Profiled screening element

Description

technical field

[0001] The invention relates to an armor element, particularly for ballistic protection, whose impact surface has a shape particularly suited for this function, a protection system comprising such an element and the method for manufacturing such an element.

[0002] The invention finds its application in particular as armor used for bulletproof vests or other armoring to protect vehicles (land, sea or air) or fixed installations (building, perimeter wall, guard post in particular). Previous technique

[0003] In particular, the added weight associated with wearing ballistic protection such as body armor or armor plating is a crucial factor, both for personal protection and for protection against vehicles. Specifically, it is essential to avoid excessive weight, which hinders rapid movement and limits range.

[0004] Systems formed by the so-called "mosaic" assembly of ceramic pieces with a specific polygonal shape, each individually resistant to projectile impact, are well known. JP2005247622, ​​for example, describes an arrangement of such shapes ranging from 20 to 100 mm in width and a few millimeters in thickness. This type of mosaic has the advantage of withstanding successive shots (known as "multi-shot" or "multi-hit" protection). However, assembling such "mosaic" structures is a lengthy and expensive process. Furthermore, maintaining tight overall tolerances can be challenging because the tolerances of each individual piece are added together to form the assembly. This impacts the width of the residual gaps between the pieces (parting lines) produced by the assembly.Furthermore, if it also has a curved shape, the gaps constitute a significant area of ​​weakness in this protection system when the projectile impacts these areas.

[0005] US2015 / 0253114A1 describes such a composite armor element formed from an assembly of ceramic discs or tiles whose impact face profile includes pointed protrusions, for example, cones or pyramids (see Figures 17A to 26C). This particular profile, called "Dragon Skin" by the applicant, would notably improve multi-impact resistance and prevent the risk of ricochet during ballistic impact.

[0006] There are other so-called monolithic systems, that is to say formed by a single piece or by a very limited number of large surface pieces, each monolith having an impact surface greater than 100 cm2, or even 150 cm2, in order to reduce the number of joints.

[0007] Many materials have been proposed, particularly for constructing armor intended for people where the mass-to-surface ratio of armor (or surface density) must remain low, typically less than 50 kg / m², or non-personal armor intended for vehicles or fixed installations where the mass-to-surface ratio of protection is typically greater than 10 kg / m².

[0008] Metals and alumina are commonly used as shielding, but they have a high surface density to achieve the desired protection.

[0009] More recently, products based on non-oxide ceramics have been proposed, whose mass-to-surface-area ratio or surface density, with equivalent impact resistance, is lower.

[0010] Beyond the general so-called mosaic or monolithic form, different configurations have been proposed. Publication EP 1380809 A2, for example, reveals a system comprising two layers of material: the first, denser layer A, formed on the surface by a carbide and a metal, for example, silicon carbide SiC and metallic silicon Si, and a second, more porous layer B formed by the carbide, for example, silicon carbide.

[0011] US6389594B1 proposes an outer shell for the monolithic ceramic armor, which is subjected to compressive stress. This shell is made of aramid-based polymer material or other ballistic protection materials, particularly those based on glass fibers. This outer shell does not prevent the monolithic block from fracturing, and if the block is larger than 100 cm² and / or if the projectile is large-caliber, the significant energy to be dissipated results in an insufficient "blocking" effect, leading to significant decohesion of the monolithic block and inadequate resistance to multiple impacts.

[0012] More recently, WO2008 / 130451 (EP2095055A1) proposed an approach to reducing the propagation of the stress wave associated with projectile impact by using an envelope formed from a permeable medium, typically a layer of organic fibers (e.g., aramid) fixed to the ceramic part and then impregnated with a hyperelastic polymer to absorb the energy associated with the projectile impact and reduce crack propagation and multifracture of the ceramic. This system is only suitable for small ceramic parts, and the tested example is made from an assembly of nine ceramic parts measuring 100 mm x 100 mm x 8 mm. The energy absorbed by this new envelope cannot prevent the decohesion of a ceramic block with a surface area greater than 150 cm².

[0013] The publication "Effects of novel geometric designs on the ballistic performance ceramics" by P. Karandikar et al. in Advances in Ceramic Armor X reveals various geometries of ceramic and metal armor plates, including plates with holes, depressions, or bumps on the impact surface. The authors observed no improvement, and even a deterioration, in performance when this texturing was applied to the impact face. However, this publication provides no information on the dimensions and exact distribution of the applied texturing.

