PROFILED SCREENING ELEMENT

Abstract

A screening element in the form of a sintered monolithic body has an outer face and an opposing inner face with an area of the faces greater than 100 cm.sup.2 and the mean thickness E.sub.m between the faces greater than 4 mm. At least a portion of the outer face is textured such that Ai decreases from the inner face from a value of i greater than at least 50, A.sub.75≥0.2×A.sub.0 and A.sub.95<0.9×A.sub.0, 0.03×A.sub.0<A.sub.95<0.5×A.sub.0 and A.sub.100<0.1×A.sub.0. Ai being the area occupied by the material alone along a plane i of internal section at the intermediate thickness E.sub.i and i corresponding in percentage to the fraction of the mean thickness E.sub.m at plane i.

Claims

1. A screening element, in the form of a monolithic body having an outer face or impact face and an inner face, opposite said impact face wherein: said body is made of a sintered material, surfaces of said inner and outer faces are greater than or equal to 100 cm.sup.2, wherein at least a portion of said impact face of said body is textured, such that, a mean thickness E.sub.m between said outer and inner faces of said body on said portion is greater than 4 mm, on said portion and along a plane i of internal section of said body parallel to said inner face, with 0<i<100 and i corresponding, in percentage, to a fraction of said mean thickness E.sub.m at plane i, starting from the inner face of area A.sub.0 and in a direction of the impact face of area A.sub.100, Ai being the area occupied by the material alone according to said plane i: a thickness E.sub.i from which the area A.sub.i decreases is greater than 50% and less than 80% of the mean thickness E.sub.m, and A.sub.i decreases along i, when A.sub.i<A.sub.0, and A.sub.75≥0.2×A.sub.0, and 0.03×A.sub.0<A.sub.95<0.5×A.sub.0 and A.sub.100<0.1×A.sub.0.

2. The screening element according to claim 1, wherein said inner and outer faces are parallel to each other.

3. The screening element according to claim 1, wherein A.sub.85<0.8×A.sub.0.

4. The screening element according to claim 1, wherein from a value of i greater than at least 50, a relative change (A.sub.i+2−A.sub.i)×100/A.sub.i is less than 30%.

5. The screening element according to claim 1, wherein from a value of i greater than at least 75, the relative change (A.sub.i+2−A.sub.i)×100/A.sub.i is less than 20%.

6. The screening element according to claim 1, wherein the thickness E.sub.i from which the area A.sub.i decreases is greater than 55% and/or less than 75% of the mean thickness E.sub.m of said body.

7. The screening element according to claim 1, wherein, on said portion, the impact face has a plurality of designs corresponding to a local variation in thickness of said body.

8. The screening element according to claim 7, wherein a width or diameter Φ of the designs of said portion is between 1 and 5 times the thickness E.sub.m.

9. The screening element according to claim 7, wherein the width or diameter Φ of the designs of said portion, is greater than or equal to 3 mm and/or less than or equal to 40 mm.

10. The screening element according to claim 7, wherein a height h of the designs, is between 0.05 and 0.5 times the thickness Em.

11. The screening element according to claim 7, wherein the height h of the designs, of said portion is greater than or equal to 0.5 mm and/or less than or equal to 5 mm.

12. The screening element according to claim 7, wherein a spacing D between two adjacent designs corresponding to a greatest distance measured between their respective centers is less than 5 times the thickness Em.

13. The screening element according to claim 7, wherein the spacing D between two adjacent designs corresponding to the greatest distance measured between their respective centers is less than or equal to 40 mm.

14. The screening element according to claim 7, wherein said design extends by translation along one direction.

15. The screening element according to claim 7, wherein said design is composed of superimposed sub-designs, the sub-designs being of the same basic shape according to a different scale.

16. The screening element according to claim 1, wherein the sintered material constituting said body has an apparent density of less than 8 g/cm.sup.3 and/or and a Vickers hardness of greater than 3 GPa.

17. The screening element according to claim 1, wherein the sintered material constituting said body comprises grains of metallic and/or ceramic and/or cermet material.

18. The screening element according to claim 17, wherein the grains have a mean equivalent diameter of less than 500 micrometers.

19. The screening element according to claim 17, wherein said grains are constituted of a carbide or boride.

20. The screening element according to claim 1, wherein said body has a mass to surface area ratio or surface density, measured in kg/m.sup.2, greater than 60 and/or less than 200.

21. The screening element according to claim 1, wherein the shape of said body is selected from a plate, a tube or another shape for making a breastplate, a shield, a chassis of a vehicle, a radar dome, a helmet.

