WO1994019660A1

WO1994019660A1 - Composites having improved penetration resistance

Info

Publication number: WO1994019660A1
Application number: PCT/US1994/001648
Authority: WO
Inventors: Gary A. Harpell; Dusan C. Prevorsek
Original assignee: Alliedsignal Inc.
Priority date: 1993-02-16
Filing date: 1994-02-15
Publication date: 1994-09-01
Also published as: CA2153403A1; JPH08507138A; EP0685058A1

Abstract

An improved flexible composite of manufacture especially suitable for use as a ballistic resistant body armor, said improved penetration resistant composite of the type comprising at least two penetration resistant layers, each layer comprising a flexible fibrous substrate comprising a fibrous network having a plurality of penetration resistant elements on a surface thereof, wherein at least one of the inner layers further comprising a fibrous element comprising fibrous network positioned between said substrate and said penetration resistance element.

Description

COMPOSITES HAVING IMPROVED PENETRATION RESISTANCE

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION

This invention relates to composites and articles fabricated therefrom. More particularly, this invention relates to composites and articles having improved penetration protection.

2. PRIOR ART

Ballistic articles such as bulletproof vests, helmets, structural members of helicopters and other military equipment, vehicle panels, briefcases, raincoats and umbrellas containing high strength fibers are known. Illustrative of such articles are those described in U. S. Patent Nos. 4,623,574; 4,748,064; 4,413,1 10; 4,737,402; 4,613,535;

4,650,710; 4,737,402; 4,916,000; 4,403,012, 4,457,985;

4,737,401 ; 4,543,286; and 4,501 ,856.

SUMMARY OF THE INVENTION

The present invention is directed to a penetration resistance composite comprising at least one external penetration resistant layer and at least one internal penetration resistant layer, said external layer positioned on the impact side of said composite and said internal layer positioned on the non-impact side of said external layer, each of said layers comprising a flexible substrate comprised a fibrous network having a plurality of penetration resistant planner elements on a surface thereof, said internal layer further comprising a fibrous element comprised of a fibrous network positioned between said elements and said substrate. Another aspect of this invention relates to articles manufactured from the composite of this invention.

Several advantages flow from this invention. For example, the composite and article of this invention provide a higher degree of penetration resistance than composites and articles of the same areal density but lacking the fibrous element of the internal layer. As used herein, the "penetration resistance" of the article is the resistance to penetration by a designated threat, as for example, an ice pick, bullet flechette, or a knife. The penetration resistance can be expressed as the total specific energy absorption (SEAT) which is the kinetic energy of the threat at its V₅₀ value divided by the areal density of the composite and the higher the SEAT value, the greater the resistance of the composite to the threat and, as used herein, the "areal density" or "ADT" is the ratio of total target weight to the area of the target strike face area and as used herein, "V₅₀" of a threat is the velocity at which 50% of the threats will penetrate the composite while 50% will be stopped.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the invention and the accompanying drawings in which:

FIG. 1 is an enlarged fragmentary sectional view of a composite of this invention. FIG. 2 is a frontal perspective view of a preferred embodiment of a ballistic resistant body armor fabrication rom the composite of this invention.

FIG. 3 is a frontal perspective view of the components cut away for purposes of illustration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The preferred invention will be better understood by those of skill in the art by reference to the above figures. The preferred embodiments of this invention illustrated in the figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It is chosen to describe or to best explain the principles of the invention and its application and practical use to thereby enable others skilled in the art to best utilize the invention.

Referring to FIG. 1 , the numeral 10 indicates a penetration resistant composite 10. The construction of composite 10 is critical to the advantages of this invention. As depicted in FIG. 1 , composite 10 comprises a backing layer 12, and a frontal layer 14. Composite 10 also comprises an outer penetration resistant layer 16 positioned on the impact side of composite 10 comprised of flexible substrate 18 comprising of a fibrous network having one or more penetration resistant elements 20 on a surface thereof and an inner penetration resistant layer 22 positioned on the non-impact side of composite 10 comprising a flexible substrate layer 24 having one or more penetration resistant planar elements 26 on a surface thereof and further comprising a fibrous element 28 comprised of a fibrous network positioned between said element 22 and said substrate layer 24. The presence of fibrous element 20 is critical to the advantage of this invention and provides for enhanced penetration resistance. While we do not wish to be bound of any theory, it is believed that a result of fibrous element 28 is that the penetration resistance of composite 10 is enhanced relative to ballistic composities which do not include fibrous element 28. Fibrous layers 18 and 24 and fibrous element 28 may be the same or different and are formed of fibers arranged in a network which can have various configurations. For example, a plurality of filaments can be grouped together to form a twisted or untwisted yarn bundles in various alignment. The fibers may be formed as a felt, knitted or woven (plain, basket, satin and crow feet weaves, etc.) into a network, fabricated into non-woven fabric, arranged in parallel array, layered, or formed into a woven or nonwoven fabric by any of a variety of conventional techniques. Useful techniques for forming fiber networks for ballistic resistance applications include those variations commonly employed in the preparation of aramid and polyethylene fabrics and uniaxial prepregs for ballistic-resistant articles. For example, the techniques described in U.S. Patent No. 4, 181 ,718;

