U.S. patent application number 11/901360 was filed with the patent office on 2012-02-09 for armor shell and fabrication methods.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. Invention is credited to Wayde R. Schmidt.
Application Number | 20120034440 11/901360 |
Document ID | / |
Family ID | 45476791 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034440 |
Kind Code |
A1 |
Schmidt; Wayde R. |
February 9, 2012 |
ARMOR SHELL AND FABRICATION METHODS
Abstract
A refractory ceramic composite for an armor shell, comprising a
ceramic core that is formable to replicate a portion of a three
dimensional surface, e.g., of an aircraft, to provide ballistic
protection. A method of making a shell of refractory ceramic armor
capable of conforming to the geometry is provided. The shell is
formed by forming a mold to replicate the surface area; arranging a
ceramic core on the mold; and removing the mold to leave said
ceramic core, and heat treating the ceramic core to a desired
hardness. The ceramic core is in the shape of the surface area.
Inventors: |
Schmidt; Wayde R.; (Pomfret
Center, CT) |
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
|
Family ID: |
45476791 |
Appl. No.: |
11/901360 |
Filed: |
September 17, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11567282 |
Dec 6, 2006 |
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11901360 |
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11455049 |
Jun 16, 2006 |
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11567282 |
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Current U.S.
Class: |
428/217 |
Current CPC
Class: |
C04B 2235/6562 20130101;
C04B 2235/5244 20130101; Y10S 428/911 20130101; B33Y 80/00
20141201; C04B 2235/656 20130101; C04B 2235/5264 20130101; Y10T
428/2918 20150115; C04B 35/573 20130101; Y10T 428/249929 20150401;
C04B 2235/6565 20130101; Y10T 29/49826 20150115; Y10T 428/249928
20150401; C04B 35/62876 20130101; Y10T 428/249924 20150401; Y10T
428/24983 20150115; C04B 2235/6586 20130101; C04B 2235/614
20130101; Y10T 428/249945 20150401; C04B 35/62873 20130101; Y10T
428/2933 20150115; C04B 35/62272 20130101; C04B 35/62281 20130101;
C04B 35/62884 20130101; F41H 5/0414 20130101; Y10T 428/24994
20150401; Y10T 428/30 20150115; C04B 35/62878 20130101; Y10T
428/24995 20150401; C04B 2235/5248 20130101 |
Class at
Publication: |
428/217 |
International
Class: |
B32B 7/02 20060101
B32B007/02 |
Claims
1. A refractory ceramic composite for an armor shell, comprising at
least a first layer, a second layer, and a third layer, said
composite being graded wherein the second layer has a hardness less
than the first layer and the third layer has a hardness less than
the second layer, wherein said first layer includes a fibrous core
and is moldable to replicate a portion of a three dimensional
surface to provide ballistic protection to said portion, wherein
fibers of the fibrous core are selected from a group consisting of
carbon pitch fibers, polyacrylonitrile resin fibers, chopped carbon
fibers, carbon nanotubes, activated carbon fibers, boron, boron
carbide, oxycarbides, oxynitrides, aluminum oxide, aluminum
oxynitride, aluminum nitride, and molybdenum fibers and
combinations thereof.
2. The refractory ceramic composite of claim 1, wherein said three
dimensional surface defines a portion of an aircraft.
3. (canceled)
4. The refractory ceramic composite of claim 1, wherein said
fibrous first layer is infiltrated with a polymer based filler to
form a polymer infiltrated layer.
5. The refractory ceramic composite of claim 4, wherein said first
layer and polymer based filler are configured to be subject to
temperatures from approximately 250.degree. C. to approximately
2000.degree. C.
6. The refractory ceramic composite of claim 4, wherein the polymer
based filler is selected from the group consisting of pre-ceramic
polymers, carbides, oxycarbides, nitrides, carbonitrides,
borocarbonitrides, oxides, oxynitrides, borides, phenolic
precursors to glassy carbon, particulate carbon powder, mixtures of
different pre-ceramic polymers and any combinations thereof.
