Shielding element with multilobe openings

Abstract

The invention relates to a shielding element in the form of an integral body having an external face or impact face (2) with a surface area larger than or equal to 80 cm2 through which a plurality of openings (4) of centre O pass, said openings comprising a central portion having an opening diameter smaller than or equal to 2 mm, which is the starting point for a plurality of lobes of median segment S, wherein the maximum distances Ly, Ly' from the wall P1, P2 with respect to the median segment are, respectively, less than 2 mm and the length of which is less than ten times the central portion of radius OI. The distance between the centres O (O1 and O2) of two openings to which the lobe ends E (E1 and E2, respectively) are closest is less than ten times the larger of the distances between O1 and E1 and between O2 and E2, respectively.

Description

[0001] Description

[0002] Title: Shielding element with multi-lobe orifices

[0003] Technical field

[0004] The invention relates to an armoring element, in particular for anti-ballistic protection, the impact surface of which has a shape of perforations particularly suited to this function, a protection system comprising such an element.

[0005] The invention finds its application in particular as a personal protection device, in particular armor used for bulletproof vests, a device for protecting a vehicle (land, sea or air), other armoring making it possible to protect vehicles (land, sea or air) or even a fixed installation (building, surrounding wall, guard post in particular), or even detection or communication equipment, for example a radome.

[0006] Prior art

[0007] In particular, systems formed by the so-called "mosaic" assembly of ceramic parts having a determined 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, for a thickness of a few mm. This type of mosaic of parts has the advantage of resisting successive shots (so-called "multi-shot" or "multi-hit" protection in English). The assembly of such "mosaic" structures is, however, long and expensive. In addition, it can be difficult to maintain a low overall tolerance of the assembly because the tolerances of each part are added to constitute the assembly. This has an impact on the width of the residual spaces between the parts (joint planes) produced by the assembly.Furthermore, if the object to be protected also has a curved shape, the spaces constitute a significant weak point for this protection system when the projectile impacts these areas.

[0008] There are other so-called monolithic systems, i.e. formed by a single piece or by a very limited number of large-surface pieces, each monolith having an impact surface greater than 100 cm 2 , or even 150 cm 2 , so as to reduce the number of joints.

[0009] Many materials have been proposed, particularly to constitute armor intended for people whose armor mass to protective surface ratio (or surface density) must remain low, typically less than 50 kg / m 2 , or non-personal shielding intended for vehicles or fixed installations whose mass to protective surface ratio is typically greater than 10 kg / m 2 .

[0010] In particular, products based on non-oxide ceramics have been proposed, the mass to armor surface ratio or surface density of which, with equivalent impact resistance, is lower than other materials such as metals or alumina.

[0011] Furthermore, in the context of ballistic protection of communication systems (radars, antennas, etc.) but also of other objects, it is necessary to combine ballistic performance at the same surface density with low interaction with electromagnetic waves, particularly at frequencies typically between 3 and 40 GHz, and in particular to take these two properties into account to judge 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 form known as mosaic or that known as monolithic, different configurations have been proposed.

[0012] The publication "Effects of novel geometric 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. The authors observe variations in performance depending on the configurations but only a very slight improvement with texturing including bumps on the impact face and truncated cones on the rear face.

[0013] There is therefore a continual need to improve the products used as armour, 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.

[0014] The object of the present invention is therefore to propose a new product, different from the products currently used in the field and responding to this problem.

[0015] Statement of the invention

[0016] According to a first general aspect, the present invention relates to an armoring 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: - the surfaces of said inner and outer faces are greater than or equal to 80 cm 2 , preferably greater than or equal to 100 cm 2 , - said body is crossed by a plurality of orifices (4), in such a way 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 surface of the impact face, and

[0017] -at least one of said orifices, preferably at least 10% in number, more preferably at least 25% in number, or even more than 50% in number, more preferably all of said orifices, comprises at least two lobes, preferably a plurality of lobes, such that, according to the plane of said impact face:

[0018] -each lobe (5) comprises two walls Pi and Pi meeting at one end E, and

[0019] -each lobe has a median segment S of length L x , delimited by the end E of said lobe, the median segments of said lobes joining and being limited at their other end by a center O of said orifice,

[0020] -the angles ai and ai' formed by said median segment S and the tangentials at point E respectively of the walls Pi and Pi in said plane are less, in absolute value, than 90 degrees, and

