U.S. patent application number 12/817909 was filed with the patent office on 2010-12-09 for multiple function, self-repairing composites with special adhesives.
Invention is credited to Carolyn Dry.
Application Number | 20100308276 12/817909 |
Document ID | / |
Family ID | 37605068 |
Filed Date | 2010-12-09 |
United States Patent
Application |
20100308276 |
Kind Code |
A1 |
Dry; Carolyn |
December 9, 2010 |
MULTIPLE FUNCTION, SELF-REPAIRING COMPOSITES WITH SPECIAL
ADHESIVES
Abstract
A system for self-repairing matrices such as concrete or
cementitous matrices, polymeric matrices, and/or fibrous matrices,
including laminates thereof. The system includes repair agents
retained in and/or on vessels, such as hollow fibers, within the
matrix. Upon impact, the vessel rupture, releasing the chemicals.
For multi-layer laminates, the systems provides a total dynamic
energetic circulation system that functions as an in situ fluidic
system in at least one layer or area. The energy from the impact
ruptures the vessels to release the chemical(s), and mixes the
chemical(s) and pushes the chemical(s) and/or resulting compound
through the matrix. The repair agents can withstand high
temperatures, such as the heat of processing of many laminates,
e.g., 250-350.degree. F.
Inventors: |
Dry; Carolyn; (Winona,
MN) |
Correspondence
Address: |
ALLISON JOHNSON, P.A.
3500 AMERICAN BLVD. W., SUITE 690
MINNEAPOLIS
MN
55431
US
|
Family ID: |
37605068 |
Appl. No.: |
12/817909 |
Filed: |
June 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11428132 |
Jun 30, 2006 |
7811666 |
|
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12817909 |
|
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60695548 |
Jul 1, 2005 |
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Current U.S.
Class: |
252/502 ;
252/500; 977/742; 977/932 |
Current CPC
Class: |
Y10T 428/24744 20150115;
B32B 2605/00 20130101; B32B 9/04 20130101; B32B 2250/05 20130101;
B32B 9/007 20130101; Y10T 428/249954 20150401; B32B 2307/306
20130101; Y10T 442/2008 20150401; Y10T 428/2971 20150115; Y10T
428/249974 20150401; B32B 2603/00 20130101; Y10T 428/30 20150115;
C04B 2111/28 20130101; C04B 28/02 20130101; C04B 28/02 20130101;
Y10T 428/2902 20150115; Y10T 428/2924 20150115; Y10T 428/31678
20150401; B32B 2250/42 20130101; B32B 2457/00 20130101; B32B
2307/558 20130101; C04B 2111/00612 20130101; Y10T 428/249924
20150401; B32B 2419/00 20130101; B32B 9/02 20130101; B29C 73/22
20130101; B32B 2262/101 20130101; B29K 2105/06 20130101; B32B
2307/762 20130101; Y10T 428/249921 20150401; Y10T 428/249994
20150401; C04B 14/42 20130101; C04B 14/42 20130101; C04B 24/24
20130101; C04B 14/34 20130101; B32B 7/04 20130101; Y10T 428/249971
20150401; C04B 28/02 20130101; Y10T 428/2913 20150115 |
Class at
Publication: |
252/502 ;
252/500; 977/932; 977/742 |
International
Class: |
H01B 1/04 20060101
H01B001/04 |
Claims
1. A multifunctional composite comprising: a matrix; conduits
disposed in the matrix; and a chemical disposed in the conduits,
the composite being at least one of able to repair damage due to
ballistic force, conductive, radar absorbing, self-repairing when
damaged, self-sensing when damaged, electricity generating when
damaged, and internally pumping when damaged, wherein when the
composite is self-repairing or self-sensing, the composite also is
at least one of able to repair damage due to ballistic force,
electricity generating when damaged, internally pumping when
damaged, conductive, and radar absorbing.
2. The composite of claim 1, wherein the composite is conductive
and further comprises at least one of an antioxidant, an
anticorrosive, and conductive particles.
3. The composite of claim 1, wherein the composite is
self-repairing, self-sensing, able to repair damage due to
ballistic force, internally pumping when damaged, and
conductive.
4. The composite of claim 3, wherein the composite is electricity
generating when damaged, radar absorbing or a combination thereof,
and further comprises at least one of an antioxidant, an
anticorrosive, and conductive particles.
5. The composite of claim 1, wherein the composite is
self-repairing and able to repair damage due to ballistic
force.
6. The composite of claim 5, wherein the composite is
self-sensing.
7. The composite of claim 5, wherein, when the conduit is damaged,
the chemical foams or becomes thixotropic.
8. The composite of claim 5, wherein the conduits are in the form
of at least one of springs and channels.
9. The composite of claim 1, wherein the composite absorbs radar
and is at least one of self-sensing, electricity generating, and
conductive.
10. The composite of claim 1, wherein the composite is
self-repairing and self-sensing and further comprises metal.
11. The composite of claim 1, wherein the conduit comprises at
least one wall and optionally a coating, the composite further
comprising a conductive material, the conductive material being
present in at least one of the at least one wall of the conduit,
the optional coating on the conduit, the chemical in the conduit,
and the matrix.
12. The composite of claim 11 further comprising additives
comprising at least one of nanotubes, metals, and carbon black.
13. The composite of claim 11, wherein the composite is
self-repairing and self-sensing.
14. The composite of claim 1, wherein the conduits are in the form
of at least one of springs, porous walled fibers, and channels.
15. The composite of claim 1, wherein the conduits comprise an
interior wall, the interior wall being coated with an acid.
16. The composite of claim 15, wherein the composite is
self-repairing.
17. The composite of claim 1, wherein the composite exhibits
internal pumping when damaged.
18. The composite of claim 17, wherein the composite is
self-repairing.
19. A multifunctional composite comprising: a conductive material;
a matrix; a plurality of conduits disposed in the matrix, each
conduit defining a volume and comprising at least one wall and
optionally a coating on the conduit; and a chemical disposed in the
conduits, the conductive material being present in at least one of
the optional coating on the conduit, the wall of the conduit, the
volume defined by the conduit, the chemical, and the matrix.
20. The composite of claim 19, wherein the composite is
self-sensing, the conduits are conductive and in a form of a web, a
grid, a weave, a three dimensional array, or a combination thereof,
and the chemical is reactive with the matrix, and further comprises
a dye that changes color when the chemical reacts with the matrix,
and conductive additives selected from the group consisting of
nanotubes, metals, and carbon black, when the composite is damaged,
the damage is detectable by eddy currents.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuing application of U.S. Ser.
No. 11/428,132, filed on Jun. 30, 2006, which claims the benefit of
U.S. Provisional Patent Application Ser. No. 60/695,548, filed Jul.
1, 2005, entitled Systems for Self Repair & Adhesives for Self
Repair of Composites, all of which are incorporated herein by
reference in their entirety.
BACKGROUND
[0002] The present invention generally relates to matrix materials
for use in a wide variety of end use fields and applications. More
particularly, the invention relates to self-repairing, settable or
curable matrix material systems, containing reactive chemicals used
in conjunction with release vessels or conduits such as fibers, the
functions of which may be multiple.
[0003] Composites include at least two materials: the matrix and
inclusions, such as reinforcement fibers or particles. Failures
often occur at the interfaces between the matrix and fibers or
particles. To prevent failure and fatigue, good bonding between the
materials is needed. Numerous systems and techniques for repairing
failed composites have been proposed.
[0004] Dry, a former professor at the University of Illinois, in
several patents the invention for which she conceived and developed
independently by 1990, e.g., U.S. Pat. Nos. 6,261,360, 5,989,334,
5,660,624, 5,575,841, and 5,561,173, described a cured matrix
having a plurality of hollow release vessels, usually fibers,
dispersed therein, the hollow fibers having a selectively
releasable modifying agent contained therein, means for maintaining
the modifying agent within the fibers until selectively released,
and means for permitting selective release of the modifying agent
from the hollow fibers into the matrix material in response to at
least one predetermined external stimulus. The cured matrix
materials have within them smart fibers capable of delivering
repair agents into the matrix wherever and whenever they are
needed.
[0005] In Dry's patents discussed above, damage was repaired by
fibers containing modifying agent. Dry found that fibers, for
retaining the chemical modifying agent, were easier to break than
beads, they could cover damage which occurred over a larger area,
could preserve strength of the structure, could act as a reservoir
to retain larger volumes of agent therein than beads and, if the
ends protruded, more chemical could be added.
[0006] Another researcher group, Professors Sottos, White and Moore
at the University of Illinois, has made various attempts to provide
self-healing composites starting in 1993, nearly 4 years after
Dry's initial work. One design was to use a fairly expensive active
chemical, such as dicyclopentadiene (DCPD) or Grubbs ruthenium in
the matrix with dicyclopentadiene (DCPD) in beads. See, for
example, U.S. Pat. No. 6,518,330. This approach, using very small
beads and such a living chemical system, was designed to not
require much force of damage but instead relied on small forces and
predict a an automatic full reaction to pull the chemical out of
the bead beads once the reaction has started. An article in Nature
magazine by White, S., Sottos, N., et al., Autonomic Healing
Polymer Composites, Feb. 15, 2001 describes this. However, the
research group later discovered that the Grubbs ruthenium ruins the
polymer matrix as described in. Their solution was to encapsulate
the ruthenium; see U.S. Patent Publication No. 2005/0250878 A1,
entitled "Wax particles for protection of activators, and
multifunctional autonomically healing composite materials". Their
solution was to encapsulate the Grubbs ruthenium in wax in the
matrix.
[0007] Subsequently, an elaborate system, called microfluidics, was
developed by this group at the University of Illinois that included
forming multiple layers of tubes, from a solidified ink which is
then coated and the ink removed based on an ink developed at Sandia
labs. The system includes in the matrix, a pump, valves in tubes to
control chemical flow, and mixing towers to provide among other
capabilities, composites with self-repair properties. See, for
example, U.S. Patent Publication No. 2004/0226620 "Microcapillary
networks". See also, for example, FIG. 10, which schematically
illustrates the self-repairing system with microfluidic aspects
developed by University of Illinois. It requires a separate form
piece for all the functions such as mixing towers, delivery tubes
in all or most layers, a pump and valves to start and stop the flow
in the tubes. The valves could be operated based on pH, and
suggestions by others have been made to use light to modulate the
valves.
[0008] U.S. Pat. No. 5,803,963 to Dry describes a self forming
composite with an ongoing chemical reaction in which one chemical
is released from a fiber into a mold containing two powders and
that chemical reacts with one powder in the mold and in that
reaction, a product is produced which reacts with the other powder
in the mold. A polymer ceramic can be made in this way or other
self forming composites.
[0009] U.S. Pat. No. 6,750,272, described a method for making a
fiber-reinforced composite, the method including dispensing a
reactive liquid into a mold, with the mold including fibers and a
single-component activator on the fibers.
[0010] U.S. Patent Publication No. 2004/0007784 to Skipor et al.,
who worked with the White group at University of Illinois,
describes a self-healing polymer composition containing a polymer
media and a plurality of microcapsules or beads of flowable
polymerizable material dispersed in the polymer media, where the
microcapsules of flowable polymerizable material contain a flowable
polymerizable material and have an outer surface upon which at
least one polymerization agent is attached. The microcapsules
supposedly are effective for rupturing with a failure of the
polymeric media, and the flowable polymerizable material reacts
with the polymerization agent when the polymerizable material makes
contact with the polymerization agent upon rupture of the
microcapsules. This is described as a way of making an initial
cured form.
[0011] U.S. Pat. No. 6,858,660 to Scheifers et al. described a
self-joining polymer composition, comprising a polymer, a plurality
of amine pendant groups attached to the polymer and a plurality of
microcapsules of flowable polymerizable material dispersed in the
polymer where the microcapsules of flowable polymerizable material
including microcapsules and flowable polymerizable material inside
the microcapsules. The microcapsules are effective for rupturing
with a failure of the polymer so the flowable polymerizable
material cross-links with the reactable pendant groups upon rupture
of the microcapsules.
[0012] Different techniques for formation of a composite structure
are discussed in U.S. Patent Publication No. 2003/0119398 to
Bogdanovich et al., where a resin distribution system and method
for use in resin transfer molding includes using a 3-D orthogonal
fiber structure having small channels therein for permitting a
fluid to flow through the structure for formation of cured
composites for use in such processes as resin transfer molding. The
3-D orthogonal fiber structure includes a woven system, having X-,
Y-, and Z-direction fiber, each of having substantially no crimp
within a body of the structure, thereby providing a system for
distributing the fluid uniformly through the structure.
[0013] Other attempts have been made to provide self-repairing
composites by other groups which used release from hollow fibers.
See, for example, Motuku et al., from the University of Alabama, in
"Parametric Studies on Self-Repairing Approaches for Resin Infused
Composites Subjected to Low Velocity Impact", Smart Material
Structure 8 (1999) 623-638, studied low velocity impact response of
glass fiber reinforced composites, which supposedly had the
potential to self-repair both micro- and macro-damage. This
University of Alabama group researched low velocity impacts for
self-repair in fiberglass composites which were prepared at a
fairly low temperature, sufficient to make fiberglass samples.
Their studies focused on a two part system which needed, in
general, mixing of more than one minute.