7-10. (canceled)
11. The refractory ceramic composite of claim 1, wherein said first
layer is infiltrated with preceramic polymers.
12-23. (canceled)
24. The refractory ceramic composite of claim 1, wherein the
hardness of the first layer is controlled at least partially by a
ratio of preceramic powder to liquid polymer.
25. The refractory ceramic composite of claim 1, wherein the third
layer has greater relative compressibility relative to the second
layer.
26. The refractory ceramic composite of claim 1, wherein the first
layer, second layer, and third layer are substantially bonded to
one another.
27. The refractory ceramic composite of claim 26, wherein the first
layer, second layer, and third layer are chemically bonded.
28. The refractory ceramic composite of claim 26, wherein the first
layer, second layer, and third layer are mechanically bonded,
wherein glass or a glass/ceramic mix are injected into voids in
said composite.
29. The refractory ceramic composite of claim 1, wherein the third
layer is polymer infiltration and pyrolysis derived, said third
layer formed from one of an inorganic polymer, an organometallic
polymer, or a polymer blend.
30. The refractory ceramic composite of claim 1, wherein said
composite has graduated density across the first layer, the second
layer, and the third layer.
31. The refractory ceramic composite of claim 1, wherein the third
layer is in communication with the surface of an aircraft.
32. A refractory ceramic composite for an armor shell, comprising
at least a first layer, a second layer, and a third layer, said
composite being graded wherein the second layer has a hardness less
than the first layer and the third layer has a hardness less than
the second layer, wherein first layer is moldable to replicate a
portion of a three dimensional surface to provide ballistic
protection to said portion, wherein said first layer comprises a
ceramic foam.
33. The refractory ceramic composite of claim 32, wherein the
ceramic foam comprises at least one of carbon pitch fibers,
polyacrylonitrile resin fibers, chopped carbon fibers, carbon
nanotubes, or activated carbon fibers .
34. A refractory ceramic composite for an armor shell, comprising
at least a first layer, a second layer, and a third layer, said
composite being graded wherein the second layer has a hardness less
than the first layer and the third layer has a hardness less than
the second layer, wherein said first layer is moldable to replicate
a portion of a three dimensional surface to provide ballistic
protection to said portion, wherein said first layer comprises a
fibrous core and a matrix in which the fibrous core is disposed,
wherein the matrix includes at least one of a glass material, a
glass/ceramic material, or a polymer derived ceramic material.
35. The refractory ceramic composite of claim 34, wherein said
matrix comprises boron carbide.
36. The refractory ceramic composite of claim 1, wherein the second
layer is formed from a ceramic powder and an inorganic based liquid
containing a preceramic polymer.
37. The refractory ceramic composite of claim 1, wherein the second
layer is formed from a blend of prepolymer and preceramic
polymer.
38. The refractory ceramic composite of claim 29, wherein the third
layer includes a fibrous reinforcement structure.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This disclosure relates to ceramic-containing armor
composites for articles, supports and vehicles, including aircraft
vehicles, such as helicopters, and the fabrication methods. More
particularly, the disclosure relates to polymer infiltrated felts
and polymer-derived ceramics used for combat vehicle armor. Still
more particularly, the disclosure relates to ceramic armor
composites having a hard phase combined with an energy absorbent
structure and the fabrication methods. One embodiment of this
disclosure contains a hard outer surface and an energy absorbent
inner core.
[0003] 2. Description of Related Art
[0004] In the combat environment there is a continuing and ongoing
need to provide improved ballistic protection to various vehicles,
e.g., aircraft and helicopters. During combat, helicopters are
extremely vulnerable to sniper attacks. Current armor technology is
capable of providing Type IIIA protection, and typically contains
fiber-reinforced polymer composite, for example, glass or
Kevlar.RTM. reinforced thermoplastic.
