, relatively inert to environmental
degradations, are not affected by electromagnetic influence, carry
no electrical current. They can be quite easily adhered to surfaces
of materials like metals, ceramics, plastics, composites, or
embedded within thereof. When applied to composite structures in
the past, optical fibers have been commonly bonded to the exterior
or embedded between layers of prepreg without adversely affecting
structural integrity. The optical fiber can be embedded in any
curable, moldable, or laminated composite material without
significantly disrupting the regular manufacturing process. While
embedded into the structure, optical fibers neither significantly
affect the mechanical characteristics of the composite nor
concentrate mass at a particular location along the structure.
Advantages of conventional fiber optic strain sensors over
conventional electromagnetic strain gauges include simplicity, low
cost, insensitivity to electromagnetic interference, immunity to
electrical potential differences, operability over wide temperature
ranges and operating environments, end use of simple and low-cost
electronics. Besides, the use of fiber optics to replace
conventional electric wires reduces the intensity of propagating
electromagnetic waves, which results in reduced detectability of
the system/device and interference with on-board computers.
[0009] A large variety of fiber optic sensors have been developed
and are currently in use. Those include displacement, strain,
temperature, pressure, moisture, wear, acoustic, magnetic, rate of
rotation, acceleration, electric, electric current, trace vapor
sensors to mention a few. The sensors may be adapted to modulate
the light in different ways so as to encode multiple signals. For
example, different characteristics of interest may be encoded by
intensity, by frequency, or by phase. The two major types of fiber
optic sensors are either phase modulated or intensity modulated
sensor devices. Phase modulated fiber optic sensors may be
characterized by their required use of coherent light sources,
single-mode fibers and the need of relatively complex optical and
electronic circuitry. This type sensor applications depend
primarily upon force field induced length changes and strain
induced refractive index changes, which are the cause of phase
shifting as the light travels through the sensing length of the
optical fiber; this can be detected using an interferometer
apparatus. The intensity modulated type fiber optic sensors, on the
other hand, depend primarily on an optical source of constant
intensity, which is ordinarily acted upon by an external force
field.
[0010] Numerous fiber optic sensors known from the prior art can be
categorized in many different ways. One of them--segregating
sensors into extrinsic and intrinsic, is of particular interest in
the context of present invention. Two sensor types belonging to
either of these groups, namely Extrinsic Fabry-Perot
Interferometric (EFPI) sensors and Bragg Grating (BG) sensors are
used here for the reduction to practice demonstration. It is well
established that EFPI sensors have much lower thermal sensitivity,
also sensitivity to lateral strains, to dynamic perturbations
(mechanical vibration, acoustic waves), and to magnetic fields than
BG sensors. It is also believed that EFPI sensors are better suited
for the use in hostile environments, which can be faced,
specifically, when the sensor is exposed to the full manufacturing
cycle of a composite material. On the other hand, an EFPI sensor
(which is a complex device itself), after it is integrated in the
composite material, has much higher potential to become a
considerable local origin of disturbance than a BG sensor (due to
the latter one is mechanically indistinguishable from its carrying
optical fiber). Also to the advantage of BG sensors--a large series
of them can be carried by a single optical fiber; it is much easier
to embed/integrate BG sensors in the composite and simultaneously
interrogate them under loading.
[0011] Present invention is related to engineered three-dimensional
fabrics and fabric preforms for composite materials instrumented
with fiber optic sensors and other types of sensing, actuating and
information transmitting systems, devices and networks which can be
suitably integrated in the said fabrics and fabric preforms. The
said fabrics and fabric preforms are treated as the carriers of the
said systems, devices and networks. From this viewpoint, the said
fabric preforms, after being processed into composite materials and
structures, become integral with them, together with their carried
said systems, devices and networks.
[0012] In order to clearly identify the novelty of the present
invention and its distinct place among prior art in the field, the
following overview of the prior art in the field of composite
materials and structures and textile fabrics with
embedded/integrated fiber optic sensors is provided, including
comments on their respective methods of their fabrication.
[0013] U.S. Pat. No. 4,221,962 teaches how an optical glass fiber
is embedded in a composite laminate to monitor and detect the
presence of moisture in the interior of the panel. According to the
invention, the optical fiber is "sandwiched" between the plies
during ply lay-up, becomes an integral part of the laminate, and as
such goes through the laminate curing cycle.
[0014] U.S. Pat. No. 4,537,469 describes a reinforced structural
member, which is composed from a plurality of high tensile strength
optical fibers, arranged into at least two parallel layers and
embedded in the resin material. Importantly, all described optical
fiber architectures in the invented composite are limited to
two-dimensional woven architectures.
[0015] U.S. Pat. No. 4,581,527 describes a system consisting of a
plurality of layers of optical fiber grids for detecting damage and
assessing its location in laminated composite materials. The
optical fiber grid system is implanted in a composite laminate
during its fabrication and becomes integral with it. Each optical
fiber grid includes two orthogonal series of optical fibers.
[0016] U.S. Pat. No. 4,603,252 also describes a plurality of light
conducting fibers, which is included in laminated composite
material. The light transmitting fibers are included, as at least
one separate layer, in between adjacent structural laminas,
importantly, in some regular pattern.
[0017] U.S. Pat. No. 4,772,092 describes method of measurement and
detection of cracks and fissures in test objects (specifically,
laminated composites), particularly under utilization of light
conducting fibers, which will break in the instance of a crack or
fissure. In the preferred embodiment of this invention, it is
described that several light conducting fibers are either inserted
within the layers of regular fibers by replacing some of the
regular fibers, or light conducting fibers are placed in between
adjacent layers of regular fibers in a mesh. After that the
respective layers are put together and impregnated in resin. The
detailed description of the invention and illustrative material do
not indicate that any type of fiber architecture other than a
unidirectional fiber placement or generic 2-D woven architecture,
has been intended in the invention.
[0018] U.S. Pat. No. 4,836,030 describes the method of embedding a
plurality of optical fibers in the composite material in
pre-determined two-dimensional configuration (a serpentine pattern,
specifically). Detection of light passing through any given optical
fiber indicates that the composite is free of damage in the area
along the extent of that optical fiber; however, integrating
optical fibers within a fabric structure that is a 2-D woven
structure or the like, where fiber paths are typically
non-orthogonal and not substantially straight due to necessary
crimping, prevents the integration of these fibers within the
fabric itself. A layer of film adhesive is formed, in which optical
fibers are embedded. The film adhesive layers are incorporated in
composite laminate at the time of its manufacture. Optical fibers,
embedded by this approach between different plies of a laminate,
provide information about damage formation through the thickness.
Two examples of practical manufacturing procedures that resulted in
successful manufacturing of composite sandwich and laminate
structures with two types of embedded fiber optics, are
comprehensively described in the patent. Based on experimental
results, it has been concluded that the subject method pinpoints
the location of delamination as well as identifies the location of
other types of damage. No fabric-type architectures of any kind
were described in the patent in the context of embedded optical
fiber configurations.
[0019] U.S. Pat. No. 4,891,511 describes a microbend sensor device,
which contains a plurality of braided fibers with at least one of
them being an optical fiber. The "braid", as it is referred to in
the invention, is a generic strand of several intertwined fibers,
including one or more optical fibers, without any reference to
specific braided fabric architecture or equipment it can be
produced on.
[0020] U.S. Pat. No. 5,023,845 teaches a new testing technique,
that has been conceptualized and experimentally validated, and is
based on the utilization of optical fibers embedded in composite
laminate. No unconventional ways or patterns of embedding optical
fibers between layers of a laminate were described in this
invention.
[0021] U.S. Pat. No. 5,029,977 describes an optical fiber mounting
system, which includes a two-dimensional rollable woven fabric
"supporting device" and an optical fiber integrated in the said
supporting device. One suggested approach of integrating the
optical fiber into said supporting device is to weave the fiber in
(as a weft or warp thread). The alternative approach is to
incorporate the optical fiber by laminating it between the sheets
of the structural fiber fabric. Further, the fabric containing the
optical fiber is incorporated into the composite structure during
the latter's manufacture. Attachment of the optical fibers to the
structure after its fabrication is another embodiment.
Significantly, the patent only suggests the use of 2-D woven
fabrics in the fabrication of the invented mounting device.
[0022] U.S. Pat. No. 5,118,931 describes a fiber optic microbend
sensor that detects changes in a material caused by deformation of
an optical fiber bonded to the structure.
[0023] U.S. Pat. No. 5,182,449 describes a sensor system for
structural composites, which includes a plurality of optical
sensors integrated with the structure, i.e., the sensor can be
either attached to the surface of the structure or embedded within
a composite structure.