Description

FIGURES

[0081] FIG. 1 describes the geometric parameters and possible shape of a screening body according to the invention.

[0082] FIGS. 2a, 2b, 2c, 2 g, 2h, 2i and 2j show a cross-sectional view of the screening bodies provided for comparison. FIGS. 2d, 2e and 2f relate to profiled screening bodies according to the invention.

[0083] FIG. 3 shows the evolution of the surface area A.sub.i/A.sub.0 as a function of the thickness E.sub.i/E.sub.m for different example embodiments. A thickness of zero (0) corresponds to the surface plane A.sub.0 of the lower face and a thickness of 100 corresponds to the plane with the maximum thickness E.sub.m.

[0084] FIG. 4 illustrates a screening body with a portion of the impact surface having joined designs.

[0085] FIG. 5 shows a screening body with a portion of the impact surface with regularly spaced designs.

[0086] FIG. 6 shows a screening body with a portion of the impact surface with two different alternate designs.

[0087] FIG. 7 shows a screening body whose impact surface comprises a circular distribution of designs.

[0088] FIG. 8 shows a screening body whose impact surface comprises sinusoidal profile designs.

[0089] FIG. 9 shows a screening body whose impact surface comprises alternate joined designs.

[0090] FIG. 10 shows an impact surface of two screening elements according to the invention comprising a complex design consisting of sub-designs, of sinusoidal type with harmonics.

[0091] FIG. 11 shows an impact surface of two screening elements according to the invention comprising a complex design of pyramid-like sub-designs with regular steps.

[0092] FIG. 12 shows a 3-dimensional view of a screening body according to example 8.

[0093] FIG. 13 shows a 3-dimensional view of a screening body according to example 9.

[0094] FIG. 14 shows a 3-dimensional view of a screening body according to example 10.

[0095] FIG. 1 schematically shows in cross-section an example of a screening body 10 according to the invention, in the form of a monolithic body having an outer face 20 (or impact face) and an inner face 30 (opposite said impact face). The body has a plate shape of mean thickness E.sub.m and total length 40. The mean thickness is determined as shown below and takes into account the texturing of the outer surface on the textured portion 50. According to the invention, the textured portion (50) represents at least 10%, preferably more than 20%, more than 30%, more than 40%, more than 50%, or even more than 75% or even 100% of the outer surface of the monolithic body of the screening element. On this portion 50, the outer face 20 is textured in such a way that the area Ai of a plane i of internal section with intermediate thickness E.sub.i, decreases starting from the inner face 30 of area A.sub.0 from a value of i greater than at least 50, i corresponding in percentage to the fraction of said mean thickness E.sub.m at plane i. The area A.sub.100 corresponds to the area of material at the mean thickness E.sub.m. As shown in FIG. 1, E.sub.sm is the thickness E.sub.i from which the area Ai decreases.

[0096] On the portion 50 of its impact face, the body has a plurality of designs corresponding to a local variation in the thickness of said body. A design 60 has a height h.sub.1, a width ϕ.sub.1 and a center C.sub.1. Spacing D.sub.1-2 between design 60 of center C.sub.1 and the one adjacent to center C.sub.2 is also shown.

Definitions

[0097] The following indications and definitions are given in connection with the preceding description of the present invention:

[0098] The mean thickness E.sub.m of said body refers to the mean thickness over the portion of the body comprising the texturing.

[0099] It is calculated by dividing: [0100] the different thicknesses measured at the location of each design or protrusion, perpendicularly to the inner face if it is flat or perpendicularly to the tangent of said inner face at the point considered, if this face is curved, [0101] by the number of protrusions or designs identified on said portion.

[0102] Reference may be made to FIG. 1, which shows the positioning of the said mean thickness.

[0103] Surface portion means the minimum polygonal surface surrounding a family of designs, this surface being delimited by linear segments tangential to the peripheral designs. A family of designs consists for example of designs such that the distance between two immediately adjacent designs is less than five times the width or diameter of the widest design. Preferably, but not necessarily, a portion can group together designs of the same morphology and/or height or width.

[0104] The center of a design is the barycenter of the surface of said design projected perpendicularly on the plane corresponding to the inner face of the body. Typically in the case of right pyramids, the center is the top of the pyramid that becomes the center of the base by projection perpendicularly on the plane corresponding to the inner face.

[0105] A plate is a geometric shape in which the surface area of the largest face is at least 5 times, preferably 10 times, greater than its thickness.

[0106] The equivalent diameter of a grain is defined as half the sum of the greatest length of the grain and the greatest width of the grain, measured in a direction perpendicular to said greatest length.