[0014] There is therefore a continuous need to improve the products used as armor, this improvement being measured in particular by their ballistic performance, for a comparable surface density. Another notable prior art: US 2005 / 235818 A1.

[0015] The object of the present invention is therefore to propose a new product, different from the products currently used in the field, and whose ballistic performance is improved, at equal surface density.

[0016] In particular, there is now a need for monolithic armor with a surface area greater than 100 cm², preferably greater than 150 cm², preferably even greater than 200 cm², or even greater than 500 cm² or even greater than 1000 cm², capable of resisting shots from armor-piercing projectiles with a diameter greater than or equal to 5.56 mm in the same region of the armor, but which nevertheless has a low apparent density, typically less than 8.5 g / cm³, or even less than 5 g / cm³, in order to protect without unduly burdening the wearer of the protection, or vehicles (land, sea or even air) or fixed installations, such as buildings, equipped with such protection. Description of the invention

[0017] According to a first general aspect, the present invention relates to an armor element according to claim 1 in the form of a monolithic body, for example a plate, a tube, or a more complex shape such as a helmet, having a top surface (or impact surface), particularly straight or curved, comprising grains of a hard material. This body may be provided on its inner face (or face opposite the impact face) with a rear energy-dissipating coating, preferably made of a material of lower hardness than the material constituting the body of the protective element.

[0018] More specifically, the present invention relates to a shielding element, in the form of a monolithic body having an outer face or impact face and an inner face, opposite said impact face, said inner and outer faces preferably being substantially parallel, preferably parallel to each other in which: said body is made of a sintered material, the surfaces of said inner and outer faces are greater than or equal to 100 cm², said body being characterized in that at least a portion of said impact face of said body is textured, in such a way that, the average thickness E m between said outer and inner faces of said body on said portion is greater than 4 mm, on this portion and along a plane i of internal section of said body parallel to said inner face, with 0 < i < 100 and i corresponding as a percentage to the fraction of said average thickness E m at plane i, starting from the inner face and in the direction of the impact face, Ai being the area occupied by the material alone at thickness E i , at the level of an intermediate surface located between the surface of the inner face of area A 0 and the outer surface of area A 100 corresponding to the area of ​​material at the level of average thickness E m , the surface of an intermediate area Ai is less than said area A 0 from a value of i greater than at least 50, (A i < A 0 if i ≥ 50) and preferably less than or equal to 80 (A i < A 0 if i ≤ 80).The thickness Ei from which the area Ai decreases, also called Esm, is greater than 50%, preferably greater than 55%, and / or less than 95%, preferably less than 90%, even more preferably less than 80% or even less than 75%, or even less than 70% of the average thickness of said body. Ai decreases continuously or discontinuously (for example, in steps) with respect to i, when Ai < A0 (or when Ei > E50). A 75 ≥ 0 , 2 × A 0 , 0 , 03 × A 0 < A 95 < 0 , 5 × A 0 , preferably 0.04 × A 0 < A 95 < 0.2 × A 0 . A 100 < 0 , 1 × A 0 .

[0019] By "continuous" we mean that A i+ε < A i for all i≥50. By "discontinuous" we mean that the relation A i+ε < A i is not verified over the entire range of the domain 100 ≥ i ≥50.

[0020] For the purposes of this invention, the section plane i under consideration is not necessarily flat. In particular, if the inner face is curved, then the section plane i is also curved. In such a configuration, the term "section plane" should be understood as the cross-sectional surface parallel to the inner face at the point under consideration.

[0021] As will be explained later, the area of ​​the intermediate surface of material along said parallel internal section plane can be easily measured by a section of said body and preferably by non-destructive methods such as tomography and the use of computer-aided design software, for example.

[0022] It is understood that the area A i occupied by the material alone also includes its possible porosity.

[0023] The advantage of the present invention lies in an optimal choice of element profile, allowing for an increased initial contact area with the projectile without a substantial increase in material. This design makes it possible to deflect projectiles and reduce their penetrating power, given the thickness of the untextured portion of the armor element, which is necessary to absorb some of the impact energy and thus limit fragmentation.