[0024] U.S. Pat. No. 5,338,928 describes the method to control
vibrations within ceramic matrix composite (CMC) or metal matrix
composite (MMC) by applying an excitation voltage to array of
piezoelectric actuators mounted on the surface of the structure and
driven in response to the phase shift of monochromatic light
transmitted through a grid of optical fibers embedded within a
composite material. The optical fibers, as described in the
invention, can be arranged in an orthogonal two-dimensional grid
pattern for detecting strain along two mutually orthogonal axes.
Once the fiber architecture in the structure is established, an
optical fiber capable of withstanding high temperature environments
can be inserted into the structure prior to chemical vapor
infiltration in the case of CMCs or prior to plasma spraying,
foil-fiber-foil construction or other processing method applicable
to MMCs. Fiber optic sensors, usable for the purpose of this
invention, can be gold-coated silica or sapphire fibers, which can
withstand the CMC or MMC processing temperatures. It is important
to note, however, that no intent of integrating optical fibers into
textile preforms can be found in the patent description.
[0025] U.S. Pat. No. 5,493,390 describes a compact and integrated
system for the real time in-service strain monitoring. The system
includes Bragg grating sensors and planar tunable opto-acoustic
filter for analyzing the optical signal. The optical fibers can be
embedded in or bonded to the structure.
[0026] U.S. Pat. No. 5,515,041 describes a concept of rotor shaft
made of composite material with integrated fiber optic sensor and a
resonant detector circuit for detecting sensor output, which is
also integrated within the structure. However, the invention does
not teach any practical means how to embed the aforementioned
sensors into a composite rotor shaft, or how to integrate the
sensing apparatus.
[0027] A different type of fiber optic sensor application, which is
outside the area of diagnostics and health monitoring of composite
materials, is described in U.S. Pat. No. 6,381,482. A fabric or a
garment structure comprising a "comfort component" serving as the
base of fabric, and an "information infrastructure component"
integrated within the comfort component, is the object of this
invention. The information infrastructure component may comprise a
plurality of sheated optical fibers, which purpose is to detect
ballistic projectile penetration. The multifunctional fabric of
this kind, incorporating the two aforementioned components, is
suggested to be manufactured as a two-dimensional woven or knitted
fabric. In addition to the aforementioned optical fibers, an
"electrical conductive component" can be integrated within the said
2-D woven or knitted fabric. The latter component may comprise
metallic fibers, intrinsically conductive polymers, doped fibers,
and combinations thereof. The electrical conductive component is
aimed at transmitting information from sensors to monitoring
devices.
[0028] Conducting rigid or flexible systems incorporated into 2-D
fabrics or embedded into polymers and composites have been used for
a variety of other applications. One of them is described in U.S.
Pat. No. 4,795,998, where the invented sensor array aimed at
sensing pressure was constructed as a grid of flexible conducting
elements incorporated in a 2-D woven fabric. No indication can be
found in the patent toward the utilization of any kind of 3-D
fabric architecture.
[0029] U.S. Pat. No. 5,103,504 describes textile fabric and
clothing made thereof, which comprises cotton fibers and 6-10
microns in diameter stainless steel fibers blended together and
spun into mixed yarn. The steel fibers have weight content 10-15%
in the mixed yarn. The purpose of such fabric, which is a
two-dimensional according to the invention description, is to
provide efficient shielding against microwaves and other types of
electromagnetic radiation to which, in particular, the hospital
personnel is exposed when operating electro-medical equipment.
[0030] U.S. Pat. No. 5,210,499 describes the method of polymeric
resin flow monitoring and cure rate monitoring by the use of
sensors as integral component of the monitored system. The sensor
threads may be woven into the fabric, however illustrations to the
patent clearly indicate that only 2-D weaving was intended within
the scope of this invention.
[0031] Another broad and fast growing area of smart structures is
related to embedment/integration of piezoelectric actuators and/or
sensors into composite materials and structures. If instrumented
with piezoelectric fibers, ribbons, tapes, films, or other suitable
shapes devices, smart composites may perform both actuation and
sensing functions in a closed-loop configuration. The piezoelectric
fiber composites are highly tailorable to specific needs by
selecting appropriate mechanical, actuation and sensing properties
of piezoelectric fibers and matrices, similarly to the case of
conventional composites, namely through selecting optimal fiber
diameter, mechanical and piezoelectrical characteristics, fiber
spacing and orientation, as well as matrix mechanical and
piezoelectric properties. The diameter of piezoelectric fibers can
be selected from a broad range--typically between 5 and 200
microns. A smaller diameter fibers may be preferable in textile
applications, due to they provide more flexibility, higher strength
and, consequently can be easier processed into the fabric. Besides,
smaller diameter piezoelectric fibers can operate at a lower
voltage. Piezoelectrical fibers may be continuous or available in
short fragments. The fiber geometry can also be varied.
[0032] The most efficient actuator materials are piezoelectric
ceramics, such as zirconate titanate (PZT), and electrostrictive
ceramics, such as lead molybdenum niobate (PMN). Unfortunately,
most of the ceramics are very brittle (have very low ultimate
strain characteristic) and have a large positive coefficient of
thermal expansion. These features create serious problems with
embedment of piezoceramic actuators/sensors in polymer matrix
composites. When a graphite fiber/epoxy resin composite, in
particular, is fabricated with embedded piezoceramic elements at
elevated temperatures, tensile thermal stresses are induced in the
piezoceramic element, which can cause cracking and degrading
functionality. Another popular piezoelectric material is
polyvinylidene fluoride (PVDF) available as a thin film. More
information on piezoelectric materials and their applications can
be found in U.S. Pat. Nos. 5,305,507; 5,869,189 and other
literature. Besides, as mentioned in the latter patent, shape
memory allows can be provided in fiber form, arranged in parallel
arrays, and embedded in polymer matrix to form a smart composite.
Such composite can be actuated by heat provided in the direction
transverse to the fiber axis by, for example, a resistive metal
layer coated on the composite.
[0033] Next a brief overview is provided of the prior art in the
area of piezoelectric actuators/sensors that is relevant to the
present invention.
[0034] U.S. Pat. No. 4,400,642 describes a laminated structural
device, which may be, generally, a combination of (i) layers made
from a piezoelectrically active, non-conductive matrix material
with a plurality of embedded electrically conductive fibers and
(ii) layers made from an electrically conductive matrix material
with a plurality of embedded piezoelectrically active fibers. The
patent does not teach about using textile preforms as reinforcement
for the invented laminated composites.
[0035] U.S. Pat. No. 4,849,668 describes a composite structural
member, which includes multiple layers of graphite/epoxy composite
with one or more embedded piezoelectric elements. In a preferred
embodiment, the piezoelectric components are formed of a ceramic
material. The composite laminate is fabricated by fitting the
piezoelectric elements into apertures in epoxy-impregnated graphite
fiber layers, laying-up the layers, and applying heat and pressure
to cure the structure. Importantly, the piezoelectric elements
intended for the embedment according to the invention are in the
form of a thin film, which has two comparable dimensions, while its
thickness dimension is about 60 times smaller than the other two.
At the same time, that thickness with added insulation film was as
large as total thickness of three prepreg plies, which asked to cut
three plies in the fabrication process to make room for each
piezoelectric element.
[0036] U.S. Pat. No. 5,195,046 describes a sensor module, which
includes a plurality of piezoelectric transducers that convert
mechanical motion experienced by the structure, into corresponding
electrical signals.
[0037] U.S. Pat. No. 5,305,507 describes a piezoelectric
actuator/sensor package and a method of embedding a ceramic
actuator/sensor in a laminated structural composite, such as
graphite/epoxy laminate. A ceramic actuator/sensor is first
encapsulated in a non-conductive fiber composite, specifically
fiberglass cloth and epoxy, which is an alternative to polyimide
film Kapton suggested for analogous purpose in U.S. Pat. No.
4,849,668. Such a package prepared for embedment is generally
planar and is placed in its selected location between layers of
structural composite, and the laminate is cured at an elevated
temperature.
[0038] U.S. Pat. No. 5,814,729 describes the system for in-situ
delamination detection in laminated composites. Both the
piezoelectric ceramic actuators and fiber optic sensors may be
embedded between the layers of composite material during its
fabrication. The embedded sensors and actuators are essentially
placed within a plane between two layers of a laminate.
