U.S. patent application number 10/658128 was filed with the patent office on 2005-03-31 for reinforced reactive material.
This patent application is currently assigned to Government of the United States of America.. Invention is credited to Vavrick, Daniel J..
Application Number | 20050067072 10/658128 |
Document ID | / |
Family ID | 34375770 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050067072 |
Kind Code |
A1 |
Vavrick, Daniel J. |
March 31, 2005 |
Reinforced reactive material
Abstract
A reactive material comprising a polymer and a metal foam is
provided. The strength of the reactive material is increased by the
inclusion of the metal foam. Also provided is a method of making a
reactive material by including a metal foam therein and ordnance
containing the reactive material. A preferred reactive material
includes polytetrafluoroethylene (PTFE) and an aluminum foam.
Inventors: |
Vavrick, Daniel J.;
(Fredericksburg, VA) |
Correspondence
Address: |
Matthew J. Bussan, Esq.
NSWCDD (XDC1)
17320 Dahlgren Road
Dahlgren
VA
22448-5100
US
|
Assignee: |
Government of the United States of
America.
|
Family ID: |
34375770 |
Appl. No.: |
10/658128 |
Filed: |
September 9, 2003 |
Current U.S.
Class: |
149/37 |
Current CPC
Class: |
C06B 27/00 20130101;
F42B 12/32 20130101; F42B 12/50 20130101; C06B 33/00 20130101 |
Class at
Publication: |
149/037 |
International
Class: |
C06B 033/00 |
Goverment Interests
[0001] The invention described herein may be manufactured and used
by or for the Government of the United States of America for
government purposes without the payment of any royalties therefor.
Claims
What is claimed is:
1. A reactive material comprising a metal foam and a polymer.
2. The reactive material of claim 1, wherein the metal foam
comprises a metal selected from the group consisting of, or an
alloy comprising one or more of, molybdenum, osmium, titanium,
boron, manganese, magnesium, aluminum, and nickel.
3. The reactive material of claim 1, wherein the metal foam
comprises aluminum.
4. The reactive material of claim 1, wherein the metal foam
consists essentially of aluminum.
5. The reactive material of claim 1, wherein the polymer is at
least partially halogenated.
6. The reactive material of claim 1, wherein the polymer is formed
from one or more monomers selected from the group consisting of
fluoroalkyl esters of acrylic acid, tetrafluoroethylene,
chlorotrifluoroethylene, dichlorodifluoroethylene,
hexafluoropropylene, and vinylidene dichloride, vinylidene
difluoride.
7. The reactive material of claim 1, wherein the polymer comprises
polytetrafluoroethylene.
8. The reactive material of claim 1, further comprising a material
selected from the group consisting of finely divided metal
particles, finely divided metal oxide particles, and mixtures
thereof.
9. The reactive material of claim 8, wherein the finely divided
metal particles comprise aluminum.
10. The reactive material of claim 8, wherein at least a portion of
the finely divided metal particles and the finely divided metal
oxide particles are in the form of a thermite mixture.
11. The reactive material of claim 10, wherein the thermite mixture
comprises aluminum particles and iron oxide particles.
12. Ordnance comprising the reactive material of claim 1.
13. A method of making a reactive material comprising a polymer and
a metal, said method comprising providing the metal as a metal
foam; and imbibing the polymer into a void volume of the metal
foam.
14. The method of claim 13, wherein a void volume of the metal foam
is held under vacuum for at least a portion of a period during
which the polymer is imbibing into the metal foam.
15. The method of claim 13, wherein the polymer is imbibed into the
metal foam under application of positive pressure for at least a
portion of a period during which the polymer is imbibing into the
metal foam.
16. The method of claim 13, wherein the polymer imbibed comprises a
powder.
17. The method of claim 13, wherein the polymer is imbibed into the
metal foam in the form of a polymer melt.
18. The method of claim 13, wherein the metal foam comprises a
metal selected from the group consisting of, or an alloy comprising
one or more of, molybdenum, osmium, titanium, boron, manganese,
magnesium, aluminum, and nickel.
19. The method of claim 13, wherein the metal foam comprises
aluminum.
