EP0041271A1

EP0041271A1 - Composite ceramic armor

Info

Publication number: EP0041271A1
Application number: EP81104223A
Authority: EP
Inventors: Alvin Eugene Gorum
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-06-02
Filing date: 1981-06-02
Publication date: 1981-12-09
Also published as: NO811845L; AU7088581A

Abstract

A composite armor for fragmenting the hard core of armor piercing projectiles has a matrix (M) of elastomeric material having a percent elongation of about 400 to about 600 embedded in which are at least two rows of parallel elongate cylindrical rods (R) formed of a hard ceramic projectile-fragmenting material. The elastomeric material of the matrix is the only substance that flows between adjacent ceramic rods.

Description

Field of the Invention

This invention relates to armor and more particularly to a light weight composite armor for protection of vehicles or the like against extremely hard, high velocity projectiles.

Description of Prior Art

The U.S. patent to King 3,481,818, March 11, 1969, discloses a lightweight protective armor plate wherein the force of a hard projectile is dissipated by shattering energy dissipating elements of the armor plate struck by the projectile, causing the projectile itself to be broken int6 fragments so that the projectile does not penetrate the armor plate. Figure 2 discloses an armor plate having a body or matrix formed of a high strength plastic material such as, for example a thermo-setting epoxy resin reinforced by fiberglass. Embedded in the body are two layers or rows of "rigidly" positioned elongated cylinders which serve as the projectile energy-dissipating elements. The cylinders are formed of a ceramic material, namely, aluminum oxide, nickel plated aluminum oxide or boron carbide. Upon impact by a projectile, and as seen in Figure 2, a cylinder in both the outer and inner layers is partially shattered and the projectile is broken into . fragments.
Undulating layers of spacing material in the form of reinforced, plastic-impregnated woven plastic sheets are em- bedded in the epoxy body and are alternately woven under and over the ceramic cylinders of each row. These reinforced fabric sheets are provided to reduce or prevent the transmission of shock waves from the projectile, which would otherwise cause shattering of the ceramic cylinders over a large area from the impact of a single projectile and which would reduce the effectiveness (multiple hit capacity) of the armor plate. The armor plate has both outer and inner layers of plastic material, like that of the plastic body in which the cylinders are embedded, which layers are either integral with or bonded to the composite armor plate assembly.
The U.S. patent to Meyer 2,723,214, November 8, 1955, discloses an elastic cascading impact absorber which operates on a principle for defeat of the projectile that is entirely different from that relied upon by the aforesaid King patent. In the Meyer patent, the armor is made up of successive layers of edge abutting plates of fiberglass resin or alloy steel with the area of the plates of each layer increasing from the outer layer to the innermost layer. Behind each layer of plates is bonded an elastomer.to act in a manner "comparable to a layer composed of a layer of small coiled springs having. their axes parallel to one another normal to the surface of the layer.". A list of elastomers suitable for this purpose is described in Cols. 7, lines 24 - 43.
The Meyer specification states that (starting at the bottom of Col. 3):

"By grading the spring constants the material of the outermost layer of elastic may be almost completely compressed befdore the material of the next layer becomes compressed appreciably. Thus, the forward motion of the projectile is halted over a maximum length of time, the rate of energy absorption increasing as the energy is transmitted to the layers of the armor and as the energy remaining decreases.
"As a result of the conversion of the kinetic energy of the bullet to store potential energy . in the compressed layers of plastic material, the stored energy is immediately available for reconversion into kinetic energy. This reconversion begins at the moment the bullet ceases to travel forward, the bullet being accelerated in a reverse direction."

