Shielding element with multi-lobe openings

Abstract

A shielding element in the form of a monolithic body having an outer face or impact face (2) with a surface area greater than or equal to 80 cm², traversed by a plurality of orifices (4) centered at O, comprising a central portion with an opening diameter less than or equal to 2 mm, from which extend a plurality of lobes with a median segment S, the maximum distances Ly, Ly' respectively from their walls P1, P2 to said median segment being less than 2 mm and the length of which is less than ten times the central portion of radius OI. The distance between the centers O (O1 and O2) of two orifices whose lobe tips E (respectively E1 and E2) are closest is less than ten times the greater of the distances between O1 and E1' on the one hand and between O2 and E2 on the other.

Description

Title of the invention: Shielding element with multi-lobe openings technical field

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

[0002] The invention finds its application in particular as a personal protection device, in particular armor used for bulletproof vests, a vehicle protection device (land, sea or air) other armoring allowing the protection of vehicles (land, sea or air) or a fixed installation (building, perimeter wall, guard post in particular), or a detection or communication equipment, for example a radome. Previous technique

[0003] Systems formed by the so-called "mosaic" assembly of ceramic pieces having a specific polygonal shape and individually resistant to the impact of a projectile are known. JP2005247622 describes, for example, an arrangement of such shapes 20 to 100 mm wide and a few millimeters thick. This type of mosaic of pieces has the advantage of resisting successive shots (so-called "multi-shot" or "multi-hit" protection). However, assembling such "mosaic" structures is time-consuming and expensive. Furthermore, maintaining a low overall tolerance for the assembly can be difficult because the tolerances of each piece are added together to form the assembly. This has an impact on the width of the residual spaces between the pieces (parting lines) produced by the assembly.Furthermore, if the object to be protected also has a curved shape, the gaps constitute a significant weak point in this protection system when the projectile impacts these areas.

[0004] 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.

[0005] Many materials have been proposed, in particular 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.

[0006] In particular, products based on non-oxide ceramics have been proposed whose mass-to-surface-shielding ratio or surface density, with equivalent impact resistance, is lower than other materials such as metals or alumina.

[0007] Furthermore, in the context of ballistic protection for communication systems (radars, antennas, etc.) as well as other objects, it is necessary to combine ballistic performance at the same surface density with low interaction with electromagnetic waves, particularly those with frequencies typically between 3 and 40 GHz, and specifically to consider these two properties when determining the best performance of this combination. In other words, a material of interest within the meaning of the present invention is characterized by a better compromise between its ballistic performance and its ability to transmit electromagnetic waves. Beyond the general mosaic or monolithic forms, various configurations have been proposed.

[0008] The publication “effects of novel geometry designs on the ballistic performance ceramics” by P. Karandikar et al in Advances in Ceramic Armor X discloses, for example, different geometries of ceramic or metal armor plates, including plates for which the impact surface has holes, hollows or bumps.

[0009] The authors observe variations in performance depending on the configurations but only a very slight improvement with a texturing including bumps on the impact face and truncated cones on the rear face.

[0010] There is therefore a continuous need for improvement of products used as shielding, and in particular a better compromise between on the one hand ballistic performance at comparable surface density and on the other hand transparency to electromagnetic waves.

[0011] The object of the present invention is therefore to propose a new product, different from the products currently used in the field and addressing this problem. Description of the invention

[0012] According to a first general aspect, the present invention relates to a shielding element (1) in the form of a monolithic body having an outer face or impact face (2) and an inner face (3) opposite said impact face in which:

[0013] -the surfaces of said inner and outer faces are greater than or equal to 80 cm2, preferably greater than or equal to 100 cm2,

[0014] - said body is traversed by a plurality of orifices (4), such that the total surface covered by said orifices, or open surface, represents between 5% and 50%, preferably between 5% and 30%, preferably between 5% and 20%, of said impact face surface, and

[0015] -at least one of said orifices, preferably all of said orifices, comprises at least two lobes, preferably a plurality of lobes,

[0016] such as, according to the plane of said impact face:

[0017] -each lobe (5) comprises two walls Pi and P2 joining at one end E, and

[0018] -each lobe has a median segment S of length Lx, delimited by the end E of said lobe, the medial segments of said lobes joining and being limited at their other extremity by a center O of said orifice,

[0019] - the angles ai and closed by said median segment S and the tangents at point E respectively of the walls Pi and P2 in said plane are less, in absolute value, than 90 degrees, and

[0020] -the two walls Pi and P2 of said lobe extend from the end E towards the center O respectively to a point I and a point I' such that:

[0021] -the line segment connecting O and I forms an angle α2 with respect to the segment S, said angle being less than 60 degrees in absolute value, preferably less than or equal to 45 degrees, and

[0022] -the distance OI between O and I is less than or equal to 2 mm, preferably less than 1.5 mm, preferably less than 1 mm, preferably less than 0.5 mm, and

[0023] -the maximum distances Ly, respectively Ly', of the wall segment between points E and I, respectively E and I', projected onto the Y axis perpendicular to the median segment X, are less than or equal to 2mm, and

[0024] -the length Lx of the median segment S is greater than the distance OI and less than or equal to 10 times OI,

[0025] -the distance between two centers O (O1 and O2) of two orifices whose lobe ends E (E1 and E2) are closest, is less than ten times the greatest of the distances between:

[0026] - the center 0(00) and the end E(Ej) of the first orifice on the one hand and

[0027] - the center O(O2) and the end E (E2) of the second orifice on the other hand.

[0028] One of the advantages of the present invention lies in an optimal choice of the perforation profile of the element, making it possible to increase the transparency to electromagnetic waves, in particular in the frequency range of 3 GHz to 40 GHz, while maintaining, or even increasing, the ballistic performance at equal surface density, in particular the ballistic resistance after several impacts.

[0029] Such an achievement makes it possible to obtain a low attenuation of electromagnetic waves in the range of 3 GHz to 40 GHz compared to a similar non-perforated shielding element, or even a conventionally perforated one, as described for example in the publication "effects of novel geometry designs on the ballistic performance ceramics".

[0030] The following are described various preferred embodiments of the present invention, which can obviously be combined with each other where appropriate:

[0031] - the number of lobes (50) of said orifice is between 2 and 10, preferably between 4 and 6, preferably distributed symmetrically around the center O of said orifices, or the two nearest median segments form an angle of 360° divided by the number of lobes. Preferably, the number of lobes is even.

[0032] - The orifice comprises at least 3 lobes, preferably at least 4 lobes, preferably again the opening comprises 4 lobes.

[0033] - The line segment connecting O and I' forms an angle a2' with respect to the segment S, said angle being less than 60 degrees in absolute value, preferably less than or equal to 45 degrees.

[0034] - The distance between O and I' is less than or equal to 2 mm, preferably less than 1.5 mm, preferably less than 1 mm, preferably less than 0.5 mm.

[0035] - The orifice comprises at least one pair of lobes extending in directions opposite, that is to say that their respective median segments are located on the same straight line passing through the center O.

[0036] - In the case where the number of lobes is even, two successive lobes around the center O forms an angle of 180° divided by the total number of lobe pairs.

[0037] - According to a particular mode, the orifice comprises two pairs of lobes. According to a In such a realization, preferably, the median segment of the first pair of lobes is perpendicular to the median segment of the second pair of lobes.

[0038] - Ly is equal to Ly'.

[0039] - The shape of the lobes is such that their median segment S is also an axis of symmetry said lobe.

[0040] - The length Lx is greater than 0.5 mm, preferably greater than 1 mm.

[0041] - The length Lx is less than 10 mm, preferably less than 8 mm, of Preferably less than 6 mm, preferably less than 5 mm.

[0042] - The distance Ly is greater than or equal to 0.2 times, preferably greater than or equal to at 0.5 times the distance OI, respectively OI' and / or less than or equal to 4 times, preferably less than 2 times, or even less than 1 time or even less than 0.6 times the distance OI, respectively OI'.

[0043] - All lobes of the same orifice have identical Lx values.

[0044] - All lobes of the same orifice have identical Ly and Ly' values.