[0014] In the U.K., Bristol University researchers Ian Bond and
Richard Trask used psuedoimpact and then heat to release and heat
to cure self-repair agents in glass tube mats placed on or in
composites, the technology suitable for use in a space environment.
Still other tactics are described, for example, in "Bleeding
Composites'--Damage Detection and Self-Repair using a Biomimetic
Approach", Pang et al., Composites: Part A 36 (2005) 183-1888.
[0015] Various matrix materials without separate chemical release
inclusions, which are said to have self repairing properties, have
been developed by numerous researchers; for example, studies have
been ongoing by Professor Wutl of UCLA, at VPI and SU (Virginia
Polytechnic Institute and State University), and at NASA Langely.
Some of these developed systems are designed to reversibly repair
damaged composites, but the materials are generally not strong
enough for structural applications. One shortcoming is that many of
the systems need heat to trigger the self-repair chemistry. Prof
Wutl suggests applications such as the glass in car headlights or
heated windshields, where a heat source is readily available, for
use of the self-repair system. The NASA system is used for
ballistic damage where heat may be produced.
[0016] The subject of self-repairing composite materials not only
includes concretes and polymeric materials, in addition to
headlights and windshields, it has been suggested that housings and
other parts of cell phones, computers and perhaps batteries could
be made self-repairing. See, e.g., U.S. Patent Publication No.
2005/0027078 to Scheifers et al., which used chemistry to repair
low energy damage such as in computer casings or cell phones by use
of reactions which are self perpetuating. Other suggested
self-repairing products include golf balls and tires.
[0017] The ideas for self-repairing composites are now widespread,
but processing of the products under heat, development of adequate
repair chemicals in terms of heat resistance, speed of repair, and
simple systems which use an in-situ system of energy and chemical
flow in a circulation system to repair well, systems to repair
medium to high impact damage, multi-use applications, and
applications to new end uses are all areas needing solutions and
invention.
SUMMARY
[0018] The present invention provides alternate designs and/or
solutions to most of the drawbacks encountered in the prior art.
The disclosure provides processing of the products under heat,
development of adequate repair chemicals in terms of heat
resistance, speed of repair, and simple in-situ systems which use
the an in situ system of energy and chemical flow in a circulation
system to repair well, systems to repair medium to high impact
damage, fatigue damage, as well as self forming/self repairing
composites as well as other multiple functional or multi-use
applications. In the simplest form, in order to be self-repairing,
a special, and applications to new end uses are all areas needing
solutions and invention.
[0019] The present disclosure provides various elements, such as
different and better repair conduits, alternate constructions for
the repair conduits, alternate manners of having the repair
conduits (e.g., fibers or channels), different and better modifying
agent is stored in a conduit embedded in a matrix. When the
resulting composite is damaged, the damage progresses through the
composite matrix, breaking the conduit and releasing the modifying
agent. The modifying agent flows into the crack and re-bonds the
cracked or delaminated faces.
[0020] An opportunistic dynamic notion of materials is included in
this approach of self-repairing materials, in that it can go beyond
self-repair, from changing and problem solving into new totally
dynamic structures in terms of their energy, design for material
flow, and chemical change of the materials. The self-repairing
composites of this disclosure utilize a system of liquid flows,
energy applications and response, and chemical reactions, all in a
synchronized way. The energy in the circulation system may come
from any of the aspects involved such as the force or damage, the
repair conduit, a coating on the repair conduit, the modifying
agent (which can be present in several parts and/or in several
locations of the system), inclusions in the matrix such as beads or
particles, the matrix itself, and the interactions of various
factors such as flow, energy produced by flow, damage and material
properties.
[0021] The present disclosure is to a composite matrix, including
polymer composite laminates, having a plurality of hollow repair
conduits dispersed therein, a modifying agent present within the
repair conduits and/or thereon, and means for permitting selective
release of the modifying agent from the repair conduits into the
matrix material in response to at least one external stimulus. Two
examples of repair conduits are hollow repair fibers and channels.
In most embodiments, reinforcing fibers are also present throughout
the matrix. The matrix and the repair conduits together form an in
situ fluidic system that transports the modifying agent(s)
throughout the matrix.
[0022] In many embodiments, the matrix, including the modifying
agent and repair fibers, is particularly suited for use in or
processing under high temperature applications, e.g., at least
250.degree. F., often 250-350.degree. F., for extended periods of
time, such as 1-3 hours. In many of these embodiments, the
modifying agent is sufficiently heat stable to withstand the high
temperatures. In embodiments where the stability of the modifying
agent under high temperatures is questionable, the modifying agent
can be put into the fiber after the high temperature processing. In
most embodiments, the resulting article can withstand heat of use
of the article and can also withstand any heat generated in the
article during use.
[0023] Additionally or alternatively, the cured matrix is
particularly suited to be a layer in a laminate material, e.g., a
material having at least one self-repairing layer. The cured matrix
is particularly suited for use with graphite and fiberglass
laminates, which typically have to be processed at high
temperatures.
[0024] The modifying agent may be present within the repair
conduits (e.g., within the hollow repair filter) on a surface of
fibers, or both. Additionally, other modifying agents, either the
same or different than the first modifying agent, may be present at
locations other than the repair conduits, for example, distributed
throughout the matrix. In some embodiments, the modifying agent(s)
may be encapsulated or beaded.
[0025] The repair conduits may be present as randomly dispersed
conduits through the matrix or may be positioned in an orderly
manner as in a layer of a laminate. In some embodiments, the ends
of the repair conduits are engulfed or otherwise retained in the
matrix, or the ends may extend out to the edges of the matrix for
later refilling if needed. Generally, the ends of the repair
conduits are sealed in the final composite, to retain the modifying
agent therein. For embodiments where the repair conduits are
fibers, the ends are typically sealed with adhesives, heat or other
manner.
[0026] In some embodiments, especially those where the resulting
composite is a layer in a laminate, the reinforcing fibers, if
present, can be provided as an orderly network of fibers. The
reinforcing fibers could be present as a dense woven or knitted
mat, or be present as a lofty non-woven mat. In other embodiments,
whether in a laminate or not, the reinforcing fibers could be
randomly dispersed throughout the matrix.
[0027] The present disclosure, in its most basic form, is directed
to self-repairing systems that retain a modifying agent until
needed. The systems include a matrix having a plurality of hollow
repair conduits dispersed therein, a modifying agent present, at
least, within the repair conduits and/or thereon. Upon a
predetermined stimulus, the modifying agent is released from the
repair conduits into the matrix material. The matrix and the repair
conduits together form an in situ fluidic system that transports
the modifying agent(s) throughout the matrix. In many embodiments,
the matrix, including the modifying agent and repair conduit, is
particularly suited for use in or processing under high temperature
applications, e.g., at least 250.degree. F., often 250-350.degree.
F., for extended periods of time, such as 1-3 hours.
[0028] One particular aspect of this disclosure is a self-repair
system having a modifying agent present in a conduit. The modifying
agent can be a one-part system or a two-part system; for a two-part
system, typically only one part is retained in the conduit, or, the
second part is retained in a second conduit. The conduit is
configured to retain the modifying agent until appropriate external
stimulus, at which time the modifying agent is released. The
modifying agent is configured to react and repair any damage within
the matrix. At least the modifying agent can withstand without
degradation exposure to high temperatures, e.g., at least
250.degree. F., often 250-350.degree. F., for extended periods of
time, such as 1-3 hours.
[0029] Another particular aspect of this disclosure is a
self-forming system in which conduits form a weave or 3-D
structure. At least one part of the modifying agent is within the
conduits, and a second part, for a two-part modifying agent, can be
in or on the fiber weave or structure. Upon appropriate stimulus,
the conduit releases the internally held modifying agent, which
contact and react with the second part, optionally forming the
matrix. This system can make composites, laminates, or pre-pregs
which can be activated later. In some embodiments, the modifying
agent can withstand without degradation exposure to high
temperatures, e.g., at least 250.degree. F., e.g., at least
350.degree. F. for 1-3 hours.
[0030] An aspect of this disclosure is to provide a polymer
graphite composite laminate, preferably having 24-32 single plies,
in which the laminate is self-repairing, by inclusion of repair
conduits with repairing modifying agent. The repair modifying agent
can resist temperatures of at least 250.degree. F. for at least one
hour and in some embodiments even at least 300.degree. F. for 2
hours, in the usual oven ramp for carbon pre-preg. Even at these
temperatures for these times, the repair modifying agent remains
sufficiently strong to repair the laminate after impact of 5 to 50
joules to about 70-80% of the non impacted control. This laminate
may be a graphite laminate. The repair conduits may be glass tubes.
The repairing agent could be an epoxy, including an epoxy vinyl
ester, a vinyl ester or an acrylate, such as a cyanoacrylate. In
some embodiments, the repairing agent can be modified to provide
desired properties such as heat resistance, fast chemical reaction,
strength, later water proofing and longer shelf life.
[0031] Another aspect of this disclosure is to provide a polymer
composite laminate, e.g., having 24-32 single plies, in which the
laminate is self-repairing. The laminate has conduits, such as
tubes or channels, with repair modifying agent(s). The repair agent
can resist heat of at least 250.degree. F. for at least one hour
and, in some embodiments, at least 300.degree. F. for at least 2
hours. The repair agent remains strong enough to repair the
laminate after impact of 5 to 50 joules to about 70-80% of the non
impacted control without any repair conduits. The repair occurs in
less than one hour. In some embodiments, the repair occurs in less
than one minutes, or even in less than 30 seconds.
[0032] This disclosure is also directed to a chemical adhesive that
has been designed to be used in a self-repairing composite system.
The chemical is a modifying agent or repair agent that can resist
the heat of processing of the composite, such as laminate
processing conditions. In some embodiments, the heat of processing
is at least 250.degree. F. for at least one hour or at least two
hours, and in other embodiments, is at least 300.degree. F. for at
least one hour or at least two hours. Even after processing of the
composite, the modifying agent is preferably able to beneficially
survive subsequent high temperatures, and in some embodiments,
moisture (e.g., liquid water) at the surface and/or internally in
the composite. In some embodiments, the modifying agent is also
designed to have an extended shelf life, prior to processing of the
composite, subsequent to processing, or both.
[0033] The disclosure also provides systems having conduits
comprising boron materials, either as the conduits or on the wall,
which can be oxidized at high temperatures in a carbon atmosphere.
At very high temperatures, the boron melts, becoming flowable
glass. As the melted boron is released from the conduit to repair
the damaged areas, in the presence of oxygen the boron reoxidizes
into a material having higher temperatures than the boron before
oxidation. This step wise increase in temperature and oxidation
resistance can occur several times with several different boron on
boron like materials.
[0034] In another aspect of this disclosure, a chemical adhesive is
provided for a laminate, the adhesive being a modifying agent that
can react with more than one part of a laminate, such as
atmospheric air, the conduit (or a portion thereof) retaining the
modifying agent, structural materials in the laminate (e.g.,
graphite) or fillers or other materials in the laminate (e.g.,
clay, carbon black, nanotubes, moisture, cement). In some
embodiments, this modifying agent is temperature resistant, e.g.,
at least up to 250.degree. F. for at least one hour or at least two
hours, and in other embodiments, at least up to 350.degree. F. for
at least one hour or at least two hours.
[0035] In still another aspect of this disclosure, two conduits are
provide for retaining a two-part system, which upon reaction,
self-repairs or self-forms a matrix. Each conduit contains one part
of the two-part system. The conduits could be any of tubes or
fibers, channels, or beads. Tubes or channels could be twisted or
twinned or otherwise in close proximity to each other.
[0036] In yet another embodiment of this disclosure, exotic
reactions are used for self-repair systems. Exotic reactions
include those that involve ROMP (ring-opening metathesis
polymerization), Bergman cyclization, Dehls Alder, Shrock
chemistry, DCDP (dicyclopentadiene), Grubbs ruthenium, tin and
iron.
[0037] In some embodiments, the repair modifying agent in the
self-repair or self-forming system is a one-part adhesive. In other
embodiments, the repair modifying agent in the self-repair or
self-forming system is a two-part adhesive.
[0038] The present disclosure also provides a reactive system for a
self-repair or self-forming system that is initiated with exposure
to air. The reactive system includes a repair agent or modifying
agent, such as urethanes, other sealants or adhesives such as
esters or cyanates which may react with moisture present in the
air. In some embodiments, this repair agent or modifying agent is
present in a repair conduit, until released by rupture of the
conduit.
[0039] In some embodiments, conduits, such as beads or tubes, may
be made from reactive materials, such as many adhesives or repair
chemicals listed in the ingredients list herein. The conduits may
be made by putting them in a reactive substance to form a shell,
and taking them out and stopping the reaction by exposure to
another chemical.
[0040] Matrices that could be made with a self-forming system
include polymeric matrices and cementitous matrices, for example,
with hexamethylene diamine and acid such as maleic or succinic to
make nylon 666 which gives off water to react with cement.
[0041] The present disclosure provides for other ways of self
forming matrices. Fibers filled with a one part repair chemical can
have the other part on the fiber surface and upon fiber breakage
the two can react and combine and create a fiber resin matrix
system. This could also be made into a pre-preg system for later
activation into a composite. Additionally the self forming system
can use the same not emptied fibers for later self repair of the
self formed matrix.