[0024] Preferably, A 75 < 0.9 × A 0. Preferably, A 75 < 0.6 × A 0. More preferably, A 80 < 0.4 × A 0. A 80 < 0.8 × A 0. Preferably, A 80 < 0.6 × A 0. More preferably, A 80 < 0.5 × A 0. Preferably, A 80 > 0.15 × A 0. More preferably, A 80 > 0.2 × A 0. A 85 < 0.8 × A 0. Preferably, A 85 < 0.6 × A 0. More preferably, A 85 < 0.5 × A 0. More preferably, A 85 > 0.15 × A 0. A90 < 0.5 × A0. Preferably, A90 < 0.4 × A0. More preferably, A90 < 0.3 × A0 or even A90 < 0.2 × A0. Preferably, A90 > 0.05 × A0. More preferably, A90 ≥ 0.1 × A0.The area A 95, corresponding to the intermediate surface of material measured along an internal cross-sectional plane of said body parallel to the inner face at 95% of the average thickness of said body, starting from the inner face towards the impact face, is greater than 3%, preferably greater than 4%, and / or less than 30%, preferably less than 20%, preferably less than 15%, or even less than 10% of the area of ​​the inner face or A 0. The area A 100, corresponding to the surface of material on the upper face (or impact face) of said body along a cross-sectional plane at its average thickness, is less than or equal to 20% of A 0, preferably less than 10% of A 0, preferably less than 7%, preferably less than 5% of A 0. Preferably, A 100 tends towards 0. From a value of i greater than at least 50, the relative variation (A i+2 -A i ) × 100 / A i is less than 30%.From a value of i greater than at least 75, the relative variation (A i+2 -A i )× 100 / A i is less than 20%. E i from which the area A i decreases, also called E sm , is greater than 4 mm. The surface area of ​​the inner face is greater than 150 cm², greater than 200 cm², greater than 250 cm², preferably greater than 400 cm², preferably greater than 500 cm², or even greater than 1000 cm². The width or diameter of the inner face is greater than 20 cm. Said body has an average thickness E m greater than 7mm, preferably greater than 10mm, preferably greater than 15mm, preferably greater than 20mm. Preferably, in particular: Said body according to the invention, on at least a portion of its impact face, has a plurality of patterns corresponding to a local variation in the thickness of said body.This local variation in thickness can follow a function or profile whose curve in a plane perpendicular to the section plane may exhibit one or more changes in curvature. These patterns may have the following characteristics: The patterns are preferably protrusions or protuberances, in the shape of cones, pyramids with a polygonal base, or patterns with a sinusoidal profile. The width or diameter ϕ of the patterns in this portion is between 1 and 5 times the thickness Em, preferably between 1.5 and 4 times the thickness Em. The width or diameter ϕ of the patterns in this portion is greater than or equal to 3 mm and / or less than or equal to 40 mm. The height h of the patterns is less than 0.5 times the thickness Em, preferably between 0.05 and 0.5 times the thickness Em. The height of the patterns in this portion is greater than or equal to 0.5 mm and / or less than or equal to 5 mm.The spacing D between two adjacent motifs, corresponding to the greatest distance measured between their respective centers, is less than 5 times the thickness Em, preferably less than 4 times the thickness Em, and more preferably less than 3.5 times the thickness Em. The spacing D between two adjacent motifs, corresponding to the greatest distance measured between the respective centers of two motifs, is less than or equal to 40 mm. Preferably, the spacing D is adapted according to the caliber of the projectile against which the armor is designed. In particular, the spacing D is preferably equal to twice the caliber of the projectile plus or minus 30%. For example, for a caliber of 7.62 mm, D is equal to 15.2 ± 4.6 mm. In one possible configuration, the motifs are contiguous, meaning that their spacing is approximately equal to their width or diameter.The number of patterns per 100 cm² of said impact surface (exterior) is greater than 10, preferably greater than 20. The pattern extends by translation along one or preferably two different directions, these two directions preferably being perpendicular to each other. In a particular manner, a pattern may be more complex and composed of superimposed sub-patterns in order to deflect projectiles of different calibers, each sub-pattern being adapted to a particular threat. Figure 10 or the figure 11This illustrates an example of such an embodiment. In one possible mode, the sub-motifs share the same basic shape but at different scales, for example, homothetically or with a fractal structure. In another possible mode, the overall shape of the motif is sinusoidal and / or comprises sub-motifs in the form of harmonics, particularly of varying amplitudes or pitches. In a particular mode, the distribution of motifs on the impact surface is regular, meaning that motifs of the same morphology (height and width) are spaced the same distance apart. In one possible mode, the body has a flat inner face. In another possible mode, the inner face and the impact face (apart from the motifs or local variations in thickness) are substantially parallel.