[0045] - All lobes of the same orifice have identical dimensions.

[0046] According to other preferred embodiments of the invention, relating in particular to pattern of a set of holes in the shielding element:

[0047] - The orifices have substantially the same dimensions and / or the same shape in said armor element.

[0048] - The distance E, E2 between the ends of the lobes of the two closest orifices is greater than 1 mm, preferably greater than 2 mm, preferably greater than 3 mm.

[0049] - The distance Ei-E2 between the ends of the lobes of the two closest orifices is less than 50 mm, preferably less than 40 mm, preferably less than 30 mm, preferably less than 20 mm, preferably even less than 10 mm.

[0050] - The OrO2 distance between the centers of the orifices whose lobe ends are The closest ones are greater than 1mm, preferably greater than 2mm, preferably greater than 3mm.

[0051] - The distance OrO2 between the centers Oi and O2 of the orifices whose ends of lobes are closest is less than 50mm, preferably less than 40mm, preferably less than 30mm, preferably less than 20mm, preferably even less than 10mm.

[0052] - The orifices are arranged on parallel lines, the mesh or the elementary pattern said orifices being a parallelogram whose four vertices correspond to the center O of four orifices and whose angle b formed by two adjacent segments of said parallelogram is, in absolute value, greater than 20°, preferably greater than or equal to 30° and / or less than 90°, preferably less than or equal to 60°. This configuration is represented in [Fig.3] described below.

[0053] According to other preferred characteristics of the shielding element: - The surface area of ​​the inner and / or outer 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 surface area of ​​the inner and / or outer face is less than 20,000 cm2, preferably less than 10,000 cm2. - The width or diameter of the inner face is greater than 20 cm. - Said body has an average thickness greater than 7 mm, preferably greater than 10 mm, preferably greater than 15 mm, preferably greater than 20 mm. - Said body has an average thickness of less than 100 mm, preferably less than 90 mm. - The inner face and the impact face (except for the holes, patterns or local variations in thickness) are substantially parallel. - The inner face and / or the impact face are flat (except for holes, patterns or local variations in thickness). The body according to the invention, on at least a portion of its impact face, exhibits a texture comprising a plurality of patterns corresponding to a local variation in the thickness of said body. This local variation in thickness may follow a function or profile whose curve in a plane perpendicular to the cross-sectional plane may exhibit one or more changes in curvature. In particular, the patterns are preferably bumps or protrusions, cavities or valleys, so as to create shapes of cones, pyramids with a polygonal base, or patterns whose profile is sinusoidal in one or more directions. said body has an apparent density of less than 8g / cm3, the grains of the material constituting said 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 said body comprises grains of metallic material and / or ceramic and / or cermet. said grains have a maximum equivalent diameter less than or equal to 500 micrometers, preferably less than or equal to 400 micrometers or even less than or equal to 300 micrometers. Preferably, the maximum equivalent diameter of said grains is greater than 5 micrometers, preferably greater than 10 micrometers or even greater than 50 micrometers. Said ceramic and / or cermet grains are preferably linked by a matrix, said matrix comprising or being made up 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. These grains are composed of a metallic carbide or boride. Preferably, they are grains of silicon carbide or boron carbide, or a mixture of these two carbides. In one possible configuration, the material constituting the 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, preferably an apparent density of less than 3.0 g / cm3. Preferably, the constituent grains of the material constituting said body are made up essentially of SiC, preferably in alpha form. - said material constituting 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 other shape allowing the making of a breastplate, a shield, a vehicle bodywork element, a radome, a helmet, from among which the armoring element according to the invention may be chosen.

[0054] The invention also relates to a ballistic protection device, in particular a personal protection device, in particular armor used for bulletproof vests, a vehicle protection device (land, sea or air), other armoring to protect vehicles (land, sea or air) or a fixed installation (building, perimeter wall, guard post in particular), or detection or communication equipment, for example a radome.

[0055] Said ballistic protection device, includes the armoring element according to the invention.