[0021] -the two walls Pi and Pi of said lobe extend from the end E in the direction of the center O respectively to a point I and a point I' such that:

[0022] -the straight line segment connecting O and I forms an angle ai with respect to the segment S, said angle being less in absolute value than 60 degrees, preferably less than or equal to 45 degrees, and

[0023] -the distance 01 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

[0024] - the maximum distances L y , respectively L y ' , 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 2 mm, and

[0025] -length L xof the median segment S is greater than the distance 01 and less than or equal to 10 times 01, -the distance between two centers O (Oi and O2) of two orifices whose lobe ends E (E2 and E2) are the closest, is less than ten times the greatest of the distances between: the center O(O2) and the end E (E2) of the first orifice on the one hand and

[0026] - the center O(O2) and the end E (E2) of the second orifice on the other hand.

[0027] 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 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.

[0028] Such an achievement makes it possible to obtain a low attenuation of electromagnetic waves in the range from 3 GHz to 40 GHz compared to a similar non-perforated or even conventionally perforated shielding element, as described for example in the publication "effects of novel geometric designs on the ballistic performance ceramics".

[0029] Various preferred embodiments of the present invention are described below, which can of course, if necessary, be combined with each other:

[0030] - the number of lobes (5i) of said orifice is between 2 and 10, preferably between 4 and 6, preferably distributed symmetrically around the center O of said orifices or two closest median segments form an angle of 360° divided by the number of lobes. More preferably, the number of lobes is even. - The orifice comprises at least 3 lobes, preferably at least 4 lobes, more preferably the orifice comprises 4 lobes.

[0031] - The straight line segment connecting O and I' forms an angle «2' with respect to the segment S, said angle being less in absolute value than 60 degrees, preferably less than or equal to 45 degrees.

[0032] - 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.

[0033] - The orifice comprises at least one pair of lobes extending in opposite directions, that is to say that their respective median segments are located on the same straight line passing through the center O.

[0034] - In the case where the number of lobes is even, two successive lobes around the center O form an angle of 180° divided by the total number of pairs of lobes.

[0035] - According to a particular embodiment, the orifice comprises two pairs of lobes. According to such an embodiment, preferably, the median segment of the first pair of lobes is perpendicular to the median segment of the second pair of lobes.

[0036] - L y is equal to L y ' .

[0037] - The shape of the lobes is such that their median segment S is also an axis of symmetry of said lobe.

[0038] - Length L x is greater than 0.5 mm, preferably greater than 1 mm.

[0039] - Length L x is less than 10 mm, preferably less than 8 mm, preferably less than 6 mm, preferably less than 5 mm.

[0040] The distance L yis greater than or equal to 0.2 times, preferably greater than or equal to 0.5 times the distance 01, respectively 01' 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 01, respectively 01'.

[0041] - All lobes of the same orifice have values ​​of L x identical.

[0042] - All lobes of the same orifice have values ​​of L y and L y ' identical.

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

[0044] According to other preferred embodiments of the invention, relating in particular to the pattern of a set of orifices of the shielding element:

[0045] - The holes have substantially the same dimensions and / or the same shape in said shielding element.

[0046] - The distance E2_E2 between the ends of the lobes of two nearest orifices is greater than 1 mm, preferably greater than 2 mm, preferably greater than 3 mm.

[0047] - The distance E2-E2 between the ends of the lobes of two closest orifices is less than 50 mm, preferably less than 40 mm, preferably less than 30 mm, preferably less than 20 mm, more preferably less than 10 mm.

[0048] - The distance O2-O2 between the centers of the orifices whose lobe ends are closest is greater than 1 mm, preferably greater than 2 mm, preferably greater than 3 mm,

[0049] The distance O2-O2 between the centers O2 and O2 of the orifices whose lobe ends are closest is less than 50 mm, preferably less than 40 mm, preferably less than 30 mm, preferably less than 20 mm, more preferably less than 10 mm.

[0050] - the distance between two centers 0 (02 and 02) of two orifices whose lobe ends E (E2 and E2) are closest is greater than the greatest of the distances between the center O(Oi) and the end E (Ex) of the first orifice on the one hand and between the center O(Û2) and the end E (E2) of the second orifice on the other hand.

