Energy dissipation plate for shielding, comprising a fibrous and porous damping material

Abstract

The invention relates to a plate for dissipating impact energy for ballistic armor. This dissipating plate consists of a damping material composed of a fibrous reinforcement bonded by an organic matrix comprising a thermosetting resin. This reinforcement comprises inorganic fibers assembled in the form of threads, and the damping material has the following characteristics: - the volumetric content of the fibrous reinforcement in the damping material is between 20% and 70%, the remainder, up to 100%, being composed of the matrix and porosity; - the fibrous reinforcement comprises, by volume, at least 50% silica fiber threads with a mass content of SiO2 greater than 90%; and - the porosity of the damping material is between 2% and 10% by volume.

Description

[0001] The invention relates to a ballistic protection device, in particular a personal protective device (e.g., a bulletproof vest), a vehicle protection device (for land, sea, or air), or a fixed installation (building, perimeter wall, guard post, etc.), or even detection or communication equipment, for example, a radome. More particularly, the invention relates to an energy-dissipating plate for armor comprising a damping material, including the material itself. Such a plate makes it possible to stop, in particular, a bullet or projectile fired from a weapon, especially a firearm.

[0002] The invention also relates to an armor plate comprising said energy dissipation plate and an impact-resistant plate, made of a hard material, positioned in front of said dissipation plate relative to the direction of the threat or projectile. Such an embodiment is particularly suitable for enhancing protection when said projectile is highly penetrating.

[0003] Among ballistic protection materials, one example is Dyneema® HB26 (US2013220106A1), a composite material comprising several layers of ultra-high-density polyethylene (UHMWPE) fibers arranged perpendicularly to each other within a polyurethane matrix. This material is reportedly used for protection against ammunition fired by assault rifles such as the AK-47 or against the impact of improvised explosive devices (IEDs) by distributing the impact energy. Ballistic protection is also known from WO 91 / 08895 A2.

[0004] In order to reduce the mass of protective devices without compromising ballistic performance, numerous materials have been proposed for personnel armor, where the armor mass-to-surface ratio must remain low, typically less than 50 kg / m², or for non-personnel armor intended for vehicles or fixed installations, where the armor mass-to-surface ratio is generally greater than 20 kg / m². Among the ceramic materials used particularly in such applications are metal carbide-based products. For example, publication WO 2013 / 186453 A1 describes a silicon carbide (SiC) product with a specified grain shape and chemical composition for use as impact-resistant armor or armor components.Publication EP1710218A1 unveils a sintered material based on silicon nitride and tungsten carbide with the aid of additives such as rare earth elements and tungsten, preferably added in oxidized form. WO2008 / 130451 (EP2095055A1) also proposed an approach to reducing the propagation of the stress wave associated with projectile impact by using an envelope formed by 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 multifracturing of the ceramic.

[0005] However, there is a continuous need for improvement of ballistic protection devices, this improvement being measured in particular by their ballistic performance in relation to their mass, in particular so as to be able to resist the dynamic deformation due to ballistic impact without increasing their mass, or even reducing it, in particular in order to improve comfort in the case of personal protection or to reduce energy consumption in the case of vehicle protection.

[0006] The object of the present invention is therefore to provide a ballistic armor plate with improved performance, in particular improved resistance to dynamic deformation, for the same surface density. This improvement results in particular from the use of the plate made of the damping material according to the invention, as described below.

[0007] According to a first general aspect, the present invention relates to an impact energy dissipation plate for ballistic armor, said dissipation plate being made of a damping material consisting of a fibrous reinforcement bonded by an organic matrix, said reinforcement comprising inorganic fibers, assembled in the form of threads, preferably long threads, said matrix comprising a thermosetting resin coating said threads, said damping material having the following characteristics: the volumetric rate of fibrous reinforcement of said damping material is between 20% and 70%, the remainder to 100% being constituted by said matrix and the porosity of said material; said fibrous reinforcement comprises at least 50% by volume of silica fiber yarns whose mass content in SiO2 is greater than 90%, the porosity of said damping material is between 2% and 10% by volume.

[0008] The inventors have indeed discovered that such a damping material in the form of a controlled porosity composite comprising an organic matrix encasing a reinforcement comprising yarns with a high silica content exhibits, compared to prior art materials, improved resistance to dynamic deformation, at the same surface density.