[0056] According to various preferred embodiments of such a device: - Said body is provided on its inner face or opposite the impact face with a back energy dissipation coating, made of a material of lower hardness than that of the material constituting said body, in which the material constituting the back coating is chosen from polyethylenes PE, in particular ultra-high density polyethylenes (UHMPE), glass or carbon fibers, aramids, metals such as aluminium, titanium or their alloys or steel. - The entire ceramic body-back coating assembly is surrounded by a containment material envelope. - The containment material constituting the envelope is chosen from glass or carbon fibers or aramids. - The orifices of the ceramic body are partially or totally filled with a material chosen from among PE polyethylenes, in particular ultra-high density polyethylenes (UHMWPE), glass or carbon fibers, aramids, metals such as aluminum, titanium or their alloys or steel. Brief description of the drawings

[0057] - Figure 1 schematically represents in cross-section an example of an element of shielding according to the invention. - Figure [Fig. 2] schematically represents an orifice passing through the body of a armoring element according to the invention, in the plane of the impact face of the armoring element. - Fig. 3 shows a portion of the surface of the body of the armor element according to the invention with quadrilobe orifices along the plane of the impact face of the armor element. - Figure 4 describes a portion of the body of an armor element according to Comparative example 2 includes circular orifices. - Fig. 5 shows a portion of the body of the shielding element of Example 3 according to the invention. - Fig. 6 shows a portion of the body of the armor element of comparative example 4. - Figure 7 shows a portion of the body of the armor element of Comparative example 5. - Fig. 8 shows a portion of the body of the armor element of comparative example 6. - Figure [Fig. 9] shows a portion of the body of the armor element of Example 7 according to the invention.

[0058] Fig. 1 schematically presents in cross-section an example of an armor element 1 according to the invention, in the form of a monolithic body 11 having an outer face 2 (or impact face) and an inner face 3 (opposite to said impact face), a plurality of orifices 4 passing through the body of the armor element.

[0059] Figure 2 represents an orifice 4 consisting of a geometric center O and four lobes (5, 5', 6, 6'). As shown in lobe 5 only, each lobe includes an end E from which the two walls Pi and P2 extend towards the center O of the orifice and where they meet. The walls Pi and P2 of lobe 5 extend to two ends I and F respectively, arranged symmetrically on either side of the median axis of lobe 5.

[0060] According to the representation in [Fig. 2], the 4 lobes are arranged symmetrically around a center O of the orifice, in two pairs of lobes, respectively (5, 5') and (6, 6'), one pair extending along the median axis X and the other along a perpendicular axis Y, which constitutes the median axis of the second pair of lobes. Two successive lobes around the central orifice O thus form an angle of 90°. Lobe 5 therefore presents a median segment S of length Lx, delimited by the end E of said lobe on one side and by the center O of said orifice on the other.

[0061] Fig. 3 schematically illustrates an arrangement of quadrilobe orifices arranged according to an elementary regular pattern represented along the plane of the impact face of the shielding element 1 according to the invention.

[0062] Fig. 4 represents the elementary pattern or mesh of an arrangement of circular orifices arranged according to comparative example 2 described below.

[0063] Fig. 5 represents an arrangement of quadrilobe orifices arranged in a regular pattern according to Example 3 of the invention described below.

[0064] Figures 6, 7, 8 represent an arrangement of quatrefoil orifices arranged in a regular pattern respectively according to examples 4, 5 and 6 (comparatives) described below.

[0065] Fig. 9 shows an arrangement of quadrilobe orifices arranged in a regular pattern of Example 7 according to the invention described below, which, compared to Example 3, also in accordance with the present invention, has orifices closer together, and shorter lobes (length Lx divided by 5). Definitions#:

[0066] The following indications and definitions are given in relation to the preceding description of the present invention:

[0067] By average thickness of said body, we mean the average thickness over the portion of the body independently of protuberances or orifices.

[0068] By open surface of the armor body we mean the ratio between the sum of the areas of the orifices passing through said body to the total surface of the impact face of said body.

[0069] According to the invention, at least one face of said body may be curved; in this case, reference will be made to the projection plane along the impact face. By projection plane, we mean the plane obtained according to a map projection, that is to say, by a projection of said face allowing the obtaining of a flat impact surface of the same area. This precaution is employed in order to take into account possible large curvatures, even if in the general case the curvature is small or even zero, and therefore the effect of this curvature is relatively negligible.