Thus, the Meyer armor does not (and could not) defeat a very hard projectile by fragmentation of an armor element at the zone of impact with the resultant fragmenting of the projectile, but rather acts on the principle of converting the kinetic energy of the projectile into potential energy.
The U.S. patent to Eger 2,318,301, May 4, 1943 discloses a bullet resisting armor having a hard steel backing plate, a body or matrix of tough vulcanized rubber having a preferred Shore-durometer of 90 and not less than 80 in which is embedded a front layer of overlapping hard steel-strips disposed at an angle of 45° to the plane of the armor plate. In operation, when projectiles strike the armor they are de- flected by the metal strips which, being mounted in the rubber composition are permitted slight cushioning movement, thus absorbing much of the energy of the projectile. Thus, the Eger armor acts on the energy conversion principle described in more detail in the patent to Meyer, namely that of temporarily converting the kinetic energy of the projectile into potential energy. As in the Meyer patent, the armor of Eger cannot shatter extremely hard projectiles or projectile cores.
The U.S. patent to Pfistershammer 2,738,297, March 13, 1956, discloses in Figure 1 a plate having a basic material or matrix formed of steel or a polyamide such as nylon in which a granulated filling material is cast. The filling material must posess great hardness and high compressive strength such as quartz, hard basalt, silicon carbonate or corundum, these being the preferred materials. When the structure such as that of Figure 12 is employed as armor, the hard granules are cast into the basic material (steel or nylon) under pressure and the filling material is crushed by the projectile and distributes the projectile energy over a wide angled cone. When the material is used as an armor for tanks, ships, aircraft, etc., the granular filling material may be made of a combination of steel and steatite (soapstone) or corundum because this material has a melting point far above that of the steel forming the basic matrix material.
Eichelberger 3,324,768, June 13, 1967 discloses panels for protection of armor against shaped charges. The pertinent forms disclosed comprise inner and outer plates of thin metal flanking a composite material consisting of glass balls, glass plates or glass blocks embedded in a filler or shock absorbing material such as 85% magnesia or bitumin.

Summary of the Invention

The armor of the present invention defeats (prevents penetration of) extremely hard projectiles or the hard cores of jacketed projectiles and absorbs their energy by literally pulverizing the projectile upon impact. This destruction of the projectile before penetration is obtained with an attendant localized or small area damage to the armor and no large armor components are dislodged or blown out at the impact zone. This provides a statistically high probability of providing multiple hit capability in the general area of a previous hit. The aforesaid projectile pulverizing and energy dissipating action is provided by a composite armor having at least two layers or rows of parallel, elongate, generally cylindrical rods formed of a hard ceramic projectile-fragmenting material (preferably silicon carbide), with all of said rods being spaced from one another.
In one form of the invention, the rods are generally circular in section and the rods of one row are staggered with respect to those of an adjacent row. In another form, the rods are generally elliptical in section with their major axes in- ' clined at about 45° to the plane of the armor, in which case the rods of adjacent rows need not be staggered.
The rods are embedded in a matrix formed of a homogenous body of elastomeric material having a percent elongation of about 400 to 600, and a Shore durometer hardness on Scale A of about 50 to about 70, the preferred elongation being 600 percent, with a hardness of A-70. The elastomeric material of the homogenous matrix body is the only substance disposed between adjacent ceramic rods. The matrix material has a sonic velocity that is much less than that of the hard ceramic rods. Such a matrix, with its low sonic velocity, restricts rod fragmentation to that portion of a rod which is struck by the hard projectile, because destructive shock waves are not pro- pogated from an impacted rod to an adjacent rod. No undulating sheet material need be interposed between the ceramic rods to hold them in place upon impact. The matrix is not relied upon to convert the kinetic energy of the projectile into potential energy, as in the aforesaid Meyer and Eger patents. Because of the relatively high percent elongation of the matrix material, - . rod and matrix fragments are not splashed out of the armor over an area surrounding the impact zone. A backing plate of tough, non-spalling material, such as aluminum or a fiberglass reinforced resin, backs up the inner side of the matrix.
Firing tests have been conducted under applicant's direction on an armor wherein two rows of ceramic projectile fragmenting rods were embedded in an epoxy matrix, a cure epoxy resin have a low percent elongation as compared to the elongation of applicant's invention. The matrix was an epoxy resin "Formulation 1 - 7 - 11" supplied by the Dow Chemical Company of Midland, Michigan. The cured resin had an ultimate percent elongation of about 100. The projectile had an armor piercing core and its caliber was somewhat over one half of the diameter of the rods. Large portion of the impacted rods as well as the adjacent rods in both the outer and inner rows were fragmented and completely dislodged or "splashed out" from a large area around the impact zone, leaving the backing plate exposed. In fact, the splashed out area was about 6 - 8 times the rod diameter. This would greatly reduce the multiple-hit capacity of the armor.
Another feature of the armor of the present invention is that of convenient field repair of armor damage. Damaged zones can be replaced by forming the principal armored areas as a group of discrete rectangular armor plate units of relatively small individual area, such as rectangles having slabs of ceramic rods that are about 18" to 36" long embedded in an elastomeric matrix. The slabs for each unit are enclosed by a shock absorbing tough metal frame, e.g. high tensile strength aluminum. The frame limits the transmission of projectile energy along the length of or across impacted rods of one unit to rods in an adjacent unit. Thus, rod damage is limited to portions of rods at the impact zone of a single framed unit. Fasteners are provided for replaceably mounting the framed armor slabs on the walls of a vehicle or the like to be protected.
If flotation is desired, a fragmentation-inducing armor steel plate can be provided and is spaced at a substantial distance outwardly from the outer face of the ceramic armor matrix. This plate (which can be penetrated by a very hard projectile of sufficient size and velocity) sets up initial shock waves in the projectile which waves are reflected back and forth along the projectile during its passage to the ceramic armor plate assembly, and this initial fragmentation-inducing shock wave action enhances the ultimate projectile pulverizing action by the ceramic rods.