M.R. Silyquist et al., J. Macromol Sci. Chem.. A7(1 ), pp. 203 et. seq. (1973); U. S. Patent Nos. 4,916,000; 4,650,710; 4,681 ,792; 4,737,401 ; 4,543,286; 4,563,392; 4,501 ,856; 4,623,574; 4,748,064; 4,457,985 and 4,403,012; and PCT WO /91 /08895 are particularly suitable.

The type of fibers used in the fabrication of layer 18 and 24 said fibrous element 28 may vary widely and can be metallic inorganic or organic fibers. For purposes of the present invention, fiber is defined as an elongated body, the length dimension of which is much greater than the dimensions of width and thickness. Accordingly, the term fiber as used herein includes a monofilament elongated body, a multifilament elongated body, ribbon, strip, and the like having regular or irregular cross sections. The term fibers includes a plurality of any one or combination of the above. Preferred fibers for use in the practice of this invention are those having relatively high tenacities and tensile modulus, as for example, a tenacity equal to or greater than about 7 g/d, (as measured by an Instron Tensile Testing Machine) a tensile modulus equal to or greater than about 40 g/d (as measured by an Instron Tensile Testing Machine) and an energy-to-break equal to or greater than about 8 joules/gram. All tensile properties are evaluated by pulling a 10in (25.4 cm) fiber length clamped in barrel clamps at a rate of 10 in/min (25.4 cm/min) on an Instron Tensile Tester. Particularly preferred fibers are those having a tenacity equal to or greater than about 10 g/d, a tensile modulus equal to or greater than about 500 g/d and energy-to-break equal to or greater than about 30 joules/grams. Amongst these particularly preferred embodiments, most preferred are those embodiments in which the tenacity of the fibers are equal to or greater than about 20 g/d, the tensile modulus is equal to or greater than about 1000 g/d, and the energy-to-break is equal to or greater than about 35 joules/grams, in the practice of this invention, fibers of choice have a tenacity equal to or greater than about 25 g/d, the tensile modulus is equal to or greater than about 1300 g/d and the energy-to-break is equal to or greater than about 40 joules/grams.

The denier of the fiber may vary widely. In general, fiber denier is equal to or less than about 4000. In the preferred embodiments of the invention, fiber denier is from about 10 to about 4000, the more preferred embodiments of the invention fiber denier is from about 10 to about 1000 and in the most preferred embodiments of the invention, fiber denier is from about 10 to about 400.

The cross-section of fibers for use in this invention may vary widely. Useful fibers may have a circular cross-section, oblong cross-section or irregular or regular multi-lobal cross-section having one or more regular or irregular lobes projecting from the linear or longitudinal axis of the fibers. In the particularly preferred embodiments of the invention, the fibers are of substantially circular or oblong cross-section and in the most preferred embodiments are of circular or substantially circular cross-section.

Useful fibers may be formed of organic materials or inorganic materials. Useful inorganic fibers include S-glass fibers, E-giass fibers, carbon fibers, boron fibers, alumina fibers, zirconia silica fibers, alumina-silicate fibers and the like and metals such as titanium, steel, aluminum, nickel, copper and alloys thereof.

