Armor for lightweight ballistic protection

Abstract

Armor for lightweight ballistic protection is made up of composite tiles which can be assembled into modules. The modules can be assembled into panels and can be mounted on vehicles and aircraft and on the walls of shelters. The tiles have core layer(s) of non-homogeneous materials provided by particles of grit distributed in a plastic, preferably rigid polymeric matrix, and which are faced by a layer of high modulus stiff material such as ceramic. The tiles are preferrably backed by elastomeric material and may have sheets of composite material between the elastomeric layer and the non-homogenous core layer. The tiles may be stacked, forming modules and the modules assembled in rows to form panels. An incoming object causes the facing layer to distribute the impact force over a large area of the non-homogeneous grit/polymeric core layer which fractures and absorbs the impact and shock waves, both the compressive direct wave and the tensile wave reflected from the back interface. The non-homogenity and distributed grit particles in the core layer also serve to reflect and disperse the shock wave. The elastomeric layer also aids in distributing the shock wave. In response to the impact and shock waves and projectile penetration, the non-homogeneous grit/polymeric core layer cracks, pulverizes and disintegrates resulting in high energy absorption by crack propagation. Also the small debris particles which are generated absorb kinetic energy as they are propelled into motion, diverted and scattered.

Claims

1. Armor structure which protects against incoming objects and which is a tile comprising a brittle first body of non-homogeneous material which is frangible upon impact, said first bocy having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface, said first and second body materials cooperating to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body.

2. Armor structure according to claim 1 wherein said first body is provided by particulate material distributed in a matrix of plastic material.

3. The armor structure according to claim 2 wherein said second body is provided by hard, stiff material such as ceramic.

4. The armor structure according to claim 3 wherein said second body consists of silicon carbide.

5. Armor structure according to claim 2 wherein the particulate material of said first body is granules of material having a modulus of elasticity that is a plurality of orders of magnitude higher than the modulus of elasticity of said plastic providing said matrix.

6. The armor structure according to claim 5 wherein said particulate material is selected from the ceramic groups including silicon carbide and quartz.

7. The armor structure according to claim 6 wherein said plastic is a polymer.

8. The armor structure according to claim 7 wherein said polymer is epoxy.

9. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said first body being provided by particulate material distributed in a matrix of plastic material, and the particulate material of said first body being granules of material having a modulus of elasticity that is a plurality of orders of magnitude higher than the modulus of elasticity of said plastic providing said matrix, wherein said particulate material is selected from the ceramic groups including silicon carbide and quartz, said plastic is an epoxy polymer, said particulate material is mixed sufficiently with said epoxy while said epoxy is fluid to provide a mixture in which particles of said particulate material are distributed, and said first body is formed by molding and curing for a time sufficient to provide impact frangible and disintegratable characteristics in the material of said first body.

10. The armor structure according to claim 1 wherein said first body has a modulus of elasticity of about 10,000 to 20,000 psi and a toughness coefficient of about 20,000 PSI (inches).sup.1/2 at room temperature.

11. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, wherein said first and second bodies are successive plates which define a tile, and said structure comprises a module containing a plurality of said tiles disposed in stacked relationship with the plates providing said first body alternating with the plates providing said second body.

12. The armor structure according to claim 11 wherein a plurality of said modules are disposed in a row to define a panel.

13. The armor structure according to claim 12 further comprising a sheet of elastomeric material supporting said row on one side thereof.

14. The armor structure according to claim 12 wherein said panel is provided by a plurality of rows of said modules, said modules in each of said rows being disposed at a different angle to the direction of said incoming objects.

15. The armor structure according to claim 14 wherein sheets of elastomeric material are disposed between adjacent ones of said rows in supporting relationship with said rows.

16. The armor structure according to claim 15 wherein said modules in each of said rows have contacts with each other, vent grooves in said modules through said contacts, and vent holes in said supporting sheets.

17. The armor structure according to claim 12 wherein at least one of said rows facing said incoming object has said plates of said module disposed at an oblique angle to the direction of said incoming objects.