20. The method of claim 13, wherein the metal foam consists
essentially of aluminum.
21. The method of claim 13, wherein the polymer is at least
partially halogenated.
22. The method of claim 13, wherein the polymer is formed from one
or more monomers selected from the group consisting of fluoroalkyl
esters of acrylic acid, tetrafluoroethylene,
chlorotrifluoroethylene, dichlorodifluoroethylene,
hexafluoropropylene, vinylidene dichloride, and vinylidene
difluoride.
23. The method of claim 13, wherein the polymer comprises
polytetrafluoroethylene.
24. The method of claim 13, wherein a material selected from the
group consisting of finely divided metal particles, finely divided
metal oxide particles, and mixtures thereof are also imbibed into a
void volume of the metal foam.
25. The method of claim 24, wherein the finely divided metal
particles comprise aluminum.
26. The method of claim 24, wherein the finely divided metal
particles and the finely divided metal oxide particles form a
thermite mixture.
27. The method of claim 26, wherein the thermite mixture comprises
aluminum particles and iron oxide particles.
28. Ordnance comprising a reactive material made by the method of
claim 13.
Description
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the field of reactive
materials, and specifically to the field of reactive materials
comprising composites of metals with polymers.
[0004] 2. Description of the Related Technology
[0005] Several patents and publications are referred to herein, as
illustrative of the contents of the art. These patents are
incorporated by reference as if set forth fully herein.
[0006] Reactive materials are commonly used in military weaponry.
These materials release amounts of thermal and/or percussive energy
sufficient to cause a target's destruction. Reactive materials are
typically delivered to targets via ordnance, that is, they are
included in projectiles, such as shells or warheads. The
projectiles may be launched from guns, cannons, or the like;
alternatively, the projectiles may comprise missiles, or may be
delivered by missiles.
[0007] Reactive materials that have common military ordnance
applications include, for example, gunpowder, trinitrotoluene
(TNT), nitroglycerin, dynamite, fissile materials, and plastic
explosives. It is also known to increase the destructive capability
of ordnance by including shrapnel, and by shaping the charge to
obtain a desired pattern of energy release. Finally, it is known to
calibrate the rate of destruction by varying the rate of energy
released from the ordnance. Typically, this is achieved by
selecting a reactive material with a reaction rate appropriate to
the type of destruction required. For example, a highly energetic
and largely percussive explosion may be desirable to destroy
certain targets, and a simple heat-induced fire may be suitable to
destroy others.
[0008] Moreover, one or more reactive materials may be combined to
create a desired destruction profile in a given type of ordnance.
For example, the Office of Naval Research is developing Reactive
Materials Warheads (RMWs) to achieve complete and visible
catastrophic structural defeat of cruise missiles and manned
aircraft. The RMW is needed because, for example, an incoming
missile may be hit and destroyed; however, its warhead may
nonetheless remain intact and function independently on impact. The
RMW, however, destroys its target to such an extent that any
remaining fragments of the target will not be independently
dangerous.
[0009] The RMWs function by enhancing the kinetic energy of inert
fragments, e.g., shrapnel, with chemical energy that is released
when reactive fragments hit the target. The reactive fragments
release heat and overpressure, thus adding to the destructive
effect of the warhead fragments' kinetic energy as they strike the
target. The reactive fragments may include, for example, a reactive
material designed to cling to the fragments of the target and
release their chemical energy relatively slowly, over a time period
on the order of several tenths of a second, for example.
[0010] Several examples of reactive materials likely to release
chemical energy over a time period on the order of several tenths
of a second are described in U.S. Pat. Nos. 6,485,586; 6,409,854;
6,402,864; 6,296,678; 6,293,201; and 4,432,816, for example.
[0011] Another desirable property for reactive materials to be used
in a missile-delivered warhead is physical integrity sufficient to
avoid excess deformation, melting or fragmentation under the
temperature and pressure conditions of an explosive launch.
Physical integrity may be modeled by the strength or glass
transition temperature (T.sub.g) of a material.