[0042] The self forming conduits with repair chemical inside and on
the surface may be present as a three dimensional (3-D) system of
fibers or channels or a weave or array. Fibers may be provided as a
dense woven or knitted mat, or be present as a lofty non-woven
mat.
[0043] In alternate embodiments, the repair conduits may be present
as a three dimensional (3-D) system of fibers or channels or a
weave or array. Fibers may be provided as a dense woven or knitted
mat, or be present as a lofty non-woven mat.
[0044] The present disclosure provides an energy circulation system
in which there is no external mechanical element or special forms
to provide, for example, mixing of reactants, pumping of liquid,
controlling fluid flow (e.g., valves). The circulation system with
chemicals in a matrix subject to damage energy includes, in situ,
elements to produce energy flow and fluid flow within the system,
without external mechanisms or special elements in form.
[0045] The present disclosure also provides an energy circulation
system, comprising a modifying agent in a conduit in a matrix.
After an impact, the modifying agent flows into voids in the matrix
created by the impact in less than 2 second. In some embodiments,
the modifying agent has filled the damages areas within one minute.
In some embodiments, all flow has ceased within about one
minute.
[0046] In some embodiments, the energy circulation system includes
metals or other inclusions which can react in the matrix in
response to damage energy. Examples of metal inclusions include
iron, aluminum and copper, and alloys and combinations of those
materials or any other metal or alloy.
[0047] The present disclosure, in some embodiments, provides for
the use of in situ release fibers designed as energy pumps in the
self-repair systems. These fibers functioning as pumps can be
impendence, osmotic, magnetic or elastomeric, or pressure release
pumping. The modifying agent is released from the conduits in
response to a stimulus for self-repair which is transmitted through
these conduit release fiber/tube pumps.
[0048] The disclosure also provides for the production of energy
within the self-repair due to movement of a fluid inside the
conduits, such as magnetic tube system. Inclusions of magnetic
spheres move and create motion, which then increase the fluid
motion and provide increased circulation throughout the system.
Magnetism and motion can yield electricity. Magnetic spheres can be
half positive and half negative for better mixing.
[0049] The disclosure also provides for the absorption of radar
energy by the system, such as with glass spheres coated with
ferrite all in a liquid. The ferrites absorb radar wave energy,
which is expelled as heat energy. The ferrites can also move in the
liquid to find the optimum angle of the radar incoming waves.
[0050] Also within this disclosure are various special applications
such as for sensing of damage and repair, repair of cryogenic tanks
exposure to low temperatures, articles which generate their own
heat as computers and tires, and space applications in which low
gravity and vacuums may affect and allow use of different chemical
release systems.
[0051] Also within this disclosure is aerodynamic motion control,
by the flow of modifying agent within the conduits The conduits,
e.g., a weave or array, contain liquid modifying agent which can
flow with the motion to create aerodynamic changes which can act to
control the shape or angel of the overall structure such as an
airplane.
[0052] Also within this disclosure is a chemical adhesive for self
repair of cementitious articles. This chemical adhesive, as a
modifying agent, reacts with an alkaline cementitous matrix when
included in a self-repairing system. In some embodiments, the
cementitious matrix includes one or all of cement, calcium
carbonate, silicates, water, sand and aggregates.
[0053] Also within this disclosure is a chemical adhesive for self
repair of cementitious articles which can resist or survive high
temperatures of cement hydration ad later in-field
temperatures.
[0054] These and other embodiments and aspects are within the scope
of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] FIGS. 1A-1D are schematic views of a self-repairing matrix
composite material, illustrating various stages of matrix repair
sequence of load-induced cracking, modifying chemical release and
subsequent repair of the matrix and rebonding of the fiber;
[0056] FIGS. 2A and 2B are schematic views of a composite material
including a matrix with randomly dispersed repair fibers;
[0057] FIGS. 3A and 3B are schematic views of a laminate composite
material including a matrix with a layer of oriented repair
fibers;
[0058] FIGS. 4A and 4B are schematic views of a self-repairing
matrix composite material, illustrating release and repair from
twisted fiber bundles, whereby compressive loading causes unlocking
of the twisted fiber bundles to release modifying agent into the
adjacent matrix;
[0059] FIG. 5 is a schematic rendition of an embodiment of a
self-repairing dynamic system;
[0060] FIG. 6 is a schematic illustration of a first in situ
osmotic pump formed by a repair conduit of a self-repairing
system;
[0061] FIG. 7 is a schematic illustration of a second in situ
osmotic pump formed by a repair conduit of a self-repairing
system;
[0062] FIG. 8 is a schematic illustration of a repair conduit of a
self-repairing system producing an electric field, which causes
fluid to pump;
[0063] FIG. 9 is a schematic illustration of a repair conduit of a
self-repairing system producing an electric field, which causes
fluid to pump;
[0064] FIGS. 10A and 10B are schematic renditions of a repair
conduit with the conduit having one part of a reagent inside and a
second part of a reagent outside of the conduit as a coating, upon
breakage of the conduit the two chemical react forming a chemical
matrix; and
[0065] FIG. 11 is a schematic rendition of the prior art
self-repair system having pumps and valves for moving the modifying
agent therethrough, tubes in many layers and mixing towers.
DETAILED DESCRIPTION
[0066] The present disclosure provides various solutions and
elements to solve problems associated with the prior art. The
repair system of this disclosure provides in situ energy management
within the shaped composite, regulating dynamic fluid flow, energy
flow and chemical reactions within the composite over time. The
present disclosure provides various elements, such as processing of
the products under heat, development of adequate repair chemicals
in terms of heat resistance, speed of repair, and simple in-situ
systems which use the energy and chemical flow in a circulation
system to repair well, systems to repair medium to high impact
damage, fatigue damage, as well as self forming/self repairing
composites as well as other multiple function applications. This
disclosure provides, for example, the use of smaller repair
conduits, the use of integral channels as well as separate repair
fibers, and the conduits could be woven, interwoven or nested with
other repair fibers or with reinforcing fibers. This disclosure
also provides improved modifying agents, one-part and two-part,
improved uses, and improved methods of incorporation into the
matrix. The modifying agents can include additives for heat
stability, shelf file, water resistance, etc.
[0067] In the simplest form, in order to be self-repairing, a
special modifying agent is stored in a conduit embedded in a
matrix. When the resulting composite is damaged, the damage
progresses through the composite matrix, breaking the conduit and
releasing the modifying agent. The modifying agent flows into the
crack and re-bonds the cracked or delaminated faces.
[0068] Referring to the figures, and particularly to FIGS. 1A-1D, a
self-repairing matrix composite and its operation in the field is
schematically illustrated. As depicted in FIG. 1A, a shaped article
is formed having a hollow repair conduit, such as a fiber,
containing a modifying agent therein and optionally coated with a
thin coating material. The repair conduit is dispersed within a
settable or curable matrix material, which may be either a polymer
or cementitious material. In FIG. 1B, a load applied to the shaped
article causes strains within the matrix, which in turn cause the
repair conduit to break (FIG. 1C) and the matrix to crack. This
causes the modifying chemical agent within the hollow repair
conduit to be released into the vicinity of the crack in the matrix
as shown in FIG. 1B. The modifying agent flows and fills the void
as shown in FIG. 1D and cures to rebond the fiber to the matrix and
to repair the fiber to itself. This schematically illustrates the
modified fiber concept of the present invention.
[0069] The self-repair system is improved over previous systems in
that one or more of the following traits are seen in composites,
including laminates, incorporating the self-repair system of this
disclosure:
[0070] (1) the repair system can withstand processing temperatures
in a range from no heat (e.g., ambient conditions) to 250.degree.
F., 300.degree. F., or 350.degree. F. for several hours, and the
resulting composite can withstand high temperatures without damage
to the repair system;
[0071] (2) the repair system can repair the large scale damage
generally experienced with laminates such delaminations as may
occur in strong graphite laminates, as well as smaller size damage
as in fiberglass laminates;
[0072] (3) the repair system can repair impact damage caused by
fast and large impacts or forces, as well as slower and lower
forces such as fatigue damage, structural cycling, thermal cycling,
movement cycling, and creep damage;
[0073] (4) the repair system can repair damage in a controlled
manner, within less than one minute or up to several days, as
desired; and
[0074] (5) the repair system provides in situ energy management,
regulating dynamic fluid flow, energy flow and chemical reactions
over time.
[0075] The following descriptions of the various components of the
self-repair systems of this disclosure provide a background for the
later, detailed discussions. It should be understood that the
following paragraphs do not limit the later discussions nor are the
later discussions limited to the materials provided here. It should
also be understood that although specifics or elements have been
provided in respect to one of the embodiments or methods, that all
the specifics and elements can be used interchangeably throughout
the teachings of this disclosure, as appropriate.
[0076] Uses for Technology
[0077] The shaped articles or composites disclosed herein or made
by the methods disclosed herein can be used in any number of goods.
Examples of uses for the composites include in materials such as
those used in construction, building, roofing, roadway, industrial,
aircraft, automotive, marine, appliances, recreational, electronic
goods, transportation and/or biomedical fields.
[0078] Examples of construction, building, roofing or roadway uses
include cement, concrete, phosphate cements, roads, infrastructure,
earthquake-resistant buildings and other structures, bridges,
tunnels, and pothole repair.
[0079] Examples of industrial applications include filament wound
cryogenic tanks, cryotanks to resist hydrogen, oxygen, nitrogen,
other gases, at various temps, cryotanks for laser systems,
thermally cycled bonds, adhesively bonded joints, nuclear power
plant towers, oil rigs and pipelines, power grids, gas pipes,
concrete girders, reinforcing tendons, structural composites,
windows, and containment structures for radioactive or chemical
wastes.
[0080] Examples of aircraft, automotive, marine and other
transportation applications include tires and tire parts, boat and
submarine hulls, airplane hulls and wings and other structures,
helicopter structures including rotor blades, space vehicles and
satellites, automotive body and frame parts, truck trailers and
tanks, and engine pistons.
[0081] Examples of recreational applications include golf balls and
clubs, bicycles, hockey and lacrosse sticks, tennis rackets, bats,
helmets, armor, padding and other safety equipment, goalposts and
net supports, pleasure craft, and floatation devices.
[0082] Examples of electronic goods include electronic packages,
printed circuit boards (PCBs) and PCB laminates, electronic
encapsulants, electronic die attach, and housings for computers,
computing devices and other electronic goods.
[0083] Examples of biomedical applications include bone grafts and
natural bone growth, implants, prostheses, smart-release bandages,
artificial skin materials, poultices and the like which include
additives which release healing chemicals or healing promoting
chemicals by upon movement of the patient or by application of
another stimulus, such as for example, a heating pad, or the like.
The composites used in these bandage applications might include
such release chemicals as oxygen releasing chemicals, moisturizers,
aloe vera, antibiotics, anti-inflammatants, analgesics, non-stick
agents or the like.
[0084] The self-repairing composites could also be used for other
miscellaneous applications such as pipe repair, rubber matrices,
plastic packaging, adhesives, impregnating resins, and paints,
finishes, sealants and coatings, which could be scratch
resistant.
[0085] In some embodiments, the self-healing composites, when
polymeric based, have a flexural modulus of from about 2,000 to
about 200,000 psi.
[0086] Matrix
[0087] As provided above, the basis for the composite materials is
a matrix material, which can include any curable, settable
material. Typically, these materials are moldable or castable to
form shaped objects or may be laminated or may be laminated or
assembled into finished products, such as those listed above.
[0088] The matrix can be organic or organic based. Examples of
matrix materials include polymeric materials, cementitious
materials, and polymeric ceramic matrix. In some embodiments, the
matrix may be self-forming, from materials present within conduits,
as is described below.
[0089] A polymeric matrix can include thermosetting resins,
thermoplastics, and elastomers. Thermosetting resins include
temperature-activated systems, polymerization agent-activated
system, and mixing-activated systems. The thermoplastics can be
noncrystallizing thermoplastics or crystallizing thermoplastics.
Examples of thermoplastics that can incorporate the self-healing
system include olefinics, vinylics, styrenics, acrylonitrilics,
acrylics, polyacrylates, polycarbonates, polyalloys, cellulosics,
polyamides, polyaramids, thermoplastic polyesters and copolyesters,
polyethers, phenol-formaldehyde resins, amine-formaldehyde resins,
poly(acrylonitrile-butadiene-styrene), polyurethanes including
foaming polyurethanes, polyolefins, polysilanes, sulfones and
polysulfones, polyimides and imide polymers, ether-oxide polymers,
ketone polymers, fluoropolymers, and heterochain polymers, and the
like. Additional examples of thermosetting resins include, for
example, epoxy systems (both one-part and two-part systems),
formaldehyde systems, urethane/urea systems, formaldehyde systems,
furan systems, allyl systems, alkyd systems, unsaturated polyester
systems, vinyl ester systems, and the like. Epoxy systems include
cycloaliphatic epoxies, diglycidyl ether of bisphenol-A or its
brominated versions, tetraglycidyl methylene dianiline, polynuclear
phenol epoxy, epoxy phenol novolac, epoxy cresol novolac, hydantoin
epoxies, and so forth. Epoxy resin systems can be processed in a
variety of manners and can be cured at low or elevated
temperatures. Formaldehyde systems include urea-formaldehydes,
phenol formaldehydes, and melamine formaldehydes.
