METHOD AND APPARATUS FOR THE MITIGATION OF EXPLOSIVELY FORMED PROJECTILES
A multi step approach to mitigating the effects of explosively formed projectiles (EFPs). The first step involves a splitting step whereby the EFP total mass is reduced into fragments having smaller masses. The fragments are then exposed to cascading armored disks in preparation for a temperature reduction or “cooling” step. Heat is reduced by conduction through a cooling medium. Temperature reduction restores some solid properties to each fragment. The EFP fragments are slowed by exposure to a series of cascading armored disks designed to disperse contact pressures from any remaining fragments.
This application claims priority to and the benefit of co-pending U.S. provisional patent application Ser. No. 61/340,281 filed Mar. 15, 2010, which application is incorporated herein by reference in its entirety.
FIELD OF THE INVENTIONThe invention relates to armor in general and particularly to an armor composition that provides protection against explosively formed projectiles.
BACKGROUND OF THE INVENTIONRecent conflicts in the Middle East and the use of improvised explosive devices (IEDs) have demonstrated the devastating tactics used in modern day asymmetrical warfare. Unconventional methods such as IEDs are the choice of the insurgents as they provide a low cost easily constructed strategic weapon of influence within the region. The explosively formed projectile (EFP, also referred to as explosively formed penetrators) is a new deadly form of IED has made its way to the battlefield. This new weapon has wreaked havoc on coalition armor and has resulted in many casualties and tremendous loss of strategic assets.
The presence of EFPs on the battlefield has given rise to a demand for improved armor protection. These projectiles have the capacity to travel at hypervelocity speeds, often in excess of 3 km/sec or approximately 9,842 feet per second. These devices are constructed of a high explosive (HE) charge placed behind a metal disk that is designed to receive the blast pressure. These disks are often made from either copper or silver because they are extremely ductile and have relatively low melting temperatures, as compared to many other metals. Upon detonation the disk collapses and forms a molten slug possessing hydrodynamic properties. Recent studies suggest these projectiles possess both solid and liquid properties. One theory attempts to explain this by suggesting the EFP slug has an outer sheath that behaves as a solid and a molten inner core. (Cullis, Fort Halstead, UK). It is thought that the molten material can alloy with armor (or dissolve the armor) that it contacts, so as to reduce the strength of the armor material and may convert the armor material to a liquid state. This alloying or dissolving process can take place in very brief amounts of time. The penetrator mass then passes through the opening so created and can do significant damage to anything that it then contacts.
If an EFP slug is moving fast enough (e.g., has enough kinetic energy), the penetrator may be considered to be only strong enough to hold the material together in a liquid form.
Conventional armor systems are unable to handle the extreme forces generated from a hypervelocity impact caused by a molten or semi-molten copper slug. Current “up armor” systems for HMMWVs (also known as Humvees) are constructed using 1 inch (25.4 mm) thick laminated hardened steel plates. Although such armor is effective in providing protection from small arms fire and indirect shrapnel, it is ineffective in preventing an armor breach by an EFP slug. Typically penetration of an EFP is directly proportional to the material's density or specific gravity. The density for solid copper is 8,960 kg/m3.
Recent developments in EFP resistant systems, for example as employed by the Marine Corps in early 2009, involves multiple layers of 18 mm steel plates. Although these systems are hardened, they still fall short of providing full protection from EFP slugs and can cost as much as $2,000 per square foot.
There is a need for lightweight EFP resistant armor that is more effective than present armor systems.
SUMMARY OF THE INVENTIONAccording to one aspect, the invention features an armor system. The armor system comprises a pair of outer layers of armor plate, one of the pair of outer layers of armor plate configured to provide an outer front surface and the other of the pair of outer layers of armor plate configured to provide an outer rear surface, the pair of outer layers of armor plate defining a volume therebetween, the outer rear surface configured to be attached to an object to be provided with armor; a splitter layer configured to receive an explosively formed projectile and configured to split the explosively formed projectile into a plurality of secondary projectiles, the splitter layer disposed within the volume between the pair of outer layers of armor and adjacent the one of the pair of outer layers of armor configured to provide the front surface; a first layer of armored disks disposed within the volume between the pair of outer layers of armor and adjacent the splitter layer, the first layer of armored disks configured to receive at least one of the plurality of the secondary projectiles and configured to disperse an impact force of the at least one of the plurality of the secondary projectiles along a plurality of directions, the first layer of armored disks comprising at least two rows of overlapping disks; a cooling layer disposed within the volume between the pair of outer layers of armor and adjacent the layer of armored disks, the cooling layer comprising a medium configured to absorb thermal energy from at least one of the plurality of the secondary projectiles and to reduce a temperature of the at least one of the plurality of the secondary projectiles; and a second layer of armored disks disposed within the volume between the pair of outer layers of armor and adjacent the cooling layer, the second layer of armored disks configured to receive at least one of the plurality of the secondary projectiles and configured to disperse an impact force of the at least one of the plurality of the secondary projectiles along a plurality of directions, the second layer of armored disks comprising at least two rows of overlapping disks.