[0012] As discussed above, most of the reactive materials commonly
used in warheads are polymers or polymer composites. In general,
these reactive materials are characterized by relatively low
molecular weights and degrees of cross-linking. As a result, their
T.sub.g and/or strength is inadequately low, resulting in
insufficient physical integrity for purposes of explosive launch
without additional containment features.
[0013] Means of increasing the strength and/or T.sub.g of polymers
are known in the art. For example, successful approaches have
included crosslinking the polymer; increasing its molecular weight;
blending with a polymer having favorable properties;
co-polymerizing with monomers of a polymer having favorable
properties; inclusion of fibers or other structural reinforcement
comprising carbon, ceramic, or a polymer having favorable
properties (e.g., Kevlar.TM., available from E.I. du Pont de
Nemours & Co. of Wilmington, Del.); and using coupling agents
to improve adhesion between the polymer and the included fibers.
Applying these strategies to known reactive materials, however,
while ensuring that their reactivity is not compromised, would
entail initiating expensive and time-consuming research
programs.
[0014] In this connection, U.S. Pat. No. 5,895,726 describes the
impregnation of metal foams with a phthalonitrile prepolymer. The
composite formed after curing the prepolymer is described as
possessing superior structural properties; however, the composite
is also said to be oxidatively stable and flame resistant, two
properties that indicate insufficient reactivity for use in a
weapon's payload.
[0015] When a reactive material is lacking sufficient physical
integrity for explosive launch, additional features must be added
to a missile designed to deliver the reactive material. For
example, the reactive material may be confined in a container, such
as a steel box within the warhead. Additional containment features
required to compensate for inadequate physical integrity of the
reactive material add expense and complication to the warhead.
[0016] There remains a need, therefore, for a reactive material
that retains its physical integrity under the temperature and
pressure conditions of an explosive missile launch.
[0017] Thus, it is an object of certain embodiments of the present
invention to provide a reactive material with improved
strength.
[0018] It is another object of certain embodiments of the present
invention to provide a method for making a reactive material with
improved strength.
[0019] These and other objects of the present invention will be
apparent from the summary and detailed description of the
invention, which follow.
SUMMARY OF THE INVENTION
[0020] In a first aspect, the invention relates to a reactive
material comprising a metal foam and a polymer.
[0021] In a second aspect, the invention relates to a method of
making a reactive material. The method comprises providing a metal
foam, and imbibing a polymer into the metal foam.
[0022] In a third aspect, the invention relates to ordnance
comprising a reactive material in accordance with the present
invention or a reactive material made by the method of the present
invention.
BRIEF DESCRIPTION OF THE DRAWING
[0023] FIG. 1 is shows a schematic view of a metal foam including
metal particles in the void volume of the metal foam.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0024] The term "reactive" as used herein, alone or in combined
form, e.g., "reactive material", refers to substances that generate
intense heat and/or pressure when caused to react by heat, shock,
radiation including light, pressure, friction, catalyst, or by
contact with air or water. Examples of reactive materials include,
without limitation, explosive materials, polymerizing materials,
oxidizers, water reactive materials, pyrotechnic substances,
incendiary materials and pyrophores, and propellants.
[0025] A reactive material may include one or more components. When
the reactive material includes more than one component, each
component may or may not be reactive in its pure state.
[0026] The term "energetic" as used herein, alone or in combined
form, e.g., "energetic material", is synonymous with
"reactive".
[0027] The term "strength" as used herein, alone or in combined
form, refers to the stress at which the a material takes a
permanent set, that is, the material's behavior is no longer
elastic. Strength is measured in units of force per area.
[0028] The term "halogen" as used herein, alone or in combined
form, e.g., metal halide, refers to fluorine, chlorine, bromine, or
iodine.
[0029] The term "foam" as used herein, alone or in combined form,
refers to a structure that defines a void volume and is
characterized by a relatively large internal surface area.
[0030] The term "imbibe" as used herein, alone or in combined form,
e.g., "imbibable", refers to placing a substance within a
structure. It is to be understood that, after imbibing a substance
into a structure, any voids that are present in the structure may
be completely or partially filled with the substance. Examples of
imbibing include, without limitation, placing solids or liquids
within the voids of a foam.