[0090] Elastomers that can be enhanced by this invention include
vulcanizable elastomers, reactive system elastomers and
thermoplastic elastomers. Examples of such elastomers include diene
and related polymers, elastomeric copolymers, ethylene-related
elastomers, fluoroelastomers, silicone polymers, and thermoplastic
elastomers. Thermoplastic elastomers can include rubbery polymers
and copolymers including, for example without limitation,
styrenebutadiene rubber (SBR), neoprene, EPDM and silicone rubbers
and the like.
[0091] Examples of thermosetting materials that can be used as a
matrix with the self-repair system include acrylates,
methacrylates, cyanoacrylate resins, epoxy resins, phenoplasts such
as phenolic resins, aminoplasts such as melamine-formaldehydes,
unsaturated polyester resins, vinyl ester resins, polyurethanes,
and so forth.
[0092] Low viscosity resins can be cast. Molding compounds can be
injection molded, compression molded, or transfer molded.
[0093] Concrete, cement, phosphate cements, sintered fly ash or
bottom ash/phosphoric acid mixtures, and asphalt are also common
matrices for the self-repair system. The system is particularly
suited to withstand survive field mixing, placement of the repair
conduits in or under the top of such articles so that future
impact, shear cracking, fatigue, creep and drying shrinkage damage
can be repaired.
[0094] The matrix materials may be cured by means of catalysts,
crosslinkers, radiation, heat, laser beam or by any means used with
monomers reacting with resins or polymers in the art for setting
up, hardening, rigidifying, curing or setting these matrix
materials to form shaped articles or objects. The matrix compound
should be formulated to minimize any potential inhibiting activity
by it relative to the modifying agent.
[0095] Repair Conduits
[0096] Throughout the matrix are distributed the repair conduits.
The repair conduits can be any suitable structure that provides a
vessel for receiving and retaining modifying agent until ruptured
and released. In most embodiments, the repair conduit has an
internal volume for receiving and retaining the modifying agent.
The structure of the repair conduit should be such to adequately
rupture or break to release the modifying agent.
[0097] Examples of fibers that can be used as repair conduits
include hollow optical fibers, glass tubes, glass pipettes, carbon
fibers, straws, and the like. Fibers have an internal volume that
can be defined by a surrounding wall. The fiber can be filled with
modifying agent prior to or subsequent to incorporation into the
composite. Some typical materials for fibers include glass,
polymeric or plastic, fiberglass, quartz, carbon and metal. Other
typical materials for fibers include hydrous metal oxide, silica,
silicates including borosilicates, silicon, and silicate type
sol-gel precursors. Examples of typical organic fibers include
polyolefin fibers, polypropylene fibers, polyester fibers,
polyamide fibers, polyaramid fibers, urea-formaldehyde fibers,
phenolic fibers, cellulose fibers, nitrocellulose fibers, GORTEX
fibers, and KEVLAR fibers. Glass fibers and similar are preferred
because of the ease of melting, bending, and forming; for example,
the ends can be melted to be sealed.
[0098] Fibers may be rigid or may be flexible and/or bendable. For
example, the fibers may be sufficiently flexible insert into
pre-pregs, tows or weaves and yet be breakable. Multiple fibers
could be woven to provide a mat of repair conduits.
[0099] In some embodiments, the fibers may have a coating or other
surface treatment to modifying the fiber properties. For example, a
coating or other surface treatment may be present to inhibit
compromise of the modifying agent, such as by the fiber material.
The fiber interior or exterior could be coating with, for example,
metal or carbonyl iron ferrite. Radar waves induce alternating
magnetic fields in carbonyl iron ferrite which causes conversion of
their energy into heat. As another example, the interior surface of
a fiber may have a coating to reduce surface tension, thus
increasing capillary flow along the surface. As another example the
interior or exterior coating may be metal to allow an electrical
current to flow along the fiber.
[0100] Volumes void of matrix, e.g., channels, can be formed (e.g.,
integrally) in the matrix and used as repair conduits for retaining
and releasing modifying agent. Such channels have an internal
volume defined by the matrix itself. The channels are generally
filled with modifying agent after incorporation into the composite.
In some embodiments, a sacrificial fiber or tube may be used to
form the channel. Upon a condition, for example heating, the
sacrificial tube or fiber may melt or otherwise disintegrate,
leaving an empty channel.
[0101] The sidewalls of the conduits are typically rupturable or
porous to permit the discharge or exiting of the modifying agent
into the surrounding matrix material upon the appropriate
stimulus.
[0102] The repair conduits may be bundled, woven or loose. They may
be held or engaged together with flexible web materials. They may
comprise twisted pairs (as in FIGS. 4A and 4B) and additionally may
include concentric structures of one or more fibers. It is not
necessary that the repair conduits have a single, elongate volume,
as do the fibers and channels described above. Multiple fibers or
channels could be interwoven and connected to form an
interconnected grid or matrix of conduits that has one large
volume. The pattern could be, for example, a honeycomb pattern or a
checkerboard pattern, having conduits positioned orthogonal to each
other. Such interconnected fiber structures have capillary channels
therein to allow the modifying agent to flow through the structure.
In some embodiments, the interconnected fiber structure is 3-D,
with X-, Y-, and Z-direction fiber systems, thereby providing a
system for distributing the modifying agent uniformly through the
matrix.
[0103] In addition, a plurality of hollow beads could be used as
repair conduits.
[0104] The repair conduits, whether fibers, channels, beads or
other structures, can be any desired size, length, have any wall
thickness or cross-sectional configuration. In most embodiments,
the repair conduits have a diameter of 100-1200 micrometers. The
conduits may be relatively small, chopped or comminuted fibers
having lengths of less than about one inch and diameters of less
than about 100 microns. The small size of the conduits is preferred
so that they do not interfere with the action of the composites,
e.g., laminated composites, no matter where they are reinserted yet
they should have sufficient volume to carry of modifying agent to
fill and repair cracks. Examples of suitable sizes of outside
diameter/inside diameter of fibers include 250/700, 500/850,
1000/1300, 1000/1600 micrometers. In some embodiments, such as when
two different modifying agents are used, or when the modifying
agent is a two-component system, two different sizes of conduits
may be used.
[0105] Modifying Agent
[0106] Retained within the repair conduit is at least one modifying
agent. In some embodiments, the repair conduit is made from the
modifying agent; i.e., the modifying agent forms its own shell,
which acts as the repair conduit.
[0107] Typically the modifying agent is liquid, so that it readily
flows out from the conduit. The modifying agent may be a one-part
material that self-reacts or two-part (or more) material. Generally
for two-part materials, one part is present in the repair conduit
and the second part is present in either the matrix or other repair
conduits. FIG. 4A illustrates two repair conduits in close
proximity to each other; in this embodiment, one conduit can
include the first part of a two-part modifying agent and the second
conduit can include the second part.
[0108] Upon damage of the composite, the modifying agent is
released from the repair conduit, moved around in the circulation
system of the self-repair system, and chemically and/or
energetically altered. In FIG. 4B, the conduits are ruptured, so
that the two modifying agents flow into the damaged area, react
together, and repair the area.
[0109] The modifying agent, present within the repair conduit, is
selected from materials capable of beneficially modifying the
matrix composite after curing. The modifying agents are selectively
activated or released in or into the surrounding matrix in use in
response to a predetermined stimulus be it internal or externally
applied. In some embodiments, additional chemicals or secondary
modifying agents are present in the matrix which can be pulled
along and self polymerized or yield a continual reaction.
[0110] The modifying agent may be a commonly available or simple
chemical or may be an `exotic` chemical. Exotic chemical have
reactions such as reactions involving condensation reaction
polymers, ROMP (ring-opening metathesis polymerization) reaction,
Bergman cyclization or Diehls Adler reactions. Some of these
reactions are intended to not require mixing but are fully consumed
by the chemical reaction itself without outside heat or mixing,
they are autonomous.
[0111] The modifying agent is a polymerizable compound and can be a
monomer, oligomer or combination thereof. Examples of polymerizable
compounds include acrylates including cyanoacrylates, olefins,
lactones, lactams, acrylic acids, alkyl acrylates, alkyl acrylic
acids, styrenes, isoprene and butadiene. The modifying agent can be
an expoxide material, either one-part or two-part.
[0112] Suitable cyanoacrylates include ethyl cyanoacrylate, methyl
cyanoacrylate, b is 2 cyanoacrylate, cyanoacrylates with silicon,
fluoroalkyl 2 cyanoacrylate, aryloxy ethyl 2 cyanoarylate,
cyanoacrylates with unsaturated groups, trimethylsilyl alkyl 2
cyanoacrylate, and stabilized cyanoacrylate adhesives, such as
taught in U.S. Pat. No. 6,642,337 and U.S. Pat. No. 5,530,037.
[0113] Olefins include cyclic olefins, e.g., containing 4-50 carbon
atoms and optionally containing heteratoms, such as DCPD
(dicyclopentadiene), substituted DCPDs, DCPD oligomers, DCPD
copolymers, norbornene, substituted norbornene, cyclooctadiene, and
substituted cyclooctadiene. Specific examples include, but are not
limited to norbornene (such as triethoxysilylnorbornene,
norbornene, ethyl norbornene, propylnorbornene, butylnorbornene,
hexylnorbornene), alkyl-substituted norbornene derivatives, and
alkoxysilynorbornenes. Corresponding catalysts for these are ring
opening metathesis polymerization (ROMP) catalysts such as Schrock
catalysts.
[0114] Lactones, such as caprolactone and lactams, when polymerized
will form polyesters and nylons, respectively. Corresponding
catalysts for these are cyclic ester polymerization catalysts and
cyclic amide polymerization catalysts, such as scandium
triflate.
[0115] Still another class of modifying agents particularly useful
in polymer matrices are solvents which permits solvent action to
actually repair microcracking damage locally at a cracking site or
possibly to dissolve the matrix or fibers or both to permit them to
re-form at a later time.
[0116] In addition to solvents, other curable monomers and
co-monomers may also serve this repair function. pH modification
agents may also be used as the modifying agents, either alkali or
acidic agents, which may be placed in the interior of the fibers
only to be released by an appropriate pH changes in the matrix.
Other additives may include flame retardant agents. Visco-elastic
polymers may also be used as modifiers.
[0117] The modifying agent may be a catalyst, which is a compound
or moiety that will cause a polymerizable composition to
polymerize, and is not always consumed each time it causes
polymerization. Examples of catalysts include ring opening
polymerization (ROMP) catalysts such as Grubbs catalyst, and also
other ruthenium, iron, osmium, rhodium, iridium, palladium and
platinum. The modifying agent may alternately be an initiator,
which is a compound that will cause a polymerizable composition to
polymerize, and is always consumed at the time it causes
polymerization. Examples of initiators are peroxides (which will
form a radical to cause polymerization of an unsaturated monomer);
a monomer of a multi-monomer polymer system such as diols,
diamines, and epoxide; and amines (which will form a polymer with
an epoxide). In other embodiments, the modifying agent may be a
native activating moiety, which is a moiety of a polymer that when
mixed or contacted with a polymerizer will form a polymer, and is
always consumed at the time it causes polymerization. Examples of a
native activating moiety include an amine moiety (which will form a
polymer with an epoxide).
[0118] Certain water barriers are particularly useful modifying
agents for cementitious matrices. These may include special ZYPEX
brand sodium silicate additives, as well as siloxane and silica
additives known as SALT GUARD and the like.
[0119] No matter what the modifying agent used for the repair, one
or more modifying agents can be present in and/or on the repair
conduit.
[0120] The modifying agent, in some embodiments, can resist high
temperatures of processing (e.g., 250.degree. F., or
300-350.degree. F.), boiling, have a long shelf life, and react
fast (e.g., in less than one minute, and in some embodiments, less
than 30 seconds). Additional details regarding high temperature
resistant modifying agents are provided below. One modifying agent
that is suited for high temperature processing is epoxy. A specific
epoxy class that has been found to be particularly suited for
moderate temperature processing is epoxy vinyl esters; such as
those commercially available under the trade designation
DERAKANE.
[0121] Means are provided for maintaining the modifying agent
within the hollow fibers. The modifying agents may be physically
trapped by, for example, drawing liquid additives into the interior
of the fibers and retaining them therein by capillary action or by
closing off the ends of the fibers.
[0122] Structural Reinforcing Materials
[0123] The matrix typically includes, as needed or desired,
dispersed therein structural reinforcing materials such as
reinforcing fibers or fillers. These reinforcing materials
generally increase any or all of tensile strength of the composite,
compressibility, toughness, ductility, and the like.
[0124] Examples of commonly used fiber reinforcements include
silica fibers, glass fibers, polymeric fibers (including nylon,
aramid, polyolefin, polyethylene and polypropylene), carbon fibers,
ceramic fibers, and metal fibers. Fiber reinforcements may be
present as individual fibers, as yarns or threads, or as mats of
multiple fibers.
[0125] Rebar is a common large-scale reinforcement for concrete
matrices.