In one embodiment, a layer of armored disks selected from the group consisting of the first layer of armored disks and the second layer of armored disks comprises circular disks.
In yet another embodiment, the circular disks have a central aperture.
In another embodiment, the circular disks are configured in an overlapping square array.
In still another embodiment, the circular disks are configured in an overlapping hexagonal array.
In a further embodiment, the cooling layer comprises a fibrous material immersed in a fluid medium.
In yet a further embodiment, the fluid medium comprises a rheopectic fluid.
In an additional embodiment, the splitter layer comprises bars.
In one more embodiment, the splitter layer comprises a first plurality of parallel bars having a length dimension disposed in a first direction, and a second plurality of parallel bars having a length dimension disposed in a second direction not parallel to the first direction.
In still a further embodiment, the bars are rolled bars.
According to another aspect, the invention relates to a method of mitigating the effects of an explosively formed projectile. The method comprises the steps of splitting a mass of an explosively formed projectile into a plurality of secondary projectiles having a respective smaller mass than the mass of the explosively formed projectile; cooling at least one of the plurality of secondary projectiles to a temperature below a temperature of the explosively formed projectile; and slowing at least one of the plurality of secondary projectiles to a velocity below a hydrodynamic termination velocity; thereby mitigating the effects of the explosively formed projectile on an object against which the explosively formed projectile is launched.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.
The objects and features of the invention can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views.
We describe a three step approach for mitigating the effects of an EFP device which is called the “SCS” system and method. The acronym “SCS” stands for “split”, “cool”, and “slow,” which describes how the explosively formed projectile is treated. This three step approach offers a unique method for mitigating the effects of an EFP by weakening or reducing the effect of the penetrator by reducing its mass, its temperature, and its velocity. Although there are three primary steps to mitigation, there exists no set value for the number of layers that compose the 3 steps. It is advantageous to manipulate both the number of individual layers as well as their perspective positions in different combinations. These modifications each have as their effects remain the same, namely to split a penetrator to reduce the mass of individual portions relative to the original mass and to increase the surface to volume ratio of the individual portions relative to the original mass, to cool the individual portions of the penetrator so as to eliminate the ability of the penetrator to act as a mass in the molten state, and slow the velocity of the individual portions of the penetrator, so as to reduce kinetic energy (E=½ Mass×velocity) and momentum (P=mass×velocity).
As one understands from the above equations, a reduction of the mass of an EFP reduces both its kinetic energy and its momentum in proportion to the reduction in mass. As one understands from the above equations, a reduction of the velocity of an EFP reduces both its kinetic energy in proportion to the square of the reduction in velocity, and reduces its momentum in proportion to the reduction in velocity. The deliberate fragmentation of the warhead, while increasing the number of projectiles, also minimizes the mass of each fragment thereby limiting their respective kinetic energies. Another feature of causing the original mass of the penetrator to be broken into a number of smaller fragments, each having a smaller mass than the original mass of the penetrator is that the surface area relative to the volume increases (e.g., the surface to volume ratio increases).
To explain this phenomenon, we consider as a hypothetical example of a liquid having density D grams per cubic centimeter. We take an original spherical sample of liquid having a volume of one cubic centimeter. The split volumes of two spheres would be 0.5 cubic centimeter each. A sphere has a volume given by Volume=4/3π(Radius)3 and a surface area given by Surface=4π(Radius). Table I presents the respective values of volume, radius, surface are and surface to volume ratio of the original 1 cm3 object and an object of 0.5 cm3.
A first structure is provided to convert the original mass of a single penetrator into a number of smaller fragments each having a smaller mass than the original mass.
A second structure comprising a multi-layered disk armor is designed to receive the smaller fragments of the penetrator and to reduce the velocities of each fragment, thereby reducing their kinetic energies and momenta, as well as their respective impact pressures. These disks provide a simultaneous dispersal of kinetic forces in several directions at each point of impact. This layer prepares the fragment to be exposed to a medium that can reduce its temperature. The medium can in various embodiments comprise a polymer in a gel.