[0031] In a first aspect, the present invention relates to reactive
materials which include a metal foam and a polymer.
[0032] Preferred reactive materials for use in the present
invention include combinations of metals and halogenated polymers.
The reactivity of these combinations is based on the large,
negative enthalpy of formation of metal halides.
[0033] In one example of a suitable reaction,
Al+fluoropolymer.fwdarw.AlF.sub.3+products of polymer reduction and
combustion
[0034] The enthalpy of formation of aluminum (III) fluoride is -313
kcal/mol. This highly exothermic reaction contributes to the
reactivity of a mixture of aluminum and polytetrafluoroethylene
(PTFE), for example.
[0035] Any polymer that can form a reactive material with a metal
is suitable for use in the present invention. The polymer may be
independently reactive, provided its reactivity is not adversely
affected to a significant extent by the metal foam component of the
reactive material, for example, nitrocellulose or guncotton may be
suitable for use in the present invention. The polymer may be a
component of a reactive composition that is capable of being
imbibed into a metal foam, for example, so-called "plastic
explosives" and the like, including "Semtex", a mixture of RDX
(cyclotrimethylenetrinitramine), PETN (pentaerythritol
tetranitrate), poly(butadiene-styrene), and oil. Alternatively, the
polymer may be reactive only in combination with the metal, for
example, Teflon.TM. PTFE, Viton.TM. fluoroelastomer, and other
halogenated polymers. Mixtures of two or more different polymers
may also be employed.
[0036] In general, halogenated polymers are preferred for use in
the present invention. Preferred halogens include fluorine and
chlorine, because they are less expensive, and because metal
fluorides and chlorides usually have especially favorable
enthalpies of formation. Halogenated polymers may be partially or
fully halogenated. Fully halogenated polymers are polymers wherein
the maximum number of hydrogen atoms are replaced by halogens.
Partially halogenated polymers are those wherein some hydrogen
atoms are replaced by halogens, but wherein it would be chemically
feasible to replaced additional hydrogen atoms with halogens, if
desired.
[0037] Preferred halogenated polymers are formed from one or more
of the following monomers: fluoroalkyl esters of acrylic acid,
tetrafluoroethylene, chlorotrifluoroethylene,
dichlorodifluoroethylene, hexafluoropropylene, vinylidene
dichloride, vinylidene difluoride, and the like. Polymers formed
from a mixture of two or more monomers may be employed in the
present invention. Such polymers may include mixtures of two or
more monomers which provide groups reactive with the metal foam,
e.g. halogens, or such polymers may be formed from a mixtures of
one or more monomers which provide reactive groups and one or more
monomers which do not provide groups reactive with the metal foam.
Thus, the structural integrity of the material could be further
enhanced by incorporating certain monomers into the polymer in this
manner. Also, the use of mixtures of two or more polymers could
provide the ability to tailor the energy release from the reactive
material by, for example, providing a situation wherein two or more
chemical reactions between the polymer and metal foam have
different reaction rates.
[0038] More preferably, the polymer consists essentially of one or
more of the following monomers: fluoroalkyl esters of acrylic acid,
tetrafluoroethylene, chlorotrifluoroethylene,
dichlorodifluoroethylene, hexafluoropropylene, vinylidene
dichloride, vinylidene difluoride, and the like.
[0039] Particularly preferred halogenated polymers include, or more
preferably consist essentially of, highly fluorinated polymers such
as Teflon.TM. (PTFE).
[0040] In general, a metal is suitable for use in the present
invention if it can be formed into a foam whose strength is
sufficient, when combined with other materials to form the reactive
material, to maintain structural integrity when subjected to
loading, for example, on explosive launch. As discussed above,
reactive materials may be delivered to a target in a variety of
different ways. Thus, the metal foam component of the present
invention is designed to provide sufficient structural integrity,
when combined with other materials to form the reactive material,
to withstand the loading to which the reactive material will be
subjected for a particular delivery method.
[0041] Preferably, the enthalpy of formation of the corresponding
metal halides is sufficiently negative for the metal to form a
reactive material in combination with a halogenated polymer.
