IL105303A - Multilayer ballistic shock damping unit - Google Patents

Description

MULTILAYER BALLISTIC SHOCK DAMPERING UNIT The present invention relates to a multilayer ballistic shock dampering unit. More particularly the present invention relates to a multilayer ballistic shock dampering unit for use in combination with ceramic armor as well as in metallic integrated multi-layer special armor.

For many years ceramic armor was a subject for extensive research and development especially for vehicle and aircraft protection systems (hereinafter referred to as light-weight protection systems) .

For more than 30 years the world-wide research continues, and numerous ideas, patents, experiments etc., were performed in order to achieve a major breakthrough in this complex field.

Usually a ceramic armor system traditionally is based on hybridization of frontal and backing packages. The frontal package consists of ceramic tiles or balls (i.e., made of: A1203, SiC, SiN, TiB2 , B4C etc.) which are clamped/glued to a relatively softer backing system i.e, metallic backing: -Al alloys, Steel alloys, rolled homogeneous armor, high hardness steel, dual hardness armor, triple hardness armor etc. or composite materials such as: evlar, Twaron, Specta, Doron, Fiberglass, Ballistic, Nylon etc., where all fabrics were impregnated/saturated with resins/compounds.

The adhesive type is varied i.e. - polyurethane based adhesives, Epoxy based adhesives and other similar plastic and/or polymer based and/or compound bonds.

After bonding, the two packages are hybridized to one and wrapped together with impregnated/saturated protection layers (usually made of Kevlar-3000 or similar replacement) .

The basic mechanism of ceramic armor subject to ballistic threat (bullets penetration/perforation in ceramic armor) was analysed for many years. Despite enormous efforts, the light-weight protection systems made . of ceramic armor still suffers from two major shortcomings: a. Poor multi-hit capability relative to conventional armor made of steel or aluminum alloys. b. High cost in comparison to alternatives such as metallic conventional or layered armor.

The only application of ceramic armor is in such cases where the weight gain in ballistic performance is dominant and more important than cost effectiveness of volume consumption.

In accordance with the present invention there is now provided a multilayer ballistic shock da pering unit comprising an inner shock absorbing and dampering multicellular structure having a plurality of cells each of which is bounded by collapsible walls; a protective layer made of materials selected from the group consisting of metal, plastic, impregnated fabric, fiber reinforced plastic or composites thereof provided along a front and back surface of said structure, said front and back protective layers serving to cover back and front surface openings of cells of said structure while being supported by the bounding walls thereof; a layer of metallic foil being provided along a front surface of said front protective layer; and a structural backing layer.

The unit of the present invention solves the aforementioned shortcomings and furthermore achieves high ballistic performance when the present unit is inserted between the two traditional frontal and backing packages described above .

The present invention gives the ceramic armor designers the ability to use whatever frontal package is desired in order to efficiently break the AP hard core projectiles which are shattered to pieces, or smash and flatten by intensive plastic deformation (up to complete fracture) the deformable bullets. This is done by substantially increasing - Tf (ceramic tile fracture time due to rarefaction waves initiation) . This time is measured from projectile impact (t=0+) to the moment when rear fracture "wave front" hits the ceramic crashed powder frontal (axial) boundary located in front of the penetrating projectile.

The invention also reduces the shock waves amplitudes and serve as an excellent damper allowing localization of the tile fracture due to the ballistic penetration process and therefore gains excellent multi-hit capability of the frontal hard and brittle package, and consequently of the entire ceramic armor system.

The two above features allow the use of relatively low cost backing packages which has only to stop the residual deformed penetrator or shattered projectile core pieces. The result is a low cost ceramic armor with excellent ballistic performance (level and multi-hit) .

Sometimes, when it is needed, a similar unit according to the present invention, low cost structure, can be used as a frontal protection to ceramic armor package against low level threats i.e., stones, hammers, axes etc., which might strike the ceramic armor, causing damages to the ceramic tiles. The unit according to the present invention, when hybridized also in front of the ceramic armor prevents any damage to ceramic tiles or balls due to the above attacks. - 4 - 105,303/3 The unit according to the present invention can be used also for other ballistic applications, i.e., shelter and bunker reinforcement, ballistic inner protection liners, etc..