[0051] - The orifices are arranged on parallel lines, the mesh or the elementary pattern of said orifices being a parallelogram whose four vertices correspond to the center O of four orifices and whose angle P 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 shown in Figure 3 described below.

[0052] According to other preferred characteristics of the shielding element:

[0053] - The surface area of ​​the interior and / or exterior face is greater than 150 cm 2 , greater than 200 cm 2 , greater than 250 cm 2 , preferably greater than 400 cm 2 , preferably greater than 500 cm 2 , or even greater than 1000 cm 2 .

[0054] - The surface area of ​​the inner and / or outer face is less than 20,000 cm 2 , preferably less than 10,000 cm 2 .

[0055] - The width or diameter of the inner face is greater than 20 cm.

[0056] - 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.

[0057] Said body has an average thickness of less than 100 mm, preferably less than 90 mm.

[0058] - The inner face and the impact face (except for holes, patterns or local variations in thickness) are substantially parallel.

[0059] - The inner face and / or the impact face are flat (except for the orifices, patterns or local variations in thickness). - Said body according to the invention, on at least a portion of its impact face, has a texturing 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 a profile whose curve in a plane perpendicular to the section plane may have one or more changes in curvature. In particular, the patterns are preferably bosses or protuberances, cavities or valleys, so as to create shapes of cones, pyramids with a polygonal base, or even patterns whose profile is sinusoidal in shape in one or more directions.

[0060] - said body has an apparent density of less than 8 g / cm 3 .

[0061] - 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.

[0062] - the material constituting said body comprises grains of metallic material and / or ceramic and / or cermet.

[0063] - 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.

[0064] - Said ceramic and / or cermet grains are preferably bound by a matrix, said matrix comprising or consisting of a silicon nitride phase and / or a silicon oxynitride phase, said matrix representing between 5 and 40% by weight, preferably between 15 and 35% by weight, of said material constituting the ceramic body. - Said grains consist of a metal carbide or boride. More preferably, they are grains of silicon carbide or boron carbide or a mixture of these two carbides. According to one possible embodiment, the material constituting said body comprises only grains of silicon carbide, with optionally a metal phase, preferably comprising the element silicon.

[0065] - said body, preferably ceramic, has an apparent density of less than 5 g / cm 3 , preferably less than 3.2 g / cm 3, preferably an apparent density of less than 3.0 g / cm 3 .

[0066] - Preferably, the constituent grains of the material constituting said body consist essentially of Sic, preferably in alpha form.

[0067] - said material constituting said body has an open porosity greater than 5%, preferably greater than 6%, more preferably greater than 7% or even greater than 8%, and less than 14%, preferably less than 13%, more preferably less than 12%.

[0068] - said body has a mass to surface ratio or a surface density, measured in kg / m 2 , preferably less than 200, preferably less than 100, preferably less than 80.

[0069] - Said body may be a plate, a tube or another shape making it possible to produce a breastplate, a shield, a bodywork element of a vehicle, a radome, a helmet, from which the shielding element according to the invention may be chosen.

[0070] The invention also relates to an anti-ballistic protection device, in particular a personal protection device, in particular armor used for bulletproof vests, a device for protecting a vehicle (land, sea or air), other armoring for protecting vehicles (land, sea or air) or even a fixed installation (building, surrounding wall, guard post in particular), or even detection or communication equipment, for example a radome.

[0071] Said anti-ballistic protection device comprises the shielding element according to the invention.

[0072] According to different preferred embodiments of such a device:

[0073] - Said body is provided on its inner face or opposite the impact face with a rear energy dissipation coating, made of a material of lower hardness than that of the material constituting said body, in which the material constituting the rear coating is chosen from polyethylenes PE, in particular ultra high density polyethylenes (UHMPE), glass or carbon fibers, aramids, metals such as aluminum, titanium or their alloys or steel.

[0074] - The ceramic body-rear coating assembly is surrounded by an envelope of a containment material.

[0075] - The containment material constituting the envelope is chosen from glass or carbon fibers or aramids.

[0076] - The holes in the ceramic body are partially or totally filled with a material chosen from PE polyethylenes, in particular ultra high density polyethylenes (UHMPE), glass or carbon fibers, aramids, metals such as aluminum, titanium or their alloys or steel.