18. The armor structure according to claim 14 or 17 wherein said plates are rectilinear and have sides and edges, a first of the said plurality of rows facing said incoming object and others of said plurality of rows being disposed behind said first row, at least the second of said plurality of rows being disposed so that one of the edges of said plates of said second row faces the sides of the plates in said first row.

19. The armor structure according to claim 18 wherein said panel includes at least a third row between said first and second rows having said sides of the plates thereof perpendicular to the direction of said incoming objects.

20. The armor structure according to claim 12 wherein said tiles are rectangular and have sides and edges along the width and the length thereof, said stacks having a plurality of layers, alternate ones of said layers having the sides of said tiles along the length thereof and the sides of said tiles along the width thereof disposed adjacent to each other and perpendicular to each other.

21. The armor structure according to claim 12 further comprising a layer of ductile material around said module.

22. The armor structure according to claim 21 wherein said layer is provided by a tube of plastic shrink wrapped around said module.

23. The armor structure according to claim 1 further comprising means providing a gap between said surface of said first body and said second body.

24. The armor structure according to claim 23, wherein said gap is of the order of 10 to 30 mils.

25. The armor structure according to claim 23 wherein said gap or gaps are of the order of 10 to 30 mils.

26. The armor structure according to claim 1 wherein said first body and said second body are first and second layers respectively, said first layer being thicker than said second layer.

27. The armor structure according to claim 26 wherein said first layer is about four times thicker than said second layer.

28. The armor structure according to claim 1 wherein said second and first bodies are second and first layers, said second layer and first layer being disposed successively in the order stated in the direction of said incoming objects such that said first layer is in back of said second layer.

29. The armor structure according to claim 28 wherein at least one layer of elastomeric material is disposed in back of said first layer and provides a third layer of said tile.

30. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said first body being provided by particulate material distributed in a matrix of plastic material, the particulate material of said first body being granules of material having a modulus of elasticity that is a plurality of orders of magnitude higher than the modulus of elasticity of said plastic providing said matrix, and said first material having a greater percentage by weight of said particulate material than of said plastic material.

31. The armor structure according to claim 30 wherein said percentage by weight is about 60-90%.

32. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said first body being provided by a plurality of separate layers disposed adjacent to each other.

33. The armor structure according to claim 32, said surface being provided on the one of said plurality of first body layers nearest to said second body, and said structure further comprising means providing gaps between said second body and said surface which is provided the one of said plurality of first bodies adjacent thereto, and means providing a gap between separate bodies which provide said first body.

34. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, and means providing a gap between said surface of said first body and said second body, said gap being of the order of 10 to 30 mils.

35. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said first and second bodies being successive plates which define a tile, said structure comprising a module containing a plurality of said tiles disposed in stacked relationship with the plates providing said first body alternating with the plates providing said second body, and means providing gaps between said tiles in said module.

36. The armor structure according to claim 35 wherein said gaps contain rheopectic material.

37. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said first and second bodies being successive plates which define a tile, said structure comprising a module containing a plurality of said tiles disposed in stacked relationship with the plates providing said first body alternating with the plates providing said second body, and ductile adhesive material disposed between adjacent ones of said tiles connecting them in laminated relationship.

38. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said first and second bodies being successive plates which define a tile, said structure comprising a module containing a plurality of said tiles disposed in stacked relationship with the plates providing said first body alternating with the plates providing said second body, said module being a cube.

39. The armor structure according to claim 38 wherein said tiles are rectangular and identical to each other in shape and are assembled into a cube.

40. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said second and first bodies are second and first layers, said second layer and first layer being disposed successively in the order stated in the direction of said incoming objects such that said first layer is in back of said second layer, at least one layer of elastomeric material being disposed in back of said first layer and providing a third layer of said structure, said third layer being a tough, flexible rubber.

41. The armor structure according to claim 40 wherein at least one composite sheet of fibers and polymeric matrix material is disposed between said first and third layers.

42. The armor structure according to claim 41 wherein said first layer consists of particulate material distributed in a matrix of polymeric material and said second layer is ceramic material.