[0025] Various preferred embodiments of the present invention are described below, which can obviously be combined with each other where appropriate:The body has an apparent density of less than 8 g / cm³, the grains of the material constituting the body have an average equivalent diameter of less than 500 micrometers and a Vickers hardness greater than 3 GPa, preferably greater than 10 GPa. The material constituting the body comprises grains of metallic and / or ceramic and / or cermet material. The grains have a maximum equivalent diameter of 500 micrometers or less, preferably 400 micrometers or less, or even 300 micrometers or less. Preferably, the maximum equivalent diameter of the grains is greater than 5 micrometers, preferably greater than 10 micrometers, or even greater than 50 micrometers.The ceramic and / or cermet grains are preferably bonded by a matrix, said matrix comprising or being composed of a silicon nitride phase and / or a silicon oxynitride phase, said matrix representing between 5 and 40% by weight, preferably between 15 and 35% by weight, of said material constituting the ceramic body. The grains are composed of a metallic carbide or boride. Preferably, they are silicon carbide or boron carbide grains, or a mixture of these two carbides. In one possible embodiment, the material constituting said body comprises only silicon carbide grains, optionally with a metallic phase, preferably comprising the element silicon. Said body, preferably ceramic, has an apparent density of less than 5 g / cm³, preferably less than 3.2 g / cm³, and preferably an apparent density of less than 3.0 g / cm³.Preferably, the constituent grains of the material forming said body are essentially composed of SiC, preferably in alpha form. Said material forming said body has an open porosity greater than 5%, preferably greater than 6%, preferably even greater than 7% or even greater than 8%, and less than 14%, preferably less than 13%, preferably even less than 12%. Said body has a mass-to-surface ratio or surface density, measured in kg / m², greater than 60 and / or preferably less than 200. Said body may be a plate, a tube, or another shape enabling the creation of a breastplate, a shield, a vehicle body panel, a radome, or a helmet, from which the armor element according to the invention may be selected.

[0026] The invention also relates to a ballistic protection device comprising the armor element according to the invention, in which: The body is provided on its inner face, or face opposite the impact face, with a back energy-dissipating coating made of a material with a lower hardness than the material constituting the body. The back coating material is selected from polyethylene (PE), particularly ultra-high-density polyethylene (UHMWPE), glass or carbon fibers, aramids, metals such as aluminum, titanium or their alloys, or steel. The ceramic body-back coating assembly is surrounded by a containment material. The containment material constituting the containment material is selected from glass or carbon fibers or aramids. Figures :

[0027] There figure 1 describes the geometric parameters and possible shape of an armored body according to the invention. figures 2a, 2b, 2c 2g, 2h, 2i and 2jThey describe in cross-section, according to a sectional plane, the armor bodies provided for comparison. figures 2d, 2e and 2f concern armor bodies profiled according to the invention. The figure 3 represents the evolution of the surface area Ai / Ao as a function of the thickness Ei / Em for different embodiments. A thickness of zero (0) corresponds to the surface plane A0 of the lower face, and a thickness of 100 corresponds to the plane with the maximum thickness Em. figure 4 illustrates an armored body in which a portion of the impact surface displays contiguous patterns. figure 5 shows an armored body, a portion of whose impact surface has regularly spaced patterns. figure 6 shows an armored body, a portion of whose impact surface features alternating patterns of two different designs. figure 7 shows an armored body whose impact surface comprises a circular distribution of patterns. figure 8shows an armored body whose impact surface includes sinusoidal profile patterns. figure 9 shows an armored body whose impact surface comprises alternating contiguous patterns. The Figure 10 represents an impact surface of two shielding elements according to the invention comprising a complex pattern made up of sub-patterns, of a sinusoidal type with harmonics. figure 11 represents an impact surface of two armor elements according to the invention comprising a complex pattern consisting of pyramid-type sub-patterns with regular steps. Figure 12 represents a 3D view of an armor body according to example 8. Figure 13 represents a 3D view of an armor body according to example 9. Figure 14 represents a 3D view of an armor body according to example 10.