The second step of mitigating the effect of an EFP involves reducing the temperature of each fragment by interaction with hydrophilic polymer fibers, or a similar cooling medium, bathed in a fluid medium that can absorb thermal energy. One such fluid medium is a glycerol/water solution that can provide a medium for transient heat reduction of each EFP fragment while providing conditions for hydrodynamic termination velocity. Preferably the fluid medium has rheopectic properties, that is, the fluid medium exhibits an increase in viscosity as shearing force is applied to it. There are rheopectic fluids that thicken or solidify when shaken. Examples of rheopectic fluids include gypsum pastes and printers inks. Some solutions of water and glycerol also exhibit rheopectic properties. Another class of materials that can be made more viscous with increase in applied stress (e.g., applied magnetic field) is magneto-rheopectic fluids. Delphi Corporation currently sells shock absorbers filled with a magneto-rheological fluid, whose viscosity can be changed electromagnetically.
In another embodiment, it is believed that one or more of the front layers or succeeding layers can be made of a piezoelectric or pyroelectric material. When a projectile impacts such a layer, the piezoelectric or pyroelectric material will generate a current. The energy so generated is expected to be used to energize a magneto-rheopectic fluid to provide a medium having properties that resist the penetration of the projectile. In this manner, the energy in the projectile can be used to aid in mitigating the effects of the projectile itself. In another embodiment, the electric generating layers are situated between the disc layers so they would provide current as the discs disperse the energy. Yet another embodiment is believed to involve making the discs out of electric generating material that could both disperse the impact energy and generate the electric current. This dual purpose layer is expected to contribute to keeping the complete systems weight to a minimum.
When cooled and slowed down, the EFP projectile loses its ability to possess hydrodynamic penetration properties and is characterized as either a plastic deformation or rigid body penetrator.
The next step of mitigating the effect of an EFP is the slowing of EFP fragments by a multi-layered armored disk designed to disperse force pressures in several directions for each individual impact point. This armor configuration offers a reduced weight solution as each layer is composed of disks rather than a heavier solid armor plating. As shown in
In the event the total velocity of each fragment is greater than zero, the reduction in speed will ultimately reduce the back spall created by any penetrations resulting in mitigating effects of each.
The slug fragments are then exposed to a multi-layered armored disk configuration designed to simultaneously spread the contact pressure in several directions at every location of impact. The result is each of the resulting pressure points are then conveyed to an additional set of plural contact points resulting in further mitigation of contact pressure. This layering technique spreads any single contact point out over an expanded area thereby reducing the pressures for each contact point and can be repeated until desired resistance has been reached. This “cascading” effect allows armor normally easily penetrated to successfully receive much higher pressures.
In one preferred embodiment the armor disks have a compressive medium sandwiched between each layer configured to absorb some kinetic energy caused by the impact.
Remaining EFP fragments surviving the layered armor are then exposed to the second step of SCS armor mitigation, the coolant medium which in a preferred embodiment is a bath made from hydrophilic polymers bathed in a glycerol/water solution. The temperature of the EFP fragments is reduced by a process of heat conduction, whereby each fragment is exposed to a substantially cooler medium than the overall fragment temperature. This significant temperature difference aids in the transfer of heat from the fragment out to the cooler medium.
In another embodiment the coolant medium is expected to be a non-aqueous medium.
EFP fragments still possessing a velocity greater than zero move onto the final step of the SCS armor mitigation, which includes an additional set of layered armored disks. Once more the contact pressures exerted on each disk is dispersed simultaneously in a multitude of directions in repeating form.
Any remaining fragments still possessing a velocity >0 after step 3 are finally exposed to the outer sheath of the SCS armor system, a hardened exterior steel plate. Any backspall generated as a result of full penetration should be significantly reduced as a result of the SCS composition.
An experiment was conducted to examine how differences between temperatures of two separate bodies were affected over time in the event of contact. The experiment showed that the greater the temperature difference between the two media, the greater the affect on their respective heat flows. The test object was copper heated to 300 degrees Celsius and immersed into water solution at room temperature of 17 degree Celsius.
Immersion was not finely controlled but averaged 0.3 seconds per contact. Trial #1 resulted in a 65% heat reduction of the copper, or a drop of 195 degrees Celsius. Trial #2 resulted in a 59% heat reduction or a temperature drop of 106 degrees Celsius. It is important to note that a temperature spike of +73 degrees occurred during trial #1 just moments after coolant medium had been removed. The initial temperature of the copper was 300 degrees Celsius which when immersed dropped to a momentary 105 degrees Celsius but spiked upwards of +73 degrees Celsius to a final temperature of 178 degrees Celsius representing a 41% spike in temperature.
The second immersion began at the 178 degree Celsius and experienced a 59% drop of temperature, or a 106 degrees Celsius drop down to 72 degrees Celsius. A temperature spike was also noted on the second immersion however its levels were significantly lower than in trial #1. In trial #2 the resulting 72 degrees Celsius was momentary and climbed to 85 degrees Celsius, or +13 degrees Celsius higher than immediate result of 72. This spike represented a 13% increase moments after immersion.