Illustrative of useful organic filaments are those composed of aramids (aromatic polyamides), such as poly (metaphenylene isophthalamide) (Nomex) and poly (p-phenylene terephthalamide) (Kevlar); aliphatic and cycloaliphatic polyamides, such as the copolyamide of 30% hexamethylene diammonium isophthalate and 70% hexamethylene diammonium adipate, the copolyamide of up to 30% bis-(-amidocyclohexyl)methylene, terephthalic acid and caprolactam, poly(hexamethylene adipamide) (nylon 6,6), poly(butyrolactam) (nylon 4), poly (9-aminononanoic acid) (nylon 9), poly(enantholactam) (nylon 7), poly(capryllactam) (nylon 8), polycaprolactam (nylon 14), poly(hexamethylene sebacamide) (nylon 14,10), poly(aminoundecanamide) (nylon 1 1 ), poly[bis-(4-aminocyclothexyl) methane 1 , 10- decanedicarboxamide] (Qiana) (trans), or combination thereof; and aliphatic, cycloaliphatic and aromatic polyesters such as poly(1 ,4-cyclohexlidene dimethyl eneterephathalate) cis and trans, poly(ethylene-1 , 5-naphthalate), poly(ethylene-2,14-naphthalate), poly(ethylene terephthalate), poly(ethylene isophthalate), poly(ethylene oxybenzoate), poly(para-hydroxy benzoate). Also illustrative of useful organic fibers are those of liquid crystalline polymers such as lyotropic liquid crystalline polymers which include polypeptides such as poly-g-benzyl L-glutamate and the like; aromatic polyamides such as poly (1 ,4- benzamide), poly(chloro-1 ,4-phenylene terephthalamide), poly(1 ,4-phenylene fumaramide), poly(chloro-1 ,4-phenylene fumaramide), poly (4,4'-benzanilide trans, trans-muconamide), polyd ,4-phenylene mesaconamide), polyd ,4- phenylene) (trans- 1 ,4-cyclohexylene amide), poly(1 ,4-phenylene 1 ,4-dimethyl-trans-1 ,4- cyclohexylene amide), poly(chloro-1 ,4-phenylene 2,5-pyridine amide), poly(chloro-1 ,4-phenylene 4,4'-stilbene amide), polyd ,4-phenylene 4,4'-azobenzene amide), poly(4,4'-azobenzene 4,4'-azobenzene amide), poly (1 ,4-phenylene 4,4' -azoxy benzene amide), polyd , 4- cyclohexylene 4,4'-azobenzene amide), poly(4,4'- azobenzene terephthal amide), poly(3,8- phenanthridinone terephthal amide), poly(4,4'- biphenylene terephthal amide), poly(4,4'-biphenylene 4,4'-bibenzo amide), polyd ,4-phenylene 4,4'-bibenzo amide), polyd , 4-phenylene 4,4'-terephenylene amide), polyd , 4-phenylene 2, 14-naphthal amide), polyd , 5-naphthylene terephthal amide), poly(3,3'-dimethyl-4,4-biphenylene terephthal amide), poly(3,3'- dimethoxy-4,4'- biphenylene terephthal amide), poly(3,3'- dimethoxy-4,4-biphenylene 4,4'-bibenzo amide) and the like; polyoxamides such as those derived from 2,2'dimethyl-4,4'diamino biphenyl and chloro-1 ,4- phenylene diamine; polyhydrazides such as poly chloroterephthalic hydrazide, 2,5-pyridine dicarboxyiic acid hydrazide) poly(terephthalic hydrazide), poly(terephthalic- chloroterephthalic hydrazide) and the like; poly(amide-hydrazides) such as poly(terephthaloyl 1 ,4 amino-benzhγdrazide) and those prepared from 4-amino-benzhydrazide, oxalic dihydrazide, terephthalic dihγdrazide and para- aromatic diacid chlorides; polyesters such as those of the compositions include poly (oxy-trans- 1 , 4- cyclohexyleneoxycarbonyl-trans-1 ,4-cyclohexylenecarbon- yl- ?-oxy-1 ,4-phenyl-eneoxyterephthaloyl) and poly(oxy-cis-1 ,4-cyclohexyleneoxycarbonyl-trans-1 ,4-c yclohexylenecarbonyhff-oxy-1 ,4-phenyleneoxyterephthaloyl) in methylene chloride-o-cresol poly[(oxy- trans-1 ,4- cyclohexylene-oxycarbonyl-trans -1 ,4 -cyclohexylenecarbonyl- ?-oxy-(2-methyl-1 ,4-phenylene)o- xy-terephthaloyl)] in 1 ,1 ,2,2-tetrachloro- ethane -o-chlorophenol-phenol (140:25:15 vol/vol/vol), poly [oxy-trans- 1 ,4-cyclohexyleneoxycarbonyl-trans-1 ,4-- cyclohexylenecarbonyl- oxy(2-methyl-1 ,3-phenylene)oxy- terephthaloyl] in o-chlorophenol and the like; polyazomethines such as those prepared from 4,4'-diaminobenzanilide and terephthaldehyde, methyl-1 ,4-phenylenediamine and terephthaldehyde and the like; polyisocyanides such as poly(phenyl ethyl isocyanide), poly(n-octyl isocyanide) and the like; polyisocyanates such as poly(n-alkyl isocyanates) as for example poly(n-butyl isocyanate), poly(n-hexyl isocyanate) and the like; lyotropic crystalline polymers with heterocyclic units such as polyd ,4-phenylene-2, 14- benzobisthiazole)(PBT), polyd , 4- phenylene-