Brief Description of the Drawings

Figure 1 is a front view of an area provided with a panel assembly embodying the armor of the present invention.
Figure 2 is a somewhat enlarged view of one of the armor panels of the invention with parts broken away.
Figure 3 is an end view of one of ceramic element spacer grid.
Figure 4 is a fragmentary perspective of the panel:- of Figure 2 with a part of the panel matrix broken away.
Figure 5 is an enlarged fragmentary front view of portions of several panels with parts of one panel broken away.
Figure 6 is a section taken on line 6 - 6 of Fig. 5.
Figure 7 is a fragmentary section through a modified form of the armor shown in Figures 1-6.
Figure 8 is a fragmentary section through preform rubber strips employed to provide a modified armor matrix.
Figure 9 is a fragmentary section of the armor showing the addition of a shock-inducing plate in front of the ceramic armor.
Figure 10 is a fragmentary section through armor panels showing a modified form of ceramic elements.

Detailed Description

Referring to Figure 1, an armor array A is made up of a closed array of composite rectangular armor panels P formed in accordance with the present invention. The construction of an individual panel P is shown in Figures 2 _- 6. The panels are detachably secured to a base structure of the vehicle or the like, to be protected.
Each panel P includes a rectangular box or mold 10 which contains a composite armor slab that includes two rows of projectile fragmenting ceramic rods R embedded in a matrix M formed of an elastomeric material. Details of the ceramic rod and matrix compositions will be described presently.
The panel box 10 is formed with end walls 12 welded to side walls 14, these walls preferably being formed of an armor grade aluminum alloy, such as one having specification No. 5083 with the heat treatment designated as T6. End and side plates 12, 14 are welded together at 15 (Figure 5) and a thin bottom plate 16 is welded to plates 12, 14 at 17 (Figure 6) to form a closed box having one open face.
The projectile fragmentation rods R are formed of a sintered ceramic material having a hardness on the Moh scale of at least 9 and preferably about 9.5. The preferred material is sintered silicon carbide which has a hardness almost as great as that of a diamond and which is relatively economical, even when supplied in the desired elongate rod form. Other material which can be employed for the projectile fragmenting rods are pure aluminum oxide (corundum), silicon nitride or boron carbide, although the latter two materials are relatively expensive as compared to silicon carbide.
In all forms of the invention, the ceramic rods R are embedded in a matrix M of an elastomeric material having a rather high percent elongation. For example, the matrix material shown in Figures 1 _- 6 is a cured polyurethane resin. In order to prepare a composite panel 10 wherein the matrix is a cured resin, rows of rods R are supported adjacent their ends by apertured spacer grids 20. As best seen in Figure 3, the grid 20 is formed with an outer row 22 of apertures 24 formed to receive a row of full section right cylindrical rods R. The grid is also formed with an inner row 26 of apertures wherein the full section apertures 24 are staggered relative to the corresponding apertures 24 in the outer row and wherein two generally semi-circular end apertures 24a are provided for the inner row. The full, generally circular section rods R are supported in the apertures 24 and generally semi-cylindrical rods Rl are supported in the end apertures 24a when the rods are first assembled in the panel box 10.
The spacer grids 20 are preferably formed of a low sonic velocity, elastomeric material, such as sheet rubber in order to minimize the transmission of shock waves between the ends of adjacent ceramic rods.
After the panel box 10 has been filled with an assembled array of staggered rows of rods R, in cases where the matrix material is supplied in the form of an uncured liquid resin such as polyurethane, the liquid is poured into the box substantially up to the level of the upper edges of its side members 12, 14. As seen in the drawings, the rods are so spaced that there is a body of the elastomeric matrix material between adjacent rods so that the rods are isolated from one another by the material. The spacing between adjacent rods is less than the rod thickness. For example, if the rods have a diameter of about 3/4" to about 7/8" their spacing will be about 3/16" to 1/8". As can be seen in Fig. 2, there is a layer 28 of the matrix material between the ends of the ceramic rods and the adjacent walls 12 of the panel boxes 10. This eliminates the propogation of destructive shock waves from the rods in one panelto those in an adjacent panel.
As mentioned, a feature of the present invention is that the matrix M is formed of a material which has a very low sonic velocity compared to that of the ceramic rods R. Since the rods are isolated from one another in the matrix, the aforesaid characteristic of the matrix material prevents transmission of a destructive shock wave generated in a rod that has been struck by a projectile to adjacent rods so that-although a directly impacted rod may be locally fragmented, adjacent rods will be relatively undamaged. This is true, even though the rod or rods which receive the impact of the projectile or a partially fragmented projectile directly, may be locally shattered. As mentioned by way of example, one matrix material suitable for this purpose is a polyurethane elastomer which is supplied in liquid form and which can be poured into the panel boxes 10 after the rods have been