The third trial resulted in even less of a temperature drop overall and experienced no return spike after cooling medium had been removed. In trial #3 the starting temperature was 85 degrees Celsius and when immersed dropped to 67 degrees Celsius where the copper temperature held steady.
The graph illustrates the varying temperature readings during each test, with Ti=Initial temperature, Tm=Momentary temperature, and Tr=Resulting temperature.
Table II lists the various layers of one embodiment of a SCS armor configuration that is expected to have a weight of 110 pounds per square foot. The layers are described by material composition, thickness, mass per square foot (Mass PSF), and the structure of the material in the layer. HHS denotes high hardened steel.
Table III lists the various layers of one embodiment of a SCS armor configuration that is expected to have a weight of 78 pounds per square foot. This configuration replaces several layers of high hardened steel with a layer of SiC disks of equal thickness. This reduces the weight by 50% or more in layers previously containing HHS.
The systems and methods of the invention are contemplated for use by military forces and/or by civilian policeforces.
Theoretical DiscussionAlthough the theoretical description given herein is thought to be correct, the operation of the devices described and claimed herein does not depend upon the accuracy or validity of the theoretical description. That is, later theoretical developments that may explain the observed results on a basis different from the theory presented herein will not detract from the inventions described herein.
Any patent, patent application, or publication identified in the specification is hereby incorporated by reference herein in its entirety. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material explicitly set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the present disclosure material. In the event of a conflict, the conflict is to be resolved in favor of the present disclosure as the preferred disclosure.
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be affected therein without departing from the spirit and scope of the invention as defined by the claims.
Claims
1. An armor system, comprising:
- a pair of outer layers of armor plate, one of said pair of outer layers of armor plate configured to provide an outer front surface and the other of said pair of outer layers of armor plate configured to provide an outer rear surface, said pair of outer layers of armor plate defining a volume therebetween, said outer rear surface configured to be attached to an object to be provided with armor;
- a splitter layer configured to receive an explosively formed projectile and configured to split said explosively formed projectile into a plurality of secondary projectiles, said splitter layer disposed within said volume between said pair of outer layers of armor and adjacent said one of said pair of outer layers of armor configured to provide said front surface;
- a first layer of armored disks disposed within said volume between said pair of outer layers of armor and adjacent said splitter layer, said first layer of armored disks configured to receive at least one of said plurality of said secondary projectiles and configured to disperse an impact force of said at least one of said plurality of said secondary projectiles along a plurality of directions, said first layer of armored disks comprising at least two rows of overlapping disks;
- a cooling layer disposed within said volume between said pair of outer layers of armor and adjacent said layer of armored disks, said cooling layer comprising a medium configured to absorb thermal energy from at least one of said plurality of said secondary projectiles and to reduce a temperature of said at least one of said plurality of said secondary projectiles; and
- a second layer of armored disks disposed within said volume between said pair of outer layers of armor and adjacent said cooling layer, said second layer of armored disks configured to receive at least one of said plurality of said secondary projectiles and configured to disperse an impact force of said at least one of said plurality of said secondary projectiles along a plurality of directions, said second layer of armored disks comprising at least two rows of overlapping disks.
2. The armor system of claim 1, wherein a layer of armored disks selected from the group consisting of said first layer of armored disks and said second layer of armored disks comprises circular disks.
3. The armor system of claim 2, wherein said circular disks are configured in an overlapping square array.
4. The armor system of claim 2, wherein said circular disks have a central aperture.
5. The armor system of claim 2, wherein said circular disks are configured in an overlapping hexagonal array.
6. The armor system of claim 1, wherein said cooling layer comprises a fibrous material immersed in a fluid medium.
7. The armor system of claim 6, wherein said fluid medium comprises a rheopectic fluid.
8. The armor system of claim 1, wherein said splitter layer comprises bars.
9. The armor system of claim 8, wherein said splitter layer comprises a first plurality of parallel bars having a length dimension disposed in a first direction, and a second plurality of parallel bars having a length dimension disposed in a second direction not parallel to said first direction.
10. The armor system of claim 8, wherein said bars are rolled bars.
11. A method of mitigating the effects of an explosively formed projectile, comprising the steps of:
- splitting a mass of an explosively formed projectile into a plurality of secondary projectiles having a respective smaller mass than said mass of said explosively formed projectile;
- cooling at least one of said plurality of secondary projectiles to a temperature below a temperature of said explosively formed projectile; and
- slowing at least one of said plurality of secondary projectiles to a velocity below a hydrodynamic termination velocity;
- thereby mitigating the effects of said explosively formed projectile on an object against which said explosively formed projectile is launched.
Type: Application
Filed: Mar 15, 2011
Publication Date: Jun 28, 2012
Inventor: Jason A. Dean (Chittenango, NY)
Application Number: 13/048,027
International Classification: F41H 5/04 (20060101);