[0009] In particular, an armor plate equipped with such a damping material shows a shallower deformation depth and a larger lateral deformation area, which, at equivalent mass, results in a greater ability to absorb energy from the impact, for example, of a projectile fired from a firearm.

[0010] Various preferred embodiments of the present invention are described below, which can obviously be combined with each other where appropriate: The apparent density of the damping material is greater than 1.0 g / cm³, preferably greater than 1.5 g / cm³, and / or less than 2.0 g / cm³, preferably less than 1.8 g / cm³; the volume fraction of fibrous reinforcement of said damping material is between 30 and 50%, the remainder consisting of porosity and matrix. The fibrous reinforcement comprises by volume at least 70% silica fiber yarns, preferably at least 80%, preferably more than 90% silica fiber yarns, and preferably consists primarily of silica fiber yarns, hereafter referred to as silica yarns for simplicity; the remaining 50% by volume of said silica yarns in the fibrous reinforcement is represented by washed glass fibers. the mass content of SiO2 of said silica wires is greater than 95%, preferably greater than 97%, more preferably at least 99%;the average equivalent diameter of said wires is between 3 and 3000 micrometers, preferably greater than 8 micrometers and / or less than 1000 micrometers, preferably less than 500 micrometers; the wires are preferably single wires; the linear density of said wires is greater than or equal to 500 tex, preferably less than 5000 tex; the average equivalent diameter of the silica fibers constituting the wires is greater than or equal to 3 micrometers, preferably greater than or equal to 5 micrometers, preferably greater than or equal to 7 micrometers; the average equivalent diameter of said fibers is less than or equal to 20 micrometers; the reinforcement consists essentially of said silica wires or is even made up of said silica wires; the twist level of the wires is on average less than or equal to Z20, preferably less than or equal to Z10, preferably less than or equal to Z3;The fibrous reinforcement takes the form of at least one ply or layer of a textile, preferably a fabric, consisting of a network of parallel warp yarns, with weft yarns preferably passing transversely, or preferably perpendicularly, through the network. In one possible configuration, the reinforcement consists of several superimposed layers of fabric, each layer being impregnated with resin to form the damping material. Preferably, the superimposed fabric layers have the same pattern or weave. This has the advantage of preventing the phenomenon of interpenetration or interlacing of the yarns of one layer with those of a layer directly in contact with it, whether above or below.The basis weight of a layer of textile or a ply of fabric is greater than or equal to 350 g / m², preferably less than 2000 g / m², preferably less than 1000 g / m², preferably less than 700 g / m². A lower basis weight leads to an increased number of fabric layers, making the manufacturing process longer and therefore more expensive. A basis weight that is too high leads to degraded performance for an equivalent surface mass. The porosity of said damping material is less than or equal to 5% by volume.said matrix has pores with an average width of between 10% and 500% of the average equivalent diameter of said fibers, preferably between 10% and 100% of said diameter, preferably between 10% and 50% of said diameter. Preferably, in number, more than 90%, preferably more than 95%, preferably more than 99% of the pores have a width greater than 1 micrometer, preferably greater than 2 micrometers, preferably greater than 5 micrometers and / or less than 50 micrometers, preferably less than 30 micrometers, preferably less than 15 micrometers; said matrix optionally includes additives such as a mineral filler; the density of said resin is between 0.8 and 1.35 g / cm³; the resin essentially comprises the chemical elements carbon (C), hydrogen (H), and oxygen (O); the matrix comprises an epoxy resin; the damping material has a Vickers hardness of less than 3 GPa;said dissipation plate has a surface area greater than or equal to 150 cm² and / or a thickness between 1 and 50 mm, preferably between 3 and 20 mm; said dissipation plate is surrounded by a containment material envelope; said ballistic armor plate includes said impact energy dissipation plate.

[0011] In particular, in certain embodiments of the present invention, an impact-resistant plate can be placed in front of the impact energy-damping or dissipation plate in order to resist highly penetrating projectiles, for example in order to comply with NIJ-IIIA, NIJ-III or NIJ-IV standards for personal protection or STANAG 4569 for non-personal protection.