43. The armor structure according to claim 41 wherein said first layer consists of particulate material distributed in a matrix of polymeric material and said second layer is ceramic material.

44. The armor structure according to claim 41 wherein said sheet is laminated to said first and third layers.

45. The armor structure according to claim 40 wherein a plurality of composite sheets of fiber and polymeric matrix material having strands of fiber in each sheet disposed transversely to each other are disposed between said first and third layers.

46. The armor structure according to claim 45 wherein said fiber strands are selected from the group consisting of glass and carbon fibers.

47. Armor structure which protects against incoming objects and which comprises a first body of non-homogeneous material which is frangible upon impact, said first body having a surface facing said incoming objects, and a second body of impact frangible material which is stiffer than said first body and is disposed upon said surface for distributing impacts from said objects over said surface whereby to enable said first body to absorb, divert and commutate the energy and shock waves due to the incoming objects by disintegration in said first body and fracturing in said second body, said second and first bodies are second and first layers, said second layer and first layer being disposed successively in the order stated in the direction of said incoming objects such that said first layer is in back of said second layer, at least one layer of elastomeric material being disposed in back of said first layer and providing a third layer of said structure, said first layer consisting of particulate material distributed in a matrix of polymeric material and said second layer being ceramic material.

48. The armor structure according to claim 47 wherein the material of said second layer is selected from the ceramic group including silicon carbide, silicon nitride, boron carbide, boron nitride and glass.

49. The armor structure according to claim 47 wherein said first layer is at least twice the thickness of said second and third layers.

50. The armor structure according to claim 47 wherein said particulate material is porous.

51. The armor structure according to claim 47 wherein said particulate material is about from 20 to 24 grit in size (flakes or cubes about 30 mils along their largest sides).

52. A composite tile armor structure especially suitable for use in providing protection against incoming, lightweight ballistic objects, said tile comprising a first body of non-homogeneous, impact frangible core material made up of grit particles distributed throughout a brittle matrix, said first body having a surface for presentation toward said incoming objects, and a second body of impact frangible facing material disposed adjacent to and in contact with said surface; said facing material having a stiffness greater than the stiffness of said core material sufficient to cause impact forces from said objects impinging on said second body to be distributed over said surface of said first body by fracturing in said second body; and said grit particles defining discontinuity sites for development of stress risers in said first body for enabling said distributed forces to be further dissipated by scattering of particles of said core material through disintegration of said first body.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view through a rectilinear (for example, square in plan view) tile which is provided in accordance with the invention.

(2) FIGS. 2A, B and C are views similar to FIG. 1 showing tiles in accordance with other embodiments of the invention.

(3) FIG. 3 is a front view of a module made up of four tiles; the module being a cube.

(4) FIG. 4 is a front view of a module made up of tiles which are rectangular paraboloids and which are stacked in offset relationship much as in a mason wall.

(5) FIG. 5 is a fragmentary top view showing a panel made up of two rows of cube shape tiles.

(6) FIG. 6 is a fragmentary top view showing another arrangement of cube tiles which provides a panel in accordance with another embodiment of the invention.

(7) FIG. 7 is a fragmentary sectional top view similar to FIG. 5 showing portions of three rows of tiles of a panel which embodies the invention, but in greater detail than shown in FIG. 5.

DETAILED DESCRIPTION

(8) Referring to FIG. 1 there is shown a section through a tile which is a rectangular prism. The opposite sides 10 and 12 of the tile may be square and in a presently preferred form are three inches in length and width. The sides 14 and 16 of the tile provide its thickness, which in a presently preferred form is of an inch. These dimensions may be varied in accordance with the threat to be protected against. For example, it may be desirable to provide modules as shown in FIGS. 3, 5, 6 and 7 which are cubes. Such modules may be made up of a stack of four tiles. Alternatively, the tiles may be 1 inches in thickness. Then only two tiles are used in each module. Likewise, thinner than tiles can be employed resulting in thinner (non-cubical) modules.

