ARMOUR PLATE

Abstract

Antiballistic armour plate includes a ceramic body including a hard material, provided, on its inner face, with a back energy-dissipating coating. The ceramic body is monolithic. The constituent material of the ceramic body includes grains of ceramic material having a Vickers hardness that is higher than 15 GPa, and a matrix binding the grains, the matrix including a silicon nitride phase and/or a silicon oxynitride phase, the matrix representing between 5 and 40% by weight of the constituent material of the ceramic body. The maximum equivalent diameter of the grains of ceramic material is smaller than or equal to 800 micrometres. The constituent material of the ceramic body has an open porosity that is higher than 5% and lower than 14%. The metallic silicon content in the material, expressed per mm of thickness of the body, is lower than 0.5% by weight.

Claims

1. An antiballistic armor plate including a ceramic body consisting of a hard material, provided, on its inner face, with a back energy-dissipating coating, wherein: said ceramic body is monolithic and has an area that is larger than 150 cm.sup.2, a thickness that is greater than 12 mm and a bulk density that is lower than 3.5 g/cm.sup.3; the constituent material of the ceramic body comprises grains of ceramic material having a Vickers hardness that is higher than 15 GPa, and a matrix binding said grains, said matrix comprising or consisting of a silicon nitride phase and/or a silicon oxynitride phase, said matrix representing between 5 and 40% by weight of said constituent material of the ceramic body; a maximum equivalent diameter of said grains of ceramic material is smaller than or equal to 800 micrometers; said constituent material of the ceramic body has an open porosity that is higher than 5% and lower than 14%; the metallic silicon content in said material, expressed per mm of thickness of said body, is lower than 0.5% by weight.

2. The armor plate as claimed in claim 1, wherein the constituent grains of the ceramic material consist essentially of SiC.

3. The armor plate as claimed in claim 1, wherein the metallic silicon is present in said constituent material of the ceramic body along a concentration gradient from the outer edges to the core of said body, in the direction of its thickness.

4. The armor plate as claimed in claim 1, which has a mass-to-area ratio, measured in kg/m.sup.2, that is higher than 60.

5. The armor plate as claimed in claim 1, wherein a total sum of rare-earth elements in the constituent material of the ceramic body is lower than 0.05% by weight.

6. The armor plate as claimed in claim 1, wherein the maximum equivalent diameter of the grains in said constituent material of the ceramic body is comprised between 10 micrometers and 500 micrometers.

7. The armor plate as claimed in claim 1, wherein the constituent material of the ceramic body contains no elements from the group of the rare-earth elements.

8. The armor plate as claimed in claim 1, wherein a mean equivalent diameter of the constituent grains of the ceramic material is larger than 5 micrometers and smaller than 300 micrometers.

9. The armor plate as claimed in claim 1, wherein the metallic silicon content of the constituent material of the ceramic body is lower than 10% by weight.

10. The armor plate as claimed in claim 1, wherein a nitrogen content in the constituent material of the ceramic body is higher than 4% by weight.

11. The armor plate as claimed in claim 1, wherein the binding matrix essentially consists of silicon nitride Si.sub.3N.sub.4 and/or silicon oxynitride Si.sub.2ON.sub.2.

12. The armor plate as claimed in claim 1, wherein the constituent material of the back coating is chosen from the polyethenes PE, glass or carbon fibers, aramids, metals, or steel.

13. The armor plate as claimed in claim 1, wherein the ceramic body-back coating assembly is surrounded by an envelope of a confining material.

14. The armor plate as claimed in claim 13, wherein the constituent material of the envelope is chosen from the polyethenes PE, glass or carbon fibers, aramids, metals or steel.

15. A monolithic ceramic body in the form of a plate and having an area that is larger than 150 cm.sup.2 and a thickness that is greater than 12 mm, and a bulk density that is lower than 3.5 g/cm.sup.3, consisting of a material comprising: grains of ceramic material having a Vickers hardness that is higher than 15 GPa, a maximum equivalent diameter of said grains being smaller than or equal to 500 micrometers; and a matrix binding said grains, said matrix comprising or consisting of a silicon nitride and/or silicon oxynitride phase, said matrix representing between 5 and 40% by weight of said constituent material of the ceramic body; said ceramic material having an open porosity that is higher than 5% and lower than 14% and a metallic silicon content in said material, expressed per mm of thickness of said body, that is lower than 0.5% by weight.

16. The armor plate as claimed in claim 1, wherein the back energy-dissipating coating consists of a material having a hardness that is lower than that of the constituent material of the ceramic body.

17. The armor plate as claimed in claim 2, wherein the SiC is in the alpha form.

18. The armor plate as claimed in claim 4, wherein the mass-to-area ratio, measured in kg/m.sup.2, is lower than 200.

19. The armor plate as claimed in claim 7, wherein the constituent material of the ceramic body contains no yttrium and/or no lanthanum.