[0012] According to a second general aspect, the present invention relates to a shielding plate as previously described, further comprising an impact-absorbing plate made of a material with a hardness greater than that of the damping material. This impact-absorbing plate generally has a thickness greater than 2 mm and is positioned in front of the damping plate, relative to the direction of impact.

[0013] Other preferred embodiments of the present invention are described below, which can obviously be combined with each other where appropriate, describing the case of an armor plate comprising an impact-resistant plate in addition to the damping plate described above: the thickness of said impact-resistant plate is greater than 4mm, preferably 6mm, preferably greater than 10mm. According to one possible method the thickness of said plate is less than 100 mm, preferably less than 50mm, or even less than 20mm; the ratio of the thickness of the energy dissipation plate to the thickness of the impact plate is preferably between 0.5 and 5, preferably greater than 1 and / or less than 3; the surface area of ​​said impact plate is greater than 150 cm²; the surface area of ​​the energy dissipation plate corresponds to at least 80% of that of the impact plate; the material of the impact plate has a Vickers hardness greater than 3 GPa, preferably greater than 5 GPa, more preferably greater than 10 GPa; the apparent density of the impact plate is less than 10 g / cm³, preferably less than 7 g / cm³, preferably less than 5 g / cm³, preferably less than 3.2 g / cm³, preferably less than 3.0 g / cm³ and / or greater than 1.0 g / cm³;The impact-resistant plate material is a sintered material comprising grains, preferably made of a metal carbide or a metal boride. Preferably, the grains are silicon carbide or boron carbide grains, or a mixture of these two carbides; in one possible embodiment, the grains are exclusively silicon carbide grains, optionally with a metallic phase, preferably comprising silicon; in one possible embodiment, the grains of said sintered material are bonded by a matrix comprising or consisting of a silicon nitride (Si3N4) phase and / or a silicon oxynitride (Si2ON2) phase and / or SiAlON; in one possible embodiment, said grains of said sintered material are bonded by a matrix which preferably represents between 5 and 40% by mass, and preferably between 15 and 35% by mass, of the mass of the impact-resistant plate material;said impact-resistant plate is bonded to said energy-dissipating plate by means of an adhesive selected from, for example, polyurethane-based, epoxy polymer, thermoplastic polymer, or elastomer-based adhesives; said shielding plate is surrounded by a containment material.

[0014] According to a third general aspect, the armor plate according to the invention, comprising said impact energy dissipation plate, is covered at least partially, preferably completely, with an external envelope of a containment material, for example in the form of a textile, for example a fabric, comprising glass fibers, or carbon fibers, or polyethylenes PE, in particular ultra-high density polyethylenes (UHMWPE), or aramid, in particular Kevlar®, or metal such as aluminum or even steel, in particular in the case of non-personal protection.

[0015] The present invention also relates to a method for manufacturing said damping material for a dissipation plate as previously described or of a dissipation plate as previously described, said method comprising the following steps: 1) preparation, preferably by weaving, of at least one fibrous layer comprising silica fiber yarns with a mass content greater than 90% SiO2 so as to obtain a reinforcement comprising at least 50% by volume of said yarns; 2) preparation of a mixture comprising a thermosetting resin whose viscosity, measured using a plate-on-plate rheometer with a diameter of 20mm and an air gap of 1mm, is between 80 and 300 Pa.s for a shear rate of 100 to 200 s-1 at 50°C; 3) impregnation of each fibrous layer by said mixture and stacking of each layer so as to obtain a preform in which the volumetric ratio of fibrous reinforcement of said damping material is between 20% and 70%; 4) Baking the preform in an autoclave at controlled pressure and temperature in order to polymerize and crosslink said resin and form a reinforcement bound by an organic matrix constituting said damping material.5) possibly shaping said damping material thus obtained into a plate, in particular by cutting or deburring.