placed therein until the boxes are filled to the top. A suitable commercially available material is Indpol Monothane marketed by Sinair Corporation of Tustin, California. This material comes in a number of grades but the preferred grade is identified as A-70 and has a percent elongation of 600. The resin is supplied as a relatively viscous liquid and can be poured when - warmed to about 70° C. After filling one or more panel boxes with the aforesaid material, the boxes are placed in a curing oven and cured for about 8 hours at about 135° C. The cured matrix has a Shore durometer hardness on Scale A of about 70, although this is the preferred hardness, materials are also available from the aforesaid corporation having Shore hardnesses of A-50 and of A-60 and these also have a percent elongation of about 600. The latter two materials are also among the preferred materials for use as a plastic matrix in the present invention. Other thermo-setting elastomers which can be employed are polypropylenes blended with rubber, ABS (rubber and styrene) and various rubbers to be mentioned presently.
Although the ceramic rods R will shatter hard core projectiles and reduce them to small low energy fragments, it is important that a backup plate or anvil be provided to ab-- sorb the energy of the projectile fragments and prevent fragment penetration of the matrix without spalling of the anvil or backup plate itself. In the form of Figs 2 - 6, this function is attained by securing each panel P to an anvil or backup plate 30 (Figure 6) which operates, in conjunction with the projectile fragmentation action of the ceramic rods R, to completely defeat the projectile and prevent all penetration of the projectile or fragments thereof, without spalling (dislodgement of backup plate fragments). The plate 30 and the panel members 12, 14 are formed of a tough material such as armor grade aluminum of specifications 5083 or 7093, having a heat treatment T6. The plate is preferably thicker than the diameter or major dimension of any of the rods R, (about one inch in the example given) but need not be as thick as the thickness of the composite panel P. The plate can also be formed of a tough fiberglass impregnated resin wherein a number of coarse woven fiberglass sheets are laminated in a curved matrix of resin such as an epoxy or a polyester.
Impact of a projectile on a panel may locally fragment one and often two of the rods R, such as an outer rod, which directly receives the impact of the projectile, and an underlying rod which receives the impact of the projectile fragments. The convexity of the rods acts to deflect the projectile from its initial trajectory, thereby reducing the effectiveness of the projectile. Two outer rods may substantially directly receive the impact of a projectile, whereupon these rods will be locally fragmented along a portion of their lengths.
Although the impact of a high velocity hard core projectile may reduce the repeat hit capability, in case of a second hit at the same area of a panel that received a previous hit while leaving the remainder of the panel at full effectiveness, it is preferable that the panels P be replaceable to restore complete integrity to the area of a partially damaged panel. For this reason, the panels are secured to the protected structure by any fastener which will prevent impacted panels from being blasted loose from their support but which will permit ready replacement of any panel. Thus, as best seen in Figures 5 and 6, the side and end walls, 12, 14 of each panel are drilled to receive securing bolts 31. The apertures 32 for the bolts 31 are best seen in Figures 2, 4 and 6. In the structure shown in Figure 6, the bolts 31 are threaded into the underlying back-up or anvil panel 30 that mounts an array of panels P.
The dimensions of the individual composite panels P are not critical, but are related to the area of the vehicle_ or the like to be armored and to the desired ease of handling of the panels in case of replacement thereof in the field. The dimensions of the panels P will also relate to the diameter or thickness of the ceramic rods R..Generally speaking, the diameters or major cross sectional dimensions of the ceramic rods will be somewhat larger than the diameter (caliber) of the projectile core to be defeated. To give a typical, but not limiting, example, a panel P having generally circular section cylindrical ceramic rods R with a diameter of about 3/4 inches to 7/8 inches can have a width of something over 12 inches and a length of about 18 inches. These dimensions are not critical and longer or both longer and wider panels can be employed. In the example illustrated 3/4" rods are so positioned that there is about 1/8 inch of matrix material between the rods at their most closely spaced zone. Thus, if the rods, for example, have a diameter of 3/4 inches, the internal width of a nominal 12 inch wide panel P will be about 12 3/8 inches. It is not possible to give any specific dimensions to the various components of each panel or of the rods because these dimensionals depend upon the caliber and velocity of the projectile which the armor is designed to defeat. As mentioned, the only concrete example that can be presented is that it is known from the present firing data, that where a panel receives the impact of a hard armor piercing core projectile directly, the rod diameter or its major sectional dimension should exceed that of the projectile core but need not be over twice the projectile caliber. Thin ceramic bodies, which, in effect, act as mere plates are not considered to be effective on an areal density basis. as compared to the rods herein described.