[0005] In heavily armored helicopters, components are designed to
withstand 12.7 mm rounds, with vital engine and rotor components
designed to be capable of withstanding 23 mm or larger fire.
Enhanced armor, such as that offering Type IV protection, is often
a composite structure that incorporates a thick, solid metal plate
or a dense ceramic phase to produce the desired degree of
hardness.
[0006] Such armor is often heavy (which is undesirable for example
in flight vehicles), difficult to manufacture in a cost effective
manner, and limited to simple geometries such as flat structures
with minimal curvature. During use, the impact force of projectiles
is often inadequately distributed in such armor because the hard
phases in the composite are poorly integrated with a more compliant
structure or flexible backing component. Such backing components
are generally fabricated with layers of organic polymer fiber-based
cloth or fabrics to provide strength and toughness. In practice,
armor is designed so that the hard face breaks upon impact with the
incoming round, thereby damaging the round, and the compliant
backing structure provides additional resistance to travel by the
broken hard face or damaged round.
[0007] Ceramics presently in use for armor are of a composite
nature having the ceramic hard surface and the more deformable
polymer based backing. The ceramic surface is generally silicon
carbide (SiC), boron carbide (B.sub.4C), alumina is
(Al.sub.2O.sub.3), zirconia (ZrO.sub.2), silicon nitride
(Si.sub.3N.sub.4), spinels, aluminum nitride (AlN), tungsten
carbide (WC), titanium diboride (TiB.sub.2) and combinations
thereof. The materials used for the backing are often fibrous and
include materials such as glass, polyimide (Kevlar.RTM.) and
polyethylene (Spectra.RTM., Dyneema.RTM.).
[0008] The methods for manufacturing such composites have numerous
limitations. Currently, their fabrication methods limit the armor
configurations to flat plates or simple planar geometries or
modestly curved shapes. Such armor is very heavy and can negatively
impact maneuverability of the vehicle. The associated fabrication
methods typically require high temperatures, e.g., above
1500.degree. C., and often above 2000.degree. C., and pressures
above 2000 psi. Such fabrication requirements are costly, energy
consuming, slow and not generally suitable for mass production. For
example, complex and expensive tooling or die sets are generally
required to form such armor structures. As a result, lightweight,
highly curved armor configurations with Type IV protection derived
from ceramic composites are not presently available.
[0009] Accordingly, there is a need for lightweight, highly curved
ceramic composites that offer ballistic or blast protection that
can be easily fabricated using a wide variety of composite
architectures suitable for different combat applications.
SUMMARY OF THE INVENTION
[0010] The present disclosure provides for a ceramic based armor
component having a lightweight, highly curved configuration.
[0011] The present disclosure also provides for a polymer derived
ceramic based armor capable of providing ballistic protection to a
combat vehicle, including to the leading edges of combat vehicles'
blades.
[0012] The present disclosure further provides for a lightweight
refractory ceramic composite armor that is infiltrated with polymer
to create a felt reinforced structure.
[0013] The present disclosure still further provides for a
lightweight polymer derived ceramic based matrix armor capable of
providing ballistic protection.
[0014] A method of making a shell of refractory ceramic armor
capable of conforming to a complex geometry is provided. The shell
is formed by forming a mold to replicate the surface area;
arranging a ceramic core on the mold; and removing the mold to
leave said ceramic core. The ceramic core is in the shape of the
complex surface area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1a illustrates a schematic diagram describing generally
the method of making the refractory ceramic when structured
primarily as a filler core according to the present invention;
[0016] FIG. 1b is a photograph of a fibrous ceramic felt of FIG.
1a.