[0039] U.S. Pat. No. 5,869,189 describes composite materials aimed
at actuating and sensing deformation and having a series of
flexible elongated electroceramic (particularly, piezoelectric)
fibers arranged in a parallel array and separated from adjacent
fibers by relatively soft polymer. The composite also includes
flexible conductive electrodes extended in the axial direction of
the electroceramic fibers. The composite may also include arrays of
fibers that are stacked in multiple layers along the thickness. The
piezoelectric fiber composite is embedded in a laminated structural
composite component and spans its entire length and width. The
structural component can be formed by pre-forming the piezoelectric
composite, placing it between the host layers, and then curing the
whole laminate. Alternatively, the host layers and piezoelectric
composite can be co-cured in a single step. The composition can
also be pre-formed in a pre-impregnated form. The conductive
electrodes are, preferably, in direct contact with carbon fibers of
the structural composite. The electrode layers may be made of a
thin polymer substrate with and ultra-thin layer of metal. In other
embodiments, the principles set forth in the invention can be used
with materials that rely on actuation phenomena other than the
piezoelectric effect. Significantly, no fabric materials were
intended for use in this invention; as such this patent teaches
away from the present invention.
[0040] U.S. Pat. No. 6,006,163 describes an active damage
interrogation system and method which utilizes an array of
piezoelectric transducers attached to or embedded within the
structure (composite structure, specifically) for both actuation
and sensing functions. An experimental validation of the invented
system was performed on composite flex beam with Active Control
eXperts (ACX) QP20W QuickPack transducers bonded to the surface of
the flex beam.
[0041] U.S. Pat. No. 6,370,964 describes a "diagnostic layer"
containing a network of actuators and sensors. The layer may be
incorporated into or placed on the surface of composite material
for structural health monitoring, including detection of the site
and extent of damage. The diagnostic layer can also be adapted to
monitor the cure process of a composite. A diagnostic layer
includes a thin and flexible dielectric substrate, a network of
embedded piezoelectric devices (actuators and sensors, which are
preferably not distinct), and a plurality of conductive elements
which are electrically interconnecting the actuating and sensing
devices. The diagnostic layer can be embedded into fiber-reinforced
composite during its fabrication.
[0042] U.S. Pat. No. 6,399,939 describes a nondestructive
monitoring system, which includes a sensor array called "discrete
sensor nodes", each of them generating an electrical signal in
response to a damage, failure or other type structural anomaly. In
the preferred embodiment, the sensor nodes are represented by a
plurality of piezoceramic fibers arranged in a planar array, in
which the fibers are aligned substantially parallel to each other.
The piezoceramic fiber ribbon can be woven as a straight fiber into
a fabric, which is, importantly, in the context of this invention,
a two-dimensional fabric.
[0043] With the great progress in miniaturization of
microprocessors, antennas, electric power suppliers, data
acquisition and storage systems, as well as many other
microelectronic systems, devices and networks, it becomes more and
more feasible to embed/integrate entire sensing, actuation, and
self-control systems into the body of an aircraft, spacecraft, or
other transportation means. This obviously includes smart composite
structures. Several examples of such embedment/integration, found
in the prior art, are described in the conclusion of this
overview.
[0044] U.S. Pat. No. 5,184,141 describes a structurally-embedded
electronics assembly for integration with the load-bearing
structure of an aircraft. The assembly includes both sensors and
antennas, the latter ones may be printed circuit antennas. The
antenna may be embedded between layers of the structural material.
As suggested in this invention, one desirable objective is to
control the permeability and permittivity of the materials
surrounding the embedded antenna in order to maximize its
performance. This can be relatively easily achieved with the use of
composite materials by adding short carbon or glass fibers, metal
particles or the like to the matrix material to change its
electromagnetic properties.
[0045] U.S. Pat. No. 5,440,300 describes embedded smart structures
that include active electronics which control and collect data from
sensors and actuators and transmit data to the exterior of the
structure by electromagnetic antenna radiation. Multiple embedded
sensors, each having its individual antenna, are powered and
interrogated by a single external powering and data interrogation
antenna. According to this concept, the smart panel can be made of
any material which is compatible with and suitable for
embedding/integrating electronics. Specifically, the panel may
contain in its interior volume a thin film package with sensors and
radio frequency antenna extending therefrom.
[0046] U.S. Pat. No. 6,529,127 describes a multidrop network of
multichannel, addressable sensing modules embedded within a
composite structure, remotedly powered, and interrogated by a
personal computer via a non-contacting inductive link. These
modules represent advanced, micro-miniature sensing network. The
invention describes the combination of embedded microprocessors,
highly integrated sensor signal conditioners, digital data
converters, and the use of networking technics, especially for
smart structure application. As suggested in the invention, by
placing the aforementioned components on a flexible polyimide
substrate, addressable sensing modules may be directly bonded to
the surface of a composite structure's main load-bearing
components. Further, the material's final protective overcoat may
be used to embed them within the composite structure. The modules
can be adapted to the physical limitations dictated by each
specific application.
[0047] It can be concluded from the above overview of the prior art
methods of embedding/integrating of a broad spectrum of systems,
devices and networks into composite materials, structures and
textile fabrics, none of them had addressed the use of
three-dimensional woven, braided, knitted, stitch bonded fabrics or
preforms for composites, as the carriers of the said systems,
devices and networks. Furthermore, no intent can be traced in the
prior art of using textile processes and machinery for
incorporating said systems, devices and networks into the processes
of manufacturing such three-dimensional fabrics and preforms for
composites. The present invention is intended to fill this gap in
the prior art.
[0048] Generally, much of the relevant prior art may be categorized
as being within a few broad areas, including fiber optic sensors,
piezoelectric sensors/actuators/transducers, conducting fibers,
electronics assemblies/networks, and fabric diagnostics. Select
references from the prior art are identified and briefly described
and distinguished from the present invention hereinbelow.
[0049] Thus, there remains a need for a 3-D fabric having systems,
devices, and/or networks integrated therewith for providing a 3-D
fabric or preform for use on its own and/or as a composite.
SUMMARY OF THE INVENTION
[0050] The present invention is directed to a 3-D fabric having
systems, devices, and/or networks integrated therewith.
[0051] Preferably, the 3-D fabric is formed by 3-D weaving,
knitting, braiding, or other 3-D fabric forming method, or
combinations thereof, for providing an integral, unitary
structure.
[0052] The present invention is further directed to a method for
forming the 3-D fabric having systems, devices, and/or networks
integrated therewith, where the systems, devices, and/or networks
are introduced before, during or after the fabric-forming method
for a fabric or preform and prior to the formation of a composite
with the preform, where the fabric is intended to be used as or
within a composite structure.
[0053] Thus, the present invention solves the problems of the prior
art and/or introduces solutions not previously taught or suggested
in the prior art.
[0054] Accordingly, one aspect of the present invention is to
provide a 3-D fabric preform for composites including a
three-dimensional engineered fiber preform formed by intersecting
yarn system components; and at least one system, device, and/or
network integrated with the preform for providing a predetermined
function, wherein the at least one system, device, and/or network
is introduced prior to formation of a composite structure including
the preform, thereby providing a 3-D fabric preform for composites.
Another aspect of the present invention is to provide a method for
forming the 3-D fabric preform for composites including a
three-dimensional engineered fiber preform formed by intersecting
yarn system components; and at least one system, device, and/or
network integrated with the preform for providing a predetermined
function, wherein the at least one system, device, and/or network
is introduced prior to formation of a composite structure including
the preform, thereby providing a 3-D fabric preform for
composites.
[0055] These and other aspects of the present invention will become
apparent to those skilled in the art after a reading of the
following description of the preferred embodiment when considered
with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a perspective view illustrating an embodiment
according to the present invention.
[0057] FIG. 2 is a perspective view of another embodiment according
to the present invention.
[0058] FIG. 3 is another perspective view of an embodiment
according to the present invention.
[0059] FIG. 4 is a schematic of another embodiment according to the
present invention.
[0060] FIG. 5 is a schematic of another embodiment according to the
present invention.
[0061] FIG. 6 is a perspective view illustrating an embodiment
according to the present invention.
[0062] FIG. 7 is a perspective view of another embodiment according
to the present invention.
[0063] FIG. 8 is a perspective view of another embodiment according
to the present invention.
[0064] FIG. 9 is a perspective view of another embodiment according
to the present invention.
[0065] FIG. 10 is a perspective view of another embodiment
according to the present invention.
[0066] FIG. 11 is a side or edge view of another embodiment
according to the present invention.
[0067] FIG. 12 shows Flexible System/Device Materials Joining Base
Material in Fabric Formation Process by Addition.