The unit of the present invention can also be used as a special insert for metallic integrated multi-layer special armor especially designed for protection against small caliber threats, as well as ball-type bullets, as described hereinafter.

U.S. Patent 3,604,374 discloses a blast-absorbing structure including a honeycomb element made up of distendible side members .

U.S. Patent 3,649,426 discloses protective armor, including honeycomb-shaped cells 20, for attenuating shock wave effects. The cells are filled with a fluid material, while protective pad 19 and facing 21 abut the cells on either side thereof.

U.S. Patent 4,836,084 discloses an armor plate composite, including supporting plate 4 consisting of an open honeycomb structure 10 of aluminum.

U.S. Patent 4,868,040 discloses an antiballistic composite armor including a shock-absorbing layer.

U.S. Patent 4,404,889 discloses a composite armor including steel honeycomb layer 20.

U.S. Patent 4,529,640 discloses spaced armor including a hexagonal honeycomb core member. A similar disclosure is found in U.S. Patent 4,566,237. 105,303/2 U.S. Patent 4,584,228 discloses a bullet-proof garment, including shock absorber 5, comprising a 3 -dimensional fabric having waffle-like surfaces.

U.S. Patent 4,111,097 discloses a laminated multi-layer armor construction, including aluminum honeycomb 20.

U.S. Patent 4,198,454 discloses composite panels including ablative or subliming material-filled honeycomb structure 16.

U.S. Patent 3,577,836 discloses an armored garment including epoxy-filled honeycomb members 36 and 43.

Despite the similarity of some of the features described in said patents with the features of the present invention, none of said patents teaches or suggests the multi-layer ballistic shock dampering unit of the present invention as defined herein, and the synergistic protective effect achieved with same.

. Ravid, S.R. Bodner and I. Holcman developed an Analytical,. Two Dimensional, Engineering Model which is schematically illustrated in Figure 1 appended hereto. The model presented by Dr. M. Ravid at the 11th Int. Symp. on Ballistics held in Brussels, Belgium May 9-10, 1989, shows clearly that in order to achieve high effective use of the ceramic tile for protection it is necessary to maximize the duration T for as long as possible, "stretching" both impact and erosion penetration stages to maximum duration as possible (MAX. T ) . When the erosion is "stretched" to a longer period, the shattering/erosion/ deformation and fracture effects induced to the penetrator are enhanced and therefore the ballistic efficiency will be improved. - 4B - 105,303/2 This is an obvious result, which can be calculated explicitly utilizing the above analystical 2D model, but to implement it to ceramic armor is very difficult. This is because rarefaction waves entering from the tile rear surface usually causes tile failure initiation and consequently fractured ceramics structure developing at "fracture wave" velocity - Vfr towards the crushed ceramic axial (frontal) boundary which developed in front of the penetrating projectile (see Figure 1). In case of balls rarefaction waves entering from the free circumfrencial surface cause early failure. - 5 - When the two boundaries merge (at t=T-j) the most effective tile resistance to penetration terminates. Usually this will happen at relatively early stages during the penetration process and thus ballistic performance is limited. Therefore, it is necessary to attenuate as much as possible the rarefaction waves magnitude by utilizing a specially designed shock absorption package. This package also has to be constructed dynamically strong enough to give the tiles or balls the necessary backing during penetration, and to limit the radial fracture of the tiles to minimum, in order to gain higher multi-hit capabilities.

The unit of the present invention is a viscoplastic shock dampering insert package arranged in 5 layers (4 interlayer bonded surfaces) which has the above properties and should be inserted between the traditional frontal and rear (backing) packages to form a low cost, high performance protection.

In preferred embodiments of the present invention, as will be described more fully also with reference to the tables presented herein and the figures appended hereto, said multicellular shock dampering structure may be of any of the various shape types existing on the market as schematically shown in cross section in Fig. 3. Thus said multicellular structure can be of the corrugated type however one of the most preferred structures is a "straw type" dampering layer composed of a bundle of a plurality of substantially parallely aligned individual tubes with thin wall thickness, usually made of Polycarbonate, that are attached together in their manufacture process.