[0126] Examples of suitable reinforcing fillers include: metal
carbonates (such as calcium carbonate (chalk, calcite, marl,
travertine, marble and limestone)), calcium magnesium carbonate,
sodium carbonate, magnesium carbonate), silica (such as quartz,
glass beads, glass bubbles and glass fibers), silicates (such as
talc, feldspar, mica, calcium silicate, calcium metasilicate,
sodium aluminosilicate, sodium silicate), metal sulfates (such as
calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium
sulfate, aluminum sulfate), gypsum, vermiculite, wood flour,
aluminum trihydrate, carbon black, certain metal oxides (such as
calcium oxide (lime)), alumina, tin oxide (e.g. stannic oxide),
titanium dioxide, metal sulfites (such as calcium sulfite),
thermoplastic particles (e.g., polycarbonate, polyetherimide,
polyester, polyethylene, polysulfone, polystyrene,
acrylonitrile-butadiene-styrene block copolymer, polypropylene,
acetal polymers, polyurethanes, nylon particles) and thermosetting
particles (such as phenolic bubbles, phenolic beads, polyurethane
foam particles). Other miscellaneous fillers include sulfur,
organic sulfur compounds, graphite, boron nitride, and metallic
sulfides. The above mentioned examples of fillers are meant to be a
representative showing of some useful fillers, and are not meant to
encompass all useful fillers.
[0127] Of course many of the filler materials named above may also
be used as a repair chemical encapsulants for example a hollow
rebar in concrete could contain a repair adhesive, as can porous
aggregates. That is, they may act as functional additives. Other
inclusions may have a significant role in self repair such as metal
particles which could heat the matrix and cause self repairing
chemicals to chemically react.
[0128] Functional Additives
[0129] The matrix may include, as desired, any number of optional
additives that modify or affect the properties of any one or more
of the repair conduit, the modifying agent, the matrix, and their
interactions with each other. A mere sampling of suitable
functional additives is provided below.
[0130] Examples of clays include silica clay, green clay,
kaolinite, bentonite, montmorillite, and nanoclays.
[0131] Examples of commonly used inclusions include metal powders,
glass flakes, mica, aluminum flakes, alumina trihydrate, calcium
carbonate, carbon black, solid microspheres and hollow
microspheres.
[0132] Examples of conductive or semi-conductive particles include
carbon; carbon black; graphite; silicon; silicon carbide; III-V
semi-conducting materials including gallium arsenide, gallium
nitride, gallium phosphide, gallium antimide, aluminum antimide,
indium arsenide, indium phosphide, and indium antimide; II-VI
semi-conducting materials including zinc oxide, cadmium sulfide,
cadmium telluride, zinc sulfide, cadmium selenide, zinc selenide;
and IV-VI semi-conducting materials including lead sulfide and lead
telluride.
[0133] Metal particles include iron, tin, zinc, aluminum,
beryllium, niobium, copper, tungsten, silver, gold, molybdenum,
platinum, cobalt, nickel, manganese, cerium, silicon, titanium,
tantalum, and magnesium mixtures and alloys thereof; metal alloys
such as steels and tool steels, stainless steels, plain carbon
steels, low carbon steels, aluminum-nickel, brass, bronze; and
alloys used for biomedical applications such as cobalt-chromium,
cobalt-chromium-molybdenum, cobalt-chromium-tungsten-nickel,
cobalt-nickel-chromium-molybdenum-titanium, and
titanium-aluminum-vanadium alloys.
[0134] Optional Additives
[0135] The matrix or resulting composite can include optional
additives such as, for example, UV stabilizers, heat stabilizers,
antioxidants, colorants, flame retardants, anti-corrosion
chemicals, anti-freeze materials, antimicrobials, odorants,
surface-modifying additives, processing aids, coupling agents,
viscosity modifiers, pH modifiers, plasticizers, and/or bulk
modifiers.
[0136] In addition these additives could be released also as a
chemical to beneficially enhance the matrix.
[0137] Of course, other additives could be added to the composite,
for any reason. It is understood that although examples of specific
materials are provided in various classes, that these materials may
provide additional advantages to the matrix and/or composite.
[0138] Providing the Article
[0139] The composites having the self-repair system can be shaped
into desired shapes by any convenient technology, including, for
example, lamination (such as form making fiber-reinforced plastics
and structural composites using fiber preforms or fiber pre-pregs,
and so forth), injection molding (such as for making
microelectronic parts, watch components, locating pins, bushings,
ribs, flanges, dashboards, outdoor furniture, and so forth),
extrusion (such as for making sheets, pipes, fibers, pellets, and
so forth), extrusion covering (such as for making sheathing for
wires and cables), film blowing (such as for making single or
multi-layer covers, and packaging applications such as wrap, can
lining, bags, and so forth), calendering (such as for making flat
films or sheets), sheet thermoforming (such as for making blister
packs, individual containers, structural panels and liners,
windows, skylights, and so forth), blow molding (such as for making
packaging and storage containers), coating on a substrate (such as
for films, tapes, structural skins, flooring, wall coverings, and
so forth), rotational molding (such as for making open containers,
seamless flotation devices, toys, structural components), casting
(such as for making encapsulated, embedded or potted electronic
parts), compression molding (such as for making electrical and
electronic goods, knobs, buttons, closures, eating utensils, tire
parts, and so forth), transfer molding (such as for making complex
or fragile polymeric products), and sintering and machining.
[0140] The basic elements and ingredients provided above can be
assembled to provide composite materials with desirable properties.
The preferred processing methods, additional matrices, modifying
agents, conduits, and uses for the composites are described in U.S.
Pat. No. 6,261,360, U.S. Pat. No. 5,989,334, U.S. Pat. No.
5,803,963, U.S. Pat. No. 5,660,624, U.S. Pat. No. 5,575,841, and
U.S. Pat. No. 5,561,173, the entire disclosures of which are
incorporated herein by reference.
1. Self-Repair of Impact Damage in Composites in General
[0141] An opportunistic dynamic notion of materials is included in
this approach of self-repairing materials. As such, it can go
beyond self-repair and solve problems with new totally dynamic
structures in terms of their energy, design for material flow and
chemical change of the materials, all over the time of the
composite (e.g., creation to final destruction). Improved over
prior self-repair systems and materials, the present invention
provides new and improved structural composite materials, including
composite laminates, having a self-healing or self-repairing
capability whenever and wherever cracks, delamination or other
damages are generated. This new understanding of the dynamic aspect
and potentialities of materials, e.g., the energy, flow of fluids
and chemical reactions over time, provides improved systems.
[0142] In some embodiments, the energy of an impact is transformed
and is equal to the energy to form the delaminations and fiber
breakage and matrix cracking. In self repairing systems the energy
of impact is transformed and is equal to the energy to form the
delaminations and fiber breakage and matrix cracking as well as the
energy of repair tube rupture and force on the chemical pushing it
out. This energy sum is matched in some proportion, preferably at
70-100%, by the energy of adhesive repair to re-attach the laminate
layers, re-attach the broken fibers and the broken repair tube.
This can be measured by strength restoration as fracture toughness
which measures the energy required to pull laminates apart, of
compression of flexure. For example, about 5-50 joules are needed
to delaminate a 16-32 ply carbon composite laminate having graphite
composite material and the repair with different repair chemicals
can be 70-94%.
[0143] These systems for self-repair of impact damage in composites
and composite laminates (e.g., graphite and fiberglass laminates)
includes chemicals that are able to withstand the heat of
processing, e.g., at least 250.degree. F. and at least 350.degree.
F. Additionally, the systems are able to repair quickly (e.g., in
less than one minute). The repair system may be a one-part or
two-part system designed to withstand levels of impact appropriate
for the application (e.g., high strength graphite).
[0144] The present disclosure is to composite matrix, including
laminates, having a plurality of hollow repair conduits dispersed
therein, a modifying agent present, at least, within the repair
conduits and/or thereon. Two examples of repair conduits are hollow
repair fibers and channels. Upon a predetermined stimulus, the
modifying agent is released from the repair conduits into the
matrix material. The matrix and the repair conduits together form
an in situ fluidic system that transports the modifying agent(s)
throughout the matrix.
[0145] In many embodiments, the matrix, including the modifying
agent and repair conduit, is particularly suited for use in or
processing under high temperature applications, e.g., at least
250.degree. F., often 250-350.degree. F., for extended periods of
time, such as 1-2 hours. In some of these embodiments, the
modifying agent is sufficiently heat stable to withstand the high
temperatures. In embodiments where the stability of the modifying
agent under high temperatures is questionable, the modifying agent
can be applied to the fiber after the high temperature processing.
In most embodiments, the resulting article can withstand heat of
use of the article and can also withstand any heat generated by
energy production in or by the article during use.
[0146] Means are provided for maintaining the modifying agent
within the hollow conduits. The modifying agents may be physically
trapped by, for example, drawing liquid additives into the interior
of the conduits and retaining them therein by capillary action or
by closing off the ends of the conduits. As described later below,
pump(s) conduits may be used to pull or push the modifying agent
out of the conduit.
[0147] Means are also provided for permitting selective release of
the modifying agent in response to the external stimulus.
Illustrative examples include cracking, breaking, bending or
otherwise breaching the wall of the conduit, for example, by
selectively removable or dissolvable coatings which give way to
permit leakage of the modifying agent in response to, for example,
stimuli such as very high heating, cooling, loading, impacting,
cracking, water infusion, chloride infusion, alkalinity changes,
acidity changes, acoustic excitation, low frequency wave
excitations, hydrostatic pressure, rolling pressure, light
sensitivity or laser excitation, thermal, load cycling or the like.
Electrical currents, voltages, electrorheological excitation,
radiation, or other energetic stimuli may also be employed or
effective to permit or cause selective release of the modifying
agent or agents from the fibers.
[0148] The selective release of the modifier occurs in the matrix
when and where it is required and may lead to improved toughness,
strength, ductility, brittleness, permeability, fire retardancy,
stiffness, dimensional stability, modulus of elasticity, fatigue,
impact resistance, and other improved properties of the matrix
composite. The selective release of the modifying agent may be
chosen to be effective to rebond the conduits to the matrix, to
repair the conduits themselves, to improve or restore the matrix to
conduit interface, to repair delaminations, and to repair
microcracks in the matrix itself which may repair or overcome
cracking or corrosion induced dimensional weaknesses and ultimately
reduced durability for the shaped articles.
[0149] It is known that alkali reactions are sometimes caused
within cementitious matrix materials when aggregate reacts with
matrix and causes an expansion of the aggregate against the matrix.
This causes internal stresses to develop within the matrix
composite or shaped article, which usually appears as cracks within
the matrix. The use of the self-repair system with modifying agent
in conduits will repair some of these cracks. In addition, instead
of adhesives, the conduits may be filled with pH modification
agents such as acidic agents to neutralize the alkali reaction. In
addition, conduits filled with the alkali reaction inhibiting
acidic modifying agent may be used in combination with the matrix
repair adhesive filled conduits.
[0150] Self-healing may be accomplished by leaving some of the
original conduits void or by adding additional conduits designed
with specialty repair agents for repairing the system. Hollow
porous conduits may be used to deliver repair agents at a later
time if damage such as cracking occurs. Repair modifying agents,
either present as an adjuvant conduit additive or added to conduits
from the outside, may be used to improve the visco-elasticity of
the entire component as desired.
2. Self-Repair of Impact Damage in Laminates
[0151] The present disclosure provides self-repair of impact damage
in composite laminates, for example, graphite and fiberglass
laminates formed from pre-impregnated layers (i.e., pre-pregs). In
most cases, this damage is in the range of 5 to 50 Joules, but
could be higher or lower. It is believed that the maximum load or
peak contact force, energy-to-maximum load, total energy, and
deflection-at-maximum load increases parabolically with an increase
in impact energy level, whereas time-to-maximum load or impact
duration at the peak load decreases linearly.
[0152] In many embodiments, to obtain self-repair system that meet
the desired criteria, this includes using developed chemicals that
can withstand the heat of processing for laminates, e.g. at least
about 250.degree. F., and often 350.degree. F. The self-repair
system is designed to withstand the levels of impact appropriate
for high strength laminates, such as graphite laminates, and repair
quickly after damage has occurred.
[0153] Referring to FIGS. 2A and 2B, a layered laminate is
illustrated. In these figures, one layer including individual
repair conduits therein. The other two layers would typically
include reinforcement materials, such as reinforcing fibers. FIG.
2A shows the laminate intact, prior to any damage.
[0154] A laminate composite article includes at least two layers or
plies of material, usually at least four layers. Up to 100 layers,
or more, can be used in laminates. For some applications, laminates
having 24-32 layers are preferred. Typically, the strength,
toughness and rigidity of the laminate increase as the number of
layers increases, however, so does the weight of the laminate.
[0155] For impact damage self-repair of laminates, the forces
caused by the impact break the repair conduits and force the
modifying agent into the damaged site within less than a second. No
pump or other mechanism is needed to move the modifying agent, as
simple pressure differences between the repair conduit interior and
the void in the laminate caused by the impact forces the modifying
agent to the damaged site. No mechanical valves are needed, as the
modifying agent fills the voids and then stops flowing out of the
conduits when the pressure differential has lessened.
[0156] When a one-part modifying agent is used, no mixing required.
The modifying agent readily reacts with the laminate layers (e.g.,
the pre-preg). For a laminate (i.e., a multilayer structure), only
one layer needs to include the repair conduits, as the modifying
agent readily flows along the layer interfaces, including up
against gravity, when an impact occurs. Additionally, the voids and
broken reinforcing fibers themselves provide conduits for flow to
damaged areas. FIG. 2B illustrates a damaged laminated with
modifying agent flowing to fill the damaged area.