[0017] FIG. 2 is a flow chart illustrating an exemplary embodiment
of a method of making the refractory ceramic of FIG. 1;
[0018] FIG. 3 is a flow chart illustrating an exemplary embodiment
of a method of making a further refractory ceramic of FIG. 1;
[0019] FIG. 4 is a flow chart illustrating an exemplary embodiment
of a method of making a further refractory ceramic of FIG. 1;
[0020] FIG. 5 illustrates a schematic diagram describing the
refractory ceramic when structured primarily as a matrix, according
to the present invention;
[0021] FIG. 6 is a flow chart illustrating an exemplary embodiment
of a method of making the refractory ceramic of FIG. 5;
[0022] FIG. 7 illustrates a schematic representation of a graded
ceramic composite of FIG. 6;
[0023] FIG. 8 is a flow chart illustrating an exemplary embodiment
of a method of making a further refractory ceramic of FIG. 5;
[0024] FIG. 9 illustrates a schematic representation of a ceramic
matrix composite with a hard outer layer of FIG. 8
[0025] FIG. 10 illustrates a schematic diagram describing the
forming of refractory ceramics into the armor shell for an
aircraft, according to the present invention.
DETAILED DESCRIPTION
[0026] Referring to FIG. 1a, a schematic diagram describing the
reinforcement structures including fibrous ceramic felts and
particulate based cores, hereinafter, reinforcement cores, of the
present invention is provided and generally referred to by
reference numeral 10. Referring to FIG. 1b, fibrous structures 5
have voids 20 and struts 15 as a feature of its architecture.
Generally fibrous structures 5 are highly porous. Voids 20 between
struts 15, permit flowing of preceramic polymers (i.e. those
polymers intentionally designed to convert to desired ceramic
phases), or particles (ceramic, metal or polymer) dispersed in a
liquid medium throughout fibrous structures 5.
[0027] Fibrous structures 5 are generally carbon based and can be
formed of for example, fibers derived from carbon pitch or
polyacrylonitrile resins, chopped carbon fibers, carbon nanotubes,
activated carbon fibers or the like. Other felts or filler
structures may be boron, aluminum, silicon or molybdenum based. The
benefit of these fibrous structures 5 is that they provide an
excellent substrate through, and on which, preceramic polymers can
flow for subsequent processes such as heating. Further, they
exhibit favorable properties at high temperatures such as
relatively high strength, low density, tailorable thermal
conductivity, electrical resistivity, oxidative resistance and
controlled thermal expansion. In addition to felts, fibrous
structures may also include carbon, boron, aluminum and
silicon-based refractory ceramics 6 such as, but not limited to
porous particulate combinations, single crystal whiskers, chopped
fibers, and mixtures of varying degrees of porosity. Particulate
matter is selected based on particle geometry, particle size, size
distribution and overall ability to be located within the porous
structure of the fibrous structures 5.
[0028] Fibrous structure 5 is infiltrated with a source of the
desired preceramic phase(s), including carbon, in step 8. The
carbon source can be any suitable carbon source such as, but not
limited to pre-ceramic polymers that create carbon in addition to
refractory phases such as carbides, oxycarbides, nitrides,
carbonitrides, oxides, oxynitrides, borides or borocarbonitrides,
phenolic precursors to glassy carbon, particulate carbon powder,
and any combinations thereof, including mixtures of different
pre-ceramic polymers. After infiltration, fibrous structures 5 are
exposed to one or more heat processing steps 9. Heat can be
delivered through any number of methods include thermal (e.g.
furnace heating) or radiation (e.g. exposure to infrared or
microwave radiation) processes. Such processing steps can include
one or more infiltration steps 8 or pyrolysis cycles 9 required for
adequate material phase development, densification and hardening.
Pyrolytic conversion occurs generally between approximately
250.degree. C. and 1100.degree. C. Crystallization generally occurs
between approximately 1150.degree. C. to approximately 2000.degree.
C., with crystal size and percent crystallinity generally
increasing with exposure temperature and time. Depending upon the
desired characteristics, including hardness or residual porosity,
additional polymeric infiltration can take place followed by
pyrolysis cycles 9. The resultant product is a ceramic matrix
composite shell 12.