[0107] Hard material means a material whose hardness is sufficiently high to justify its use in armor or screening elements.

[0108] The maximum and mean equivalent diameters are conventionally determined from the observation of the microstructure of the material constituting the ceramic body, conventionally by virtue of images taken in SEM (scanning electron microscopy) on a cross section of the sintered product. It has been verified in the following examples that said microstructure is substantially identical, regardless of the orientation of the cross section.

[0109] The “apparent density” of a product, within the meaning of the present invention, means the ratio equal to the mass of the product divided by the volume occupied by said product. It is conventionally determined by the Archimedes method. For example, the ISO 5017 standard specifies the conditions for such a measurement. This standard also makes it possible to measure the open porosity within the meaning of the present invention.

[0110] Cermet refers to a composite material composed of a ceramic reinforcement and a metal matrix.

[0111] “Matrix” refers to a crystallized or non-crystallized phase that provides a substantially continuous structure between the grains. It is obtained, during the preparation of the material, typically during its firing, from the constituents of the starting charge and possibly from the constituents of the gaseous environment of this starting charge and/or from a molten metal infiltrating the porosity of said material during or after its firing. A matrix substantially surrounds the grains of the granular fraction, i.e. coats them.

[0112] Sintering of a material is a process for manufacturing parts such as the screening element according to the invention consisting of heating a mixture comprising a powder without bringing it to melting. Under the effect of heat, the grains weld together, which forms the cohesion of the part.

[0113] In a ceramic body according to the invention, the ceramic grains are bound by the matrix. During the firing or sintering process, they substantially retain the same shape and chemical nature as in the starting charge. In the sintered ceramic body, the matrix and the grains together represent 100% of the mass of the product. In the case of ceramic bodies with a nitride matrix, one or more metals are preferably added to the charge, which react with the nitrogenous atmosphere to form one or more nitrogenous crystallized phases. The resulting increase in volume, typically from 1 to 30%, advantageously makes it possible to fill the pores of the matrix and/or to compensate for the shrinkage caused by the sintering of the grains. This reactive sintering thus makes it possible to improve the mechanical strength of the sintered product. The reactively sintered products thus exhibit closed porosity that is significantly lower than other sintered products under similar temperature and pressure conditions. During the firing process, the reactively sintered products essentially exhibit no shrinkage.

[0114] The crystallographic composition of the material constituting the monolithic body is normally obtained by X-ray diffraction and Rietveld analysis.

[0115] The crystallized phases, especially the nitrogenous crystallized phases, were measured by X-ray diffraction and quantified by the Rietveld method.

[0116] Elemental nitrogen (N) levels in sintered products were measured using LECO analyzers (LECO TC 436DR; LECO CS 300). Values are provided in mass percentages.

[0117] The residual silicon in metallicform in the sintered material or afterfiring is normally measured according to the method known to skilled persons and referenced underANSI B74-151992 (R2000).

[0118] The Vickers hardness of grains can be measured with a standardized diamond pyramid tip with a square base and an apex angle between faces equal to 136°. The imprint made on the grain therefore has the shape of a square; the two diagonals d1 and d2 of this square are measured with an optical device. The hardness is calculated from the force applied to the diamond tip and the mean d value of d.sub.1 and d.sub.2 according to the following formula:

[00001]$H_V=0.189.Math.\frac{F}{d^2}\mathrm{with}\begin{array}{c}\begin{array}{c}{H}_V=\mathrm{Vickers}\mathrm{hardness}\\ F=\mathrm{Applied}\mathrm{force}\left[N\right]\end{array}\\ d=\mathrm{Mean}\mathrm{of}\mathrm{diagonals}\mathrm{of}\mathrm{the}\mathrm{imprint}\left[\mathrm{mm}\right]\end{array}$

[0119] The strength and duration of the application are also standardized. The reference standard for ceramic or cermet materials is ASTM C1327:03 Standard Test Method for VICKERS Indentation Hardness of Advanced Ceramics. For a sintered metal material, the reference standard is ISO6507-1.

[0120] Unless otherwise specified, all percentages in this description are mass percentages.

[0121] The screening element according to the invention enables protection in particular against any type of projectile, for example a bullet, a shell, a mine or an element projected during the detonation of explosives, such as splinters, bolts, nails (or IED for “Improvised Explosive Device”), but also with respect to bladed weapons and normally constitutes an armor element for vehicles, generally in the form of modules such as plates.