Preferably, the metal is selected from the group consisting of
molybdenum, osmium, titanium, boron, manganese, magnesium,
aluminum, and nickel. Aluminum is a particularly preferred metal
and a particularly preferred metal foam consists essentially of
aluminum. The metal may also be in the form of an alloy containing
one or more of the metals listed above.
[0042] The metal foams may be made by any known method for forming
metal foams, such as, for example, those described in U.S. Pat.
Nos. 3,940,262; 3,981,720; 4,569,821; and other methods that are
known to those of skill in the art.
[0043] In addition to increasing the strength of the reactive
material, the metal foam provides a relatively large contact area
between the metal and the polymer in the polymer-metal mixture,
thereby favoring the kinetics of the reaction between the metal and
the polymer. Consequently, it is desirable that the metal foam be
characterized by a relatively large surface area. Preferably, the
metal foam employs the maximum surface area obtainable for a given
suitable, predetermined strength. Also, it is preferable that the
metal foam contain sufficient internal void volume to permit at
least a stoichiometric amount of the polymer to be imbibed into the
void volume of the metal foam.
[0044] The void volume of the metal foam is also preferably
substantially contiguous, so that a vacuum applied to a portion of
the structure can cause a significant amount of polymer to be drawn
into the foam. Likewise, in an alternative method of synthesizing
the reactive materials of the invention, a positive pressure may be
used to drive a significant amount of polymer into the foam, in
which case the void volume of the metal foam is also preferably
substantially contiguous. Other process parameters that may be
relevant to making an aluminum/PTFE containing reactive material
are set forth in U.S. Pat. No. 6,547,993.
[0045] The amount of polymer employed relative to the metal foam
may be determined based on a number of factors. For example, it is
desirable to provide an amount of polymer that maximizes the energy
output of the reaction between the polymer and the metal foam. This
amount may depend on the stoichiometry of the reaction between the
polymer and the metal foam, the surface area of the metal foam and
the conditions under which the reaction between the polymer and
metal foam will take place. Other factors to be considered in
determining the appropriate amount of polymer will be the void
volume of the metal foam, the degree to which the amount of polymer
may affect the overall structural integrity of the reactive
material, and other materials that may be included in the reactive
material. For example, it may be desirable to employ a larger
amount of polymer than required by the stoichiometry of the
reaction between the polymer and the metal foam, if additional
reactive metal not forming part of the foam is included in the
reactive material.
[0046] Typically, the amount of polymer and metal employed in the
reactive metal is from about 65% to about 85% polymer and about 15%
to about 35% metal. The relative amounts of the polymer and metal
employed in a specific embodiment of the invention will depend, to
some extent, on the particular polymers and metals employed in that
embodiment.
[0047] Other materials may optionally be included in the reactive
material of the present invention. For example, it may be desirable
to add finely divided metal particles to the polymer. The finely
divided metals may be useful to improve the stoichiometry of the
reaction between the metal foam and the polymer, for example, when
the mass of the polymer is too great to react completely with the
metal foam. Also, the use of finely divided metals can potentially
increase the surface contact area between the polymer and the
reactive metal by providing contact area between the polymer and
the finely divided metal in addition to the contact area between
the polymer and the surface of the metal foam. The finely divided
metal particles preferably contain one or more of the metals listed
above which are suitable for use in the metal foams of the present
invention.
[0048] Referring to FIG. 1, there is shown a schematic view of a
metal foam matrix 10, having void volume 12. Within the void volume
12 of the metal foam matrix 10 is shown metal particles 14.
[0049] Also, it may be desirable in some instances to include
finely divided metal oxide particles in the polymer. The finely
divided metal oxide particles preferably contain metal oxides that
are reactive with the polymer in order to adjust the energy output
from the reactive material. Metal oxide particles can also be used,
for example, to tailor the energy output of the reactive material
by providing a second, different energy-producing reaction in the
reactive material, in addition to the reaction between the polymer
and the metal foam. The metal oxide particles preferably contain
metal oxides, which are capable of undergoing an exothermic
reaction with the polymer. Suitable metal oxides are known to
persons skilled in the art and may include, for example, oxides of
molybdenum, osmium, titanium, boron, manganese, magnesium,
aluminum, and nickel.