[0029] Referring to FIG. 2, a method of making a first embodiment
of the fibrous structure 5 is shown and generally referred to by
reference numeral 40. In this example, a silicon-containing fiber
core, such as silicon carbide (SiC) 45 is infiltrated with a
polymer during the infiltration step 50. Infiltration is generally
accomplished by immersing the silicon-containing fiber core 45 in a
liquid polymer or polymer-containing liquid chosen to provide the
matrix phase of the composite. For example, an immersed SiC fiber
core is heated during step 55 to temperatures ranging from to
approximately 250.degree. C. to approximately 2000.degree. C. Step
50 and step 55 may be repeated depending on the desired properties
of the end product. By altering the volume of polymer that is
infiltrated during step 50, modifying the process conditions, such
as temperature, of step 55, and varying the cooling times, the
properties of the resultant SiC felt reinforced ceramic matrix
composite 60 can be varied.
[0030] Referring to FIG. 3, a method of making a second embodiment
of the core reinforcement 10 is shown and generally referred to by
reference numeral 70. In this example, a boron carbide (B.sub.4C)
particulate core structure 75 is used to provide reinforcement to
form a ceramic matrix composite shell 95. During step 80 B.sub.4C
particle core structure 75 is infiltrated with polymer. Similar to
process 40, the infiltrated B.sub.4C core enters the pyrolytic
phase 85 and is heated to temperatures ranging from approximately
250.degree. C. to approximately 2000.degree. C., depending on the
type of polymer selected and the desired matrix phase(s). During
step 90, the B.sub.4C core structure can be optionally cooled or
treated (e.g. to enhance crystallization of the converted polymer
phase) prior to a further infiltration step 80. Steps 80 through 90
may be repeated depending on the desired properties of the end
product. By altering the volume of polymer that is infiltrated
during step 80, the processing conditions, such as temperature
profile, of step 85, or the time and temperature profile during
step 90, the properties of the end product can be customized for
the ballistic application.
[0031] Conventional densification of boron carbide panels to full
theoretical density is commonly done by hot pressing or hot
isostatic pressing and typically requires temperatures greater than
approximately 2000.degree. C., pressures above 2000 psi, and highly
controlled processing techniques. The use of boron carbide
particulate, in combination with polymer infiltrants that convert
to ceramics below approximately 1600.degree. C. offers several
processing advantages. For example, the desired hardness of the
boron carbide phase is provided by the particulate, and when
preceramic polymers to either B.sub.4C or SiC are used, the voids
initially between the boron carbide particles are filled with
additional B.sub.4C or SiC, respectively, at relatively lower
temperatures. Thus, a relatively dense structure, desirable for
ballistic protection, is provided at temperatures below those
required by conventional means.
[0032] Referring to FIG. 4, a method of making a third embodiment
of reinforcement core 10 of FIG. 1 is shown, and generally referred
to by reference numeral 100. In this example, a ceramic foam 125 is
formed and used as the reinforcement phase to form a ceramic foam
reinforced ceramic matrix composite 140. In step 110, an organic
polymer foam 105 (e.g. polyurethane) is infiltrated with powder
slurry 115. Powder slurry 115 is formed by mixing very fine and
hard ceramic powders with water, solution, or another medium such
as a mixture of preceramic polymer and particulate, or combinations
thereof. Powder slurry 115 may also contain sintering or
densification aids. During step 120, infiltrated polymer foam 105
is heated to burn out the organic polymer foam 105, partially dry
the structure and generally increase its rigidity. Alternate means
of removing the polymer foam are also contemplated, such as solvent
removal. After step 120, a ceramic foam core 125 remains having a
porous structure. Ceramic foam 125 is infiltrated with a preceramic
polymer in step 130 and heated in step 135. During step 135, the
infiltrated ceramic form core 125 is subsequently heated to
temperatures ranging from approximately 250.degree. C. to
approximately 2000.degree. C. or greater, depending on the type of
polymer selected and the desired matrix phase(s). Step 135 may be
repeated depending on the desired properties of the end product. By
altering the volume of polymer that is infiltrated during step 130,
and the time, temperature and atmosphere used in step 135, the
properties of the ceramic foam reinforced ceramic matrix composite
140 can be customized for the ballistic application.