(9) The tiles effectiveness in providing lightweight ballistic protection arises from the combination of two principal bodies which provide the core 18 and the facing 20 of the tile. These bodies are in effect layers of the tile. The core and facing are both of frangible material. The stiffness of the facing 20 is greater than the stiffness of the core. The facing 20 which is presently preferred is hot pressed or sintered/fired silicon carbide which is a ceramic material. Other ceramic materials which have high stiffness modulus may also be used. The facing is adjacent to the surface 22 of the core 18 which faces in the direction of the threat (the incoming objects). Because of its greater stiffness the facing distributes the impact force over the surface 22. Because the core is of frangible material which is both non-homogeneous and contains sites for stress risers to develop at each grit particle, there occurs cracking and indeed pulverization and disintegration of the core into millions of pieces (small sand-like particles when a high velocity object is incident on the facing 10).

(10) The core has a high population of particles, preferably ceramic or quartz grit distributed throughout in a matrix of plastic. The plastic in a preferred embodiment is a brittle polymer, specifically an epoxy polymer. The grit is either ceramic or quartz particles. The particles are preferably of a size range from twenty to twenty-four grit maximum with low percentages of smaller particles and larger particles in the population passed through the sieve or other sizing mechanism. Grit is a size measure in accordance with standards promulated by ASTM. Both cubic and flake-form grit, can be employed. It is presently believed that the cubic shape is more effective for energy absorption than the flake shape. The flakes or cubes are desirably no larger than about 30 mils on their largest side.

(11) In the event ceramic is used, crushed silicon carbide is presently preferable. Quartz (sand) may be found preferable in some cases because of its lower cost than ceramic particles.

(12) The ceramic particles may be porous. For example, the ceramic which is used to provide the particles may be compressed sintered material where the compression and sintering allows for the formation of microscopic pores. It has been found that the air in such pores is advantageous in reflecting and distributing shock waves caused by the impact of incoming objects and enhances the cracking and pulverization process.

(13) Because of its non-homogeneous nature, but mainly due to discontinuities introduced by the grit particles, the impact and shock waves create stress risers at each grit particle which causes the core to crack up and allow the cracks to propagate. This is a powerful energy absorption mechanism. Moreover, the particles prevent the shock waves from propagating as a uniform wavefront and in effect reflect the shock wave and block some of the energy. The cracking and particles cause propagation of the wave to be scattered in all directions thereby further spreading impact load and enhancing cracking. Moreover, the disintegration of the core into millions of particles even in the case of elastic collision results in a scattering of low mass particles. These particles have total integrated absorbed kinetic energy which is a significant fraction of the initial projectile energy but for an individual particle the energy is insufficient to penetrate the tile catcher-wall support sheets (70FIGS. 5, 6 & 7). Thus, the debris causes no damage to the persons and property in the protected area behind the tile, tile module or panel of modules. The cracking and disintegration also precludes the generation of spall into the space beyond a panel of modules.

(14) The core contains a much larger grit component than polymetric component. The grit component in a preferred embodiment makes up 80% of the core by weight. The weight percent range may suitably be from 60-90%.

(15) A tile which is of an inch in thickness, the facing 20 may be inch thick while the core is approximately inch thick.

(16) In fabricating the core, two parts by weight epoxy resin are mixed with one part by weight of hardener. The epoxy resin may, for example be epon 828 resin and the hardener yutak which are available from the Cumming Company. Another suitable resin is Hysol resin type RE203 with Hysol type HD3561 hardener. Hysol is obtainable from the Hysol Division of the Dexter Corporation, 15051 East Don Julian Road, Industry, California 91749 USA. Eighty percent by total weight of crushed quartz or silicon carbide grit is mixed with the resin so that the grit particles are uniformally distributed. The mixture is placed in a mold to define the rectangular prism shape of the core 18. The mold and mixture is set up for two hours at 150 F. After setting up the core is a solid body and is removed from the mold. A post-mold cure is accomplished by returning the body to the oven and allowing it to bake for 16-20 hours at 150 F.