2,14-benzobisoxazole)(PBO), polyd , 4-phenylene-1 , 3,4-oxadiazole), polyd ,4-phenylene-2, 14-benzobisimidazole), poly[2,5(14)-benzimidazole] (AB-PBI), poly [2,14-(1 , 4-phenylene)-4- phenylquinoline], polyd , 1 '-(4,4'-biphenylene)-14, 14'- bis(4-phenylquinoline)] and the like; polyorganophosphazines such as polyphosphazine, polybisphenoxyphosphazine, poly[bis(2,2,2' trifluoroethylene) phosphazine] and the like; metal polymers such as those derived by condensation of trans-bis(tri-n-butylphosphine)platinum dichloride with a bisacetylene or trans-bis(tri-n- butylphosphine)bis(1 ,4- butadinynyDplatinum and similar combinations in the presence of cuprous iodine and an amide; cellulose and cellulose derivatives such as esters of cellulose as for example triacetate cellulose, acetate cellulose, acetate-butyrate cellulose, nitrate cellulose, and sulfate cellulose, ethers of cellulose as for example, ethyl ether cellulose, hydroxymethyl ether cellulose, hγdroxypropyl ether cellulose, carboxymethyl ether cellulose, ethyl hydroxyethyl ether cellulose, cyanoethylethyl ether cellulose, ether-esters of cellulose as for example acetoxyethyl ether cellulose and benzoyloxypropyl ether cellulose, and urethane cellulose as for example phenyl urethane cellulose; thermotropic liquid crystalline polymers such as celluloses and their derivatives as for example hydroxypropyl cellulose, ethyl cellulose propionoxypropyl cellulose, thermotropic liquid crystalline polymers such as celluloses and their derivatives as for example hydroxypropyl cellulose, ethyl cellulose propionoxypropyl cellulose; thermotropic copolyesters as for example copolymers of 14-hydroxy-2-naphthoic acid and p-hydroxy benzoic acid, copolymers of 14-hydroxy-2-naphthoic acid, terephthalic acid and p-amino phenol, copolymers of 14-hydroxy-2-naphthoic acid, terephthalic acid and hydroquinone, copolymers of 14-hydorxy-2-naphtoic acid, p-hydroxy benzoic acid, hydroquinone and terephthalic acid, copolymers of 2, 14-naphthalene dicarboxylic acid, terephthalic acid, isophthalic acid and hydroquinone, copolymers of 2,14-naphthalene dicarboxylic acid and terephthalic acid, copolymers of p-hydroxybenzoic acid, terephthalic acid and 4,4'-dihydoxydiphenyl, copolymers of p-hydroxybenzoic acid, terephthalic acid, isophthalic acid and 4,4'-dihydroxydiphenyl, p-hydroxybenzoic acid, isophthalic acid, hydroquinone and