[0033] Referring to FIG. 5, a schematic diagram describing the
refractory ceramic of the present invention, when structured
primarily as a matrix phase, is provided and generally referred to
by reference numeral 150. Refractory matrix 150 is generally not as
porous as the fibrous structures of FIGS. 1 through 4. Refractory
matrix 150 is, for example, a ceramic, glass, glass/ceramic
mixture, polymer-derived ceramic phase(s) or combinations thereof,
and may include oxides or silicon carbide or boron carbide ceramic
phase(s). For example, silicon carbide and boron carbide matrix
materials 155 are conveniently derived from grinding hardened
preceramic polymers to produce a powder. Glass powders 155 such as
silica-based glasses, including borosilicates may be selected based
on their desired viscosity at a given temperature, such that they
will flow into at least a portion of voids with processing and
thereby increase the overall density of the structure. Mixtures
prepared by combining ground, hardened powders derived from
preceramic polymers with liquid forms of preceramic polymers can
also be used. Generally, these preceramic polymers can be further
successively hardened in step 156 and crystallized when exposed to
higher temperatures and extended times, such that resultant ground
powders have a very dense crystalline structure and are extremely
hard. Such powders are exposed to temperatures ranging from
approximately 250.degree. C. to approximately 2000.degree. C. or
greater, depending on the type of polymer selected and the desired
matrix phase(s). Proper control of the ratio of powder to liquid
polymer, as well as the number, type and duration of successive
heating steps, provides the ability to tailor both the amount of
porosity, as well as the hardness, of the resulting structure. Such
control is important to create a composite 158 with appropriate
ballistic protection.
[0034] Referring to FIGS. 6 and 7, the method of making a graded
ceramic composite 200 is shown, and generally referred to by
reference numeral 160. Graded ceramic composite 200 is
distinguished in that it provides differing degrees of hardness in
a single ceramic composite. Graded ceramic composite 200 features
regions of differing hardness, such as a very hard outer coating or
top layer 205, an intermediate layer 210 of reduced hardness
relative to the harder top layer and a somewhat softer layer 215.
Layer 205 is particular suited for deflecting, damaging and
defeating ballistic impacts because if its immense hardness. In
contrast, layer 215 is suited to absorb some of the impact of the
ballistic impact due to its relative softness, compressibility and
greater toughness relative to the harder top layers. It is
important that the various layers are substantially bonded to one
another, that is that the topmost layer is well bonded to the
intermediate layer(s) and the intermediate layer(s) are
sufficiently bonded to the inner most layer(s). This bonding is
important to maintain communication between the topmost layer and
the innermost layers, i.e. to effectively dissipate impact energy
to the layers of the graded composite.
[0035] Layers 205 and 210 are formed from a mixture of ceramic
powders and a dispersive liquid 165 that form a slurry 170. The
dispersive liquid can be water, a water based solution, or an
organic or inorganic based liquid or solution. The dispersive
liquid may also contain a preceramic polymer. Solutions can also
contain various dispersion agents and surfactants as necessary.
Slurry 170 is heated during a processing step 175 to form hard
outer layers 205 and 210. Slurry 170 is heated to temperatures
ranging from approximately 250.degree. C. to approximately
2000.degree. C., depending on the type of ceramic selected and the
composition of the slurry components, as well as the structure and
composition of the desired matrix phase(s). Hard outer or top layer
205 and intermediate hardness layers 210 are optionally reheated in
step 175 and further hardened to the desired hardness to form the
harder layers of the graduated composite 200. Hard outer or top
layer 205 may be heated to a greater degree (higher
temperatures/longer exposure) than intermediate hardness layer 210
to ensure additional hardness. Layers 205 and 210 can be
alternatively formed by modifying an existing layer. For example,
residual porosity in a layer 205 can be reduced by filling this
porosity with desired phase(s) using a variety of methods.