20. The armor plate as claimed in claim 7, wherein the constituent material of the ceramic body contains no elements from the group of the actinides.

21. The armor plate as claimed in claim 11, wherein the binding matrix essentially consists of silicon nitride Si.sub.3N.sub.4.

22. The armor plate as claimed in claim 12, wherein the polyethenes PE are ultra-high-molecular-weight polyethenes (UHMPEs).

23. The armor plate as claimed in claim 12, wherein the metals are aluminum, titanium or their alloys.

24. The armor plate as claimed in claim 14, wherein the constituent material of the envelope is chosen from ultra-high-molecular-weight polyethenes (UHMPEs).

25. The armor plate as claimed in claim 14, wherein the metal is aluminum.

26. The monolithic ceramic body as claimed in claim 15, wherein the ceramic material is metal carbide or boride.

27. The monolithic ceramic body as claimed in claim 15, wherein the ceramic material is silicon or boron carbide or a mixture of these two carbides.

Description

EXAMPLES

[0119] In all of the following examples, a ceramic tile in the form of a plate having a 500 mm500 mm26 mm format has initially been produced by casting, in a plaster mold, a suspension according to the process described above and the formulations described in table 1 below.

[0120] The ceramic body thus obtained is used as a ceramic plate in an armor plate. More specifically, said ceramic body is bonded, using an epoxy adhesive, to a glass fiber layer forming the link with a plate of ultra-high-molecular-weight polyethene (UHMWPE) marketed by DSM Dyneema. The assembly is enveloped in a Kevlar layer that is also bonded by means of an epoxy resin. The initial formulation of the various mixtures and the exact conditions of the process for obtaining the armor plate are given in table 1.

[0121] Comparative example 4 has been produced according to the principles described in application JP2005247622 mentioned above.

[0122] Its purpose is to demonstrate the multi-hit resistance of an assembly of ceramic elements put together in the form of a mosaic, each individual ceramic element of the ceramic being produced according to the same process and using the same material as example 1 according to the invention.

[0123] The tiles used in this mosaic assembly have an individual size of 3 cm by 3 cm and have been assembled into a plate of 50 cm50 cm according to the process described in example 1 of JP2005247622.

[0124] Comparative example 5 consists of an antiballistic plate that is primarily made of metal produced according to conventional techniques based on combining a 10 mm-thick steel plate marketed by Thyssen under the reference Secure 500, and a 20 mm back coating of styrofoam bonded by means of an epoxy adhesive, another 10 mm-thick Secure 500 steel plate and a 15 mm bonded Twaron (Teijin) T750 aramid coating. The overall assembly is enveloped in a layer of Dupont Kevlar, also bonded by an epoxy resin.

[0125] For each embodiment, the properties of the ceramic body and the composition of the various constituent materials thereof are collated in table 2.

[0126] The ballistic properties of the final armor plate are collated in table 3. The ballistic performance of the various armor plates has been evaluated using the AEP 55 and STANAG 4569 standards, specifically ballistic protection level 4 (14.5 mm API B32 projectile). Four shots have been fired at the various armor plates in stand-alone configuration while observing the protocols and directives described in the AEP 55 and STANAG 4569 standards (firing speed, distance between impacts, verification of piercing or otherwise using the control plate, etc.).

[0127] The results given in the following tables 1 to 3 show the advantages provided by using a monolithic armor plate of large size according to the invention: examples 1 to 3 according to the invention exhibit improved resistance to piercing such that they are capable of resisting successive projectile impacts. Their ballistic resistance thus appears to be substantially equivalent to steel-based plates as illustrated by comparative example 5. The mass-to-area ratio of the plates according to the invention is however much lower than that of such steel-based plates, as illustrated in table 3.

[0128] The comparative examples further show the influence of the parameters on the ultimate ballistic performance levels obtained for the armor plate:

[0129] Comparative example 1 shows that the level of residual silicon, i.e. metallic silicon that has not reacted with nitrogen during firing, must be minimized down to the core of the constituent material of the ceramic body. In particular, when the heat treatment is not suitable and the level of residual metallic silicon in the material is too high (0.5% residual silicon per mm of thickness of the ceramic body), in particular in the core of the ceramic body (i.e. substantially in the middle of the thickness of the ceramic plate), the result is lower resistance to piercing, as can be seen in the ballistic test results given in table 3.

[0130] According to comparative example 2, the constituent grains of the constituent material of the ceramic body are larger in size than according to the present invention, resulting in poorer ballistic performance. Thickening the ceramic plate according to comparative example 3 does not compensate for this deficiency.

