Patent Application
20110083549
This invention relates to ballistic armor, particularly those suited to protect against fragmentation.
When designing ballistic armor, for example, for protecting a vehicle, consideration must be given to the type or types of projectile against which the armor must protect. Some arrangements of armor will not protect at all against a certain type of projectile. For example, an array of ceramic tiles or pellets can protect against kinetic energy (KE) threats, such as direct hits of armor-piercing penetrators, while they generally do not provide protection against a plurality, i.e., hundreds, of fragments traveling at a high rate of speed as a consequence of an improvised explosive device (IED) exploding in the vicinity of an armored vehicle. Typically, the heavy fragmentation impacts resulting from the explosion of an IED destroy the hard, brittle ceramic, exposing the vehicle to be pierced by direct hit shots of sniper rifles or other similar threats.
When performing ballistic tests, it is not practical to explode an IED near an armor prototype. Therefore, fragment-simulating projectiles (FSPs) of different types are used. The impact of an FSP having a certain velocity on ballistic armor simulates the impact of a fragment resulting from an explosion of a known class of IED. Different size FSPs and their impact velocities correspond to different IEDs, such as mortars or artillery shells of a given diameter. By testing the armor prototype with an FSP, its ballistic capability against an IED threat can be determined.
An important consideration which must be taken into account when designing ballistic armor is the weight per coverage area of the armor. Theoretically, armor can be constructed to protect against almost any threat or combination of threats. On the other hand, the resulting weight of the armor needed for such protection has to be practical for the intended use, especially when the protection of vehicles such as trucks, armored infantry fighting vehicles, or armored personnel carriers, is concerned.
The present invention is directed to lightweight ballistic armor which can protect against both armor piercing projectiles and high speed fragments resulting from a nearby explosion of an IED or a high energy shell.
According to the present invention, there is provided a ballistic armor adapted to protect against armor piercing projectiles and to withstand multiple impacts of FSPs of a predetermined type, traveling at an initial velocity not exceeding a first specified velocity, and a method of such protection.
The armor comprises a main armor layer and a front auxiliary layer facing the projectiles, the main armor layer being adapted to absorb most of the energy of the armor piercing projectiles and to withstand the impacts of said FSPs when their velocity does not exceed a second velocity which is lower than the first specified velocity. The auxiliary layer is adapted for being perforated by said FSPs such the deformation of the auxiliary layer caused by its perforation by the FSPs is localized in the area of each perforation and the energy loss of the FSPs associated with the deformation and perforation gives rise to a reduction in velocity of the FSPs from their initial velocity to a velocity not exceeding the second velocity.
In order to be capable of the deformation as described above, the auxiliary layer is made of a material that, when perforated, undergoes ductile failure mode, also known as ductile exit. This mode as well as the associated perforation mechanism is described in detail in “Dynamic Perforation of Viscoplastic Plates by Rigid Projectiles” (M. Ravid & S. R. Bodner, International Journal of Engineering Science, Vol. 21, No. 6, pp 577-591, 1983) and “Penetration into Thick Targets—Redefinement of a 2D Dynamic Plasicity Approach” (M. Ravid & S. R. Bodner, International Journal of Impact Engineering, Vol. 15. No. 4, pp 491-499, 1994.
The material of which the auxiliary layer is made is further characterized in that it is of such hardness and thickness that sufficient energy of the FSPs is absorbed thereby to ensure the reduction in velocity of the FSPs from their initial velocity to a velocity not exceeding the second velocity. Experimental results show that this is obtained in materials whose the Brinell hardness is in the range of about 65 to about 165 kgf/mm2. Additionally, it is desirable that the material have an elongation greater than about 8%, and the yield strength in the range between about 11 and about 52 kgf/mm2 when tested at standard quasi-static test conditions.
Examples of materials having the above properties, and therefore suitable to be used for the auxiliary layer in the armor of the present invention, are aluminum alloys such as Al 6061, Al 7075, Al 2024, Al 5083, Al 7017, or Al 7019, and materials having similar properties.
Experiments show that the use of the auxiliary layer made of aluminum alloys as described above allows the armor to stop FSPs of diameters as large as 20 mm having velocities as high as 1500 m/s. This is a surprising effect, since aluminum is known to have relatively low ballistic protection capabilities when used as a frontal material, for which reason it is normally used in internal or backing layers. It is further surprising that commercial and common aeronautical alloys may be used successfully for ballistic protection as suggested in accordance with the present invention, though normally only special armor alloys are used for military applications. While there may be no significant weight difference between military and non-military aluminum alloys, the latter are normally less hard and are cheaper than the former.
The main armor layer may comprise a base layer made from a high density material of an appropriate thickness, such as high hardness steel and an additional, e.g., an add-on, layer. The latter may, for example, be of the kind comprising a plurality of tiles or pellets with or without a composite backing. The tiles or pellets may be made from, or comprise, metal (such as ultra high hardness steel) or a refractory or ceramic material such as alumina (Al2O3), silicon carbide (SiC), silicon nitride (Si3N4), or boron carbide (B4C). The add-on layer typically is a frontal layer with respect to the base layer. The main armor layer may also be provided with an inner liner, which covers the base layer from behind. When the armor is designed to protect a vehicle, in particular its sidewall, the base layer may be constituted by said sidewall and the inner liner may be attached to the sidewall so as to protect the interior of the vehicle from shrapnel, and for absorbing remaining kinetic energy from armor piercing projectiles and fragments. The inner liner may be made from or comprise aramid materials, fiberglass, HDPE or laminated hybrids of such materials.