[0028] There figure 1A schematic cross-sectional illustration of an example of an armor body 10 according to the invention is shown, 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 the shape of a plate with an average thickness Em and a total length 40. The average thickness is determined as indicated below and takes into account the textured surface of the outer 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 100% of the outer surface of the monolithic body of the armor element.On this portion 50, the outer face 20 is textured such that the area Ai of a plane i with internal cross-section at intermediate thickness E i decreases from the inner face 30 of area A 0 from a value of i greater than at least 50, i corresponding as a percentage to the fraction of said average thickness E m at plane i. The area A 100 corresponds to the area of ​​material at the level of the average thickness E m. As shown on the figure. figure 1 , E sm is the thickness E i from which the area Ai decreases.

[0029] On portion 50 of its impact face, the body exhibits a plurality of patterns corresponding to a local variation in the thickness of said body. A pattern 60 has a height h1, a width ϕ1, and a center C1. The spacing D1-2 between the pattern 60 with center C1 and the neighboring one with center C2 is also shown. Definitions :

[0030] The following indications and definitions are given in relation to the preceding description of the present invention: By average thickness Em of said body, we mean the average thickness over the portion of the body comprising the texture. It is calculated by dividing: the different thicknesses measured at the location of each pattern or protuberance, perpendicular to the inner face if it is flat or perpendicular to the tangent of said inner face at the point considered, if this face is curved, by the number of protuberances or patterns identified on said portion.

[0031] One can refer to the figure 1 which shows the positioning of said average thickness.

[0032] A surface portion is defined as the minimal polygonal area surrounding a family of patterns, this area being delimited by straight line segments tangent to the surrounding patterns. A family of patterns, for example, consists of patterns such that the distance between two immediately adjacent patterns is less than five times the width or diameter of the largest pattern. Preferably, but not necessarily, a portion may group patterns of the same morphology and / or the same height or width.

[0033] The center of a motif is the centroid of the surface of that motif projected perpendicularly onto the plane corresponding to the inner face of the body. Typically, in the case of right pyramids, for example, the center is the apex of the pyramid, which becomes the center of the base when projected perpendicularly onto the plane corresponding to the inner face.

[0034] A plate is a geometric shape whose surface area of ​​the largest face is at least 5 times, preferably 10 times, greater than its thickness.

[0035] The equivalent diameter of a grain is understood to be 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.

[0036] Hard material is defined as a material whose hardness is high enough to justify its use in armor or shielding components.

[0037] The maximum and average equivalent diameters are conventionally determined by observing the microstructure of the material constituting the ceramic body, typically using scanning electron microscopy (SEM) images of a cross-section of the sintered product. The following examples have demonstrated that this microstructure is essentially identical regardless of the cross-section's orientation.

[0038] The apparent density of a product, as defined in the present invention, is the ratio of the product's mass to its volume. It is conventionally determined using Archimedes' method. ISO 5017, for example, specifies the conditions for such a measurement. This standard also allows for the measurement of open porosity as defined in the present invention.

[0039] Cermet is a composite material consisting of a ceramic reinforcement and a metallic matrix.

[0040] The term "matrix" refers to a crystalline or non-crystalline phase that provides a substantially continuous structure between the grains. It is obtained during the material's processing, typically during firing, from the constituents of the initial feedstock and possibly from the gaseous environment of that initial feedstock, and / or from molten metal that infiltrates the material's porosity during or after firing. A matrix essentially surrounds the grains of the granular fraction, that is, it coats them.

[0041] Sintering a material is a manufacturing process for parts such as the armor element according to the invention, consisting of heating a mixture containing a powder without melting it. Under the effect of heat, the grains bond together, forming the cohesion of the part.

[0042] In a ceramic body according to the invention, the ceramic grains are bound by the matrix. During firing or sintering, they substantially retain the shape and chemical composition they had in the initial feed. In the sintered ceramic body, the matrix and grains together represent 100% of the product's mass. In the case of ceramic bodies with a nitride matrix, one or more metals are preferably added to the feed, which react with the nitrogen atmosphere to form one or more nitrogen-containing crystalline phases. The resulting volume increase, typically from 1 to 30%, advantageously fills the pores of the matrix and / or compensates for the shrinkage caused by grain sintering. This reactive sintering thus improves the mechanical strength of the sintered product.Reactively sintered products exhibit significantly lower closed porosity than other sintered products under similar temperature and pressure conditions. During firing, reactively sintered products show virtually no shrinkage.