[0077] Figures:

[0078] - Figure 1 schematically represents in section an example of a shielding element according to the invention.

[0079] - Figure 2 schematically represents an orifice passing through the body of a shielding element according to the invention, in the plane of the impact face of the shielding element.

[0080] - Figure 3 shows a surface portion of the body of the shielding element according to the invention with quadrilobe orifices according to the plane of the impact face of the shielding element.

[0081] - Figure 4 describes a portion of the body of a shielding element according to comparative example 2 comprising circular orifices.

[0082] - Figure 5 shows a portion of the body of the shielding element of example 3 according to the invention.

[0083] - Figure 6 shows a portion of the body of the shielding element of comparative example 4.

[0084] - Figure 7 shows a portion of the body of the shielding element of comparative example 5.

[0085] - Figure 8 shows a portion of the body of the shielding element of comparative example 6.

[0086] - Figure 9 shows a portion of the body of the shielding element of example 7 according to the invention.

[0087] Figure 1 shows schematically in section an example of an armoring 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 said impact face), a plurality of orifices 4 passing through the body of the armoring element.

[0088] Figure 2 represents an orifice 4 consisting of a geometric center 0 and four lobes (5, 5', 6, 6'). As shown on lobe 5 only, each lobe comprises an end E from which the two walls Pi and Pi extend towards the center 0 of the orifice and where they meet. The walls PI and P2 of lobe 5 extend to two ends respectively I and I' arranged symmetrically on either side of the median axis of lobe 5. According to the representation of figure 2, the 4 lobes are arranged symmetrically around a center 0 of the orifice, according to 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 0 therefore form an angle of 90°. Lobe 5 thus has a median segment S of length L x, delimited by the end E of said lobe on the one hand and by the center O of said orifice on the other hand.

[0089] Figure 3 shows a diagram of an arrangement of quadrilobe orifices arranged in an elementary regular pattern represented according to the plane of the impact face of the shielding element 1 according to the invention.

[0090] Figure 4 represents the pattern or elementary mesh of an arrangement of circular orifices arranged according to comparative example 2 described below.

[0091] Figure 5 shows an arrangement of quadrilobe orifices arranged in a regular pattern according to example 3 according to the invention described below.

[0092] Figures 6, 7, 8 represent an arrangement of quadrilobe orifices arranged in a regular pattern respectively according to examples 4, 5 and 6 (comparative) described below.

[0093] Figure 9 shows an arrangement of quadrilobe orifices arranged in a regular pattern of Example 7 according to the invention described below, which has, compared to Example 3, also according to the present invention, closer orifices and shorter lobes.

[0094] (length L x divided by 5. Definitions:

[0095] The following indications and definitions are given, in relation to the preceding description of the present invention:

[0096] By average thickness of said body is meant the average thickness over the portion of the body independently of protrusions or orifices.

[0097] By open surface of the armor body is meant the ratio between the sum of the surfaces of the orifices passing through said body on the total surface of the impact face of said body. According to the invention at least one face of said body can be curved, we will then refer to the projection plane according to the impact face. By projection plane is meant the plane obtained according to a cartographic projection, that is to say by a projection of said face allowing the obtaining of a flat impact surface and of the same area. This precaution is used in order to take into account possible strong curvatures even if in the general case the curvature is weak or even zero and therefore the effect of this curvature relatively negligible.

[0098] 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.

[0099] Equivalent diameter of a grain means half the sum of the greatest length of the grain and the greatest width of the grain, measured in a direction perpendicular to the said greatest length.

[0100] Hard material means a material whose hardness is high enough to justify its use in armor or shielding elements.

[0101] The maximum and average equivalent diameters are conventionally determined from the observation of the microstructure of the material constituting the ceramic body, conventionally using images taken by SEM (scanning electron microscopy) on a section of the sintered product. It has been verified in the examples which follow that said microstructure is substantially identical, whatever the orientation of the section.

[0102] By apparent density of a product, we mean, for the purposes of the present invention, 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. The ISO 5017 standard, for example, specifies the conditions for such a measurement. This standard also makes it possible to measure open porosity for the purposes of the present invention.

[0103] Cermet is a composite material composed of a ceramic reinforcement and a metal matrix.

[0104] By "matrix" is meant a crystallized or non-crystalline phase, ensuring a substantially continuous structure between the grains. It is obtained, during the production 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 into the porosity of said material during or after its firing. A matrix substantially surrounds the grains of the granular fraction, that is to say, coats them.