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
The armor 10 comprises an auxiliary layer 12 and a main armor layer, which may or may not be separated by a gap 22, as shown in
The main armor layer 14 comprises a base layer 16, an add-on layer 18 and, optionally, an inner liner 20.
The base layer 16 is typically made from a hard metallic material such as RHA or high hardness steel which may have a thickness between 4 mm and 20 mm. In the present embodiment, this layer is constituted by the sidewall of the vehicle protected by the armor 10.
Alternatively, the base layer may comprise dual hardness armor (DHA). For example, such DHA may comprise a layer of UHH steel facing the projectile, and a layer of HH steel therebehind, the two layers being integrally attached to each other to form the base layer. The UHH layer may be thinner than the HH layer, e.g., its thickness may be about one third of the total thickness of the DHA, and the thickness of the HH layer may be two thirds thereof. With the base layer being made of DHA, the armor may provide an essentially enhanced ballistic protection.
The add-on layer 18 comprises an array of tiles or pellets 30, such as those composed of armor-grade alumina, another appropriate ceramic, or ultra high hardness steel. This layer may be constructed according to any one of a plethora of arrangements which are well known in the art and have an appropriate thickness for protection against armor piercing projectiles.
The inner liner 20 may be made from a composite laminate such as aramid, E-glass or S-glass fiberglass, high density polyethylene, or a hybrid thereof. This layer is attached to the inner side of the base layer 16, for example by gluing or bolting, as appropriate.
The add-on and base layers are adapted to absorb and dissipate kinetic energy of armor piercing projectiles and of FSPs, or residual fragments of improvised explosive devices, which will perforate the auxiliary layer 12, mainly due to the deformation and shattering thereof. The inner liner 20 is designed absorb remaining kinetic energy of, and to stop, any residual fragments which may pass the base layer.
The auxiliary layer 12 is made from a relatively soft ductile material, such as aluminum. The auxiliary layer 12 may be made from any material which experiences local deformation due to a ductile failure mode, as described in “Dynamic Perforation of Viscoplastic Plates by Rigid Projectiles” (M. Ravid & S. R. Bodner, International Journal of Engineering Science, Vol. 21, No. 6, pp 577-591, 1983) and “Penetration into Thick Targets—Redefinement of a 2D Dynamic Plasicity Approach” (M. Ravid & S. R. Bodner, International Journal of to Impact Engineering, Vol. 15. No. 4, pp 491-499, 1994), whose contents are incorporated herein by reference. As explained in the above articles, when material of the kind of which the auxiliary layer is made, is perforated by a projectile, the material's deformation during such perforation includes the stages of dynamic plastic penetration, bulge formation and bulge advancement stage at the end of which the projectile exists so that the exit lips at the rear surface of the material usually do not shear out. This leads to the material of the auxiliary layer being locally deformed at a plurality of locations upon its perforation by a plurality of FSPs, whereby multi-hit capability of the armor is ensured.
Additionally, the material has an elongation of greater than 8 percent, a yield strength not greater than 52 kgf/mm2, and a Brinell hardness not be greater than 165 kgf/mm2.
In operation, FSPs such as the FSP 24 which are typically between 0.3″ and 20 mm in diameter, and which travel at a high initial velocity, e.g., up to a first velocity of about 1500 m/s, pierce the auxiliary layer 12 in a plurality of separate locations, whereby a substantial portion of the kinetic energy of the FSPs is mitigated and their velocity is reduced to a second velocity within the range against which the main armor layer 14 can provide protection against the slowed down FSPs. The auxiliary layer 12 may also alter the trajectory and stability of the armor piercing projectiles so that they develops a yaw angle, which reduces their penetration capability. This effect is more pronounced in a case of oblique impacts of the armor piercing projectiles on the armor 10. In general, although armor piercing projectiles such as the APP 26, may also loose part of their kinetic energy when penetrating the auxiliary layer 12, this does not have to be the case since the main armor layer 14 may be adapted to protect against armor piercing projectiles without their previous energy absorption provided by the auxiliary layer 12.
In ballistic tests, different ballistic armors, each according to the present invention, were successfully tested against both FSPs and small caliber armor piercing projectiles at different velocities. All of the armors comprised auxiliary layers made of the same commercial aluminum alloy but having different thickness and base layers made of steel having different hardness and thickness. Some armors comprised an add-on ceramic layer made of cylindrical pellets held together by a thermoplastic or thermoset binder, the pellets being made of alumina (Al2O3 98%), and having diameter 12.7 mm, and height 8 mm, and having domed front ends. Some of the armors comprised inner liner made of aramid and fiberglass. The test particulars are summarized in the table below.
Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be made without departing from the scope of the invention mutatis mutandis.
| Number | Date | Country | Kind |
|---|---|---|---|
| 170119 | Aug 2005 | IL | national |
| 170119/2 | Apr 2006 | IL | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2006/000874 | 7/27/2006 | WO | 00 | 1/31/2008 |