[0068] FIG. 13 shows Flexible System/Device Materials Joining Base
Material in Fabric Formation Process by Substitution
[0069] FIG. 14 shows Rigid System/Device Materials Joining Base
Material in Fabric Formation Process by Addition
[0070] FIG. 15 shows Rigid System/Device Materials Joining Base
Material in Fabric Formation Process by Substitution
[0071] FIG. 16 shows Flexible System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Addition
[0072] FIG. 17 shows Rigid System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Addition
[0073] FIG. 18 shows Flexible System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Substitution
[0074] FIG. 19 shows Flexible System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Addition
[0075] FIG. 20 shows System/Device Materials Integrated during
Preforming Emerge in Dangling Fashion from Composite According to
Design
[0076] FIG. 21 shows System/Device Materials Integrated during
Preforming Meet Surface of Composite for Access According to
Design
[0077] FIG. 22 shows Example of 3-D Braided Fabric/Preform with
Integrated System/Device Materials
[0078] FIG. 23 shows a 3-D Braided T-Stiffener Preform Showing
Integration of System/Device Materials Along both Axial and
Braiding Pathways.
[0079] FIG. 24 shows a 3-D Multi-Axial Woven Fabric/Preform with
System/Device Materials Integrated into Warp, Fill and Bias
Pathways
[0080] FIG. 25 shows a 3-D Multi-Axial Warp-Knitted or
Stitch-Bonded Fabric/Preform with System/Device Materials
Integrated into Warp, Fill and Bias Pathways
[0081] FIG. 26 shows an Illustration of Addition or Substitution of
System/Device Materials into Fabric/Preform During Regular Fabric
Formation
[0082] FIG. 27 shows an Illustration of Addition or Substitution of
System/Device Materials into Fabric/Preform After Regular Fabric
Formation
[0083] FIG. 28 is a digital photograph of Optical fiber included in
fiber supply for additive integration into 3-D weaving.
[0084] FIG. 29 is a digital photograph of Laser light going into
network material in standard supply "creel" and into loom.
[0085] FIG. 30 is a digital photograph of Rigid EFPI is miniature
and was integrated automatically in 3-D weaving.
[0086] FIG. 31 is a digital photograph of Optical fiber emerging
from 3-D woven preform.
[0087] FIG. 32 is a digital photograph of 32 Preform being
processed into composite by VARTM method.
[0088] FIG. 33 is a digital photograph of Carbon fiber composite
beam test specimens with rigid integrated sensors along straight
paths.
[0089] FIG. 34 is a digital photograph of Fabric with integrated 11
optical fibers in 3 axes.
[0090] FIG. 35 is a digital photograph of Braided preform with
integrated optical fibers in axial looped circuit (2 round
trips).
[0091] FIG. 36 is a digital photograph of Composite produced with
preform having optical sensing fiber pulled in additively after
fabric formation; it contains hundreds of sensors.
[0092] FIG. 37 is a digital photograph of Heat from fingers
touching sensing fiber.
[0093] FIG. 38 is a digital photograph of Fibers and signal emerge
from completed fabric showing signal still coming from supply.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0094] In the following description, like reference characters
designate like or corresponding parts throughout the several views.
Also in the following description, it is to be understood that such
terms as "forward," "rearward," "front," "back," "right," "left,"
"upwardly," "downwardly," and the like are words of convenience and
are not to be construed as limiting terms.
[0095] Referring now to the drawings in general, the illustrations
are for the purpose of describing a preferred embodiment of the
invention and are not intended to limit the invention thereto. As
best seen in FIG. 1, a 3-D fabric preform for composites is
provided, generally referenced 10, for providing a
three-dimensional engineered fiber preform formed by intersecting
yarn system components 4, 6, and 8, respectively; and at least one
system, device, and/or network from a supply 12, 14 integrated with
the preform for providing a predetermined function, wherein the at
least one system, device, and/or network is introduced prior to
formation of a composite structure including the preform, as
illustrated in this figure, thereby providing a 3-D fabric preform
for composites. The supply may include a flexible network or device
12 and/or a rigid network or device 14.
[0096] In one preferred embodiment of the present invention, as
shown in FIG. 1, a fabric preform being formed on a fabric forming
machine includes, as part of the fabric forming process, the
addition and integration of at least one system, device, and/or
network along with the fiber systems used to form the fabric
structure; this may be done automatically, semi-automatically, or
manually, depending upon the specific system, device and/or network
being used.
[0097] In another preferred embodiment of the present invention, as
shown in FIG. 2, a fabric preform 18 that has already been formed
on a fabric forming machine is now having the addition and
integration of at least one system, device, and/or network 26, 20,
22, within the fiber systems used to form the fabric structure;
this may be done automatically, semi-automatically, or manually,
depending upon the specific system, device and/or network being
used. FIG. 2 further illustrates the addition of a device/network
material(s) by insertion, stitching, or as with "embroidery" 16, as
well as the addition of rigid device/network materials by
insertion, displacement, or pull-through along straight paths 20,
and the addition of flexible device/network materials by insertion,
displacement, or pull-through along straight paths 22.
[0098] FIG. 3 shows an example of a special shaped fabric or
preform with integrated network, device, and/or sensors. In
particular, flexible network/device/sensor materials are shown
following a convoluted path 24 and rigid flexible
network/device/sensor materials are shown following a straight
path.
[0099] FIG. 4 illustrates by a schematic view the addition of
network, device, and/or sensor materials to a textile system supply
28, which proceed through any textile processing system 30
according to the present invention as set forth herein, to provide
a textile fabric or preform 32 having integrated network, device,
and/or sensor materials therewith as part of the integral, unitary
construction of the 3-D fabric or preform.
[0100] FIG. 5 illustrates by a schematic view the addition or
substitution 42 of network, device, and/or sensor materials 44 into
a textile fabric or preform, wherein the fabric or preform are
first formed from a textile system supply 34 having standard
materials only in the supply, i.e., not including any network,
device, and/or sensor materials, the standard supply proceeding
through any textile processing system 36 according to the present
invention as set forth herein, to provide a textile fabric or
preform having integrated network, device, and/or sensor materials
therewith as part of the integral, unitary construction of the 3-D
fabric or preform 46.
[0101] The preform according to the present invention may be formed
by various fabric-forming processes, resulting in 3-D woven fabric,
3-D braided fabric, and/or 3-D multiaxial fabric structures. Where
a 3-D braided fabric is used, preferably the systems, devices,
and/or networks are provided in the axial direction of the
structure. In some specific systems, such as conductive components
or sensors may be used in other directions within the structure.
For a typical 3-D braided fabric formed on an automated machine, 64
carriers with holes or tubes for axial fibers are preferably used
to integrate the systems, devices and/or netowrks via the tubes
into the braided fabric in an automated manner. Semi-automated and
manual introduction may be used as well or as an alternative. In
the case of a 3-D multiaxial fabric, typically stitch-bonded or
multi-axial warp-knitted fabrics (stitched through the thickness)
or insertion fabrics (generally not composites applications) may be
used.
[0102] FIG. 6 is a perspective illustration showing the addition of
relatively smaller rigid system/device materials to certain
elements within a Multi-Axial Warp Knit, Stitch Bonded, or other
insertion fabric/perform such as that manufactured by the Liba,
Mayer, or other similar 3-D fabric formation processes. The
un-crimped in-plane pathways allow for the integration of both
rigid and flexible system/device materials. Knitting/Stitching
which alternate from top to bottom, binding the assembly, follow a
more complex path, allow for the integration of only the most
flexible system/device materials, while rigid system/device
materials may merely be inserted between the base yarns in the
through thickness direction as if a needle through fabric. As seen
in FIG. 6, rigid or flexible system, device, network, and/or sensor
materials 38 are added to the base materials; also, knitting or
stitching yarns 40 are shown, along with in-plane 0.degree.,
90.degree., +45.degree., -45.degree. yarns 42 in the base fabric
structure.
[0103] FIG. 7 is a perspective illustration showing the
substitution of relatively equal sized rigid system/device
materials for certain elements within a Multi-Axial Warp Knit,
Stitch Bonded, or other insertion fabric/perform such as that
manufactured by the Liba, Mayer, or other similar 3-D fabric
formation processes. The un-crimped in-plane pathways allow for the
integration of both rigid and flexible system/device materials.
Knitting/Stitching which alternate from top to bottom, binding the
assembly, follow a more complex path, allow for the integration of
only the most flexible system/device materials while rigid
system/device materials may merely be inserted between the base
yarns in the through thickness direction as if a needle through
fabric. As seen in FIG. 7, rigid or flexible system, device,
network, and/or sensor materials 46 are being substituted for the
base materials; also, knitting or stitching yarns 44 are shown,
along with in-plane 0.degree., 90.degree., +45.degree., -45.degree.
yarns 48 in the base fabric structure.