(17) The resulting core and equivalent cores which may be used in the tile have a low modulus of elasticity and a high toughness. The modulus of elasticity (E) of the core may be from 10,000 to 20,000 psi. This is orders of magnitude lower than the modulus of elasticity of the grit particles. It is also desirable that the core have a high toughness. A toughness (K) of 20,000 psi (inches).sup.1/2 is suitable. Because of its high toughness and low modulus the energy absorption per unit length of crack in the core is high. Such energy absorption per unit length of crack is approximately equal to

(18) $\frac{\left(K^{2}m\right)}{E}$
where (m) is the distance through the which the energy travels. In this case (m) in the thickness of the core 18. The total energy absorption per unit length of developed crack

(19) $\frac{\left(K^{2}m\right)}{E}$
is enhanced by the cracking, pulverization and disintegration of the core since this introduces a very large crack length. Also, in addition to absorbing energy, the non-homogeneity of the core and the included grit particles acts to reflect and disperse the shock wave.

(20) In addition to the high energy absorption from crack propagation, a large amount of energy is dissipated by shearing and strain energy to failure of the materials and by kinetic energy imparted to the small broken pieces of debris.

(21) A backing 24 sandwiches the core between the ceramic facing 20 and the backing and is provided by a layer of elastomeric material, preferably a tough but elastic rubber. In a preferred embodiment EPDM rubber, or 12% carbon rubber which may be synthetic nitrille rubber, may be used. The backing is flexible and facilitates cracking and pulverization as the shock wave causes strain in the backing 24. In other words, the elastic backing 24 acts as a shock absorber and deflects the shock wave while holding the tile in place and providing time until the disintegration mechanism is completed. It also distributes the energy of the compression shock wave which returns as a tensile wave through the core from the backing. Any rupturing of the elastic backing also absorbs energy and in addition serves to catch small particles of debris.

(22) It has also been found desirable to use composite sheets of fiber and polymeric matrix material. The fibers may be strands of carbon or glass. The carbon fibers have a much higher strength than glass. Two sheets are preferably used in which the fibers are disposed in transverse directions and preferably perpendicular to each other. In a preferred embodiment the thickness of the composite sheet layer is between 30 and 60 mils. Prior to final curing of the polymer matrix, the composite sheets 26 and 28 are known as prepreg material and are available commercially. It has been found that type 30346 manufactured by ICI FIBERITE, Winona, Minn. is suitable. However, sheets of final cured prepreg laminates may also be used and depending upon the final assembly process may be preferred.

(23) The tile may be fabricated individually or stacked with other tiles and assembled to form a module. If assembled individually, adhesive such as room temperature vulcanizing (RTV) silicone may be used between the ceramic facing and the surface 22 and rubber cement may be used between the bottom sheet 28 and the upper surface of the elastic layer 24. Then the tile composite assembly is allowed to cure for about one-half hour at 300 F. with approximately a three pound clamping force. This cures the prepreg sheets and laminates them together and to the core 18.

(24) At least one and preferably two layers 26 and 28 (total thickness of between 30 and 60 mils) of composite material are used. They enhance the flexural strength of the elastic layer 24 providing additional energy absorption as they splinter or pull apart while at the same time they do not eliminate the desired elastic compliance and shock absorbing functions of the elastomer 24. They also assist the elastic backing in deflecting the shock wave. In effect, the sheets interpose a short (picosecond) delay which facilitates the distribution of energy to the elastomeric backing 24 and back into the core layer 18.

(25) It may be desirable to secure the individual elements by encasing them in a tube of plastic which is then shrink wrapped around the core. This provides a coating of elastomeric polymer around the facing which retards back scatter when the facing breaks up or due to the reflected shock wave. Plastic tape wrapped around the tile may also be used. A coating of elastomeric polymer on the outside of the facing 10 may alternatively be used.