[0105] Sintering a material is a process for manufacturing parts such as the shielding element according to the invention, consisting of heating a mixture comprising a powder without bringing it to the point of melting. Under the effect of heat, the grains weld together, which forms the cohesion of the part.

[0106] 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 nature that they had in the initial 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 having a nitride matrix, one or more metals are preferably added to the charge, which react with the nitrogen atmosphere in order 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.Reactively sintered products thus exhibit significantly lower closed porosity than other sintered products under similar temperature and pressure conditions. During firing, reactively sintered products exhibit substantially no shrinkage.

[0107] The crystallographic composition of the material constituting the monolithic body is normally obtained by X-ray diffraction and Rietveld analysis.

[0108] The crystallized phases, especially the nitrogenous crystallized phases, were measured by X-ray diffraction and quantified according to the Rietveld method.

[0109] Elemental nitrogen (N) contents in the sintered products were measured using LECO analyzers (LECO TC 436DR; LECO CS 300). Values ​​are provided as mass percentages.

[0110] Residual silicon in metallic form in the sintered material or after firing is normally measured according to the method known to those skilled in the art and referenced under ANSI B74-151992 (R2000).

[0111] The Vickers hardness of grains can be measured using a standardized pyramidal diamond point 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 dl 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 d value of di and d2 according to the following formula:

[0112] 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 ISO6507-1.

[0113] Unless otherwise indicated, in this description all percentages are mass percentages.

[0114] The armouring element according to the invention provides protection against any type of projectile, 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 bladed weapons and normally constitutes an armour element for vehicles, generally in the form of modules such as plates.

[0115] 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 for example steel or aluminum alloys, in the form of plates. Adhesives, for example based on polyurethane or epoxy polymers, are used to bond the different elements constituting the shielding element.

[0116] Under the impact of the projectiles, the material of the monolithic body fragments and its main role is to break the piercing 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 containment envelope.

[0117] The following examples are given for purely illustrative purposes and do not limit the scope of the present invention in any of the aspects described.

[0118] Examples:

[0119] In all the following examples, ceramic plates of different formats were produced by casting a suspension in a plaster mold using the process described previously and the formulation described in Table 1 below.

[0120] The average and maximum equivalent grain diameters were determined from the observation of the microstructure of the material constituting the ceramic body, conventionally using images taken by scanning electron microscopy on a section of the sintered product.

[0121] [Table 1]

[0122] Different shapes of plates with or without holes have been produced.

[0123] In order to avoid machining after baking, the holes 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.

[0124] After firing, all the armor plates in the following examples (according to the invention and comparative) are monolithic and have dimensions of 10 cm by 10 cm (i.e. 100 cm 2 ) .

[0125] For each example, three assemblies were made by bonding the face of the ceramic plate opposite the impact to a polycarbonate plate using 3M 950™ double-sided tape from 3M.

[0126] Each assembly was then placed in front of thirty 10 mm thick polycarbonate plates. The whole assembly was shot at a distance of 15 meters with a 5.56x45mm NATO (SS109) caliber at a speed of 940 m / s. The ballistic performance was assessed by measuring the penetration depth of the bullet in 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 depth proportionally and the lower the ballistic performance.

[0127] 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 crossed, respectively, 2 cm, 5 cm and 3 cm in diameter, these devices being conventionally used to measure the permittivity of ceramics. The power loss is measured in air and at 20°C taking into account a power PI of a signal having crossed the plate with respect to a power P2 of the input signal according to the following formula:

[0128] The power loss at 33GHz (representative of the 3-40GHz range) of the reference plate in example 1 corresponds to the index 100. The lower the index, the proportionally lower the power loss expressed in logarithm and therefore the greater the transparency to waves.

[0129] The percent open area was measured as described previously.

[0130] The surface density p a was calculated for example 1 according to the following formula p a = txp v where: p a is the surface density expressed in kg / m 2 t is the thickness of the plate, expressed in m pv is the apparent density expressed in Kg / m 3 typically measured according to ISO 18754.

[0131] The thickness of the plate in Example 1 was 7.7 mm.