[0070] A plate is a geometric shape whose surface area of ​​the largest face is at least five times, preferably ten times, greater than its thickness.

[0071] By equivalent diameter of a grain is meant 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.

[0072] By hard material is meant a material whose hardness is sufficiently high to justify its use in armor or shielding elements.

[0073] The maximum and average equivalent diameters are conventionally determined from observation of the microstructure of the material constituting the ceramic body, typically using scanning electron microscopy (SEM) images of a cross-section of the sintered product. It has been verified in the following examples that said microstructure is substantially identical, regardless of the cross-sectional orientation.

[0074] For the purposes of this invention, the apparent density of a product is defined as the ratio of the product's mass to its volume. It is traditionally 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 this invention.

[0075] Cermet is understood to be a composite material composed of a ceramic reinforcement and a metallic matrix.

[0076] 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 constituents of the gaseous environment of this initial feedstock, and / or from molten metal that infiltrates the porosity of the material during or after firing. A matrix substantially surrounds the grains of the granular fraction, that is, it coats them.

[0077] Sintering a material is a manufacturing process for parts such as the armor element according to the invention, consisting of heating a mixture comprising a powder without melting it. Under the effect of heat, the grains bond together, which forms the cohesion of the part.

[0078] 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 the 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 the sintering of the grains. This reactive sintering thus improves the mechanical strength of the sintered product.Reactively sintered products thus exhibit significantly lower closed porosity than other sintered products under similar temperature and pressure conditions. During cooking, reactively sintered products show virtually no shrinkage.

[0079] The crystallographic composition of the material constituting the monolithic body is normally obtained by X-ray diffraction and Rietveld analysis.

[0080] The crystalline phases, in particular the nitrogen-containing crystalline phases, were measured by X-ray diffraction and quantified according to the Rietveld method.

[0081] The elemental nitrogen (N) content in the sintered products was measured using LECO analyzers (LECO TC 436DR; LECO CS 300). The values ​​are given as mass percentages.

[0082] 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).

[0083] 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 device. The hardness is calculated from the force applied to the diamond point and the average value d of di and d2 according to the following formula: .BV = Hardness - .4- with F - Force applied d - Average of the fempremte [nrol

[0084] 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 a sintered metal material, the reference standard is ISO 6507-1.

[0085] Unless otherwise stated, in this description all percentages are mass percentages.

[0086] The armor element according to the invention provides in particular 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.

[0087] According to the invention, it classically comprises at least two layers: a first ceramic piece as described above associated with another, less hard and preferably ductile material on the back face, classically called "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 polymer-based, are used to bond the various elements constituting the armor component.

[0088] Upon impact with projectiles, the material of the monolithic body fragments and its primary role is to break the penetrating power of the projectiles. The role of the rear face, associated with the material constituting said body, is to absorb the kinetic energy of the debris and to maintain a certain level of containment of said body, further optimized by the containment envelope.

[0089] 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:

[0090] In all the following examples, ceramic plates of different formats were produced by casting in plaster molds a suspension according to the process described above and the formulation described in Table 1 below.

[0091] The mean and maximum equivalent grain diameters were determined from the observation of the microstructure of the material constituting the ceramic body, classically using images taken by scanning electron microscopy on a section of the sintered product.

[0092] [Tables 1] Composition of the initial mixture (mass %) SiC powder 10-150 µm D50 = 75 µm 39.5 SiC powder 0.1-5 µm D50 = 2.5 µm 37.5 Si powder 0.5-50 µm D50 = 20 µm 17 Alumina powder D50 = 2.5 µm 5.0 Fe2O3 2.5 µm 0.5 B4C 95% <45 µm D50 = 18 µm 0.5 Total minerals (%) 100 Added water (%) +12.5 Added dispersant (%) +0.5 Shaping and firing conditions Casting in plaster mold Demolding after hardening Drying (T7 duration) 110°C / 24h Firing (T7 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

[0093] Different shapes of plates with or without holes have been produced.