Said tubes can be of square, circular or hexagonal cross section as shown in figure 3 and said structure preferably has a thickness of about 5 - 10 mm. - 6 - 105,303/2 Alternatively, said shock absorbing and dampering multicellular structure can be of a sponge type plastic material, such as that sold under the names RohacellR, NidaplastR and ExcellR, or it can be of a felt-like material produced by a needling method and impregnated with a phenolic resin, polyurethane, or a polyester such as Recycled Kevlar/Twaron Needled Felt, having a weight of about 300-5000 gm/m2.

Preferably, each of said structural protective layers has a thickness of about 0.5 to 2.0 mm, and said metallic foil layer has a thickness of about 0.3 to 1.2 mm.

In preferred embodiments of the present invention, said structural backing layer may be made of metallic foil, or may be made of a material selected from the group consisting of plastic, impregnated fabric, fiber reinforced plastic or composites thereof. In especially preferred embodiments, said structural backing layer is made of an alluminum alloy metallic foil.

Also, in especially preferred embodiments of the present invention, each of said protective layers is made of fiberglass or S2-Glass.

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invent n. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Figs. 1A-1H are schematic illustrations of the idealized five-stage process of ballistic penetration in ceramic/ metal armor, as presented by Dr. M. Ravid, et al., in the Proc. of the Eleventh Int. Symp. on Ballistics, Brussels, Belgium (May 1989) Fig. 2 is a cross-sectional view of a unit according to the present invention; Figs. 3A-3E are cross-sectional views of five different possible configurations of the multicellular structure used in the unit of the present invention; and Figs. 3F and 3G are top cross-sectional views of two additional possible configurations of the multicellular structure used in the unit of the present invention.

Referring first to the schematic illustrations of Figs. 1A-1H, it can be seen that the penetrator 10 strikes the composite target, composed of brittle ceramic frontal layer 11 and relatively soft backing layer 12, at Ua. Due to the impact, two main shock waves are generated at interface 13: US shock wave, moving up through the penetrator with current front 14; and XS^ shock wave, moving into target structure with current front 15. At Tx, shocks are reduced significantly by rarefaction waves, when the target's shock front 16 still exists and "ceramic powder flow" zone 17 is defined in the ceramic structure. When - 7A - 105,303/2 the target shock wave hits the interface 24, shock wave is generated at the backing 19, while the differential pressure at interface 24 causes factrure wave 18, which fractures the back of the ceramic structure 20 until merging with the crushed zone 17 front, and the ceramic structure 21 is completely broken. In this broken ceramics 21, the penetrator 10 generates "crushed ceramic flow" zone 22, which grows until it hits the interface 24 and generates a "plastic flow" zone 23 in the backing structure 12.

The final stage of the perforation process is the backup plate perforation. During stages 1 and 2 (Figs. 1A through ID) , the penetrator suffers erosion in length and possible rear fracture 24 when the shock or elastic-plastic wave causes intense rarefaction from its rear surface. The effectiveness of such combination of ceramic He layer 11 and backing Hb layer 12 depends on both material parameters, geometry, bonding at interface 24, and threat type.

Referring to Fig. 2, there is seen a multilayer unit 6 according to the present invention.

Referring now to Figs. 3A-3G, it can be seen that structures are made of horizontal walls 31 and vertical walls 33, with air cells 30 which can be filled with sponge type materials or other light weight collapsible materials. The simple configuration shown in Fig. 3B can be replaced by corrugated, collapsible walls 32 as shown in Fig. 3A, or vertical walls in brick-type setting 36 as shown in Fig. 3E. Utilizing traditional honeycombs with the polygonal cells 35 of Fig. 3D is also possible, while the straw type strucute of Fig. 3C, with joint straws 34, is more effective. A two-skinned type, collapsible structure, shown in Figs. 3F and - 7B - 105,303/2 3G with skins 37 and 38, collapsible walls 33 with possible reinforcement (x type) 39, and air 30, can be also used with high efficiency.