[0104] FIG. 8 is a perspective illustration showing the addition of
relatively smaller system/device materials to certain elements
within a Multi-Axial 3-D woven fabric/perform. The un-crimped
in-plane pathways allow for the integration of both rigid and
flexible system/device materials. Z-yarns, which alternate from top
to bottom of 3-D Multi-Axial weave, connecting the assembly, follow
a more complex path, which allows only for the integration of
continuous flexible system/device materials or discrete rigid
system/device materials. As seen in FIG. 8, rigid or flexible
system, device, network, and/or sensor materials 50 are being added
to the base materials; also, z-yarns 52 are shown, along with
in-plane 0.degree., 90.degree., +45.degree., -45.degree. yarns 54
in the base fabric structure.
[0105] FIG. 9 is a perspective illustration showing the
substitution of relatively equal sized rigid system/device
materials for certain elements within a Multi-Axial 3-D woven
fabric/perform. The un-crimped in-plane pathways allow for the
integration of both rigid and flexible system/device materials.
Z-yarns, which alternate from top to bottom of 3-D Multi-Axial
weave, connecting the assembly, follow a more complex path, which
allows for the integration of continuous flexible system/device
materials or discrete rigid system/device materials. FIG. 9 shows
isolated system, device, network, and/or sensor materials 56 in the
filling or bias direction, isolating base materials 58, and common
system/device materials 60 forming a simple circuit from the
isolated system, device, network, and/or sensor materials in the
filling or bias direction.
[0106] FIG. 10 is perspective illustration of how the system/device
materials in Filling or Bias directions are included in simple
circuit formed by planned intersections with system/device
materials in special Z-yarn. This is exemplary of how the sequence
of interlacement of various elements within the fabric may be
controlled or manipulated in three dimensions so as to allow
periodic access to a system/device, or to form planned
intersections with in-plane elements and thus circuits as desired.
As seen in FIG. 10, rigid or flexible system, device, network,
and/or sensor materials 62 are being substituted for the base
materials; also, z-yarns 64 are shown, along with in-plane
0.degree., 90.degree., +45.degree., -45.degree. yarns 66 in the
base fabric structure.
[0107] FIG. 11 is an edgewise illustration of how the system/device
materials in Filling or Bias direction are included in simple
circuit formed by planned intersections with system/device
materials in special Z yarn and the sequence of interlacement may
be controlled or manipulated so as to allow periodic access to a
system/device, or to form planned intersections with in-plane
elements and thus circuits as desired. FIG. 11 shows Z/Axial 74
having an altered path making intended intersection with other
system/device materials, a circuit path A-A 76, along with in-plane
0.degree., 90.degree., +45.degree., -45.degree. yarns 72, 70, 68,
respectively, in the base fabric structure.
[0108] FIG. 12 shows Flexible System/Device Materials Joining Base
Material in Fabric Formation Process by Addition.
[0109] FIG. 13 shows Flexible System/Device Materials Joining Base
Material in Fabric Formation Process by Substitution.
[0110] FIG. 14 shows Rigid System/Device Materials Joining Base
Material in Fabric Formation Process by Addition
[0111] FIG. 15 shows Rigid System/Device Materials Joining Base
Material in Fabric Formation Process by Substitution
[0112] FIG. 16 shows Flexible System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Addition
[0113] FIG. 17 shows Rigid System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Addition
[0114] FIG. 18 shows Flexible System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Substitution
[0115] FIG. 19 shows Flexible System/Device Materials Joining Base
Material after Initial Fabric Formation Process by Addition
[0116] FIG. 20 shows System/Device Materials Integrated during
Preforming Emerge in Dangling Fashion from Composite According to
Design
[0117] FIG. 21 shows System/Device Materials Integrated during
Preforming Meet Surface of Composite for Access According to
Design
[0118] FIG. 22 shows Example of 3-D Braided Fabric/Preform with
Integrated System/Device Materials
[0119] FIG. 23 shows a 3-D Braided T-Stiffener Preform Showing
Integration of System/Device Materials Along both Axial and
Braiding Pathways.
[0120] FIG. 24 shows a 3-D Multi-Axial Woven Fabric/Preform with
System/Device Materials Integrated into Warp, Fill and Bias
Pathways
[0121] FIG. 25 shows a 3-D Multi-Axial Warp-Knitted or
Stitch-Bonded Fabric/Preform with System/Device Materials
Integrated into Warp, Fill and Bias Pathways
[0122] FIG. 26 shows an Illustration of Addition or Substitution of
System/Device Materials into Fabric/Preform During Regular Fabric
Formation
[0123] FIG. 27 shows an Illustration of Addition or Substitution of
System/Device Materials into Fabric/Preform After Regular Fabric
Formation
[0124] FIG. 28 is a digital photograph of Optical fiber included in
fiber supply for additive integration into 3-D weaving.
[0125] FIG. 29 is a digital photograph of Laser light going into
network material in standard supply "creel" and into loom.
[0126] FIG. 30 is a digital photograph of Rigid EFPI is miniature
and was integrated automatically in 3-D weaving.
[0127] FIG. 31 is a digital photograph of Optical fiber emerging
from 3-D woven preform.
[0128] FIG. 32 is a digital photograph of 32 Preform being
processed into composite by VARTM method.
[0129] FIG. 33 is a digital photograph of Carbon fiber composite
beam test specimens with rigid integrated sensors along straight
paths.
[0130] FIG. 34 is a digital photograph of Fabric with integrated 11
optical fibers in 3 axes.
[0131] FIG. 35 is a digital photograph of Braided preform with
integrated optical fibers in axial looped circuit (2 round
trips).
[0132] FIG. 36 is a digital photograph of Composite produced with
preform having optical sensing fiber pulled in additively after
fabric formation; it contains hundreds of sensors.
[0133] FIG. 37 is a digital photograph of Heat from fingers
touching sensing fiber.
[0134] FIG. 38 is a digital photograph of Fibers and signal emerge
from completed fabric showing signal still coming from supply.
[0135] Manufacturing methods for, and resultant fiber/tow paths
within various 3-D fabrics or preforms may be manipulated and
exploited so as to allow a relatively easy integration of special,
actively or passively functional, flexural or rigid materials
within them, by adding said materials to one or more of the host
fibers/tows or, alternatively, by replacing one or more fibers/tows
with the said material. In this way, a fabric is created, which
includes various systems, devices, networks, etc. Such 3-D fabrics
and preforms containing integrated systems/devices/networks are the
principal object of this invention.
[0136] Some immediate examples are 3-D fabrics and preforms with
integrated optical fibers/fiber bundles and sensors integrated
within them, which is one particular object of this invention;
actuation means such as piezoelectric fibers, fiber bundles,
ribbons, and other suitable elongated bodies for shape control,
vibration and dynamic instability suppression, which is another
particular object of this invention; electrical conductors like
metal wires, filaments, strands made of stainless steel, copper,
carbon, or electrically conductive polymers, which is another
particular object of this invention. Besides, fast progress in the
area of microelectronics and nanomaterials makes it feasible to
associate complex microelectronic devices, systems and networks to
textile fibers/tows and then integrate them into 3-D fabrics and
preforms, which is yet another particular object of this
invention.
[0137] Making use of complex fiber architecture in 3-D weaves,
braids or knits provides endless opportunities for creating large
arrays or networks of sensors, actuators, circuits, conduits and
other systems and devices that may serve such purposes as
transmitting light, providing controllable light displays for
signals or screens or camouflage, conducting electricity and heat,
performing logical functions, providing data and power
infrastructure in structures, serving as antennae or emitters for
sound or electrical power radiation, shielding electromagnetic
waves, diffusing radiation or signals, inducing movement or shape
change, de-icing, just to mention a few.
[0138] The system/device materials of interest may be integrated
into 3-D fabric/preform during its formation on the respective
machine or mechanism during the regular textile process, which is
another object of this invention. Alternatively, they can be
integrated after the fabric/preform has been produced, which is yet
another object of this invention. Flexible system/device materials
may be introduced along any pathway followed by the regular
fiber/tow forming the fabric, specifically, in three, four or five
directions, which are most typical cases for the 3-D fabrics of our
primary interest. It is very important to ensure that going along
such pathways does not impart severe damage to the system/device
material, or does not substantially hurt the functional ability of
that system/device. The ability and freedom of the 3-D preforms to
provide straight pathways suitable for many device materials, while
at the same time providing efficient structural performance is an
advantage of the present invention over the inclusion of similar
device materials in 2D fabrics which are limited in this
respect.
[0139] Integration may take place in several fashions, including
simply substituting the system/device material for the fiber/tow
host material in desired locations during fabric formation,
addition of the system/device material to the host materials during
formation, replacement/substitution of the host materials after
formation, and addition of the system/device materials to the host
materials after formation. The described methods of integrating
relatively flexible systems/devices into 3-D fabrics and preforms
is another object of this invention. Straight (or nearly straight)
pathways used in 3-D textile manufacturing processes (the immediate
examples are warp fiber direction in 3-D orthogonal weaving,
multiaxial 3-D weaving or multi-axial knitting/stitch bonding, and
longitudinal fiber direction in 3-D braiding) allow even relatively
rigid materials to be used, along with the regular fibers/tows
without distortion or functional impingement to the integrated
system/device material. This statement has been thoroughly verified
through experimentation with both rigid and flexible optical
devices and fibers, ceramic fiber, and stainless steel wire bundles
on the available automated 3-D weaving and 3-D braiding machines.