[0094] In order to avoid machining after baking, the orifices were obtained by placing inserts of the corresponding size in the molds, adapted according to the shrinkage or swelling of the material during drying and baking.

[0095] After baking, all the shielding plates of the following examples (according to the invention and comparatives) are monolithic and of dimensions of 10 cm by 10 cm (i.e. 100cm2).

[0096] 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.

[0097] Each assembly was then placed in front of thirty 10 mm thick polycarbonate plates. The assembly was then fired from a distance of 15 meters using a 5.56x45mm NATO (SS 109) round at a velocity of 940 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 from Example 1 and set at 100. The lower the index, the greater the proportional depth of penetration and the lower the ballistic performance.

[0098] For each example, the transparency to electromagnetic waves between 3 and 40 GHz was measured on a plate using a coaxial probe generating the signal (for the range between 3 and 18 GHz) and in free space (for the ranges 18 to 28 and 28 to 40 GHz), and an MVNA 350 analyzer on a circular surface traversed by the plate, with diameters of 2 cm, 5 cm, and 3 cm, respectively. These devices are conventionally used to measure the permittivity of ceramics. The power loss, given a power PI of a signal that has passed through the plate, is measured in air at 20°C with respect to a power P2 of the input signal according to the following formula: [°°"1 dl^pnls„œ=10^

[0100] The power loss at 33GHz (representative of the 3-40 GHz range) of the reference plate of Example 1 corresponds to the index 100. The lower the index, the lower the power loss expressed in logarithms is proportionally.

[0101] The open area as a percentage was measured as described previously.

[0102] The surface density pa was calculated according to the following formula pa = txpv where:

[0103] pa is the surface density expressed in Kg / m2

[0104] t is the thickness of the plate, expressed in m

[0105] pv is the apparent density expressed in Kg / m3 typically measured according to ISO 18754.

[0106] The results reported in Table 2 below show the advantages related to the implementation of a monolithic armor plate according to the invention.

[0107] [Tables2] Ex.l ** Ex.2 ** Ex.3* Ex.4 ** Ex.5 ** Ex. 6* * Ex.7* Representative figure 4 5 6 7 8 9 al (degrees) NA NA 39 21 30 53 45 al' (degrees) NA NA 45 21 30 53 45 a2 (degrees) NA NA 28 19 24 47 11 a2' (degrees) NA NA 28 19 24 47 11 Distance OI (mm) NA 2 2 1.8 3 1.5 0.8 Distance OI' (mm) NA 2 2 1.8 3 1.5 0.8 Distance Ly (mm) NA NA 1.0 1.8 2 3 0.2 Distance Ly' (mm) NA NA 1.0 1.8 2 3 0.2 length Lx (mm) NA NA 5.0 19.8 15 12 1 Open Area (%) 0 14 9 7 14 17 5 El-E2 Distance (mm) NA NA 6 10 2 8 4 O1-O2 Distance (mm) NA 10 16 48.8 32 32 6 b (degrees) NA 90 90 90 90 90 60 pa (Kg / m2) 21 18 16 16 15 14 18 Electromagnetic Power Loss Index at 33GHz 100 80 30 90 71 57 53 Ballistic Performance Index 100 67 79 83 65 63 87

[0108] *according to the invention **comparative “NA” = not applicable

[0109] Example 3 according to the invention by comparison with reference example 1 (solid plate) and comparative example 2 (plate with circular orifices) presents a much better compromise between ballistic performance and transparency to electromagnetic waves for a comparable surface density.

[0110] Comparative example 4 (length Lx > 10 01, i.e., lobes that are too long) shows very insufficient transparency to waves. Comparative examples 5 (distance 01 greater than 2 mm, i.e., a central hole that is too large) and 6 (lengths Ly and Ly greater than 2 mm, i.e., lobes that are too wide) also exhibit degraded ballistic performance.

[0111] Example 7 according to the invention, which has a configuration with an angle b of 60° and lobes of relatively smaller length compared with example 3, makes it possible to obtain the best ballistic performance among plates with orifices while preserving acceptable transparency to electromagnetic waves, unlike the comparative examples.