The main parameter of all structures is a localized deformation/damaged area adjacent to the perforation zone, where the cells 30 should be in the order of magnitude of the penetrator' s radius and up to the maximum of its diameter. Average compressive bare strength of the structure should be greater than 0.5 N/mm2.

In the following Table 1, there is presented a listing of the layers of said unit 6 according to the present invention and preferred materials used therein. 8 - TABLE 1 VISCOPLASTIC SHOCK DAMPERING INSERT PACKAGE LAYER DESCRIPTION Partial list of available basic materials - 9 - All layers of the unit according to the present invention are constructed together as follows: Layer 3 is "coated" on both sides by layers 2 & 4 where the composite woven material impregnated/saturated with the adhesive and wrapped over both sides of the shock dampering layer closing its surface pores/holes and spaces. Special care should be taken to prevent the adhesive material from entering and penetrating into the empty pores/cells volumes.

The metallic layers 1 and 5 are surface prepared, primered and coated by the proper adhesive filament/spread layer and glued to close the package (layers 2,3,4) from both sides.

The package is placed under carpenters type pressing eguipment, moderately pressed, heated up to 50-70 degrees celsius (depends on adhesive type) , for a certain period of time (again, depending on adhesive type) . Package assembly can be done also in a frame format (i.e., made of aluminum or Polyethylene) and placed under press in a vaccumed heated autoclave chamber during adhesive curing time.

After complete curing of adhesive, depending on the specification of the chosen adhesive type (which should be viscoplastic) , the unit according to the present invention is ready to be hybridized between the frontal and backing packages utilizing a proper viscoplastic adhesive type, with or without surface preparing and primering (depends on adhesive type) .

Ballistic performance is a complex function of the hybridization of the ceramic frontal package type with the unit according to the present invention and choosing the proper backing.

The unit according to the present invention, when hybridized in the ceramic armor, gives the needed backing for the frontal ceramic package resulting in the extension - 10 - of-Tf, due to rarefaction magnitude supression, and due to its shock dampering properties and viscoplastic dynamic behavior, reduces radial fractured area and causing localization of the damaged hit zone to a minimum, resulting in excellent multi-hit capability of the frontal ceramic package (up to two hits on the same tile 50 x 50 mm) . Due to the high efficiency gained from the frontal package, the rear package which handles the residual shattered/smashed penetrator pieces relatively easily, therefore all ceramic armor containing the unit of the present invention can be optimized for performance versus light-weight (LW-P) or low price performance (LP-P) .

In Table 2, presented hereinafter, there is set forth a preferred embodiment of the present invention with regard to materials to be used in each of the layers and preferred thickness range of each layer said materials and thicknesses being optimized based on considerations of low price performance. - 11 - TABLE 2 For protection of the ceramic tiles against low velocity ballistic threats i.e., stones, hammers, axes etc., which might strike ceramic armor, the unit of the present invention (similar to Table 2) can be used to protect the ceramic armor frontal package for total protection against tile damage due to those threats. Layer 1 can be 1-2 mm of polycarbonate. The unit of the present invention can be successfully used for other applications, such as : ballistic liner for the protection of inner compartments of armoured vehicles against residual penetration hazards, - 12 - shelters, bunkers and enhances structural reinforcement against ballistic threats when it is needed.

In those cases the unit of the present invention (usually constructed as in Table 2) is inserted in the inner protection package or between inner wall surface and protection package. Layer 3 can be reduced to 3 mm thickness while layer 5 can be totally eliminated or be reduced to 0.1-0.3 mm.

In Table 3, presented hereinafter, there is set forth a preferred embodiment of the present invention with regard to materials to be used in each of the layers and preferred thickness range of each layer said materials and thicknesses being optimized based on considerations of light weight performance. - 13 - TABLE 3 Note : Layer 1 can be replace by: 0.2, 0.3, 0.4-0.5 mm Ti 6,4 foil or Proteus material foil (depends on ceramic armor frontal package) .