[0157] FIG. 5 illustrates an alternate embodiment with one layer of
repair conduits in a laminate. In this self-repair system, (1)
pumping occurs by impact force affecting the repair conduit, a
basic impedance pump requiring no mechanical parts, (2) there is a
one part modifying agent which requires no mixing, (3) only one
layer of repair conduits is used because the repair conduits break
and allow the modifying agent to rush into damaged areas, and (4)
valves are not needed to push or halt the flow of modifying
agent.
[0158] A second active agent, in addition to the modifying
agent(s), could be added to the system. This second active agent
could be selected to benefit the composite structure at a different
time, separate from the destructive impact.
[0159] Overall, the whole laminate acts as a circulatory
microfluidic device. This is in keeping with the biomimetic
principles of keeping the design simple and the source of energy
intrinsic.
3. Self-Repair of Fatigue Damage
[0160] The present disclosure provides self-repair of non-forceful
damage such as fatigue and thermal cracking that might occur over
time a material. In such designed composites, integral channels
within the matrix are preferred, although fibers would also be
suitable.
[0161] Embodiments are designed to withstand levels of impact
appropriate for the high strength graphite laminates and also for
fatigue, thermal cycling and creep, which is a lower level force
over longer time. Both laminates and single layer composites
undergo fatigue, and the technology described herein can be used
for both laminates and single layer composites.
[0162] The repair conduits may be present within the composite in a
homogenous manner (e.g., randomly distributed) or in a layer. FIGS.
2A and 2B illustrate a matrix having many repair conduits, with the
conduits randomly distributed through the layers. This is a matrix
such as concrete, or a polymer matrix without a laminate structure
FIGS. 3A and 3B, illustrate a laminate having one layer of repair
conduits. In alternate embodiments, the repair conduits may be
present as a three dimensional (3-D) system of fibers or channels
or a weave or array or in layers orthogonal to each other. Fibers
may be provided as a dense woven or knitted mat, or be present as a
lofty non-woven mat. When pre-preg sheets are used, upon heating
the resin from the sheets can readily flow and flow around the
repair fibers thus incorporating the system of repair conduits into
the laminate without much diminution in structural properties.
[0163] Low energy cracking or damage systems include applications
such as bonded joints in electronics and cryogenic filament wound
tanks. In these applications, the release of self-repair materials
is elicited by service loading conditions: thermal cycling in space
environments, static creep and mechanical fatigue imposed by joint
configurations, and residual stresses due to mismatch of thermal
expansion (bonded joints) or fabrication processes (filament wound
cylinders). The self-repair system, particularly the modifying
agent, must not cure or degrade during thermal cycling over a
temperature range that spans from cryogenic temperatures to well
above the typical composite cure temperature.
[0164] For fatigue environments, e.g., mechanical fatigue, thermal
cycling and static creep, all of which can result in cracking that
leads to crack propagation, a different set of forces apply, as
compared to impact environments. Often, the dynamic system fatigue
is caused by less force and repeated over a longer schedule of
time. For a single layer composite, the damaging forces would be in
a smaller area or volume than in a laminate.
[0165] The damage causes a space or void such as a crack to form in
the composite. The damage also ruptures the repair conduit, which
causes the modifying agent to at least ooze of flow out. As the
modifying agent fills the void, it reacts, either by itself or with
a second part. Generally, the modifying agent stops flowing when
the space is filled or there is no more pressure differential or
void creation to push or attract the modifying agent out from the
conduit.
[0166] Together, a total system is created, the system including
the created breaks in the repair conduit, together with the cracks
or voids in the matrix, ruptured conduits, and modifying agent
migrating out of the conduits into the cracks.
4. Multifunctional Applications with Self-Repair
[0167] In some embodiments, it is desired to provide the
self-repair systems with additional properties in addition to the
self-repairing properties. For example, repair conduits, e.g.,
hollow glass fibers, can be filled with colored or tinted modifying
agent which provides a color change upon reaction, thus providing
visual indication when the modifying agent has been activated. In
some embodiments, the electronic properties of the materials may be
affected by the release of the modifying agent.
[0168] Electrically active or magnetic material (e.g., beads or
particles, either solid or coated) could be used to create
circulation energy, e.g., when retained in a fluid. Ferrite
particles or a ferrite coating could be included to absorb radar
energy and produce heat.
[0169] The ferrites can be positioned at various appropriate angles
to the radar angle by the interaction of the charges on the
individual magnetic particles. In general, the ferrites are free to
move in a more active way in a liquid modifying agent, the heat
from the energy conversion can be transported away via the in situ
circulation system of the self-repair system, and the overall
system can be multifunctional and self-repairing.
5. Self-Formation of Matrix
[0170] During a composite's life, the composite it formed over
time, it functions over time and deteriorates over time, after
which it may be thrown away. The composite may have various
functions at the same time. A preferred composite is a
multifunctional system in matrices with repairing modifying agent
that can withstand the heat of processing and any other heat of
uses. It is efficient to envision materials which are planned from
formation, repair, function and disposal. This disclosure provides
methods of making materials (e.g., matrices) by using conduits to
both form the composite material and provide self-repair properties
to it.
[0171] The preferred embodiment of a self-forming composite
includes a total dynamic energetic circulation system that
functions as an in situ fluidic system; for a laminate, this in
situ fluidic self-forming system is present in at least one layer
or area. An impact or fatigue energy or other energies are
delivered to the composite or laminate to cause energies which in
turn cause energy evolution and also creation of the composite
structure. Usually subsequent to the forming of the composite, the
energy self-repairs any damage to the composite.
[0172] At the same time (in impact or fatigue) or subsequently (in
fatigue), failure energies or cracking of the conduit or coating
release any remaining modifying agent and the energies act as a
impedance pump, pushing out the modifying agent. The void caused by
the failure has an attractive force and the modifying agent flows
into the void. The energy also either mixes two-part modifying
agents, pushes the modifying agent to the matrix walls, or causes
the modifying agent to react with the force alone or the force
causes the modifying agent to react with particles or causes
particles to react.
[0173] In an embodiment of the invention, the modifying agent is a
curable composition which reacts after release to cure within the
matrix composition. The matrix composition includes a co-reactive
component which reacts directly with the modifying agent upon
release of the modifying agent. Optionally, another co-reactive
component can be delivered or provided in the matrix which further
reacts with by-products of a cure reaction of the modifying agent,
e.g., for subsequent damage repair.
[0174] In various embodiments wherein the curable matrix
composition has at least one curable monomer, the modifying agent
may be a reactive co-monomer, crosslinking agent, hardening agent,
crosslinking catalyst, or a mixture of any of these which is
capable of affecting the rate or participating in a cure reaction
of each curable monomer. In some applications, the modifying agent
may be coated on the outside of the fiber.
[0175] Repair conduits may be used to influence curing through
thermal means. Such a system is particularly suitable for affecting
curing of thick material sections more quickly or in any curing
matrix formation wherein thermal control is desired, such as to
prevent cracking from thermal stress due to nonuniform or
excessively fast curing. Other composition reactive agents can be
actuated by heat. To this end, a method for making an article
includes providing a plurality of hollow conduits surrounded with a
shapeable curable matrix composition. A temperature-enhancing
fluid, such as a coolant, steam or other heating fluid, is
introduced or flowed into the interior portion of at least one of
the hollow conduits. Heat is thereby transmitted or absorbed from
the intermediate portion of the hollow conduit into the curable
matrix composition to either initiate or influence time of curing
of the matrix composition and the modifying agent into a shaped
matrix composite material.
[0176] Different conduits could be used for retaining and releasing
modifying agents having different functions or intended to be
released at different times. For example, a first conduit could be
used for formation of the pre-preg, and a second conduit for later
self-repair. Still additional conduits could be used for desired
qualities, such as optical sensing. In some embodiments, conduits
may be present that retain no modifying agent, but act only as
reinforcement or filler. In some embodiments, conduits or other
fillers or fibers could be used to produce energy, such as
heat.
[0177] By encasing the modifying agent in repair conduits, this
self-repair system permits more efficient use of materials in the
self-healing composite. In some applications, even a single repair
conduit with modifying agent may be adequate for healing. In
addition, by placing the modifying agent on specific surfaces,
versus a dispersed second phase of homogenous modifying agent, this
technique permits engineering of the self-healing reaction directly
on the surfaces of reinforcement materials that might be present to
further blunt or divert crack growth.
[0178] In some designs, second active agent, in addition to the
modifying agent(s) and its reactant, could be added to the
conduits, e.g., a 3-D system of conduits, to benefit the structure
at a later time. It could be used to wet the conduits of the
original structure and then also stay in the conduits to act as a
self-repairing material at a later time.
[0179] In preferred embodiments, the modifying agent should be able
to resist the high temperatures of the processing for formation and
later heating, so that the composite can later self-repair. For
example, such as when the composite is combined with a regular
pre-preg which is processed at high temperatures of 250.degree. F.
and 350.degree. F., such as for 1 to 2 hours at each
temperature.
[0180] As an example, a laminate using pre-preg materials can be
made with hollow conduits having a two-part modifying agent system
with one component inside the repair conduit and the other on the
outside, or a one-part modifying agent system with the component on
the inside. The modifying agent can be activated by release from
the inside the conduit to react with the chemical on the outside
make a composite or to make a pre-preg for even later full
activation. Additionally, after formation of the shaped article, an
amount of the modifying agent may remain unreacted, available later
for self-repair. Solvent may remain, waiting to be released from
the conduit for later destruction and/or disposal of the
article.
[0181] In some embodiments, a co-reactive component can be
delivered or provided in the matrix which further reacts with
by-products of a cure reaction of the modifying agent. For example,
the heat of the initial curing reaction can activate a
heat-activatable component to cause a secondary reaction. An
example of such a self-forming matrix is a polymer ceramic
composite, made by the following procedure. A mass of cement powder
matrix, with appropriate sand and/or aggregate, is combined with a
resin reactant, such as malic acid or maleic or succinic acid. A
second part of the resin reactant, such as hexamethylene diamine, a
liquid, is supplied in conduits. Upon rupture of the conduits, the
modifying agent flows from the hollow conduit to the powders. The
two resin reactants, i.e., the hexamethylene diamine and acid,
react via polymer condensation reaction, forming nylon and a
by-product, water. The resulting water hydrates the cement, forming
concrete. Another example of such as self-forming matrix can
include non-biological but biomimetic materials, wherein a polymer
matrix containing crystallizable mineral elements such as alumina
alkoxide may be provided. A condensation reactive element or
ingredient provided inside the self-repair conduits may be released
on application of appropriate external stimulus from the conduits
within the matrix containing the alumina crystals. The by-product
water of the condensation reaction in this case may be used to
cause alumina crystals to grow at specified locations within the
shaped article.
[0182] In various embodiments wherein the curable matrix
composition contains at least one curable monomer, the modifying
agent may be a reactive co-monomer, crosslinking agent, hardening
agent, crosslinking catalyst, or a mixture of any of these which is
capable of affecting the rate or participating in a cure reaction
of each curable monomer.
[0183] Also, a one-part matrix component may be provided through
some or all of the conduits. The one-part component permeates
through the conduit walls and enters and optionally surrounds the
matrix. The one-part component can be a simple adhesive, however,
the one-part component preferably comprises a liquid compound,
e.g., epoxy resin, containing a latent or inert catalyst component.
This latent catalyst is activatable by a suitable external
stimulus. For example, the latent hardener component may be a
light-activatable photoinitiator stimulated by light, a
heat-activatable component activatable by a heat source such as a
laser, a radiation-activatable component activated by ultraviolet,
electron beam, or gamma radiation. The external stimulus breaks
down the inert, latent agent into activated catalyst to initiate
curing. The latent catalyst or modifying agent may also be
delivered through a conduit at a delaminated location or through a
break in a conduit caused by a break or crack in the composite
structure.
[0184] The conduits could thermally influence a matrix, such as
during curing. It is recognized that some curing reactions such as
polymerization can generate a substantial amount of heat.
Particularly in conventional thick-section composite formations,
heat is not efficiently dissipated and can build to excessive
levels. If the heat exceeds the thermal stress limits of the matrix
composition, the material can be damaged by cracking and weakening.
Such damage may also result by uneven curing rates within the
composite formation.
[0185] In some embodiments, the conduit is a conductor, such as
metal, which can be charged by a voltage source in order to achieve
a migration of ions through a curing composite structure. The metal
conduits may have holes located in their walls to deliver
initiator, repair, or thermal fluids.
6. Dynamic Matrix
[0186] The self-repair system, and especially the self-forming
matrix, is provided by a series of chemical reactions to form a
composite material in which a modifying agent, either a one-part or
two-part system, is present as a fluid in a solid matrix. Upon
damage, the solid is broken and the modifying agent(s) mix with the
matrix, thus forming a solid or a fluid that then becomes a solid
by a reaction. The purpose of the reaction is to repair damage such
as cracks, voids, or delamination.
[0187] The self-repair systems of this disclosure provide a dynamic
matrix material which is transformed by external forces (such as
impact) in which the conduit and modifying agent are present within
the matrix to repair the matrix or provide the matrix itself. The
resulting matrix may react to any result caused by impact, such as
chemical melting due to chemistry, heat causing flow, reaction,
etc.