(26) It may be desirable that means be provided for causing a small air gap (suitably from 10 to 30 mills) in thickness between the ceramic facing 20 and the core 18 as shown in FIG. 2A. FIG. 2A omits the composite sheets 26 and 28. The means for providing the gap may be protuberances on the surface 22 of the core 18. The gap allows the facing to move laterally with respect to the core and serves to chop any plasma jet due to the projectile or the shock wave, and even, to divert the projectile itself, thereby absorbing energy and slowing the projectile.

(27) As shown in FIG. 2B, the core 18 may be made up of two layers 30 and 31 each having projections to provide two air gaps 32 and 34. This further enhances the chopping effect. Air gaps also represent changes of acoustic impedance which further helps control the progress of the shock wave. Instead of the air space, the core 18 may be made up of two layers of non-homogeneous core with grit particles 36 and 38 which are separated by a composite sheet 40 as shown in FIG. 2C. More than two core layers may be used depending upon the threat. Plural layers are desirable when a long (needle-like) projectile is the expected threat.

(28) Referring to FIG. 3, there is shown a cubic module 42 made up of four tiles 44, 46, 48, and 50. These modules are assembled by surrounding them with a shrink wrap tube 52 of plastic or by tape. As noted above, the tube or tape may be dispensed with if the module is laminated together. To this end, rather than placing individual tiles in an oven under clamping pressure to cure the prepreg sheets 26 and 28, successive layers of elastomeric backing 24, composite prepreg sheets 26 and 28, polymeric/ceramic core 18 and ceramic facing 20 may be stacked so as to provide four distinct tile layers. Rubber cement between the elastomeric backing and the last prepreg sheet and RTV silicone between the surface 22 and, the ceramic facing 10 may be used. Then the entire assembly is clamped and while clamped and held, heated in an oven (at 300 F.) for a sufficient period (e.g. one hour) to cure the prepreg sheets. The module will then be an integrated assembly of tiles.

(29) Spacers, such as plastic disks 54 may be located between the individual tiles 44, 46, 48 and 50 to provide gaps 56, 58 and 60. These gaps afford air spaces which enhance energy absorption capability. Energy absorption may be further enhanced by filling the gaps with rheopectic material. Such material has the characteristic that its viscosity increases with shear rate. In other words, it is originally putty-like in consistency, but becomes stiffer when a projectile passes through it. Suitable rheopectic materials may be selected depending upon the threat (the velocity of the expected projectiles and their shape). A discussions of such materials may be found in the following text: A. H. Skelland, Non-Newtonian Flow and Heat Transfer, published by John H. Wiley (1967). See, for example, page 13. Other rheopectic materials are discussed in in U.S. Pat. Nos. 3,952,365 and 4,497,923. Of course, when rheopectic material is confined in the gaps, the entire module 42 is desirably enclosed, for example, in shrink wrap material 52.

(30) Referring to FIG. 4, there is shown another module 62 which is made up of tiles which are rectangular on their top and bottom surfaces, for example 1 inches long by inch wide and are assembled together in offset relationship, much like a brick wall. This arrangement further enhances spreading of the impact load from a point on the front tile to the entire area of the tiles in subsequent tile layers of a module. Such a tile module 62 is also shown in FIG. 7.

(31) It will be noted that in each tile the acoustic impedance decreases in the direction in which the incoming object travels. Such a decrease causes an interface which tends to reduce the transmission of acoustic (shock) waves and enhances their reflection. Thus the shock waves, as well as the projectiles, are stopped and disintegration which absorbs energy in the cores 18 of each tile is enhanced.

(32) It should be appreciated that there are many factors which are responsible for the effectiveness of the armor structure provided by the invention. Nothing herein should be construed to limit the invention to any particular mechanism or mode of operation.