[0131] Comparative example 4 further shows that a mosaic structure according to the prior art exhibits much lower levels of ballistic performance with respect to plates of large size according to the invention.

[0132] Of course, the present invention is not limited to the described and represented embodiments provided by way of examples. In particular, combinations of the various described embodiments also come within the scope of the invention.

[0133] Neither is the invention limited by the shape or the dimensions of the sintered product based on silicon carbide.

TABLE-US-00001 TABLE 1 invention invention invention comparative comparative comparative comparative example 1 example 2 example 3 example 1 example 2 example 3 example 4 Composition of the initial mixture (% by weight) SiC powder 80.2 80.2 100 m-1100 m D.sub.50 = 600 m SiC powder 39.5 20-200 m D.sub.50 = 100 m SiC powder 39.5 39.5 39.5 39.5 10-150 m D.sub.50 = 75 m SiC powder 37.5 37.5 37.5 37.5 37.5 0.1-5 m D.sub.50 = 2.5 m Si powder 17 17 17 17 16.0 16.0 17 0.5-50 m D.sub.50 = 20 m Calcined clay 3.0 3.0 Alumina powder 5.0 5.0 5.0 5.0 5.0 D.sub.50 = 2.5 m Fe.sub.2O.sub.3 2.5 m 0.5 0.5 0.5 0.5 0.5 B.sub.4C 95% < 45 m 0.5 0.5 0.5 0.5 0.8 0.8 0.5 D.sub.50 = 18 m total minerals % 100 100 100 100 100 100 100 added water % 12.5 12.5 12.5 12.5 6 6 12.5 added dispersant 0.5 0.5 0.5 0.5 0.2 0.2 0.5 Shaping conditions Drying 110 C./24 h 110 C./24 h 110 C./24 h 110 C./24 h 110 C./24 h 110 C./24 h 110 C./24 h (T/duration) Firing 1420 C./8 h/ 1420 C./4 h/ 1420 C./8 h/ 1350 C./4 h/ 1420 C./8 h/ 1420 C./8 h/ 1420 C./8 h/ (T/duration/time) Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen

TABLE-US-00002 TABLE 2 invention invention invention comparative comparative comparative comparative example 1 example 2 example 3 example 1 example 2 example 3 example 4 Ceramic material body properties thickness (mm) 26 26.5 25.7 27 27 35 26 Shape of plate monolithic monolithic monolithic monolithic monolithic monolithic mosaic area (cm.sup.2) 50 50 50 50 50 50 50 50 50 50 50 50 3 3 Granular fraction SiC/75% SiC/75% SiC/77% SiC/75% SiC/75% SiC/75% SiC/75% (nature/relative weight) Maximum equivalent 0.150 mm 0.150 mm 0.2 mm 0.150 mm 1.1 mm 1.1 mm 0.150 mm diameter of SiC grains in material Mean equivalent 30 m 30 m 80 m 30 m 600 m 600 m 30 m diameter of SiC grains in material Matrix binding grains Si.sub.3N.sub.4*/25% Si.sub.3N.sub.4*/25% Si.sub.3N.sub.4*/22% Si.sub.3N.sub.4*/25% Si.sub.3N.sub.4*/25% Si.sub.3N.sub.4*/25% Si.sub.3N.sub.4*/25% (nature/relative weight) open porosity % 10 11.5 9 13 14 14 9.7 bulk density % 2.81 2.75 2.84 2.7 2.67 2.67 2.83 N content 10% 5% 9% 3.5% 10% 10% 10% % residual Si <0.5 9 0.7 13.5 <0.5 <0.5 <0.5 (in the material) % residual Si/mm <0.02 0.35 0.03 0.50 <0.02 <0.02 <0.02 thickness Back coating properties Chemical nature Glass fibers + Glass fibers + Glass fibers + Glass fibers + Glass fibers + Glass fibers + Glass fibers + high- high- high- high- high- high- high- molecular- molecular- molecular- molecular- molecular- molecular- molecular- weight PE weight PE weight PE weight PE weight PE weight PE weight PE Thickness 21 mm 21 mm 21 mm 21 mm 21 mm 21 mm 21 mm Confining envelope properties Chemical nature Aramid Kevlar Kevlar Kevlar Kevlar Kevlar Kevlar fibers (Kevlar) *23% Si.sub.3N.sub.4 by weight, 2% Si.sub.2ON.sub.2 by weight

TABLE-US-00003 TABLE 3 invention invention invention comparative comparative comparative comparative comparative example 1 example 2 example 3 example 1 example 2 example 3 example 4 example 5 Armor plate properties mass-to-area 95 95 95 95 94 115 96 175 ratio Ballistic tests Visual No piercing No piercing No piercing Piercing Piercing Piercing Piercing No piercing inspection after firing