The described methods of integrating relatively rigid
systems/devices into 3-D fabrics and preforms is another object of
this invention.
[0140] Prior to formation of the fabric with integrated
system/device material such as optical fiber, or metallic
conductor, or piezoelectric/magneto-strictive actuator/sensor, or
shape memory alloy element, may be wound together with the host
fiber/tow in the desired ratio onto the standard spools or beams,
thus forming a hybrid tow, which is loaded into the 3-D weaving,
braiding or knitting machine so as to be included in the fabric
formation process. Alternatively, the system/device material may be
used as substitute for some number of regular fibers/tows by adding
it to the supply of a textile machine as if weaving a simple plaid,
ribbed, or hybrid fabric. Where the effects of the additional
volume, mass, or other physical property of the system/device
material causes no undesirable effects, the system/device material
may be simply added to the existing host materials by methods
including but not limited to fastening the system/device material
to a host material and allowing it to be pulled into the already
formed fabric as a parasite, or by allowing the system/device
material to be inserted by the rapiers, needles, or fluid jets
along with the resident host material. Standard "color picker"s and
jacquard heddle controls used for plaids and upholstery fabrics
allow for on-demand placement of system/device material in looms,
and the grippers on standard rapiers can accommodate rigid
materials. The described methods of incorporating a system/device
material into the tow/yarn supply system is another particular
object of this invention.
[0141] The fundamental concept of integrating various
systems/devices into 3-D fabrics and fabric preforms described
above enables the next step, namely to manufacture polymer matrix,
ceramic matrix, metal matrix, carbon-carbon or carbon-silicon
composite materials and structures instrumented with such
systems/devices. This concept, which is the second principal object
of this invention, extends to any composite material, which can be
made with the use of the aforementioned instrumented fabric
preforms. Any suitable fabrication technique can be utilized for
this purpose. In the case of polymer matrix composites one can use
methods like Resin Transfer Molding, Vacuum Assisted Resin Transfer
Molding, Resin Film Infusion, Pultrusion, Hot Press Forming,
Autoclave Curing, etc. Of course, special care has to be taken to
protect the integrated system/device against elevated cure
temperatures/pressures or against elevated temperatures/pressures
required for thermal forming of a composite structural part. The
integrated system/device should not contain any structural
elements, adhesives, coatings or other (typically polymeric)
components that would not withstand the projected composite
processing and/or in-service temperatures/pressures.
[0142] The above requirement becomes much more severe in the case
of ceramic matrix, metal matrix and carbon-carbon composites, which
must be processed at high temperatures, and likely exposed to high
temperatures in service. The selection of appropriate
systems/devices that can be safely integrated into these types of
composites without special thermal protection means asks for
special attention and care. For example, even if pure glass fibers
and pure ceramic fibers can withstand high temperatures used for
processing some of the aforementioned composites, conventional
fiber optic sensors or piezoceramic actuators based, respectively,
on glass or ceramic materials, may include various polymeric
elements (claddings, substrate films, insulating casings, etc.),
which will not withstand the high processing or in-service
temperatures. To substantiate this point, we make a reference to
U.S. Pat. No. 5,338,928, where it was suggested that "an optical
fiber capable of high temperature environments can be inserted into
the structure prior to chemical vapor infiltration as in the case
of CMCs or prior to plasma spraying, foil-fiber-foil construction,
or other assembly methods as in the case of MMCs". However,
according to that patent, each optical fiber was clad with an inert
cladding, such as gold or iridium. Also, gold-coated silica fibers
or sapphire fibers were suggested as the preferred types of fibers
for integration into high-temperature composites.
[0143] Piezoelectric sensors/actuators commonly used for embedment
into graphite fiber composite laminates require a suitable
insulating casing, which can be, for example, a polyimide film
Kapton, as suggested in U.S. Pat. No. 5,195,046 or a fiberglass
fabric/epoxy composite, as recommended in U.S. Pat. No. 5,305,507.
Of course, other suitable approaches can be explored. One possible
solution, which is another object of this invention, is inspired by
the nature of 3-D fabrics. Its essence is to functionally hybridize
the fabric, i.e., substitute glass fiber or other insulating
material fiber tows for some of graphite fiber tows in those parts
of the fabric where piezoelectric sensors/actuators have to be
integrated. This approach enables to naturally surround the
piezoelectric element with sufficient amount of insulating material
fibers and thus ensure its insulation from graphite fibers
contained in the other neighboring tows.
[0144] Electrical conductors, like metallic wires/fibers/strands or
polymeric conducting fibers/yarns, represent another category of
systems/devices that can be integrated into 3-D fabrics, preforms
and composites, though they require special treatment before being
used in the integration process. Depending on the functional
purpose, different pre-integration treatments of this kind
systems/devices can be applied. They may be intentionally left bare
and allowed for mutual contacts at the crossover points, thus
providing a conductive circuit. They may be left bare, but in a
non-interlacing pattern (as dictated, for example, by the
application considered in U.S. Pat. No. 5,210,499). They can be
locally insulated by polymeric fibers/tapes or may be separated at
the crossover points by special electrically partially resistive
material (like in the case of the pressure sensor construction in
U.S. Pat. No. 4,795,998). Some of these requirements can be
naturally fulfilled by using another object of this invention,
which is to purposefully choose those layers of warp, weft, and/or
bias fibers/tows and specific locations within the 3-D fabric,
where the electrically conductive system/device should be
integrated. Yet, according to another object of this invention, an
electrically conductive system/device, depending on its intended
functional designation, can be either left bare without a host tow
(e.g. by using the substitution approach) or being encapsulated
within the necessary amount of insulating fibers of its host tow
(e.g. by using the addition approach). With no doubt, the
capability of using 3-D fabrics as the carriers of various
conducting systems/devices/networks far exceeds the capability of
2-D fabrics and will inspire new efficient solutions.
[0145] Other technicalities of the invention in the parts of
manufacturing 3-D fabrics, preforms and composites, will be clear
to those skilled in the art, after getting familiar with the
illustrations, their detailed description, and several reduction to
practice examples.
[0146] The systems, devices, and/or networks integrated with the
preform of the present invention are generally not required to
provide any structural function within the preform, although they
may optionally do so in particular embodiments.
[0147] In one embodiment of the present invention, optical fibers
are integrated within the fabric preform of the present invention
prior to composite formation, where the preform is intended for
later use as a composite material or component.
[0148] Both optical capabilities and structural characteristics may
be enhanced by using ribbons or bundles of fibers in place of
single, discrete fibers integrated with the fabric preform of the
present invention. Ribbons may comprise parallel strands for
scanning devices, or interlaced strands to add structural integrity
to the composite. Alternatively, interwoven bundles may be employed
for structural purposes or to provide large cross section optical
paths for illumination energy to be conducted from remote light
sources to areas where illumination is desired for enhancing
vision.
[0149] The present invention further includes a method for forming
a 3-D preform for composites including the steps of: providing yarn
system component for forming a three-dimensional engineered fiber
preform formed by intersecting textile system components; and
providing at least one system, device, and/or network integrated
with the preform for providing a predetermined function, wherein
the at least one system, device, and/or network is introduced prior
to formation of a composite structure including the preform,
thereby providing a 3-D fabric preform for composites. Additional
steps may include introducing device/network materials to the
textile system supply for integration with the preform in at least
one fiber or pathway of the network materials; and producing the
preform via a textile processing system; thereby producing a 3-D
fabric having integrated networks/devices therein. Furthermore, the
at least one fiber or pathway of the network materials, device
and/or sensors may either be a substantially straight pathway, as
in the case of optical fibers, especially glass fibers, or the at
least one fiber or pathway may be flexible, as in the case of a
flexible material/fiber where a non-straight pathway, e.g., an
electrical circuit or network produced by integration of a
plurality of convoluted pathways having predetermined intersection
or contact points. Importantly, the method of the present invention
provides for the introduction of the systems, devices, and/or
networks and integration thereof with the preform prior to any
composite formation steps, which obviously are intended to occur
after the integration of the components with the preform according
to the present invention where the preform is intended for use as a
composite material.
[0150] Other method steps may be included or substituted without
departing from the scope of the present invention, depending upon
the particular systems, devices, and/or networks and combinations
thereof that are integrated with the 3-D fiber preform and the
application for the composite material that may ultimately be
formed therewith.