[0050] Alternatively, the finely divided metal powder may form one
component of a thermite mixture, which is a combination of a metal
and a metal oxide. In the thermite reaction, the metal oxide is
reduced to an elemental metal, and the metal starting material is
oxidized. Often, the thermite reaction is highly exothermic. For
example, one well-known thermite reaction is:
Fe.sub.2O.sub.3+Al.fwdarw.Al.sub.2O.sub.3+Fe
[0051] The enthalpy of this reaction is -203 kcal/mol, and the iron
metal product is typically molten. It is thus apparent that the
reactivity of the energetic material of the invention may be
improved by including a thermite mixture.
[0052] It may be desirable to include oxidizing salts in the
reactive material of the present invention. Examples of oxidizing
salts are described in U.S. Pat. Nos. 3,753,811 and 3,513,043,
e.g.
[0053] It may also be desirable to include plasticizers in the
reactive materials of the present invention. The plasticizers may
be reactive, such as those described in U.S. Pat. No. 6,325,876, or
nonreactive.
[0054] Other additives that may be used in the compositions of the
present invention include binders and other miscellaneous
additives. Examples of other additives are a 50/50 mixture of
bis(2,2-dinitropropyl)acetal/bis(2- ,2-dinitropropyl)formal,
amorphous silicon oxides such as Cab-O-Sil.RTM. M-5,
tris-.beta.-chloroethyl-phosphate, dioctylphthalate, polyurethanes
such as Estane.RTM. 57-2-F1, vinyl chloride/chlorotrifluorethylene
copolymer in a 1.5/1 ratio of monomers such as FPC.RTM. 461,
chlorotrifluoroethylene/vinylidene fluoride copolymer in a 3:1
ratio of monomers, such as Kel-F.RTM. 800, polystyrene,
poly(dimethylsiloxanes) such as Sylgard.RTM. 182, and vinylidene
fluoride/hexafluoropropylene copolymer in a ratio of 60%/40% such
as Viton.RTM. A.
[0055] In another aspect, the present invention relates to a method
of making a reactive material comprising a polymer and a metal. The
method of the present invention comprises providing a metal foam
and imbibing a polymer into the metal foam. As noted above, the
polymer may be imbibed into the metal foam by any suitable method
for filling the void volume of a foam with a polymer, using, for
example, positive pressure, a vacuum, and polymer powder, melt, or
solution. Preferably, when vacuum is applied, at least a portion of
the void volume of the metal foam is held under vacuum as the
polymer is imbibed into the void volume of the metal foam. When
positive pressure is applied, at least a portion of the polymer is
preferably imbibed into the void volume of the metal foam while
positive pressure is applied to the polymer.
[0056] The polymer may be imbibed into the void volume of the metal
foam in any suitable form. Preferably, the polymer is imbibed into
the void volume of the metal foam in the form of a powder or
liquid. Imbibing the polymer into the metal foam in the form of a
polymer melt is preferred and is generally applicable since the
polymeric materials tend to have significantly lower melting points
than the metals contained in the metal foam, thereby allowing the
polymer to be contacted with the metal foam in the melt form
without adversely affecting the structural properties of the metal
foam.
[0057] The method of the present invention can be used to provide
increased strength to the reactive material, relative to a reactive
material consisting of a mixture of the same polymer and the same
metal provided in the form of finely divided metal particles. The
increased strength of the reactive material is provided with little
or no reduction in the energy output of the reactive material since
the metal foam provides a relatively large contact area between the
polymer and the reactive metal and because it is still possible to
add additional reactive metal in the form of, for example, finely
divided metal to the reactive material of the present invention to
further enhance the energy output.
[0058] In a first preferred method in accordance with the present
invention, a metal foam is provided. Air is evacuated from all or a
substantial portion of the void volume of the metal foam and
polymer is melted and imbibed into the void volume of the metal
foam. The polymer and metal foam are then consolidated by
cooling.