[0016] Various preferred embodiments of the present invention are described below, which can obviously be combined with each other where appropriate: The organic matrix resin is a thermosetting resin selected from phenolic resins; epoxy resins; polyimide resins; polyurethane; or their derivatives, or a mixture of these products. The resin additives are selected from: a catalyst, a reinforcing agent, a release agent, and a hardener. The resin mixture represents at least 30%, preferably more than 35%, preferably more than 40%, and less than 70%, preferably less than 60%, preferably less than 55%, by mass based on said mixture from step 2. The resin is preferably an epoxy resin. The epoxy equivalent weight of said resin, measured according to ASTM D1652, is greater than 200, preferably greater than 220. This is the mass in grams of resin required to provide one mole of epoxy group.A lower weight results in a resin with a higher bonding surface area to the silica fibers of the fibrous reinforcement, and a dissipative material with lower porosity. The preform is preferably baked at less than 200°C between 1 and 5 bar. Preferably, it comprises a first stage with a holding period between 80 and 120°C and preferably a second stage with a holding period between 130 and 180°C.

[0017] The present invention also relates to the use of a dissipation plate or an armor plate as previously described as ballistic protection: of a person, said protection being chosen from a bulletproof vest, a helmet, or of a land, sea or air vehicle, or of a fixed installation chosen from a building, a perimeter wall, or a guard post, or of a radome or of detection or communication equipment, in particular optronic equipment.

[0018] Such a use can be implemented, without departing from the scope of the invention, in the form of a plate, a tile, a mosaic, for example in the form of hexagons or nodules, a breastplate, a shield, a helmet, a door, a seat, a tube.

[0019] The following indications and definitions are given below, in relation to the preceding description of the present invention: A "fiber" is a structure oriented in one direction and made of the same material, with a length greater than 5 times its equivalent diameter. A "long fiber" is a fiber with a length greater than 1 mm and less than 10 mm. A "continuous fiber" is a fiber with a length greater than 10 mm. A yarn is made up of several fibers. A "long yarn" is a yarn made up of long fibers. A "continuous yarn" is a yarn made up of continuous fibers with a length greater than 10 mm. The equivalent diameter of a fiber or yarn is the diameter of a disk with the same area as its cross-section at half its length. A "single yarn" is an assembly of fibers that, in cross-section, has more than 10 and preferably fewer than 500,000 fibers, and whose length is greater than 5 times its diameter.The fibers are assembled so that they are either wound or not upon themselves according to a twist level S or Z, depending on the direction of winding, and whose index from 0 to 30 corresponds to the number of turns per meter. A twist level Z 0 corresponds to a yarn whose fibers are not wound and are arranged parallel to each other. A "staple yarn" is an assembly of single yarns which, in cross-section, preferably contains more than 2 and preferably fewer than 500 single yarns. A parallel assembly of single yarns after warping to align them (or "staple yarn") is also a secondary assembly.A textile can be: an organized structure of yarns, single or joined, such as a knit, braid, canvas, or fabric; or a random structure of yarns, single or joined, such as a voile, and / or of fibers not incorporated in the form of yarns. Such a random structure could be, for example, paper or felt, although a random structure is not preferred. The weave of a canvas or fabric refers to the way in which the yarns intersect, thus contributing to defining a particular pattern. Equivalent grain diameter is defined as half the sum of the longest grain and the widest grain, measured in a direction perpendicular to the longest grain.The maximum and average equivalent diameters of particles, fibers, or yarns are conventionally determined by observing the material's microstructure, typically using scanning electron microscopy (SEM) images of a cross-section of said material. The term "matrix" refers to a crystalline or non-crystalline phase that provides a substantially continuous structure between the grains, or fibers or yarns in the case of a fibrous material. This matrix is ​​obtained from the constituents of the initial filler and may undergo heat treatment. A matrix substantially surrounds the grains, or fibers or yarns in the case of a fibrous material; that is, it encases them. In an organic matrix composite, such as the damping material according to the present invention, the fibrous reinforcement is bonded by a thermosetting resin matrix.It is obtained by impregnating a fibrous textile with a resin mixture comprising at least one or more prepolymers, a hardener, and preferably a catalyst and a reinforcing agent, or even a release agent, followed by baking or a heat treatment to harden the resin, thus polymerizing and cross-linking it to form a thermosetting resin matrix. In a sintered ceramic body, such as an impact-resistant plate, the ceramic grains are bound together by the matrix obtained by sintering a preform. During sintering, they retain essentially the shape and chemical composition they had in the initial feedstock. In the sintered ceramic body, the matrix and the grains together represent 100% of the product's mass. Apparent density, as used in the present invention, is defined as the ratio of the product's mass to its volume.It is classically determined using Archimedes' method. ISO 5017, for example, specifies the conditions for such a measurement. This standard also allows for the measurement of the open porosity of a ceramic material. The porosity of the damping material is measured according to ASTM D3171-15.