[0151] The systems, devices, and/or networks integrated with the
preform of the present invention are generally not required to
provide any structural function within the preform, although they
may optionally do so in particular embodiments.
[0152] In one embodiment of the present invention, optical fibers
are integrated within the fabric preform of the present invention
prior to composite formation, where the preform is intended for
later use as a composite material or component.
[0153] Both optical capabilities and structural characteristics may
be enhanced by using ribbons or bundles of fibers in place of
single, discrete fibers integrated with the fabric preform of the
present invention. Ribbons may comprise parallel strands for
scanning devices, or interlaced strands to add structural integrity
to the composite. Alternatively, interwoven bundles may be employed
for structural purposes or to provide large cross section optical
paths for illumination energy to be conducted from remote light
sources to areas where illumination is desired for enhancing
vision.
[0154] Regarding conductive materials, a conductor may comprise
single- or multi-stranded wires, and suitable materials include
stainless steel, tinned copper or carbon fiber.
[0155] Regarding applications wherein a structural component has
piezoelectric fiber composite the structural layers are made, for
example, of standard carbon fiber reinforced composite material.
Preferred embodiments include epoxy polymers, which are chemically
and mechanically compatible with the polymers in the host composite
structures, i.e., the piezoelectric composite epoxy is bondable to
the structural composite epoxy and has similar mechanical and
electrical properties. Preferably, the conductive layers are in
direct contact with the fibers. The conductive electrode layers are
relatively flexible. Thin metal layers are desirable, because they
do not restrain the composite of the structural component during
actuation. Silver is preferred. Other metals, which may be used,
include aluminum, copper, and gold, as well as non-metallic
conductors such as conductive polymers. In embodiments, the
electrode layers may be formed of a thin polymer substrate coated
with an ultra-thin layer of metal. The electrodes may be etched in
a pattern. The electrode layers may adhere directly to structural
materials.
[0156] The composites may be used in many structural components.
For example, in aeroelastic structures for active control of
composite wings to suppress flutter at high airspeeds by applying
AC fields, thereby effectively increasing the top speed of an
aircraft. The composites can be used for both sensing and actuation
in a closed-loop configuration. The anisotropic nature of
piezoelectric displacement can be maximized by choosing a polymeric
material and piezoelectric ceramic material, which have large
differences in their mechanical stiffnesses.
[0157] In the embodiment where a health monitoring system is used
with the present invention, it may be based on the use of vibration
signature of the structure to determine its mechanical and thermal
state. Sensor modules are located throughout the structure and are
connected to the host CPU by the high speed databus, by way of
example and not limitation. A principle underlying the operation of
a Health Monitoring System (HMS) of the present invention is the
use of specimen vibration signatures to determine mechanical and
thermal properties. A specimen vibration signature is derived from
the dynamic response or reaction of the structure to a stimulus.
Such dynamic response typically is the varying electrical output of
transducers attached to the structure. The HMS applies this concept
to obtain dynamic response characteristics corresponding to failure
or damage of structural components. Specifically, HMS mechanically
excites the structure and monitors its dynamic response through
sensors or feedback transducers. The excitation energy is
preferably in the form of a single pulse, which generates a
wideband frequency range of vibration of the structure. The
feedback transducers are preferably piezoelectric film transducers.
Pattern recognition techniques are used to process vibration
signals and classify the type and location of structural damage. In
addition to the pattern recognition techniques, key components of
the overall HMS include intelligent sensor modules, a host central
processing unit (CPU), and a high speed databus. The sensor module
contains an actuation mechanism to generate a physical impulse and
apply it to the structure, and feedback transducers and signal
processing circuitry to detect the corresponding vibration signals,
process them, and transmit the preferably digitized data to the
host CPU when queried. The sensor module is also provided with an
embedded processor for controlling the actuation mechanism as well
as for data acquisition. The host CPU executes pattern recognition
software which distinguishes among fatigue cracks, rivet line
failure, ice or material buildup on the structure, and other
disturbances.
DESIGN EXAMPLE(S)
[0158] This section outlines a few design examples, not necessarily
optimized or intended to limit the scope of the invention thereto,
but illustrative of what can be done for a fabric preform having
integrated systems, devices, and/or networks according to the
present invention, wherein the systems, devices, and/or networks
are integrated with the preform prior to composite formation, where
the fabric is intended for later composite applications. These
design examples include, but are not limited to, the following:
[0159] In the practical implementation of the present invention,
various embodiments may be constructed using a range and
combination of many types of system or device materials according
to the desired function of the complete system or device within the
fabric or composite structure/part made with it. Combinations of
passive, active, conductive, fluidic conduit, optical conduit and
many more may be employed so to achieve the desired functions.
Among the most commonly desired features of diagnostics and health
monitoring of a structure or part is to determine, measure, or
monitor the strain, stress, damage, delamination, cracks,
temperature, moisture, acceleration, and other performance
characteristics, which are usually hidden in the interior of the
materials or in parts of the structure which are difficult to
access for inspection, as was described in section "BACKGROUND OF
THE INVENTION". This is one of many applications referred to as
smart materials or smart structures. Current application of optical
sensors in aircraft and spacecraft requires bonding optical sensors
to the surfaces, or embedding them between plies of a laminated
composite. This leaves delicate fibers exposed, the fibers may move
during infusion or curing, and may induce delamination along the
delicate bond line between the laminate plies.
[0160] Several prototypes of embodiment of the present invention
have been demonstrated toward this particular purpose. It should be
noted that the prototypical demonstrations are not exhaustive but
rather exemplary of modifications to composite construction methods
and might be considered a sub-element of a larger composite
structure or vehicle such as a fuselage section, hull skin, wing
panel, composite beam or strut within a boat or aircraft, windmill
blade, or rotor shaft among others.
[0161] Continuous supply of warp (axial) optical fiber from creels
or beams has proven to be quite suitable in automation. Likewise,
continuous optical fibers were placed uncut repeatedly, back and
forth, across the width of the preform in the weft direction at
several levels forming a regular grid. The transmitted light
intensity was measured during weaving and efficiencies found to be
suitable. Experimental data collected from tested specimens allowed
mapping strains and clearly indicated internal strain gradients
near stress risers and loading sites.
[0162] Manufacture of said smart structure prototypes included the
accomplishment of several step-wise tasks. Automated production of
preforms for composite materials instrumented with fiber optic
sensors has been performed. Optical fibers and sensors have been
integrated into 3-D woven and 3-D braided preforms by addition, and
substitution, both before and after initial preform fabric
formation. Continuous automated integration of optical fibers into
3-D weaving process during fabric formation was performed, sensors
of both rigid and flexible types were integrated into 3-D fabrics,
several methods were utilized to mark and map optical fiber and
sensor positions within composites, demonstration of various
methods of connection to the optical systems have been applied and
refined, and testing of composite coupons instrumented with large
number of integrated sensors has yielded useful data quantifying
the internal strain state of the material.
[0163] In one particular demonstration, eleven spools were wound
with one optical fiber each having acrylic coating, the bound end
of each was connected to by fusion slicing, whereupon those same
spools were mounted in a creel, and in filling stands, along with
hundreds of other spools having variously carbon, glass, or Kevlar
tows arranged to supply the weft, warp, and z yarns to a loom for
producing a multi-layer 3-D woven hybrid fabric. The free end of
each optical fiber was passed through standard, or modified guides
so as to merge with selected base fabric structural fibers in the
warp, weft, and z directions within the fabric. Those optical
fibers added to the weft supply merged with the weft yarns near the
tips of the rapiers used by the machine during insertion of weft
yarns during the process of weaving and passed through the final
rapier eyelets as an integral part of the weft yarn at that point
during weaving. The z yarns were passed through particularly chosen
heddles and followed those harness motions during weaving. A laser
detector was connected to the optical fibers near the fell of the
fabric at the loom after the optical fibers were teased from their
parent and carrier structural fibers. Laser light was injected into
the optical fibers at the supply spool, and the intensity of the
light transmitted was documented during weaving as all effects of
the weaving system and the effects of integration in the fabric
accumulated. Light transmission was found to be suitable,
efficient, and particularly so in the straight, in-plane
weft-directional optical fibers. Results of weaving trials showed
that transmission efficiencies are nearly unaffected by the fiber
path in the warp and weft directions within the fabric. Losses do
occur at tight bends in the z-directional fibers at the bends seen
at the top and bottom surfaces, though those losses may be
mitigated by manipulation of the z yarn paths and choice of fiber
and signal types.
[0164] In another demonstration, one E-glass 3-D braided preform
was produced containing 4 optical fibers incorporated in axial
tows. Transmission efficiency was measured after braiding. Not
surprisingly, the losses in the practically straight axial fibers
were very low.