First Modified Form

Figure 7 illustrates a first-modified form of armor Al wherein the side members of each panel P1 are welded directly to a coextensive anvil or backup plate 30a and the thin bottom plate 16, previously described, is not required. In the partial section of Figure 7; one of the side members 14a is shown welded at 15a to the relatively thick anvil plate 30a. The bolt apertures, such as aperture 32 appearing in Figure 7,are aligned with bolt apertures 32a in the backup plate 30a so that the entire panels 10A form complete armor units which can be secured to a supporting wall of a vehicle or the like to be armored. In this panel construction, full section generally circular section cylindrical ceramic rods R and partial section rods Rl are embedded in an elastomeric matrix M, such as that previously described. ?

Modified Form Of Matrix

Figure 8 is a fragmentary section showing a preliminary stage in the formation of a matrix for the ceramic rods which, instead of being formed of a cured elastomeric resin material that can be poured into a panel box before curing is formed of a synthetic or natural rubber. The matrix Ml is made of three rubber pre-forms which can be either molded or extruded and if initially cured at all after their formation, are only partially cured. For example, in order to achieve the array of rods such as that shown in Figures 1 - 7, an inner pre-form 40 is formed with edge channels 42 for receiving semi-circular rods Rl and half round channels 44 for receiving full section rods R. The opposing face of an intermediate pre-form 46 is provided with companion channels 42a and 44a. The other face of the intermediate pre-form 46 is formed with a row of half round channels 48 for receiving full section ceramic rods. One outer pre-form section 50 is provided with half round channels 48a corresponding to the channels 48 in the intermediate pre-form 46. The pre-forms just described are assembled in a panel box (not shown) like either of those previously described along with the ceramic rods in an obvious manner. After assembly, the box (rods and matrix pre-forms) are bagged in accordance with conventional rubber curing procedure and one or more of the assembled panels are cured in a conventinal curing oven. In order to isolate the ends of the rods from adjacent box end members, such as the members 12, previously described, thin strips of uncured rubber are inserted between the ends of the rods and the end members of the panel. Pressure can be applied to the pre-forms during curing by the introduction of an inert gas under pressure in the vulcanizing or curing oven, in accordance with conventional practice. This unites the pre-forms along their mating surfaces and produces a one-piece homogenous rubber matrix Ml, Although natural rubber can be employed,an acrylo- mitrile and butadiene based synthetic rubber is also suitable and is less costly than natural rubber. A neophrene rubber can also be employed. The rubber will have a Shore durometer hardness of about 50A to about 70A with 70A preferred.