[0122] According to the invention, it conventionally comprises at least two layers: a first ceramic part as described previously associated with another less hard and preferably ductile material, on the rear face, conventionally called “backing”, such as polyethylene fibers (e.g.: Tensylon™, Dyneema®, Spectra™), aramid (e.g.: Twaron™, Kevlar®), glass fibers, or metals such as steel or aluminum alloys, in the form of plates. Adhesives, for example based on polyurethane or epoxy polymers, are used to bind the various elements constituting the screening element.

[0123] Under the impact of the projectiles, the material of the monolithic body fragments and has the main role of breaking down the perforating power of the projectiles. The role of the rear face, associated with the material constituting said body, is to consume the kinetic energy of the debris and to maintain a certain level of containment of said body further optimized by the containment shell.

[0124] The following examples are for illustrative purposes only and do not limit the scope of the present invention in any of the aspects described.

EXAMPLES

[0125] In all the following examples, ceramic plates of different sizes were made by casting a suspension in a plaster mold according to the process described above and the formulation described in Table 1 below.

[0126] The mean and maximum equivalent grain diameters were determined from the observation of the microstructure of the material constituting the ceramic body, conventionally by virtue of images taken by scanning electron microscopy on a cross section of the sintered product.

TABLE-US-00001 TABLE 1 Composition of the initial mixture (% by mass) SiC powder 10-150 μm D.sub.50 = 75 μm 39.5 SiC powder 0.1-5 μm D.sub.50 = 2.5 μm 37.5 Si powder 0.5-50 μm D.sub.50 = 20 μm 17 Alumina powder D.sub.50 = 2.5 μm 5.0 Fe.sub.2O.sub.3 2.5 μm 0.5 B.sub.4C 95% <45 μm D.sub.50 = 18 μm 0.5 total minerals % 100 water added % +12.5 added dispersant % +0.5 Forming and firing conditions Casting plaster mold demolding after hardening Drying (T °/duration) 110° C./24 h Firing (T °/duration/time) 1420° C./8 h/Nitrogen Mean equivalent diameter of SiC grains in 80 the material after firing (micrometers) Maximum equivalent diameter of SiC grains in 0.2 the material after firing (mm)

[0127] Different shapes were made from molds whose geometric surface was modified in order to vary the profile of said surface. For each configuration, the thickness was adjusted in order to obtain a constant surface density of material for all the examples. The different profiles are shown in FIG. 2. The profile in example 1 corresponds to a flat plate without designs. The profiles of examples 2 to 7 have a sinusoidal profile whose height h varies according to the function a×cos(b×x), x being the abscissa in an axis of the section plane parallel to the rear face, x varying from 0 to π/b. For each implementation, the geometrical characteristics of the plates thus realized are gathered together in Table 2.

[0128] For each example, three assemblies were made by bonding the side of the ceramic plate opposite to the impact to a polycarbonate plate using 3M 950™ double-sided tape from the company 3M.

[0129] Each assembly was then placed in front of thirty 10 mm thick polycarbonate sheets. The whole was fired at from a distance of 15 meters with a 7.62×51 mm P80 caliber at a velocity of 820 m/s. Ballistic performance was assessed by measuring the depth of penetration of the bullet in the polycarbonate plates. An index was calculated based on a reference plate set at 100. The higher the index, the higher the depth proportionally and the lower the ballistic performance.

[0130] The surface density ρ.sub.a is calculated according to the following formula

ρ.sub.a=t×ρ.sub.v where:

ρ.sub.a is the surface density expressed in Kg/m.sup.2
t is the thickness of the plate, expressed in m
ρ.sub.v is the apparent density expressed in Kg/m.sup.3 typically measured according to ISO 18754.

[0131] The results reported in Table 2 below show the advantages of using a monolithic screening plate according to the invention.

[0132] In Table 2 below:

A.sub.0 is the area occupied by the material on the inner surface of the plate.

[0133] E.sub.m (in mm) is the mean thickness of the body, according to the meaning previously described.

[0134] E.sub.sm (in mm) is the thickness E.sub.i from which the area Ai decreases, i.e. the thickness from which the texturing appears in the plate, measured from the inner face of the plate (see FIG. 1).

[0135] A.sub.75 (in mm.sup.2) is the area occupied by the material alone (i.e. excluding the unfilled areas between each design), according to a sectional plane parallel to the inner face of the plate and located at a distance from said inner face equal to 75% of the thickness E.sub.m.

[0136] A.sub.95 (mm.sup.2) is the area occupied by the material alone (i.e. excluding the unfilled areas between each design), according to a sectional plane parallel to the inner face of the plate and located at a distance from said inner face equal to 95% of the thickness E.sub.m.