Specifically, voids volume can be reduced by deposition of ceramic
phase from the vapor (physical or chemical vapor deposition), from
electrophoretic or electrostatic deposition from an additional
ceramic slurry, by infiltration with ceramic-filled polymer pastes,
and combinations of these or similar methods.
[0036] Layer 215 is formed from an inorganic or organometallic
polymer or polymer blend 180 that is heat processed in step 185 in
a controlled atmosphere and converted into one or more ceramic
phase(s) 215. Preferably the ceramic phase(s) 215 contain
additional reinforcement structures such as particulate or fibrous
structures 5, such that a polymer-derived ceramic matrix composite
215 results. This (Polymer Infiltration and Pyrolysis) PIP-derived
CMC 215, layer 205 and layer(s) 210 are bonded to form graduated
ceramic composite 200. While discrete steps to create a bonded
graduated ceramic matrix composite 200 have been described, this
disclosure includes the formation of a similarly graded PIP
[0037] CMC which can be bonded to harder layers 205 and 210. The
benefit of such a graduated ceramic composite structure is that it
offers multiple functionality in a single armor component. The
integral structure of the hard upper surface and energy absorbent
softer sub layers allow integration of what was previously
accomplished by two separate components. Accordingly, the graduated
ceramic structure is stronger and lighter than a similarly sized
piece of armor that was previously available. The lightness is
achieved because prior armor structures were monolithic in nature
and did not offer graduated hardness or density. Further, the
integrated structure reduces the need for a separate flexible layer
proximate the surface of the aircraft to absorb the energy of a
ballistic impact.
[0038] Referring to FIGS. 8 and 9, the method of forming an
alternate ceramic matrix composite structure 300, generally
referred to by reference numeral 250, is shown. Ceramic matrix
composite 300 is formed having a hard top or outer layer 275 and a
much softer preceramic polymer-derived lower or internal composite
layer 295. Ceramic matrix composite 300 is produced in a similar
fashion as the graded ceramic of FIGS. 6. and 7 except that it does
not contain intermediate layer 210. A slurry 270 is formed and is
heated during a processing step such as a heating step 265 to form
hard top or outer layer 275. Slurry 270 is heated to temperatures
ranging from approximately 250.degree. C. to approximately
2000.degree. C., depending on the type of ceramic selected and the
composition of the slurry components, as well as the structure and
composition of the desired matrix phase(s). Hard outer layer 275 is
optionally reheated in step 265 and further hardened to the desired
hardness to form the harder layer of the composite 300. Hard outer
layer 275 may be heated to a greater degree (higher
temperatures/longer exposure) than layer 295 to ensure additional
hardness. Residual porosity in a hard outer layer 275 can be
reduced by filling this porosity with desired phase(s) using a
variety of methods. Specifically, voids and void volume can be
reduced by deposition of ceramic phase from the vapor (physical or
chemical vapor deposition), from electrophoretic or electrostatic
deposition from an additional ceramic slurry, by infiltration with
ceramic-filled polymer pastes, and combinations of these or similar
methods.
[0039] Softer layer 295 is formed from a prepolymer, preceramic
polymer or blend 280 that is processed with desired heat, pressure,
atmosphere conditions in step 285 and infiltrated during step 290.
Steps 285 and 290 are repeated until the desired hardness and/or
phase(s) of pyrolytic derived composite matrix composite 295 is
achieved. Layers 275 and 295 are bonded to form the composite
consisting of a hard ceramic top layer and the polymer infiltrated
pyrolytic and composite matrix composite. Individual layers can be
bonded together through chemical or mechanical means or a
combination of bonding methods. For example, a thin adhesive can be
used to bond the hard top coat to the underlying polymer-derived
composite structure. In practice, it is preferred if the layers are
strongly bonded together. One means to bond the layers together is
to fix the topmost layer to the composite structure and to inject a
glass, glass/ceramic or ceramic forming polymer into voids
intentionally left in the structures. In this manner, glass/ceramic
would fill at least a portion of the voids, and further processing
could be used to crystallize the ceramic phase. Also in this
manner, the injected preceramic polymer would fill at least a
portion of the voids, and further processing could be used to
convert the polymer into additional ceramic phase(s). Thus, the
layers would be mechanically joined and integrated.