(33) Referring to FIGS. 5 and 6, there is shown a panel made up of rows 64, 66 and 68 of modules. These modules may be of the type shown and described in connection with FIG. 3 or with FIG. 4. The modules are supported on the catcher shield sheets, for example, inch thick sheets which are preferably UHMPE (ultra high modulous polyethylene). One such material sold under the trade name Spectra by Allied Chemical Company of Petersburg, Va. is suitable for use as the support sheets 70. These sheets may be vented between the modules as shown at 72 in FIG. 7. While two rows 64 and 68 are shown in FIG. 5 and three in FIG. 7, it will be appreciated that one row, or as many as needed depending upon weight constraints and the threat, may be used. The rows are supported in a structural frame which may be of wood or other suitable material. Two side members 74 and 76 of this frame are shown in FIG. 5. In the preferred embodiment, the frames are sectionalized within a large panel wall and limited in size for ease in removal and replacement for damage repair and the section size is defined for instance by handling weight constraints. The individual frames can be attached to and supported by a wide variety of standard structural support columns not shown. There may be, for example, 4 or more modules in a row. In some instances, only a single tile may be provided instead of a module in each row. Two or three tiles may also be provided instead of cubic modules that employed four 33 tiles per module in the present embodiment. In successive rows, the surface of the tiles facing the incoming threat are inclined obliquely (e.g. 45) to the direction of the incoming objects which constitute the threat. In FIGS. 5 and 7, the tiles in successive rows are disposed perpendicularly to each other with the edges of the tile in the second row 66 facing the surfaces of the tile in the first row.

(34) In accordance with another arrangement as shown in FIG. 6, there may be three rows of modules 78, 80 and 82. The modules in the first and third rows are oblique to the direction of some incoming objects from one direction while the modules in the second row would be perpendicular to the direction of these incoming objects but in turn would be oblique to incoming objects from another direction. In the embodiment shown in FIG. 5 as well as the embodiment shown in FIG. 6, there are different angles and obliqueness of the surfaces of the modules so as to provide assurance that some modules will be disposed obliquely to all incoming objects.

(35) It will be appreciated that several larger panels may be provided each with its own module frame sections and used to construct protective walls or even used alone as the walls of revetments or temporary structures.

(36) As shown more particularly in FIG. 7, the edges of the adjacent modules in each row are in contact. Vent groves 86 are provided. These vent groves and the vent holes in the support sheet 70 allow for the propagation of any compressed air through the panel.

(37) The modules are adhesive mounted to the catcher shield support sheets 70 which as formerly mentioned also serve to restrain the tile disintegration debris. When a high velocity object hits a module, one or more tiles will disintegrate. The replacement of the module is an easy task since the module is confined to a small frame which is readily removeable from a panel and the damaged module merely has to be removed after which the frame is returned into the panel. Individual module rows mounted to the support sheets 70 are integral within the frame and can be pulled forward out of the frame to gain access to all rows.

(38) The modules and all other materials can be monolithic, ceramic or plastic materials which are not subject to rusting and are relatively insensitive to temperature. Any expansion merely moves the modules about which does not render the armor structure any less effective, since the tiles and modules are intentionally supported to slide and move about under impact from the incoming objects and to do so as an enhancement in the process of absorbing energy and preventing the penetration of the object or any spall into the protected area.

(39) From the foregoing description, it will be apparent that there has been provided improved armor structures which are both effective and light in weight. The area density of this effective ballistic protective structure is far less than steel. For example, an individual 33 thick tile as described in connection with FIG. 1 weighs about 0.54 pound. Three inch cubic modules (i.e., 4 tile layers per module) of such tile that are oriented at 45 to the direction of the incoming objects as shown in FIGS. 5, 6 and 7 have a projected frontal area density of about 24.45 pounds per square foot for a one row configuration. A three row 45 oriented arrangement of three inch cubical modules then has a projected frontal area density of only 73.35 pounds per square foot which is equivalent to 1.76 inches of steel plate facing at 0 to the threat direction. Moreover, the effectiveness of ballistic protection of the armor structure provided by the invention is three to four times that of the steel plate. Thus, a 3 row configuration as shown in FIGS. 6 and 7 has great threat stopping potential and even a one row arrangement has the potential of handling a vast majority of expected projectile threats. Other advantages, as well as variations of modifications of the herein described armor structure and the methods of fabricating and assembling same, within the scope of the invention, will undoubtedly suggest themselves to those skilled in the art. Accordingly, the foregoing description should be taken as illustrative and not in a limiting sense.