[0043] The crystallographic composition of the material constituting the monolithic body is normally obtained by X-ray diffraction and Rietveld analysis.

[0044] The crystalline phases, in particular the nitrogen-containing crystalline phases, were measured by X-ray diffraction and quantified according to the Rietveld method.

[0045] Elemental nitrogen (N) content in sintered products was measured using LECO analyzers (LECO TC 436DR; LECO CS 300). Values ​​are given as mass percentages.

[0046] Residual silicon in metallic form in the sintered material or after firing is normally measured according to the method known to the person skilled in the art and referenced under ANSI B74-151992 (R2000).

[0047] The Vickers hardness of grains can be measured using a standardized diamond pyramidal point with a square base and apex angle between faces of 136°. The indentation made on the grain is therefore square; the two diagonals d1 and d2 of this square are measured using an optical instrument. The hardness is calculated from the force applied to the diamond point and the average value d of d1 and d2 according to the following formula: H V = 0 , 189 ⋅ F d 2 with HV = Vickers hardness. F = Applied force [N] d = Average of the diagonals of the footprint [mm]

[0048] The force and duration of the support 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 sintered metal materials, the reference standard is ISO 6507-1.

[0049] Unless otherwise stated, in this description all percentages are mass percentages.

[0050] The armor element according to the invention provides protection against all types of projectiles, for example a bullet, a shell, a mine or an element projected during the detonation of explosives, such as shrapnel, bolts, nails (or IED for "Improvised Explosive Device") but also against edged weapons and normally constitutes an armor element for vehicles, generally in the form of modules such as plates.

[0051] According to the invention, it conventionally comprises at least two layers: a first ceramic piece as described above, bonded to another, less hard and preferably ductile material on its back face, conventionally called the "backing," such as polyethylene fibers (e.g., Tensylon™, Dyneema®, Spectra™), aramid fibers (e.g., Twaron™, Kevlar®), glass fibers, or metals such as steel or aluminum alloys, in the form of plates. Adhesives, for example, polyurethane-based or epoxy polymers, are used to bond the various elements constituting the armor element. Under the impact of projectiles, the monolithic body material fragments and its primary function is to break the penetrating 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 confinement of said body further optimized by the confinement envelope.

[0052] The following examples are given for illustrative purposes only and do not limit the scope of the present invention in any of the aspects described. Examples :

[0053] In all the following examples, ceramic plates of different sizes were produced by casting a suspension in a plaster mold according to the process described above and the formulation described in Table 1 below.

[0054] The mean and maximum equivalent grain diameters were determined from observation of the microstructure of the material constituting the ceramic body, classically using scanning electron microscopy images on a section of the sintered product. [Table 1] Composition of the initial mixture (% by mass) SiC powder 10-150µm D 50 = 75 µm 39,5 SiC powder 0.1-5µm D 50 = 2.5 µm 37,5 Si powder 0.5-50µm D 50 = 20µm 17 Alumina powder D 50 = 2.5 µm 5,0 Fe2O3 2.5 µm 0,5 B 4 C 95% <45µm D 50 =18 µm 0,5 total minerals % 100 added water % +12,5 Added dispersant % +0,5 Shaping and cooking conditions Plaster mold casting, demolding after hardening Drying (Temperature / Duration) 110°C / 24h Cooking (temperature / duration / time) 1420°C / 8h / Nitrogen Mean equivalent diameter of SiC grains in the material after firing (micrometers) 80 Maximum equivalent diameter of SiC grains in the material after firing (mm) 0,2

[0055] Different shapes were created using molds whose geometric surface was modified to vary the profile of said surface. For each configuration, the thickness was adjusted to obtain a constant surface density of material across all examples. The different profiles are represented according to the figure 2The profile in example 1 corresponds to a flat plate without any patterns. The profiles in examples 2 through 7 exhibit a sinusoidal profile whose height h varies according to the function a×cos(b×x), where x is the abscissa along an axis of the cutting plane parallel to the back face, and x varies from 0 to π / b. For each embodiment, the geometric characteristics of the plates thus produced are summarized in Table 2.

[0056] For each example, three assemblies were made by gluing the face of the ceramic plate opposite the impact to a polycarbonate plate using 3M 950™ double-sided tape from 3M.