[0059] Another preferred method in accordance with the present
invention may be employed if an additional metal powder is to be
incorporated into the reactive material. In this method, a metal
foam is provided and air is evacuated from all or a substantial
portion of the void volume of the metal foam. The polymer is melted
and mixed with the additional metal powder, preferably using
sufficient mixing to provide an intimate mixture of metal powder
and melted polymer. Alternatively, the polymer and metal powder can
initially be mixed in powder form and subsequently the polymer can
be melted. The melted polymer and metal powder mixture is then
imbibed into the void volume of the metal foam. Once the melted
polymer is imbibed into the void volume, the metal foam and
polymer/metal powder mixture may be consolidated by cooling or by
compressing the metal foam and polymer/metal powder mixture and
then cooling.
[0060] All of the various types of polymers, metals, and optional
additives described above for the reactive material of the present
invention, may also be employed in the methods of the present
invention. Thus, the optional additives are preferably imbibed into
the void volume of the metal foam in the form of a mixture with the
polymer.
[0061] Also provided by the present invention is ordnance including
a reactive material comprising a polymer and a metal foam. Methods
of making ordnance are well known to those of skill in the art.
Examples of such techniques may be found in Joseph Carleone, Ed.;
Tactical Missile Warheads, Progress in Astronautics and
Aeronautics, Vol. 155, American Institute of Aeronautics and
Astronautics, 1993; Lloyd, R., Conventional Wahead Systems Physics
and Engineering Physics and Engineering Design, Progress in
Astronautics and Aeronautics, Vol. 179, American Institute of
Aeronautics and Astronautics, 1998; and Lloyd, R. Overview of
Kinetic Energy Rod Warhead Technology, Multinational Conference on
Threater Missile Defence, Minich, Germany, June 1996. More advanced
techniques, such as forming shaped charges, fragmentation warheads,
etc., may also be used in ordnance of the present invention.
[0062] The reactive material of the present invention is
characterized by a relatively high degree of structural integrity.
As a result, when the reactive material of the present invention is
incorporated into ordnance, it may be possible to avoid using
additional structure in the ordnance to maintain the structural
integrity of the reactive material. For example, in some
applications, reactive material must be encased in an additional
canister to protect it from the stresses to which it is subjected
upon, for example, launch. The present invention may permit the
fabrication of suitable ordnance without using additional structure
to protect the reactive material.
[0063] In addition, the reactive material of the present invention
could be used to replace part or all of one or more structural
elements in ordnance to thereby increase the overall energy output
of that ordnance relative by inclusion of additional reactive
material therein.
[0064] Ordnance in accordance with the present invention may
contain one or more of the same optional ingredients that may be
incorporated into the reactive material, as described above.
Ordnance in accordance with the present invention preferably
contains reactive material made by one of the methods of the
present invention.
[0065] The invention will be further illustrated by the following
example, which is not to be construed as limiting the invention in
any way.
EXAMPLE
[0066] The strength of a suitable polymer was 3200 psi. The
strength of aluminum was 30,000 psi. An aluminum foam with 96% void
volume was used. The strength of the composite material formed by
the polymer and the aluminum foam was
0.96(3200 psi)+0.04(30,000 psi)=4272 psi
[0067] Thus, the inclusion of the aluminum foam increases the
strength of the composite by 33.5% over the strength of the polymer
alone. The increase in strength due to the aluminum foam is more
significant at elevated temperatures, because the strength of the
polymer decreases more rapidly than the strength of the aluminum
with increasing temperature.
[0068] Assuming that the material is elastic-perfectly plastic, the
ultimate strength is achieved when both materials carry their
maximum load. The strength relationship is linear until the first
material yields, then a second linear relationship occurs until the
second material fails. However, in reality, since the aluminum is
less elastic than the polymer, the aluminum will yield first, but
its higher strength will allow the aluminum to carry additional
load until the polymer yields.
[0069] Changes may be made in carrying out the methods and to the
compositions of the invention above set forth above without
departing from the spirit and scope of the invention. It is
intended that all matter contained in the above description shall
be interpreted as illustrative and not in a limiting sense. The
scope of this invention is to be determined from the claims
appended hereto.
* * * * *