[0040] Similarly, following fixturing of the layers adjacent one
another, a vapor deposited phase could be introduced into the
residual porosity, thereby creating a bonding mechanism. In
addition, a molten metal or glass phase could be introduced into
residual porosity in a layered structured, followed by cooling to
solidify the molten phase in place. In one embodiment for a layered
composite consisting of a hard face and a polymer derived
composite, a molten glass could be forced into the residual
porosity of both layers, and the structure then cooled to solidify
the glass phase and rigidly join the layers in an integrated
fashion. Glass compositions would be chosen to minimize reaction
with the existing composite phases. Some glass compositions could
be further processed to create ceramic/glass mixed phases.
[0041] The filler and matrix materials and structures described
above are excellent for forming ballistic protection, e.g., for
articles, supports and vehicles, including aircraft vehicles, and
particularly for helicopters in the form of ceramic-containing
armor shells. The ceramic armor shells can be formed in any
three-dimensional shape of the surface of the helicopter. Of
course, it is most desirable to produce the armor shells with
minimal thickness to maintain reduced weight while still providing
for a sufficiently hard surface for ballistic protection.
[0042] In operation, the molding process suitable for creating the
disclosed ceramic armor shells will be described with respect to
the polymer infiltration and pyrolysis and ceramic matrix composite
(PIP-CMC) material as shown in FIG. 10, and generally referred to
using reference numeral 400. In a first step 410 a mold is formed
to replicate the outer geometry of the helicopter components
targeted for protection. The fibrous structures 5 or particulate
based structures 4 to be infiltrated are positioned within, around,
upon or against mold or temporary tooling in step 420 during shell
formation. Following partial rigidization in step 425, the mold or
temporary tooling is removed in step 430 leaving the reinforced
structure in the desired shape with remaining porosity. Iterative
impregnation and/or heating (or alternate processing) steps 440 are
effected until the desired density, phase composition(s),
mechanical properties and residual porosity are achieved. The armor
450 is removed and trimmed as desired in step 460. Molds and
temporary tooling can be fabricated using any known methods
including machined metal or plastics, rapid prototyping (metal,
ceramic, polymer and combinations thereof), waxes, and the like.
Similar processing can be used to fabricate the other
architectures. For example, separate structures for multiple
layered composites (e.g. harder and softer layers) can be
fabricated independently and subsequently joined using the methods
described above.
[0043] Further, placement of the variably shaped armor components
450 can be placed as desired over the helicopter structure. The
most vulnerable regions of the helicopter can be protected with
armor having the most resistant architecture. Further, parts of the
helicopter such as the blades can also be protected against
ballistic firing. Protective armor shell articles can be attached
to the aircraft structure in a variety of ways known in the art,
including adhesives, bonding, mechanical fixturing, inserts, etc.
Separate armor components can be positioned adjacent, overlapping
or both relative to other armor components, and can be configured
to have alignment or interlocking features to aid positioning and
increase ballistic protection.
[0044] While the present disclosure has been described with
reference to one or more exemplary embodiments, it will be
understood by those skilled in the art that various changes may be
made and equivalents may be substituted for elements thereof
without departing from the scope of the present disclosure. In
addition, many modifications may be made to adapt a particular
situation or material to the teachings of the disclosure without
departing from the scope thereof. Therefore, it is intended that
the present disclosure not be limited to the particular
embodiment(s) disclosed as the best mode contemplated, but that the
disclosure will include all embodiments falling within the scope of
the appended claims.
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