[0188] The dynamic self-repair system relies on a system of liquid
flows, energy applications and response and chemical reactions in a
synchronized way. The energy in the system, either chemical or
physical movement, may come from any of the aspects involved, such
as the force caused by the impact or fatigue, the breaking of the
conduit, a coating on the conduit that initiates the formation of
chemical energy, the modifying gent (which can be in several parts
and in several locations such as in the repair conduits and
throughout the matrix), inclusions in the matrix (such as optional
beads or particles), the matrix itself, the interactions of various
factors such as flow, the energy produced by flow, and the material
properties themselves.
[0189] In other words, any aspect of the overall dynamic system may
be responsible for the remedial, beneficial, or repair action such
as (1) the force combined with the modifying agent, (2) the heat of
the force combined with the modifying agent, (3) the chemistry of
the matrix itself, (4) inclusions in the matrix, (5) excess
reactivity in the matrix that reacts with the force, (6) modifying
agent that reacts with heat, or (7) leftover modifying agent is
activated by environmental intrusion (e.g., moisture). In general,
the dynamic matrix material is transformed by external forces,
either by formation of the matrix or repair of the matrix.
[0190] The self-repair system is a total three dimensional
composite system that functions as a dynamic circulation system in
at least one layer (for a laminate) or area (for a single layer
composite). The interaction of the various components provides a
system that functions on its own energy. The force of the damage to
the composite creates a damaged space or void, such as a crack or
delamination. This damaged area draws the modifying agent out of
the conduit, acting as an impedance pump or providing suction.
Also, the modifying agent flows out from the broken conduit. Heat
may be created by the reaction of the modifying agent; the
modifying agent stops moving when the damaged space is filled or
there is no more pressure differential to push or pull it out of
the conduit. The total system is one of created breaks in a
composite or matrix, voids in the matrix, broken conduit and
modifying agent flowing from the conduit and out into the damaged
areas.
[0191] The self-repair system includes a total dynamic energetic
circulation system that functions as an in situ fluidic system. The
impact or fatigue energy or other energies are delivered to the
composite or laminate to cause failure initiation energies which in
turn cause damage evolution and failure in the composite structure.
At the same time (in impact or fatigue) or subsequently (in
fatigue), failure energies or cracking of the conduit or coating
release the modifying agent and the energies act as a impedance
pump, pushing out the modifying agent. Additionally, the void
caused by the failure has an attractive force and the modifying
agent flows into the void. The energy also either mixes two-part
modifying agents, pushes the modifying agent to the matrix walls,
or causes the modifying agent to react with the force alone or the
force causes the modifying agent to react with particles or causes
particles to react.
7. Magnetics and Radar Creating Energy
[0192] To further increase the energy in the dynamic, self-repair
system, the repair conduits or other elements of the system can be
configured to, directly or indirectly, create electricity or other
energy. The dynamic circulation system can have an adaptable energy
producing self-repair system, which is caused by the flow of liquid
(e.g., modifying agent) in a series of tubes (e.g., repair
conduits). In some embodiments, electrically charged materials,
moving inside of the conduits (e.g., glass or magnetic fibers),
creates additional energy; the conduit, or the modifying agent
itself may be charged or may carry charged particles. See, for
example, FIG. 8. In other embodiments, in a magnetically charged
conduit, the modifying agent within the conduit may include
magnetically charged particles, such as glass beads, in the
modifying agent to create circulation and energy. Ferrite particles
may be used, which absorb radar energy and create heat. In some
embodiments, the conduits may be metal, include metal inclusions,
or have a metal coating thereon. Magnetic tubes and magnetic
particles which are half of each polarity cause dielectric current
production; see FIG. 9. The modifying agent can be driven around
and out from the repair conduit with an electrical field applied to
a magnetic field from the conduit.
[0193] Any of the materials may be designed to carry color, change
color when electronic properties are sensed, or to release a
secondary chemical. In some embodiments, the released modifying
agent can provide an electronic signal to the matrix.
[0194] The creation of energy (e.g., electricity) or heat can then
be used to provide further pumping of the modifying agent through
the matrix. The motion of the modifying agent may then give rise to
additional electrical production. The presence of conductive
modifying agent released into a matrix, such as a carbon matrix,
can be read as electrically conductivity matrix but with different
resistivity than the matrix.
8. Pumps
[0195] A pump or series of pumps may be operably part of the
conduit, typically to facilitate release from the conduit of the
modifying agent. Examples of useable conduit pumps and/or their
inclusion into the system follows. An impedance pump, which is
really a hollow fluid containing tube which can be impacted to
siphon modifying agent from one place to another when the conduit
is sharply hit. Conduit pumps such as elastic balloon pumps, can be
used to release the modifying agent into the damaged area under
pressure, thus when the conduit breaks, the modifying agent comes
out very quickly due to the pressure. Electronic pumps can be used;
for example, a solution of hydrazine sulfate is driven by
electrolysis to produce nitrogen and hydrogen (the mixing of the
two chemical in a conduit would break the conduit and force the
modifying agent out into the damaged area). Vapor pressure pumps
utilize a propellant gas in one chamber which liquefies when
compressed, and drives the modifying agent in the other part out
into the damaged areas.
[0196] Osmotic pumps, which have two chambers, might be present in
the system. See, for example, FIGS. 6 and 7, wherein one chamber
retains modifying agent and a second chamber retains salt and is
open to water. The water will flow into the salt chamber, swells in
it, thus driving out the repair agent into the damage site. These
are also known as Theeuwes pumps. A magnetic system, in which small
magnetic beads are dispersed in the matrix, could be used. An
oscillating magnetic field causes the beads to compress the matrix,
opening channels through which the modifying agent is released into
the damage areas. A simple pressure release phenomenon can also be
used as a pump. In this case the repair chemical is inserted into
the conduit under pressure.
9. Additives to Modifying Agent or Reagent
[0197] In some embodiments of self-repair systems, the modifying
agent has been designed to withstand, without degradation,
processing temperatures in a range from no heat to at least
250.degree. C. for at least one hour, and, e.g., at least two
hours. In some embodiments, the modifying agent is designed to
withstand at least 300-350.degree. F. for at least one hour and,
e.g., at least two hours. To provide the high heat resistance to
the modifying agent(s), various additives can be included to
prevent damage during heating and to prevent over heating and/or
boiling.
[0198] It was found that adding an amount of certain additives, at
a level of at least about 1% to the modifying agent, provides
improved heat resistance. Both one-part and two-part modifying
agents benefit from these additives. Examples of suitable additives
include cyclic organic sulfates, sulfites, sulfoxides, sulfinates,
such as esters of sulfurous acid (e.g.,
2-oxo-1,3,2-dioxathiolanes), hydroquinone, and antioxidants, e.g.,
phenolic antioxidant, such as butylated hydroxyanisole, including
butylated hydroxyanisole (BHA; tert-butyl-4-hydroxyanisole) and
butylated hydroxytoluene (BHT; 2,6-di-tert-butyl-p-cresol), and
those antioxidants available under the trade designation IRGANOX.
Hydroquinone and 2 ethyl hexyl methacrylate inhibit boiling of the
modifying agent. In most designs, the level of the additive is
between about 2-10%, and in some embodiments, about 4-8%.
[0199] Other additives could be added to the modifying agent to
provide additional or alternate characteristics. For example,
sulfur dioxide may be added to increase shelf life of the modifying
agent (e.g., to 6 months), plasticizers may be added to inhibit the
material obtained from becoming brittle. Chemicals which change
color upon reaction could be added.
[0200] In some embodiments, it is preferred that the modifying
agent is fast-acting, i.e., it reacts in less than one minute, and
often, in less than 30 seconds. Various additives that may increase
the reaction time of the modifying agent include silicon, styrene
and alpha-methylstyrene, and bis-cyanoacrylate, and particles such
as clay, nanoclays, montmorillite clay, and carbon black. NaOH,
either as a 50% solution in water or as pellets could also be added
to increase the reaction rate, e.g., for cyanates. Gases, e.g.,
ammonia, may increase reactivity. Additives could be added to
increase the pressure within the modifying agent, thus forcing it
out of the repair conduit quicker; these include triacetone
triperoxide and butane. Some of these same additives may improve
water resistance of the reacted product. Bis-cyanoacrylate may also
increase the strength of the reacted product.
[0201] The additive may be added directly into the modifying
agent(s), or, be provided in conduits or other sources proximate
the modifying agent. Alternately, the conduit could have the
additive or the modifying agent(s) on its surface.
[0202] According to the present disclosure, it is proposed to coat
fibers with a modifying agent or other second modifying agent which
can have a ROMP reaction and react more than once, or go on
reacting past where it touches first. It is believed that coating
conduits such as fibers with certain modifying agents can have a
beneficial effect and produce a fast, efficient reaction but also
could be used to create a pre-preg or composite material in one
step with no mixing. Rather than being provided on the outside, the
modifying agent could alternately be encapsulated, and only a small
amount needs to be released to start the reaction with the
modifying agent and formation of the resin. The components can
later be activated for self-repair.
10. Various Features
[0203] The following lists provide various features such as
ingredients for matrices, conduits, modifying agents, additives,
etc. that can be used in any or all of the applications described
in this disclosure. Also provided are different properties and
characteristic of various features.
[0204] The damage forces that the systems of this disclosure can
repair include: impact fatigue; cycling; thermal cycling creep.
Also forces form processing such as inherent stresses can be
damages which can be utilized later for repair.
[0205] The force of damage may be moderate, e.g., from 5 to 50
joules, may be high force (e.g., for graphite with tubes) to
ballistic forces (e.g. if repair chemical in the matrix as a metal
particle and uses heat or melting to flow). The velocity of the
damage may occur at the speed of gravity to bullet speed. The
damage itself may be delamination, cracking, fiber breakage, or
buckling. The damage may be caused by one or multiple damaging
events. The damage may be instantaneous or occur over several
years, e.g., for fatigue, thermal cycling and creep which happens
repeatedly over time.
[0206] The flow of the repair modifying agent out from the conduit
could occur within a nanosecond (e.g., for a very thin material,
e.g., 100-1000 centipoise) to several days.
[0207] The speed of complete chemical reaction, for the modifying
agent, may be less than a week, less than a day, a few hours, less
than a minute, or even less than 30 seconds. In some embodiments
the speed of repair may be less than 1 second.
[0208] In general, for fiberglass laminates, the heat of processing
is from ambient to 250.degree. F., usually for at least one hour;
for graphite laminates, the heat of processing is from ambient to
300-350.degree. F., usually for at lest two hours. Either or both
may be at pressure of 0 psi (total vacuum) to 10,000 psi. The
preferred manufacturing of self repairing laminates may include
vartm, scrimp, the use of an autoclave, manual or hand lay up,
resin transfer molding, resin injection, etc.
[0209] For self-repair composite, the matrix may include polymer,
pre-preg laminates, laminates, metal, metal-polymer, ceramic,
glass, and even wood. The polymers can be thermosetting or
thermoplastic materials. Polyetheretherketone (PEEK) and poly
phenylene-ether (PPE) related polymer are examples. The composites
could be processed at temperatures over 200.degree. F., and as high
as 300.degree. F. Thermosetting materials can be processed at
250.degree. F. for one hour and alternately or additionally at
300/350.degree. F. for 2 hours. Some thermoset laminates are
processed at 250.degree. F. for one hour and alternately or
additionally at 300/350.degree. F. for 2 hours. Some thermoset
laminates and polymers can be processed at 30-700.degree. F.
Usually, thermoplastics are processed up to 200.degree. F., and can
be processed at pressures of 40 to 10,00 psi.
[0210] Other matrices could be metals or aluminum foam with polymer
infill that self repairs.
[0211] Numerous examples of repair chemicals or modifying agents
have been provided above. Of course, these include epoxies, cyanate
esters, cyanoacrylates and could include DCPD, Grubb's ruthenium,
iron, tin, osmium, etc. These modifying agent need to survive the
heat and pressure of processing, and in some designs, can remain
reactive at minus 65 F, can repair damages from 2 to 60 joules of
energy, can repair delamination of 1.times.1 to 21/2 by 21/2 inches
by many layers deep, can move in 1 to 30 seconds and chemically
react fast in less than 30 seconds.
[0212] Examples of useable epoxy resins include: e-05 CL Hysol; 608
Hysol; Hysol EA 9396 QT system; Resin lab EP1121 clear (Part B);
Resin lab EP 750 clear (Part A); Ultra interior latex semi-gloss
enamel; Epon Resin 828; Epoxy and fiber glass thinner; Bisphenol
F-Epoxy resin (EPALLOY 8230); Resorcinol Diglycidyl ether (ERISYS
RDGE); Epoxy phenol novalac resin (ERISYS RN-3650); Bisphenol
F-epoxy resin (ERISYS RN-25); Epoxidized phenol-Novolac resin
(ERISYS RF-50); Epon resin 8161; Epon resin 8021; Epon resin 8111;
Fireban Hardener (NFC 2836); Fireban Resin; NFE-3038; NFE-2835;
NFA-4822; NFA-3444; Fireban hardener (NFA 3140); Phenolic Novolac
resin; and Epoxy novolac resin. For most, the difference between
these epoxies and the commonly known epoxies is that these are
formulated with Bis F or novolac epoxy resins (as compared to
`ordinary` Bis an epoxy resins). They provide an increase in
chemical resistance as compared to the normal epoxies.