[0165] In another demonstration, at least 9 EFPI fiber optic
sensors with 830 nm optical fiber leads were integrated into an
8-weft and 7-warp layer 3-D woven carbon fiber preform during
weaving on a digitally controlled automated 3-D weaving machine.
The rigid sensors and their flexible leads were carried into the
fabric along with the regular carbon fiber material in the weft
direction periodically, and in several of the 8 weft layers within
the 0.8 inch thick multi-layer fabric. The preform was cut in the
weft direction down to nominally 12".times.18". Each of the fibers
having one EFPI sensor along their length passed across the preform
intimately with one carbon weft yarn yielding a preform with 9 EFPI
sensors at several depths through the fabric. Additionally, during
momentary pauses of the loom, several EFPI sensors were placed
through the thickness of the fabric by lowering them through the z
corridor at the fell until stopped by a tape flag adhered at a
known location leaving the EFPI suspended at a known depth in the
fabric when the loom was released, and the fabric continued to
form. Also, certain of the sensor/fiber assemblies had FC type
connectors applied prior to weaving and as such, those connectors
were integrated into the fabric and were located at the selvedge of
the same. The ends of the sensing fibers were left long, extending
as if fringe beyond the edges of the fabric, and the z axis sensor
leads were bent 90 degrees at the surface and integrated into the
topmost weft yarn until they reached the edge of the fabric.
[0166] The 3-D carbon fiber preforms were placed under a simple
vacuum bag on a flat surface with an olefin platen on top, and with
vacuum grease packed into the connectors to exclude resin from
them, while the free ends of the optical fibers were sleeved with a
small flouro-polymer tubes, and passed across and shallowly
embedded in the mastic vacuum seal. The preform was infused with an
epoxy modified vinyl-ester resin, cured at room temperature,
removed from the bag, and post-cured for several hours at 250 F per
the resin manufacturers recommendations. Three instrumented test
coupons were cut from different sections of the same panel.
Connections to those fiber ends left free were made by cleaving,
and fusion splicing of FC connecterized 1550 nm SMF leads, using a
Fujikura semi-automated splicer. Connection to those fibers with
the connectors woven in were made by rinsing out the grease, and
mating with the corresponding male FC connector to the
interrogation system. Finally, resistive foil strain gauges were
adhered to the surfaces as references, and the internally
instrumented composite specimen was mechanically tested in 4-point
bending. The optical sensors were interrogated during loading by
commercially available demodulation systems. Strains at several
points within the composite beams were displayed in real time
during loading, and clearly reflected internal strain gradients
within the composite material near stress risers and loading
sites.
[0167] In another demonstration, at least 16 EFPI fiber optic
sensors with 830 nm optical fiber leads were integrated into a 7
weft.times.6 warp layer 3-D woven carbon fiber preform during
weaving on a digitally controlled automated 3-D weaving machine.
The rigid sensors and their flexible leads were carried into the
fabric along with the regular carbon fiber material in the weft
direction periodically, and in several of the 7 weft layers within
the 0.5 inch thick multi-layer fabric. The preform was cut in the
weft direction. Each of the fibers had one EFPI sensor along their
length passed across the preform intimately with one carbon weft
yarn yielding a preform with 9 EFPI sensors at several depths
through the thickness. Additionally, during momentary pauses of the
loom, several EFPI sensors were placed through the thickness of the
fabric by inserting them through the z corridor at the fell until
stopped by a tape flag adhered at a known location, leaving the
EFPI suspended at a known depth in the fabric when the loom was
released, and the fabric continued to form. Also, certain of the
sensor/fiber assemblies had FC type connectors applied prior to
weaving, and as such, those connectors were integrated into the
fabric and were located at the selvedge of the same. The ends of
the sensing fibers were left long, extending as if fringe beyond
the edges of the fabric, and the z axis sensor leads were bent 90
degrees at the surface and integrated into the topmost weft yarn
until they reached the edge of the fabric.
[0168] The 3-D carbon fiber preforms were placed under a simple
vacuum bag on a flat surface with an olefin platen on top, while
the free ends of the optical fibers were sleeved with a small
flouro-polymer tubes, and passed across and shallowly embedded in
the mastic vacuum seal. The preform was infused with an epoxy
modified vinyl-ester resin, cured at room temperature, removed from
the bag, and post-cured for several hours at 250 F per the resin
manufacturers recommendations. Three instrumented test coupons with
special notch-like features were milled from the same panel using
carbide cutters. Connections to those fiber ends left free were
made by cleaving, and fusion splicing of FC connecterized leads,
using a semi-automated splicer. Finally, resistive foil strain
gauges were adhered to the surfaces as references, and the
internally instrumented composite specimen was mechanically tested
in tension. The EFPI sensors were interrogated during loading by
commercially available demodulation systems. Strains in the test
direction and through thickness at several points within the
composite beams were monitored using the sensors in real time
during loading, and clearly indicated internal strain gradients
near the notches.
[0169] In another demonstration, at least ten flexible DSS brand
optical fibers manufactured by Luna Innovations were integrated
into a previously formed 3-D woven carbon fiber preform in the weft
direction by attaching the optical fibers to duplicates of the
selected host yarns, fastening the joined pair to the selected host
yarn and pulling out the host, thereby replacing the regular yarn
with the instrumented yarn. This was performed periodically, and in
five of the nine layers within the 0.235 inch thick multi-layer
fabric, which had been cut to nominally 12".times.18". Each of the
optical fibers having multiple Bragg gratings each 5 mm long and
paced every 10 mm along the fiber length passed across the preform
intimately with one carbon weft yarn, returned with another and so
on, yielding a preform with more than 360 Bragg grating sensors
within the confines of the preform. The ends of the sensing fibers
were left long, extending as if fringe beyond the edges of the
fabric. The 3-D carbon fiber preforms were then placed under a
simple vacuum bag on a flat surface while the free ends of the
optical fibers were sleeved with a small flouro-polymer tubes, and
passed across and shallowly embedded in the mastic vacuum seal. The
preform was infused with an epoxy modified vinyl-ester resin, cured
at room temperature, removed from the bag, and post-cured for
several hours at 250 F per the resin manufacturers recommendations.
Connections were made by cleaving, and fusion splicing of FC
connecterized 1550 nm SMF leads, using a Fujikura semi-automated
splicer. Notches were machined into certain specimens after elastic
testing with 1/2 hole at each edge, thus inducing a strain
gradient. Finally, resistive foil strain gauges were adhered to the
surfaces as references, and the internally instrumented composite
specimens were mechanically tested in 4-point bending. The Bragg
gratings were interrogated during loading by commercially available
demodulation equipment produced by Luna Innovations. Strains at
hundreds of points were displayed in real time during loading, and
clearly indicated internal strain gradients near stress risers and
loading sites.
[0170] In another demonstration, at least eighteen flexible DSS
brand optical fibers manufactured by Luna Innovations were
integrated into a previously formed 3-D woven carbon fiber preform
in the weft direction periodically, and in five of the nine layers
within the 0.235 inch thick multi-layer fabric which had been cut
to nominally 12".times.24". Each of the optical fibers having
multiple Bragg gratings each 5 mm long and spaced every 10 mm along
their length passed across the preform intimately with one carbon
weft yarn, returned with another and so on, yielding a preform with
more than 550 Bragg grating sensors within the confines of the
fabric. The ends of the sensing fibers were left long, extending as
if fringe beyond the edges of the fabric. The 3-D carbon fiber
preforms were placed under a simple vacuum bag on a flat surface,
while the free ends of the optical fibers were sleeved with a small
flouro-polymer tubes, and passed across and shallowly embedded in
the mastic vacuum seal. The preform was infused with an epoxy
modified vinyl-ester resin, cured at room temperature, removed from
the bag, and post-cured for several hours at 250 F per the resin
manufacturers recommendations. Two sensor instrumented, and two
sensor-free coupons were cut from different sections of the same
panel and bonded to form a double-lap joint specimen using epoxy
adhesive. Connections were made by cleaving, and fusion splicing of
FC connecterized 1550 nm SMF leads, using a Fujikura semi-automated
splicer. Next, resistive foil strain gauges were adhered to the
surfaces as references, and the internally instrumented double-lap
composite bonded joint specimen was mechanically tested in tension.
The Bragg gratings were interrogated during loading by commercially
available demodulation equipment produced by Luna Innovations.
Strains at hundreds of points were displayed in real time during
loading.
[0171] Certain modifications and improvements will occur to those
skilled in the art upon a reading of the foregoing description. All
modifications and improvements have been deleted herein for the
sake of conciseness and readability but are properly within the
scope of the following claims.
* * * * *