4,4'-dihydroxybenzophenone, copolymers of phenylterephthalic acid and hydroquinone, copolymers of chlorohydroquinone, terephthalic acid and p-acetoxy cinnamic acid, copolymers of chlorohydroquinone, terephthalic acid and ethylene dioxy-4,4'-dibenzoic acid, copolymers of hydroquinone, methylhydroquinone, p-hydroxybenzoic acid and isophthalic acid, copolymers of (1-phenylethyDhydroquinone, terephthalic acid and hydroquinone, and copolymers of poly(ethylene terephthalate) and p-hydroxybenzoic acid; and thermotropic polyamides and thermotropic copoly (amide-esters). Also illustrative of useful organic fibers for use in the fabrication of layer 14 and fibrous element 20 are those composed of extended chain polymers formed by polymerization of σ, ?-unsaturated monomers such as polystyrene, polyethylene, polypropylene, polyacrylonitrile, poly(vinyl alcohol), and the like. In the preferred embodiments of this invention, layer 18 and 24 and fibrous element 28 are formed of organic fibers. In the most preferred embodiments of the invention, layers 18 and 24 is formed of polyethylene fibers, polyester (e.g. poly(ethylene terephthalate) fibers, polyamide (e.g. nylon 6, nylon 6,6, nylon 6,10 and nylon 1 1 ) fibers, aramid fibers or mixtures thereof. U.S. P. 4,457,985 generally discusses such high molecular weight polyethylene and the disclosure of this patent is hereby incorporated by reference to the extent that it is not inconsistent herewith. In the case of polyethylene, suitable fibers are those of molecular weight of at least 150,000, preferably at least one million and more preferably between two million and five million. Such extended chain polyethylene (ECPE) fibers may be grown in solution as described in U.S. Patent No. 4,137,394, or U.S. Patent No. 4,3514,138, or fiber spun from a solution to form a ge structure, as described in German Off. 3,004,699 and GB 2051667, and especially described in U.S. Patent No.4,551 , 296 (see EPA 144,1 147, published Nov. 10, 1982). As used herein, the term polyethylene shall mean a predominantly linear polyethylene material that may contain minor amounts of chain branching or comonomers not exceeding 5 modifying units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 wt% of one or more polymeric additives such as alkene-1 -polymers, in particular low density polyethylene, polypropylene or polybutylene, copolymers containing mono-olefins as primary monomers, oxidized polyolefins, graft polyolefin copolymers and polyoxymethylenes, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated by reference.

In the case of aramid fibers, suitable aramid fibers formed principally from aromatic polyamide are described in USP 3,671 ,542, which is hereby incorporated by reference. For example, poly(phenylene terephthalamide) fibers produced commercially by Dupont Corporation under the trade name of Kevlar 29, 49, 129 and 129 having moderately high moduli and tenacity values are particularly useful in forming ballistic resistant composites. Also useful in the practice of this invention is poly(metaphenylene isophthalamide) fibers produced commercially by Dupont under the tradename Nomex. Bodies 20 and 26 are the same or different and are formed of a hard material as for example a ceramic, a metal or a metal ceramic composite which cannot be penetrated by the point of the threat. Useful ceramic materials may vary widely and include those materials normally used in the fabrication of ceramic armor which function to partially deform the initial impact surface of a projectile or cause the projectile to shatter. Illustrative of such materials are those described in D.F. Laible, Ballistic Materials and Penetration Mechanics. Chapters 5-7 (1980) and include metal and non-metal oxides such as aluminum oxide, boron carbide, zirconium carbide, beryllium carbide, aluminum, beride, aluminum carbide, boron carbide, silicon carbide, beryllium oxide, titanium oxide, aluminum carbide, zirconium oxide, titanium nitride, boron nitride,titanium bodie, tungsten oxide, titanium diburide, iron carbide, aluminum nitride, iron nitride, barium titanate, aluminum nitride, titanium niobate, boron carbide, silicon boride, as well as other useful materials.

Useful metals may vary widely and include nickel, manganese, tungsten, magnesium, titanium, aluminum and steel plate. Illustrative of useful steels are carbon steels which include mild steels of grades AISI 1005 to AISI 1030, medium-carbon steels of grades AISI 1030 to AISI 1055, high-carbon steels of the grades AISI 10140 to AISI 1095, free-machining steels, low-temperature carbon steels, rail steel, and superplastic steels; high-speed steels such as tungsten steels, molybdenum steels, chromium steels, vanadium steels, and cobalt steels; hot-die steels; low-alloy steels; low-expansion alloys; mold-steel; nitriding steels for example those composed of iow-and medium-carbon steels in combination with chromium and aluminum, or nickel, chromium and aluminum; silicon steel such as transformer steel and silicon-manganese steel; ultrahigh-strength steels such as medium-carbon low alloy steels, chromium-molybdenum steel, chromium-nickel-molybdenum steel, iron-chromium-molybdenum-cobalt steel, quenched-and-tempered steels, cold-worked high-carbon steel; and stainless steels such as iron-chromium alloys austenitic steels, and chromium-nickel austenitic stainless steels, and chromium-manganese steel. Useful materials also include alloys such a manganese alloys, such as manganese aluminum alloy, manganese bronze alloy; nickel alloys such as, nickel bronze, nickel cast iron alloy nickel-chromium alloys, nickel-chromium steel alloys, nickel copper alloys, nickel-molybdenum iron alloys, nickel-molybdenum steel alloys, nickel-silver alloys, nickel-steel alloys; iron-chromium-molybdenum-cobalt-steel alloys; magnesium alloys; aluminum alloys such as those of aluminum alloy 1000 series of commercially pure aluminum, aluminum-manganese alloys of aluminum alloy 300 series, aluminum-magnesium-manganese alloys, aluminum-magnesium alloys, aluminum-copper alloys, aluminum-silicon-magnesium alloys of 14000 series, aluminum-copper-chromium of 7000 series, aluminum casting alloys; aluminum brass alloys and aluminum bronze alloys.