Third Modified Form

Figure 9 is a partial section through a third modified form of armor A3. This armor is intended to defeat hard core projectiles having a somewhat greater caliber than those for which the previous forms of the invention were designed, or possibly the projectiles may have a higher initial velocity than the projectiles for which the previous forms of armor were designed. The armor A3 of Fig. 9 can be made up of a panel 10C like the panels previously described. In the form shown, each panel includes a bottom member 16 that is bolted to a full area anvil or backing plate 30 like that of Fig. 5. The armor employs a row of staggered ceramic rods R as before and an elastomeric matrix M like either of those previously described.
In order to generate shock waves in the projectile, and weaken its structure before it strikes the composite armor slab itself, a hard steel plate 60 of armor grade steel is mounted some distance in front of the outer face of the matrix _M of the composite armor. The panel walls, such as wall 14C can mount the plates 60. In case flotation is desired, as in the case of amphibious vehicles, a body 62 of foam rubber, foamed polypropylene or the like is interposed between the armor plate 60 and the matrix M of the composite armor. The spacing between the steel armor plate 60 and the front face of the composite armor is several times the diameter of the rods R. The purpose of this spacing is to permit shock waves engendered in the projectile core, when it impacts and penetrates the plate 60, to make one or more excursions back and forth along the length of the projectile core. This action facilitates subsequent fragmentation of the core when it strikes one or more rods R, or Rl of the composite armor. The construction of Figure 9 can either be fabricated employing panels with a thin bottom plate 16 for mounting on a large area plate 30 or panels which are secured directly to a relatively thick coextensive anvil 30a, as in the construction of Figure 7.

Fourth Modified Form

In the modification of Figure 10, all of the ceramic rods R4 can be of the same configuration and yet they supply full row or layer protection action without the addition of partial section, gap filling rods in one row, such as the semi-cylindrical rods Rl shown in the previous embodiments.
In the embodiment shown in Figure 10, the armor A4 is illustrated as formed of individual panels 10D in which case an array of panels is provided as in Figure 1. As shown in Figures 2 - 6 the panels have end members 12 (not shown in Figure 10) and side members 14 and the bottom is closed by a thin bottom plate 16. The rods R4 are made of a hard ceramic material such as those previously described but in this case they have a cross-sectional shape that is generally eliptical. The major axes of the elipses are inclined relative to the inner or outer faces of the panel by an angle, preferably an angle of about 45°. In this construction, the. rods in one row need not be staggered relative to the rods in an adjacent row because due to the inclination of their axes, no gaps between rods are presented to the projectile between rods, as indicated by the line c -c even though the trajectory of the projectile at the armor is perpendicular to the outer face thereof as indicated by the dashed arrow T in Figure 10.
In the preferred arrangement of the rods R4 in Fig. 10, the major axes of the individual elipses falls substantially on a line d - d which is the preferred angle of about 45° to the base 16. However, so long as the rods in each row are arranged in each row so that there are no substantial gaps in the direction of line c -c, it is to be understood that the major axes of the individual elliptical rods of one row need not be in exact alignment with the major axes of the eliptical rods in an adjacent row. Although the matrix M illustrated in the form of Figure 10 may be of an elastomeric polyurethane material like that previously described, it may also be formed of a natural or synthetic rubber such as that of the matrix Ml shown in Figure 8. It is also contemplated that instead of employing a thin bottom plate 16 for the panels 10D in the armor of Figure 10, the panels may have coextensive bottom plates formed of a thicker base material, such as the plates 30a shown in the form of Figure 7.
The various side panels 12, 14, etc. have sufficient depth, measured in a direction normal to the base plate 16, to defeat a projectile which strikes the panels directly and which would be defeated by the ceramic rods.
As to the shape of the generally eliptical rods R4 of Figure 10, in the preferred form, the length of the major axis of the rods is about twice that of the minor axis thereof, although these dimensions are not exact. Also, the length of the major axis should be somewhat greater than the diameter of the projectile which the armor is designed to defeat.
In the strictest mathematical sense, the term "ellipse' refers to a closed conic section and can be defined by the Cartesian equation
, where a and b are the semi- major and semi-minor axes of the ellipse. In the appended claims the term "ellipse" or "elliptical" is not limited to a rod having a cross-sectional configuration that exactly corresponds to the aforesaid geometrical and mathematical definitions of an ellipse but rather to rods having a cross-sectional shape which perform the same function as that of a true ellipse, even though all portions of curved boundaries of the rod section are not mathematically exact elliptical elements. Also; in the appended claims, the term, "cylinder" or "cylindrical" is intended to refer to the more general definition of this term, namely a surface traced by a straight line, called the generatrix or element moving parallel to a fixed straight line. This definition of the term "cylinder" encompass the rod geometry of the rods R of the forms of Figures 1 - 9 wherein the right section of the cylinder is substantially circular. The aforesaid definition of the term "cylindrical" also encompasses the rod configuration of Figure 10, wherein the right section of the cylinder is elliptical, or is substantially elliptical.
In the appended claims which include the term "rectangular" as applied to a panel this term includes a square panel,-the square being merely a special form of rectangle.