[0137] A.sub.100 (mm.sup.2) is the area occupied by the material alone (i.e. excluding the unfilled areas between each design), according to a sectional plane parallel to the inner face of the plate and located at a distance from said inner face equal to the thickness E.sub.m.

[0138] The ratio E.sub.sm/E.sub.m corresponds to the value of i at which the surface of an intermediate area A.sub.i is less than the area A.sub.0.

TABLE-US-00002 TABLE 2 Ex.1** Ex.2** Ex.3** Ex.4* Ex.5* Ex.6* Ex.7** Ex8* Ex9** Ex10** FIG. 2a 2b 2c 2d 2e 2f 2g 2h 2i 2j A.sub.0 (cm.sup.2) 100 100 100 100 100 100 100 100 100 100 E.sub.m (mm) 7 11.4 10.5 9.9 8.5 9.9 7.1 10 6.6 8.5 E.sub.sm (mm) NA 5.4 6.5 5.9 6.5 5.9 6.9 5.9 5.3 6.5 E.sub.sm/E.sub.m (%) NA 47 62 60 70 60 97 59 82 76 A.sub.50 (cm.sup.2) 100 65 100 100 100 100 100 100 100 100 A.sub.75 (cm.sup.2) 100 21.2 14.7 30.7 100 30.3 100 29.2 100 100 A.sub.80 (cm.sup.2) 100 15 10 20 50.2 22.5 100 21.1 100 50.2 A.sub.85 (cm.sup.2) 100 10.1 5.1 15.5 31.3 15.9 100 14.0 88.7 32.2 A.sub.90 (cm.sup.2) 100 5.9 2.5 10 18.5 10.0 100 7.8 80.7 16.1 A.sub.95 (cm.sup.2) NA 2.9 0.3 4.5 8.4 4 100 2.8 51.4 11.1 A.sub.100 (cm.sup.2) NA 0 0 0 0 0 0 0 0 10.5 design NA a = 3 a = 1 a = 2 a = 1 a = 2 a = 0.12 NA NA NA profile b = 0.4 b = 0.4 b = 0.2 b = 0.4 b = 0.4 b = 0.4 a b Height h 0 6 4 4 2 4 0.25 4.1 1.25 2.03 of the designs (mm) Diameter Φ NA 15.2 15.2 30.5 15.2 15.2 15.2 30.5 15.2 15.2 of the designs (mm) Spacing D NA 15.2 22.9 30.5 15.2 15.2 15.2 30.5 15.2 15.2 between designs (mm) ρ.sub.a (Kg/m.sup.2) 19.6 19.6 19.6 19.6 19.6 19.6 19.6 18.7 20.1 19.7 Ballistic 100 130 84 43 72 49 98 85 95 90 results *according to the invention **comparative “NA” = not applicable

[0139] The change in surface area A.sub.i/A.sub.0 as a function of the thickness E.sub.i/E.sub.m for different example embodiments is shown in FIG. 3.

[0140] Examples 4, 5 and 6 according to the invention have a significantly improved ballistic performance compared to the comparative examples, especially example 1 (flat plate without a design). The comparison of examples 2 and 7 (outside the invention) with examples 5 and 6 (according to the invention) shows that the selection of the height, width and spacing of equal designs so as to obtain a profile such that E.sub.sm is between 0.5×E.sub.m and 0.95×E.sub.m improves ballistic performance.

[0141] The comparison of example 3 (outside the invention) with example 4 (according to the invention) shows in particular that despite the increased spacing of wider designs, the choice of a profile adapted according to the invention with a corresponding surface area A.sub.95 of the screening element greater than 3% of the inner surface area A.sub.0 (A.sub.95>0.03 A.sub.0) makes it possible to increase performance very significantly. Of course, the present invention is not limited to the embodiments described and shown, provided by way of examples. In particular, combinations of the various embodiments described are also within the scope of the invention.

[0142] Example 8, representative of the publication US2015253114A1, shows a profile with cone-shaped tips whose surface area A.sub.95 is less than 3% of A.sub.0. It appears from the results reported in the preceding Table 2 that this profile is less efficient than that of example 4 with a surface area A.sub.95 greater than 3% of A.sub.0.

[0143] The comparative example 9 shows, on the contrary, that a less “pointed” profile, i.e. such that the surface area A.sub.95 is greater than 50% of A.sub.0, leads to a lower ballistic performance than examples 5 and 6 with equivalent surface density of designs.

[0144] The comparative example 10, whose impact surface is formed by truncated pyramids, shows that a surface area A.sub.100 greater than 10% of A.sub.0 leads to a lower ballistic performance, in contrast to example 5 according to the invention.