[0057] Each assembly was then placed in front of thirty 10 mm thick polycarbonate plates. The entire assembly was then fired from a distance of 15 meters using a 7.62x51mm P80 round at a velocity of 820 m / s. Ballistic performance was assessed by measuring the depth of bullet penetration into the polycarbonate plates. An index was calculated based on a reference plate set at 100. The higher the index, the greater the penetration depth and the lower the ballistic performance.

[0058] The surface density ρ a is calculated using the following formula: ρ a = t×ρ v where: ρ a is the surface density expressed in Kg / m 2< t is the thickness of the plate, expressed in m ρ v is the apparent density expressed in Kg / m 3< typically measured according to ISO 18754.

[0059] The results reported in Table 2 below show the advantages associated with the implementation of a monolithic armor plate according to the invention.

[0060] In Table 2 below: A 0 is the area occupied by the material on the inner surface of the plate.

[0061] E m (in mm) is the average thickness of the body, in the sense previously described.

[0062] Esm (in mm) is the thickness Ei from which the area Ai decreases, that is, the thickness from which the texture appears in the plate, measured from the inner face of the plate (see the figure 1 ).

[0063] A 75 (in mm 2< ) is the area occupied by the material alone (i.e. excluding the unfilled areas between each pattern), according to a cutting 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 m .

[0064] A 95 (in mm 2< ) is the area occupied by the material alone (i.e. excluding the unfilled areas between each pattern), according to a cutting 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 m .

[0065] A 100 (mm 2< ) is the area occupied by the material alone (i.e. excluding the unfilled areas between each pattern), according to a cutting plane parallel to the inner face of the plate and located at a distance from said inner face equal to the thickness E m.

[0066] The ratio E sm / E m corresponds to the value of i from which the area of ​​an intermediate area A i is less than the area A 0 . [Table 2] Ex.1** Ex. 2** EX.3** Ex. 4* Ex. 5* Ex. 6* Ex.7** Ex8** Ex9** Ex10** Figure 2a 2b 2c 2d 2e 2f 2g 2h 2i 2j A 0 (cm 2< ) 100 100 100 100 100 100 100 100 100 100 E m (mm) 7 11,4 10,5 9,9 8,5 9,9 7,1 10 6,6 8,5 E sm (mm) N / A 5,4 6,5 5,9 6,5 5,9 6,9 5,9 5,3 6,5 E sm / E m (%) N / A 47 62 60 70 60 97 59 82 76 A 50 (cm²) 100 65 100 100 100 100 100 100 100 100 A 75 (cm 2< ) 100 21,2 14,7 30,7 100 30,3 100 29,2 100 100 A 80 (cm 2< ) 100 15 10 20 50,2 22,5 100 21,1 100 50,2 A 85 (cm 2< ) 100 10,1 5,1 15,5 31,3 15,9 100 14,0 88,7 32,2 A 90 (cm 2< ) 100 5,9 2,5 10 18,5 10,0 100 7,8 80,7 16,1 A 95 (cm 2< ) N / A 2,9 0,3 4,5 8,4 4 100 2,8 51,4 11,1 A 100 (cm²) N / A 0 0 0 0 0 0 0 0 10,5 pattern profile a N / A a=3 a=1 a=2 a=1 a=2 a=0,12 N / A N / A N / A b b=0,4 b=0,4 b=0,2 b=0,4 b=0,4 b=0,4 Pattern height h (mm) 0 6 4 4 2 4 0,25 4,1 1,25 2,03 Diameter Φ of the patterns (mm) N / A 15,2 15,2 30,5 15,2 15,2 15,2 30,5 15,2 15,2 Clearance D between patterns (mm) N / A 15,2 22,9 30,5 15,2 15,2 15,2 30,5 15,2 15,2 ρ a (Kg / m 2< ) 19,6 19,6 19,6 19,6 19,6 19,6 19,6 18,7 20,1 19,7 Ballistic results 100 130 84 43 72 49 98 85 95 90 *according to the invention **comparative “NA” = not applicable The evolution of the surface area A i / A o as a function of the thickness E i / E m for different embodiment examples is shown on the figure 3 .

[0067] Examples 4, 5, and 6 according to the invention exhibit significantly improved ballistic performance compared to the comparative examples, particularly example 1 (flat plate without pattern). A comparison of examples 2 and 7 (outside the scope of the invention) with examples 5 and 6 (according to the invention) shows that selecting equal height, width, and pattern spacing to obtain a profile such that Esm is between 0.5 × Em and 0.95 × Em improves ballistic performance.