Operation

Although the operation of the composite arm of the present invention has been mentioned briefly, some further observations are believed to be in order. Applicant's licensee has a firing range facility and an X-ray examination facility for studying the capabilities of armor against various projectiles. After the applicant has formed destructive examinations of armor made 'in accordance with the present invention after it has defeated hard core projectiles,it is found that the armor has shattered and fragmented the projectile core, as evidenced by the fact that granules of the projectile are found distributed adjacent the base or backing plate of the armor. No large projectile core fragments are normally found and most of the projectile fragments are mere granules and pulverized particles.
Due to the convex surfaces presented to the impac,ting projectile and any fragments that might be broken off thereof, the projectile is diverted from its original trajectory upon impact which diversion itself absorbs some of the projectile energy. Upon impact of the projectile or a portion thereof with a ceramic rod, projectile kinetic energy is dissipated by the rod which converts the projectile energy into the energy required to locally fracture and fragment the rod. This initial impact with a hard core must also fracture and fragment the projectile to the extent that the projectile is cracked and fragments thereof are deflected from the first row of rods, penetrate the intervening matrix and impacting upon the second row of rods. The projectile fragments are not only slowed down, their mass is less than that of the complete projectile, hence kinetic energy of each individual fragment is greatly diminished. At the underlying row, the action is repeated and the fragments of the projectile are themselves broken up into the small granules or particles found at the inner portion of the matrix. When one or more rods are locally fragmented, the fragmented portions of the rods retain their configurational envelope.
Although portions of the rods which are directly impacted by the projectile are fragmented for some distance along their length, the.rod fragmentation is localized, for example, along a length of about two-three times the rod thickness. Also, a portion of the rods in the inner or rear row thereof may also be locally fractured or even partially fragmented. An important feature of the armor of the present invention is that due to the provision of an elastomeric matrix surrounding the rods, which matrix has a much lower sonic velocity than that of the rods themsleves, shock waves generated in an impacted rod are not transmitted by the matrix with sufficient force to directly fragment adjacent non-impacted rods. In other words, rods that are fragmented by the projectile are fragmented only by direct impact by the projectile or by fragments thereof. Furthermore, large rod fragments are not splashed out at the impact zone.
As previously mentioned, test firings were conducted against an armor having spaced ceramic'rods formed of alumina, wherein the rods were embedded in a resin matrix having a relatively low percent elongation and a correspondingly high sonic velocity. Such armor stopped the projectile but would not provide acceptable multiple hit protection. For example, a matrix formed of a tough epoxy resin having a relatively high percent elongation for an epoxy (about 100%), causes a large area of the armor surrounding the zone of impact to be disrupted and the ceramic rods at the impact area and at adjacent areas blow or "splash" out from the support, thereby seriously reducing the multiple hit capacity of an epoxy matrix armor.
The zone of repeat hit weakness in the armor of the present invention is relatively small so that even after sus- taining a hit, most of the area of the armor surrounding the impact point retains its integrity as a projectile defeating assemblage. Rather than splashing out, as is the case wherein the rods are embedded in an epoxy resin, the rods at the impact zone remain in place, although they may be locally fractured. If multiple hits are received on a single panel, (where the armor is fabricated of panels) and if they are close enough to reduce the integrity of the entire panel to an unacceptable extend, the impacted panel is easily replaced by a new one in the field.
As previously mentioned, where considerations of armor weight are important, (and this is the case with most land, sea, air or amphibious vehicles) it is customary to design a given unit of armor to defeat a projectile up to a given caliber and at a given maximum velocity. Thus, in designing the armor to incorporate the-present invention, the ' maximum acceptable weight or areal density of the armor is the primary consideration. Once an areal density (unit weight per unit armor area) is selected, this dictates the maximum weight of the ceramic rods that can be employed over a given area and hence dictates rod sectional size.
As mentioned before, the rods should have a sectional thickness that is somewhat greater than the caliber of the projectile to be defeated. It is essential that the matrix of elastomeric material have a relatively high percent of elongation (e.g. about 400% or greater) as previously described and that the matrix isolates the rods one from the other as well as isolating them from the walls and base members of each panel, assuming that the armor is assembled in panel form. Although high purity aluminum oxide (corundum) silicon nitride or boron carbide are acceptable materials, the preferred material for the composition of the rods is sintered silicon carbide. This material, which has a hardness on the Moh scale of at least 9 is relatively economical to fabricate and when rods formed of silicon carbide are embedded in an elastomeric matrix of the type described, such rods are, for practical purposes, as effective as those formed of more expensive materials such as boron carbide or the like. ^-'
Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention as defined in the appended claims.