Useful metal composites may vary widely and include composites in which one of the aforementioned metals form the continuous matrix having dispersed therein one or more ceramic materials in any form as for example as short or continuous fibers or as low aspect ratio domains. Useful ceramic materials include metal and non-metal borides, carbides and nitrides such as silicon carbide, titanium carbide, iron carbide, silicon nitride and the like.

In the preferred embodiments of this invention bodies 20 and 26 is formed from a metal or metal composite and is most preferably formed of a metal. Bodies 20 and 26 is more preferably formed from titanium, steel and alloys thereof, aluminum and alloys thereof and combinations thereof and is most preferably formed from titanium. The composites of this invention can be used for conventional purposes. For example, such composites can be used in the fabrication of penetration resistant articles and the like using conventional methods. Such penetration resistant articles include meat cutter aprons, protective gloves, boots, tents, fishing gear and the like. The shape of planar bodies 20 and 26 may vary widely. For example, planar bodies 20 and 26 may be of regular shapes such as hexagonal, triangular, square, octagonal, trapezoidal, parallelogram and the like, or may be irregular shaped bodies of any shape or form. In the preferred embodiments of this invention, planar bodies 18 and 24 are regular shaped bodies, irregularly shaped bodies or combination thereof which completely or substantially completely (at least 90% area) cover the surface of substrate layer 14. In the more preferred embodiments of the invention, planar bodies 16 are of regular shape (preferably having rounded or substantially rounded edges), and in the most preferred embodiments of the invention planar bodies 16 are triangular shaped bodies (preferably right angle triangles, equilateral triangles or a combination thereof and more preferably equilateral triangles) or a combination of triangular shaped bodies and hexagon shaped bodies trapezoidal shaped bodies, parallogram shaped bodies and combination thereof, which provide for relative improved flexibility relative to ballistic articles having planar bodies 20 and 26 of other shapes of equal area.

The number of inner layers 22 included in composite 10 of this invention may vary widely depending on the uses of the composite, for example, for those uses where composite 10 would be used as ballistic and/or blast protection, the number of layers 18 would depend on a number of factors including the degree of ballistic and/or blast protection desired and other factors known to those of skill in the ballistic and/or blast protection art. In general, for this application, the greater the degree of protection desired the greater the number of layers 18 included in composite 10 for a given weight of the article. Conversely, the lesser the degree of ballistic and/or blast protection required, the lesser the number of layers 18 required for a given weight of composite 10. In the preferred embodiments of the invention a minimum number of layers is employed for comfort of the user. The number of inner penetration resistant layers 22 may vary widely provide that composite 10 includes at least one layer 22. Usually, composite 10 includes from about 3 to about 60 layers 22, preferably from about 5 to about 40 layers 22, more preferably from about 10 to about 40 layers 22 and most preferably from about 15 to about 30 layers 22.