[0068] Comparing Example 3 (outside the scope of the invention) with Example 4 (according to the invention) shows in particular that, despite the increased spacing of wider patterns, choosing a profile adapted according to the invention with a corresponding A95 surface area of ​​the shielding element greater than 3% of the internal surface area AO (A95 > 0.03 A0) makes it possible to significantly increase performance. Of course, the present invention is not limited to the embodiments described and illustrated, which are provided by way of example. In particular, combinations of the different embodiments described also fall within the scope of the invention.

[0069] Example 8, representative of publication US2015253114A1, presents a profile with cone-shaped peaks whose surface area A95 is less than 3% of A0. It appears from the results reported in Table 2 above that this profile is less efficient than that of Example 4, which has a surface area A95 greater than 3% of A0.

[0070] Comparative example 9 clearly shows, on the contrary, that a less "sharp" profile, i.e. one where the surface area A 95 is greater than 50% of A 0, leads to a lower ballistic performance than examples 5 and 6 of equivalent surface pattern density.

[0071] Comparative example 10, whose impact surface is formed of truncated pyramids, shows that an A100 surface greater than 10% of A0 leads to lower ballistic performance, contrary to example 5 according to the invention.

Claims

1. A screening element, in the form of a monolithic body (10) having an outer face (20) or impact face and an inner face (30), opposite said impact face wherein: - said body (10) is made of a sintered material, whose ceramic material grains have an average equivalent diameter of less than 500 micrometers and a Vickers hardness greater than 3 GPa, - the surfaces of said inner and outer faces are greater than or equal to 100 cm2, at least a portion (50) of said impact face of said body is textured, such that, - the mean thickness Em between said outer and inner faces of said body on said portion (50) is greater than 4 mm, - the impact face on said portion (50) has a bunch of patterns that match up with a local change in thickness of said body, - said local change in thickness follows a function or profile whose curve in a plane perpendicular to the section plane has one or more changes in curvature; - the width or diameter ϕ of the patterns is greater than or equal to 3 mm and less than or equal to 40 mm, - the height h of the patterns is greater than or equal to 0.5 mm and less than or equal to 5 mm - the spacing D between two adjacent patterns, corresponding to the greatest distance measured between their respective centers, is less than or equal to 40 mm, - the width or diameter ϕ of the patterns of said portion is between 1.5 and 4 times the thickness Em, - on this 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 the fraction of said mean thickness Em at plane i, starting from the inner face of area A0 and in the direction of the impact face of area A100, Ai being the area occupied by the material alone according to said plane i: - the thickness Ei from which the area Ai decreases is greater than 50% and less than 80% of the mean thickness Em, and - Ai decreases along i, when Ai < A0, and - A 75 ≥ 0.2 × A 0 , and - 0.03 × A 0 < A 95 < 0.5 × A 0 and - A 100 < 0.1 × A 0 - A 85 < 0.1 × A 0 .

2. The screening element according to the preceding claim, wherein the thickness Ei from which the area Ai decreases is greater than 55% and less than 75% of the mean thickness Em of said body.

3. The screening element according to one of the preceding claims, wherein the height h of the designs, is between 0.05 and 0.5 times the thickness Em.

4. The screening element according to one of the preceding claims, wherein the spacing D between two adjacent designs corresponding to the greatest distance measured between their respective centers is less than 5 times the thickness Em.

5. The screening element according to one of the preceding claims, wherein said design extends by translation along one or preferably two different directions.

6. The screening element according to one of the preceding claims, wherein said design is composed of superimposed sub-designs, the sub-designs being of the same basic shape according to a different scale.

7. The screening element according to one of the preceding claims, wherein the general shape of the pattern is a sine wave.

8. The screening element according to one of the preceding claims, wherein the general shape of the pattern comprises sub-patterns in the form of harmonics of different amplitudes or heights.

9. The screening element according to one of the preceding claims, wherein the inner face and the impact face (excluding patterns or local variations in thickness) are substantially parallel.

10. The screening element according to one of the preceding claims, wherein said body has a mass to surface area ratio or surface density, measured in kg / m2, greater than 60 and less than 200.

11. The screening element according to one of the preceding claims, 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.