Claims

1. A composite armor for fragmenting the hard core of an armor piercing projectile, the armor being of the type having a matrix of polymeric material, in which is included at least two rows of parallel, elongate, rounded section cylindrical rods formed of a hard ceramic projectile, fragmenting material embedded in the matrix, wherein all of the rods are spaced from one another by a distance which is substantially less than the thickness of the rods, characterized in that matrix is formed of a homogenous body of elastomeric material having a percent elongation which is in the range of about 400 to about 600, that the elastomeric material of the matrix is the only substance disposed between and along the major length of adjacent ceramic rods, that the elastomeric material has a sonic velocity that is much smaller than that of the ceramic rods, thereby restricting rod fracture to substantially those portions of the rods which are impacted by the projectile without substantial fracture of the non-impacted rods by the transmission of shock waves from impacted rods through the matrix.

2. The armor of claim 1; comprising a backing plate of tough, non-spalling material juxtaposed against the rear face of said matrix with a layer of matrix material disposed between the innermost row of rods and said plate.

3. The armor of claim l; wherein said matrix-is formed of a cured polyurethane resin.

4. The armor of claim 1; wherein said matr,ix is formed of rubber.

5. The armor of claim l; wherein said matrix has a Shore durometer of about 70-A.

6. The armor of claim 1; wherein said matrix has a percent elongation of about 600.

7. The armor of claim l; wherein said rods are substantially circular in section with the rods of each layer being staggered relative to those of an adjacent layer.

8. The armor of claim 7; wherein there are two layers of rods.

9. The armor of claim 8; wherein all of the rods in the outermost row of rods are of substantially circular section, their being a rod of substantially semi-circular section at each side of the underlying row of rods with the remainder of the rods in said underlying row also being of substantially circular section.

10. The armor of claim 1; wherein said rods are spaced from one another by a distance that is about 1/8 of the major cross-sectional dimension of a rod.

11. The armor of claim 1; wherein said rods are elliptical in section, the major axes of the rod sections being inclined to the face of the armor at angles of about _· 30° to about 60°:

12. The armor of claim 11; wherein said inclination angle is about 45⁰.

13. A composite armor as in claim 1 wherein the matrix and the embedded rods are formed as a discrete panel, characterized in that the panel is in the form of a box-like member having a bottom wall and side walls formed of a tough armor material that enclose the matrix, that there is a layer of matrix material between the rods and the walls of the box-like member, and that means is provided for attaching the panel 'to a vehicle structure.