[0132] For the plates in examples 2 to 7, the surface density expressed in Kg / m 2was determined by weighing the plates and dividing by their impact surface area (100 cm 2 ) . The results reported in Table 2 below show the advantages linked to the implementation of a monolithic armor plate according to the invention.

[0133] [Table 2] *according to the invention **comparative “NA” = not applicable

[0134] Example 3 according to the invention, compared 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.

[0135] Comparative example 4 (length L x > 10 01, i.e. lobes that are too long) shows very insufficient transparency to waves. Examples 5 (distance 01 greater than 2 mm, i.e. a central hole that is too large) and 6 (lengths L y and L y, greater than 2 mm, i.e. lobes that are too wide), comparative, also have degraded ballistic performance. Example 7 according to the invention, which has a configuration with an angle P of 60° and lobes of relatively smaller length compared to example 3, makes it possible to obtain the best ballistic performance among the plates with orifices while preserving acceptable transparency to electromagnetic waves, unlike the comparative examples.

Claims

CLAIMS 1. 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: - the surfaces of said inner and outer faces are greater than or equal to 80 cm 2 , said body is crossed by a plurality of orifices (4), so that the total surface covered by said orifices represents between 5% and 50% of said surface of the impact face, at least one of said orifices, preferably all of said orifices, comprises at least two lobes such that, according to the plane of said impact face: - each lobe (5) comprises two walls Pi and Pi meeting at one end E, and each lobe (5) has a median segment S delimited by the end E of said lobe of length L x, 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 ai' formed by said median segment S and the tangentials at point E in said plane respectively of the walls Pi and Pi are less, in absolute value, than 90 degrees, - the two walls Pi and Pi of said lobe (5) extend from the end E in the direction of the center O respectively up to a point I and a point I' such that: - the straight line segment connecting O and I forms an angle ai with the median segment S, said angle being less, in absolute value, than 60 degrees, - the distance 01 between O and I is less than or equal to 2 mm, and - the maximum distances L y , respectively L y ' , of the wall segment between points E and I, respectively E and I' , projected onto the Y axis perpendicular to the median segment S, are less than or equal to 2 mm, and - length L x of the median segment S is greater than the distance 01 and less than or equal to 10 times the distance 01, - the distance between two centers 0 (Oi and O2) of two orifices whose lobe ends E (E2 and E2) are closest, is less than ten times the greatest of the distances between: the center 0(02) and the end E (E2) of the first orifice on the one hand and - the center 0(02) and the end E (E2) of the second orifice on the other hand.

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

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

4. Shielding element according to 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 one of the preceding claims, in which the median segment S is also an axis of symmetry of said lobe.

6. Shielding element according to one of the preceding claims, in which the length L x is greater than 0.5 mm and / or less than 10 mm.

7. Shielding element according to one of the preceding claims, in which all the lobes of the same orifice have values ​​of L x identical.

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

9. Shielding element according to one of the preceding claims, in which the distance L y is greater than or equal to 0.2 times the distance 01, respectively 01' and / or less than or equal to 4 times the distance 01, respectively 01'.

10. Shielding element according to one of the preceding claims, in which the distance E2E2 between the ends of the lobes of two closest orifices is greater than 1 mm and / or less than 50 mm.

11. Shielding element according to one of the preceding claims, in which the distance 0i02 between the centers of the orifices whose ends of the lobes are closest is greater than 1 mm and / or less than 50 mm.

12. Shielding element according to one of the preceding claims, in which the orifices are arranged on parallel lines, the elementary pattern being a parallelogram whose four vertices correspond to the center 0 of four orifices and whose angle P formed by two adjacent segments of said parallelogram is greater than 20° and / or less than 90°.

13. Shielding element according to one of the preceding claims, in which said body has an average thickness greater than 7 mm.

14. Shielding element according to one of the preceding claims, wherein said body has an apparent density of less than 8g / cm 3 , 15. Shielding element according to one of the preceding claims, in which the material constituting said body has an apparent density of less than 8g / cm 3 and / or a Vickers hardness greater than 3 GPa.

16. Shielding element according to one of the preceding claims, in which the material constituting said body comprises grains of metallic material and / or ceramic and / or cermet.

17. Armor element according to one of the preceding claims, in which the shape of said body is chosen from a plate, a tube or another shape making it possible to produce a breastplate, a shield, a bodywork element of a vehicle, a radome, a helmet.

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