As depicted in the FIG. 1 , composite 10 preferably includes at least inner one layer 22 and at least one outer layer 16 in which each layer 16 and 22 is composed of a substrate layer 18 which is partially covered with planar bodies 20 or 26, preferably forming an alternating pattern of covered areas 32 covered with a planar body 20 or 26 and uncovered areas 34. These layers are positioned in composite 10 such that uncovered areas 34 of layer 16 are aligned with covered areas 32 of layer 22 and/or the uncovered areas 34 of one inner layer 22 is aligned with covered areas of another layer 22 (preferably an adjacent layer) providing for partial or complete coverage of uncovered areas 34 of one layer 16 or a layer 22 by covered areas 36 of another layer 22 or layer 16 and vice versa. The layers 22 and 16 can be secured together by some suitable arrangement to maintain areas 32 and 34 in substantial alignment with bodies 20 or 26, where the bodies are positioned such that covered areas 32 on one side of a layer 16 or 22 are substantially aligned with uncovered areas 34 on the other side of layers 16 or 22. In the preferred embodiments of the invention the surfaces of layers 18 and 24 covered with planar bodies 20 or 26 such that the bodies are uniformly larger than uncovered mated areas 34 of the other layer 16 or 22 providing for complete overlap. This is preferably accomplished by truncation of the edges of the bodies 20 or 26 or otherwise modification of such edges to allow for close placement of the bodies on the surface such that a covered area is larger than the complementary uncovered area.

The degree of overlap may vary widely. In general, the degree of overlap is such that preferably more than about 90 area %, more preferably more than about 95 area% and most preferably more than about 99 or 100 area % of the uncovered areas 32 of layers 16 and 22 are covered by a corresponding planar body 20 or 26 on the other outer surface of a layer 16 or 22. The article 10 of this invention may be fabricated through use of conventional techniques. For example, bodies 20 or 26 may be sewn to layers 18 and 24 using conventional sewing techniques, preferably at one or more points of body 20 or 26, more preferably a distance from the edge of a body 20 or 26. By sewing a distance from the edge of body 20 or 26 flexibility is enhanced. To prevent extensive disalignment between various layers 16 and 22 adjacent layers can be stitched together.

Means for attaching planar bodies 16 to substrate layer 18 and 24 may vary widely and may include any means normally used in the art to provide this function. Illustrative of useful attaching means are adhesives such as those discussed in R.C. Liable. Ballistic Materials and Penetration Mechanics. Elsevier Scientific Publishing Co. (1980). Illustrative of other useful attaching means are bolts, screws, staples mechanical interlocks, stitching, or a combination of any of these conventional methods. In the preferred embodiments of the invention planar bodies 20 and 26 are stitched to the surface of layer 18 or 24. Optionally, the stitching may be supplemented by adhesive.

The thread used to stitch bodies 20 and 26 to substrate layers 18 and 24 can vary widely, but is preferably a relatively high modulus (equal to or greater than about 200 grams/denier) and a relatively high tenacity (equal to or greater than about 15 grams/denier) fiber. All tensile properties are evaluated by pulling a 10in. (25.4 cm) fiber length clamped in barrel clamps at 10 in/min (25.4cm/min) on an Instron Tensile Tester. In the preferred embodiments of the invention, the modulus of the fiber is from about 400 to about 3000 grams/denier and the tenacity is from about 20 to about 50 grams/denier, more preferably the modulus is from about 1000 to about 3000 grams/denier and the tenacity is from about 25 to about 50 grams/denier; and most preferably the modulus is from about 1500 to 3000 grams/denier and the tenacity is from about 30 to about 50 grams/denier. Useful threads and fibers may vary widely and include those described herein above in the discussion of fiber for use in the fabrication of substrate layers 18 and 24. However, the thread or fiber used in stitching means is preferably an aramid fiber or thread (as for example Kevlar^® 29, 49, 129 and 141 aramid fiber), an extended chain polyethylene thread or fiber (as for example Spectra^® 900 fiber and Spectra^® 1000 polyethylene fiber) or a mixture thereof.

As depicted in FIGs. 2 and 3, the composite of this invention is especially useful in the fabrication of penetration resistance article using techniques known in the art. Illustrative of such articles are bullet proof vests indicated by the numeral 36 in FIGs 2 and 3. The following examples are presented to provide a more complete understanding of the invention and are not to be construed as limitations thereon.

EXAMPLE I A 15 inch (38 cm) square hybrid test panel, consisting of 12 layers of SPECTRA 1000 fabric (62 x 62 yarns/inch, 24.4 x 24.4 yarns/cm), plain weave SPECTRA^® 1000 fabric from 215 denier yarn and having an areal density of 0.127 kg/m²)a and a number of titaium alloy triangular plates (titanium 90 parts, 6 parts aluminum and 4 parts vanadium produced by Timet Inc., and having an areal density of 5.75 kg/m²). The apexes of the titanium triangles having original side length of 2.2 inches (5.6 cm) were truncated by straight cuts parallel to the opposite side, producing new side lengths of 1.6 inches (4.1 cm). These triangles were sewn between layers using SPECTRA^® 1000 sewing thread. The target was constucted in the following manner:

1 . An equilateral tringular grid, having a side length of 2.36 (6.0 mm) was inked onto the front panel.