[0213] Examples of useable cyanate resin ester monomers include:
2,2-bis(4-cyanatophenyl)propane (Badcy); Aquafill 5003; Aquacore
1024; Aquapour 4015; Aquapour 1024; Aqua seal 3036; Aqua seal 3818;
Aquacore premium 6001; Resbond 944; Luperox DHD-9; Resbond 940; and
epoxy vinyl ester resin. These are highly innovative
high-temperature, water-soluble mandrel materials.
[0214] Additional examples are: MY0150 resin; Trithanolamine; Resin
beads; Urethane pour foam (PART A); Urethane pour foam (PART B);
McLube 1725; Resbond 940 (Fast cure adhesive); and D.E.R 354 liquid
epoxy resin.
[0215] Examples of suitable solvents, for missing of epoxies and
other adhesives, include: acetone extra strength; glycerol 99% for
high temp production; and Duratec Black recoating.
[0216] Example of aromatic amines that could be used include:
Aradur 976-1 aromatic amine; and Two part Amine compound.
Methylmethacyrlates, could be used, as could methacylic acid.
[0217] Some useable polymer chains cleave leaving hydrogen of poly
phenylene-ether (PPE) related polymer composites, re-bonding
reaction proceeded at the chain ends with copper/amine complex
added as a catalyst. Redox reaction for supplying oxygen
continuously in the oxidation state of copper is changed from a
mono-valent state to a di-valent state that was active for the
re-combination reaction between chain ends in polymer.
[0218] Other chemicals for polymers self repair chemical include
bistriazine, which reacts with tripehenol phosphenes in 15 minutes
at room temperature, and cross-links at higher temperatures;
resourcenol diglyceride ether mixes.
[0219] High temperature resistant materials, such as boron fibers,
are suitable. B.sub.4C (boron carbide) in carbon composite, when it
melts, oxidizes to B.sub.2O.sub.3 having a higher melting
temperature. SiC which oxidizes into SiO.sub.2 may also be
suitable.
[0220] Various additives may be added for matrix strength. These
have a good polar functionality hence can trap hydroxyls on their
surfaces: Nanoclay, and carbon lampblack.
[0221] Heat producing chemicals may be added for heat production,
potassium permanaganate, and a mixture of glycerin and potassium
permanganate. Electrical wire may be physically inserted, such as
for deicers on helicopters. Additives may be used that repair based
on heat generated by the product--e.g., tires, computers.
[0222] The repair conduits, also sometimes referred to as tubes or
fibers, could be fiberglass, cement, asphalt, hydroxyapatite,
glass, ceramic, metal, polyolefin, polyester, polycarbonate,
polyacrylate, polyarylate, polyamide, polyimide, polyaramide,
polyurethane, carbon, graphite, cellulose, nitrocellulose,
hydrocarbon, or piezoelectric material. Other examples include
silicon glass tubes of 600 to 1200 micrometer outer diameter,
borosilicate glass tubes, optical fibers from Polymicro
Technologies, having an outer diameter of 60 to 1200 micrometers,
silicon with polyimide or other polymer coatings, polyethylene
tubes. Various processes could be done to treat the tubes.
[0223] The conduits or tubes could be nanofibers, electrospun
nanotubular fibers, nanotubes, or hollow nanowhiskers. The
nanofibers and like are sufficiently small enough so that no (or
minimal) bumps are raised between pre-preg plies. Some fibers could
be as small as 20-120 micrometers.
[0224] Some of the following features can be used for treating
tubes (e.g., borosilicate) in order to reduce the curing rate of
the modifying agent material therein, (e.g., cyanoacrylate):
distilled white vinegar (e.g., overnight), muriatic acid, DL-maliec
acid, dichloro, and dimethyl silane. These materials can be used
for coating the glass tubes in order to make them hydrophobic
and/or slippery. The tubes could be etched to make them more
susceptible to breakage on impact.
[0225] The tubes, channels, fibers, or the like may be present as a
weave of interconnected conduits. This weave could be designed to
first carry the structure forming resins, resin infusion or scrimp,
and then in the same channels carry self-repairing chemicals. The
conduits could be used for secondary purposes, such as to carry
light, energy or electricity.
[0226] Dyes or color changing indicators could be added to the
matrix, modifying agent, or any additives. These include food
colors, bromocresol purple, bromocresol green, bromothymol blue,
sulforhodamine B, and cyanoacrylate that can indicate that it has
reacted by a color change. Some cyanoacrylate changes color when
reacted.
[0227] Any part of the composite may be configured to sense changes
of one type or another. The composite may include nanotubes, carbon
black, metal particles, reinforcements such as fibers, clay, carbon
black, beads. The sensing may be based on visual change, energy
release, eddy currents, energy differential, or the like.
[0228] Functionally gradient materials can be added anywhere within
the composite. Functionally gradient materials can be thought of as
spatially varied but produced by changes over time. To create
gradient materials by changes during processing, they can be formed
with fibers different from the pre-preg, by adding the variant
fibers in between two non-zero bleed pre-preg layers to make an
in-situ pre-preg layer. The bleeding of the resin during processing
will form a prepare layer incorporating these fibers. Another way
of making an in-situ laminate layer, in this case using different
resin systems, is to lay in resin rods or a plaque which melt
during processing and can fill in around dry fibers. These two
in-situ ways of making pre-pregs with various resins and fiber
contents will not disturb the manufacturing process and will allow
the incorporation of various composite functionally graded
properties.
[0229] The incorporation of the variant fibers needs a source of
extra resin, either from the extra resin from other layers or
additional resin from tubes or plaques. The variant resin needs
fibers to attach to, either from the adjacent pre-preg layers or
fibers. The combined system would consist of variant fibers or
fiber performs set in a layer with a variant set of resin tubes or
a plaque.
[0230] The particular application for development is for improved
gradient thermal protection, oxidation protection, and impact
strength property systems. For some embodiments, e.g., self-forming
systems, the following materials could be used: gydroxyapatite
chemicals, (which are polymers that react with water forming
hydroxyapatite bone structures or cement polymer composites),
hydroxyapatite nanocrystals, and B-TCP hydroxyappetite
nanocrystals. For ceramic/polymer self-forming structures, nylon
polymer could be made with maleic acid and hexamethylene diamine.
Succinic acid could also be used.
[0231] Uses force from processing inherent stresses for later
release such as electrostatic charge in paint.
[0232] The systems of this disclosure provide various advantages
for concrete systems. The adhesive is flexible itself and keeps on
releasing with each brittle failure, i.e., crack. The ability to
fill in for dimensional gaps with chemicals that foam, even with
internally released stiff non-foaming adhesives, such as
cyanoacrylates. The self-repair system can replace the tensile
strength given by steel rebar. In full scale bridge applications,
surface drying cracks can be avoided by creating in-situ control
joints. The system can transform an entire structure into a ductile
material, with energy dissipated all over as cracks form, and
consequently, catastrophic failure, due to the enlargement of any
one crack, would be prevented. The system helps prestressed members
by re-bonding the tendons to the concrete, should any become
debonded.
11. Examples
[0233] The following illustrative examples show that the modifying
agent(s) survived high temperature processing (e.g., 250.degree. F.
processing for fiberglass and 300-350.degree. F. processing for
graphite laminates) and were still reactive after the exposure.
[0234] Two different modifying agents were used, epoxy and DERAKANE
epoxy vinyl ester. The matrix used was a graphite epoxy made by
Hexcel.
[0235] Thirty-two (32) plies of unidirectional carbon pre-preg were
used and extra plies were added to level out the samples, i.e., to
reduce any waviness caused by the addition of the repair tubes. The
carbon pre-preg was cut to remove material to allow for tube
placement in the center of the stack of pre-preg plies.
[0236] The 32 layers were stacked in a quasi-isotropic manner.
After half (i.e., 16) of the layers were positioned, several filled
conduit tubes were placed on top. For two-part adhesives, such as
epoxy, twinned conduit tubes were placed next to each other. For a
unidirectional laminate, the layout of the tubes was at 45 degrees
to the pre-preg direction. Ten (10) pre-preg layers were cut to
seat round the tubes, e.g., to level out the top of the tubs with
the cut pre-preg layer. The other 16 plies were placed on top, so
that 32 plies of pre-preg (plus 10 plies of pre-preg that had been
cut) were combined to form the laminate.
[0237] The experimental graphite sample laminates, made with 32
plies of carbon pre-preg and 10 extra plies between the tubes, were
made using conventional laminate forming procedures. The stack
included a release ply, a perforated release ply, and bleeder
cloth, with a vacuum bag with a central valve. The samples were
autoclaved using a vacuum bag at temperature of 250.degree. F. and
350.degree. F. and a pressure of 40 psi with a curing ramp for 34
minutes to 250.degree. F., then a 70 minute soak at 250.degree. F.,
then a 22 minute ramp to 350.degree. F. and a soak for 70 minutes
and then finally cool to ambient temperature. The sample laminates
were made as large pieces and then cut into smaller individual
samples.
[0238] The control samples were similar laminates with no repair
tubes or with empty tubes. Of course, the experimental samples had
the repair tubes filled with modifying agent.
[0239] The samples were tested by impacting with 200 foot pounds of
weight. The impacts ranges from 9 to 24 inches drop of a 20 pound
weight in a Gardner impactor.
[0240] The samples were then tested in flexure or compression to
failure in an Instron machine. The computerized results were
normalized and the standard deviations studied and comparative
result made. The difference between modulus on flexure of the
control-no-tubes and the control-with-tubes provided any penalty
for tube insertion into the pre-preg.
[0241] The comparison of the experimental samples to the
control-no-tubes did not provide information regarding the overall
repair value of the repair tubes. The comparison of the
control-with-tubes to the experimental samples provided information
regarding the strength contribution of the modifying agent. Results
are provided below.
TABLE-US-00001 TABLE Sample Category Modulus in Flexure (msi)
Controls, no tubes, not impacted 9.535 Controls, no tubes, impacted
(est. 4.479 from other data) DERAKANE, flexed 1 day after impact
4.86 DERAKANE, flexed 5 days after impact 5.78 DERAKANE, flexed 9
days after impact 8.425 Epoxy, flexed 5 days after impact 7.2
Epoxy, flexed 9 days after impact 7.19
[0242] In fiberglass samples, a visual inspection with light
penetrating through the samples was done using a dyed modifying
agent for easier identification of the damaged area. In graphite
samples, the laminate was pulled apart to assess the size of the
delamination and the spread of the modifying agent.
[0243] The samples that used epoxy as the modifying agent, the
results were acceptable. In examples using DERAKANE as the
modifying agent, these samples did not withstand the high
temperatures of processing.
[0244] In subsequent tests, the DERAKANE was added to the tubes
after the heat processing of the laminate; i.e., the DERAKANE was
added to open ended tubes. The samples were processed as above but
the open ended tubes were plugged during the heating process so as
to not take in resin flowing during the processing. After heating,
the tube ends were unplugged and filled with DERAKANE by a syringe
pressure set up.
[0245] Although the DERAKANE modifying agent was not able to
withstand the high temperatures in this experiment, DERAKANE
modifying agent is valuable in that it can gain strength earlier
than the epoxy type reaction, which required time for diffusion,
even though the epoxy has a higher ultimate strength. Additionally,
in these examples, the DERAKANE epoxy vinyl ester provided a higher
repair yield than epoxy, about 88% compared to 74%, but both of
which are acceptable. The epoxy vinyl esters survived all
processing temperatures attempted, although most samples were
processed at 300.degree. F.
[0246] The following illustrative examples show that doubling the
number of repair tubes present in the laminate (e.g., in the top
and bottom plies), restored damaged areas properties better than
single sets.
[0247] Samples were made in same way as above except twinned repair
tubes with a two-part epoxy (i.e., one part in each tube) were
placed two layers from the top and two layers from the bottom of
the stack of 32 pre-preg sheets. The tubes were placed along the
exterior edges of the stack.
[0248] With double layers of repair tubes, after impact, the
repaired laminate had a modulus 300% higher than the impacted
controls. It was estimated that the impacted control was 50% of the
non impacted one, the non impacted control would be 4.2 msi and
repaired samples would have a 40% higher modulus than the undamaged
control for a repair value of 140%.
[0249] General conclusions reached for graphite laminate composites
were:
[0250] 1. The repair system had no effect on the laminate, i.e. a
thick sample with the embedded glass tubes in the neutral axis
behaves the same as one without tubes, in modulus and in
flexure.
[0251] 2. The repair system works, i.e. stiffness is lost after
impact and the stiffness is greatly restored as a result of the
release of repair agent.
[0252] Although several different matrix materials have been
disclosed or suggested herein, others may still be used by those
skilled in this art. Although a number of different kinds of fibers
have also been described, still other fibers might also be used by
those skilled in this art in accordance with the principles of this
invention. Different modifying agents and different mechanisms for
selective release of the modifying agent in response to an external
stimuli or internal stresses caused by other external occurrences
might also be developed and designed by those skilled in the art
given the principles provided herein. Accordingly, all such obvious
modifications may be made herein without departing from the scope
and spirit of the present invention as defined by the appended
claims.
* * * * *