Referring now to figure 3 there is seen a frontal view of five different possible configurations of the shock absorbing and dampering multicellular structure according to the present invention.

Figure 3A shows a corrugated type structure for use in the - 14 - present invention wherein the wave like walls 7 of said structure serve as a support for the protective layer 2 attached thereto (as illustrated in Figure 1) .

Figures 3B and 3E illustrate two variations of a multicellular structure having cells of square cross section wherein in the structure of figure 3b the cells are simply aligned in columns and rows while in Figure 3e said cells are aligned in a staggered brick like array.

Figure 3C illustrates an especially preferred embodiment of the present invention which is . a "straw type" dampering layer composed of a bundle of a plurality of substantially parallely aligned individual tubes with thin wall thickness, usually made of Polycarbonate, that are attached together in their manufacturing process.

Figure 3D illustrates another embodiment wherein the cells are arranged in a honeycomb type array said cells having hexagonal cross section.

As will be noted in the multicellular units of figures 3b, 3D and 3E the cells share a common wall with an adjacent cell while in the especially preferred embodiment of figure 3 each cell is bounded by its own encircling wall thereby providing increased support to the protective layers applied to the front and back thereof.

In another embodiment of the present invention (not shown) there can be provided a metallic faced special armor utilizing a unit using the multilayer ballistic shock dampering unit as described said special armor consisting of a backing package made of metallic or non-metallic single or multi-layer composite backing material having a thickness of about 5 to 10 mm; an intermediate shock dampering unit according to the present invention wherein the inner shock absorbing and dampering multicellular structure has a width of about 8 to 18 mm and a frontal package consisting - 15 - of ultra high hardness steel, homogeneous plate or perforated structure (perforated with more than 30% weight saving i.e., 4 mm). Said frontal package having a thickness of about 3 to 8 mm.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (12)

- 16 - WHAT IS CLAIMED IS:

1. A multilayer ballistic shock dampering unit comprising an inner shock absorbing and dampering multicellular structure^ having a plurality of cells each of which is bounded by collapsible walls; a protective layer made of a material selected from the group consisting of plastic, impregnated fabric, fiber reinforced plastic or composites thereof provided along a front and back surface^ o^E said structure, said front and back protective layers ^serving to cover back and front surface openings of cells of said structure while being supported by the bounding walls thereof; a layer of metallic foil being provided along a front surface of said front protective layer; and a structural backing layer.

2. A multilayer ballistic shock dampering unit as claimed in claim 1 wherein said multicellular structure is composed of a bundle of a plurality of substantially parallely aligned tubes.

3. A multilayer ballistic shock dampering unit as claimed in claim 1 wherein said cells are of square, circular or hexagonal cross section.

4. A multilayer ballistic shock dampering unit as claimed in claim 1 wherein said multicellular structure is composed of sponge type plastic material.

5. A multilayer ballistic shock dampering unit as claimed in claim 1 wherein said multicellular structure is composed of a plastic impregnated needled felt material.

6. A multilayer ballistic shock dampering unit as claimed in claim 1 wherein said structural backing layer is made of metallic foil. - 17 - 105,303/2

7. A multilayer ballistic shock dampering unit as claimed in claim 1, wherein said structural backing layer is made of a material selected from the group consisting of plastic, impregnated fabric, fiber reinforced plastic, or composites thereof.

8. A multilayer ballistic shock dampering unit as claimed in claim 1, wherein said structure has a thickness of about 5-18 mm.

9. A multilayer ballistic shock dampering unit as claimed in claim 1, wherein each of said protective layers has a thickness of about 0.5 to 2.0 mm.

10. A multilayer ballistic shock dampering unit as claimed in claim 1, wherein said metallic foil layer has a thickness of about 0.3 to 1.2 mm.

11. A multilayer ballistic shock dampering unit as claimed in claim 1, wherein each of said protective layers is made of fiberglass.

12. A multilayer ballistic shock dampering unit as claimed in claim 1, wherein said structural backing layer is made of an aluminum alloy metallic foil. for the Applicant: WOLFF, BREGMAN AND GOLLER