2. Ten titanium triangles were sewn between fabric layers 1 and 2, and this section of the target was designated Section A. (In this section fabric layers 1 through 5 were sewn together along seam directions used to confine the triangles).

3. Ten titanium triangles were sewn between fabric layers 5 and 6, and were designated Section B of the target. 4. Ten SPECTR^® 1000 equilateral triangular patches, having frou fabric layers and side length of 2.2 inches (5.57 cm), were constructed from ten 4.4 inch SPECTRA^® 1000 triangles. These fabric triangles were sewn around their perimeter using SPECTRA^® 1000 sewing thread. 5. A Section C was constructed in an identical manner to

Section B, except that a fabric triangle was placed behind each titanium triangle and sewn between fabric layers 5 and 6 with the titanium triangle.

6. The entire target was sewn together with SPECTRA^® 1000 sewing thread around the perimeter of 15 inch (38 cm) square.

The V50 velocity for each section was determined against a designated thread. The kinetic energy was calculated for the threat at the V50 velocity for each section. This kinetic energy was divided ty the total areal density for that section at the position of impact (centrally onto titanium triangles) to generate a Specific Energy

Absorption of the Target, SEAT, which is useful measure of ballistic merit. The results, shown in Table 1 , indicate that Section B is less ballistically efficient that Section A. Fabric layers on the impact side of the titanium triangles are less effective. The overall ballistic effectiveness of Section C is equivalent to that of Section A, in spite of that fact that it contains the same number of ballistically less effective fabric layers as Section B. This indicates that the fabric patch provides enhanced ballistic effectiveness, above that of the fabric from which it is constructed. Examination of Section C indicated that the fragments punched through the titanium plate, cutting a section of plate out having almost identical cross-section as the fragment. The backing patch was highly distorted. For shot 7, having striking velocity of 1825 ft./S (556.6 m/s) the patch captured the titanium plate section backed by the fabric and the entire assembly, (patch, plate section and fragment) where pushed through layers 7 and 8 and captured on layer 9.

TABLE I

Relative Ballistic

Effectiveness Against Designated Threat

SECTION ADT (kg/m2) RELATIVE SEAT DESIGNATION

A 7.27 1.00

B 7.27 0.83

C 7.78 1.01

Claims

WHAT IS CLAIMED: - 19 -

1 . An improved penetration resistant composite of the type comprising an outer penetration resistant layer and at least one internal penetration resistant layer, said external layer positioned on the impact side of said composite, and said internal layer positioned on the non-impact side of said composite each of said internal layers and said external layer comprising a fibrous substrate layer comprised of a fibrous network having one or more planar penetration resistant elements affixed to a surface thereof, the improvement comprising a fibrous element comprised of a fibrous network positioned between said planar elements and said substrate layer of said at least one internal penetration resistant layer.

2. A composite as recited in claim 1 wherein said fibrous layer and said fibrous element comprises a network of high strength fibers having a tensile strength of at least about 5 g/denier.

3. A composite as recited in claim 2 wherein said tensile strength is equal to or greater than about 10 g/d, said modulus is equal to or greater than about 500 g/d, and said energy-to-break is equal to or greater than about 20 j/g-

4. A composite as recited in claim 2 wherein said fibers are polyethylene fibers, aramid fibers, metal fibers, polyester fibers, nylon fibers, glass fibers or mixtures thereof.

5. A composite as recited in claim 4 wherein said fibers are polyethylene fibers.

6. A composite as recited in claim 4 wherein said fibers are aramid fibers.

7. A composite as recited in claim 2 wherein said fibrous substrate layers and said fibrous elements are formed from at least one sheet-like uniaxial fibrous layer in which said fibers are arranged substantially parallel to one another along a common fiber direction.

8. A composite as recited in claim 7 wherein said uniaxial layers are dispersed in a polymeric matrix.

9. A composite as recited in claim 1 wherein said planar penetration resistant elements are formed from a metal or a metal alloy.

10. A composite as recited in claim 9 wherein said metal is titanium.