Claims

Demands

1. A shielding element (1), in the form of a monolithic body having an outer face or impact face (2) and an inner face (3) opposite said impact face, wherein: - the areas of said inner and outer faces are greater than or equal to 80 cm2, - said body is traversed by a plurality of orifices (4), such that the total area covered by said orifices represents between 5% and 50% of said impact face area, - at least one of said orifices, preferably all of said orifices, comprises at least two lobes such that, along the plane of said impact face: - each lobe (5) comprises two walls Pi and P2 joining at an end E, and - each lobe (5) has a median segment S delimited by the end E of said lobe of length Lx, the median segments of said lobes joining and being limited at their other end by a center O of said orifice,- the angles ai and closed by said median segment S and the tangents at point E in said plane of the walls Pi and P2 respectively are less than 90 degrees, - the two walls Pi and P2 of said lobe (5) extend from the end E towards the center O respectively to a point I and a point I' such that: - the line segment connecting O and I forms an angle α2 with the median segment S, said angle being less than 60 degrees, - the distance O1 between O and I is less than or equal to 2 mm, and - the maximum distances Ly, respectively Ly', of the wall segment between points E and I, respectively E and I', projected onto the axis Y perpendicular to the median segment S, are less than or equal to 2 mm, and - the length Lx of the median segment S is greater than the distance OI and less than or equal to 10 times the distance OI,- the distance between two centers O (O1 and O2) of two orifices whose lobe ends E (E1 and E2) are closest, is less than ten times the greatest of the distances between: - the center O(O1) and the end E (E1) of the first orifice on the one hand and, - the center O(O2) and the end E (E2) of the second orifice on the other hand.

2. Shielding element according to claim 1, wherein the number of lobes of said orifice is between 2 and 10.

3. Shielding element according to claim 1, wherein the orifice comprises at least 3 lobes, and preferably at least 4 lobes, the straight segment connecting 0 and I' forming an angle a2' with respect to segment S, said angle being less than 60 degrees in absolute value.

4. Shielding element according to any one of the preceding claims, wherein said orifice comprises at least one pair of lobes extending in opposite directions, preferably two pairs of lobes extending in opposite directions.

5. Shielding element according to any one of the preceding claims, wherein the median segment S is also an axis of symmetry of said lobe.

6. Shielding element according to any one of the preceding claims, wherein the length Lx is greater than 0.5 mm and / or less than 10 mm.

7. Shielding element according to any one of the preceding claims, wherein all lobes of the same orifice have identical Lx values.

8. Shielding element according to any one of the preceding claims, wherein the orifices have substantially the same dimensions and / or the same shape.

9. Shielding element according to any one of the preceding claims, wherein the distance Ly is greater than or equal to 0.2 times the distance OI, respectively OI' and / or less than or equal to 4 times the distance OI, respectively OI'.

10. Shielding element according to any one of the preceding claims, wherein the distance EiE2 between the ends of the lobes of two nearest orifices is greater than 1mm and / or less than 50mm.

11. Shielding element according to any one of the preceding claims, wherein the distance OiO2 between the centers of the orifices whose lobe ends are closest is greater than 1mm and / or less than 50mm.

12. A shielding element according to any one of the preceding claims, wherein the openings are arranged on parallel lines, the elementary motif being a parallelogram whose four vertices

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17. correspond to the center O of four orifices and whose angle b formed by two adjacent segments of said parallelogram is greater than 20° and / or less than 90°. An armor element according to any one of the preceding claims, wherein said body has an average thickness greater than 7 mm. An armor element according to any one of the preceding claims, wherein said body has an apparent density of less than 8 g / cm³. Shielding element according to any one of the preceding claims, wherein the material constituting said body has an apparent density of less than 8g / cm3 and / or a Vickers hardness greater than 3 GPa. Shielding element according to any one of the preceding claims, wherein the material constituting said body comprises grains of metallic material and / or ceramic and / or cermet. Armor element according to any one of the preceding claims, wherein the shape of said body is chosen from a plate, a tube or other shape enabling the making of a breastplate, a shield, a vehicle body element, a radome, a helmet.

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