[0020] In particular, the volumetric fiber reinforcement ratio Tf is the percentage ratio between the apparent volume of fibers and the apparent volume of the damping material. It is calculated using the following formula: Tf = Vfibres Vcomp = Mfibres × dcomp Mcomp × dfibres Or : V fibers is the apparent volume of fibers, M fibers is the mass of fibers, d fibers is the density of fibers, V comp is the apparent volume of the damping material, M comp is the mass of the damping material, d comp is the density of the damping material

[0021] The mass of the composite can be measured by simply weighing the damping material, the apparent density of said material being determined by hydrostatic weighing according to Archimedes' principle.

[0022] The mass of the fibers can be determined after combustion / digestion of the resin according to ASTM D3171-15. The apparent density of the fibers can then be determined by hydrostatic weighing. - The pore width of the damping material is measured by scanning electron microscopy image analysis. - The SiO2 mass content of the silica fibers in the reinforcement can be measured by X-ray fluorescence. - The phase composition of the material constituting the impact plate is normally obtained by X-ray diffraction and Rietveld analysis. Elemental nitrogen (N) content in the sintered products was measured using LECO analyzers (LECO TC 436DR; LECO CS 300). Values ​​are given as mass percentages. Crystalline phases, particularly nitrogen-containing or residual metal crystallized phases, can be determined by X-ray diffraction and quantified using the Rietveld method.- The Vickers hardness of a material can be measured using a standardized diamond pyramidal point with a square base and apex angle between faces of 136°. The resulting indentation 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 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]

[0023] The force and duration of the support are also standardized. The applicable reference standard for ceramic materials in particular is ASTM C1327 "Standard Test Method for Vickers Indentation Hardness of Advanced Ceramics". The median diameter or median size of a set of particles, particularly a powder, is defined as the 50th percentile (D50). This is the size that divides the particles into first and second populations equal in volume, these first and second populations consisting only of particles larger or smaller than the median size, respectively. A constituent present in the initial feed and still present in the sintered product obtained from this initial feed is called a "residual." Impurities are understood to be unavoidable constituents, introduced unintentionally and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but merely tolerated. "Containing," "comprising," or "featuring" means "containing at least one," unless otherwise specified.

[0024] Unless otherwise stated, in this description all percentages are mass percentages.

[0025] Unless otherwise stated, all averages are arithmetic means.

[0026] There figure 1 shows a scanning electron microscope view of a cross-section of the damping material of Example 3 according to the invention, the reinforcement of which consists of several plies or layers (A, B, C, D) of fabric. The fabric is made of silica fibers 1a and 1b assembled into single yarns. The silica fiber yarns are formed into a network with warp yarns (made up of the 1a fibers) and weft yarns (made up of the 1b fibers), substantially perpendicular to each other, as shown by the figure 1The wires are coated with matrix 2 made of a resin. Porosity is present within the matrix and at the interface between the wires in the form of pores 3 with an average width of approximately 3 micrometers.

[0027] The product according to the invention allows, depending on the configurations chosen, protection against different types of projectiles, for example a bullet, a shell, a mine or an element projected during the detonation of explosives, such as bolts, nails (or IED for "Improvised Explosive Device") and normally constitutes an armor element for vehicles or as protection for people, fixed installations or communication equipment, generally in the form of modules such as plates.

[0028] Under the impact of projectiles, as is known, an armor plate fragments to absorb the projectile's impact energy. When the projectile has high penetrating power, an impact-absorbing plate is necessary, placed between the threat and an impact energy dissipation plate. The primary role of the impact-absorbing plate is to break the core of the projectile upon contact with the armor plate. The role of the energy dissipation plate is to absorb the kinetic energy from the projectile's impact through plastic deformation and to maintain a level of containment for the armor plate, advantageously optimized by a containment envelope.Within the framework of the present invention, the applicant company has thus developed a new damping material for an armor plate capable of resisting, for example, a 0.30-0.6-APM2 type threat, the damping material having a mass-to-surface ratio typically less than 20 kg / m². This results in a reduction of the total weight of the armor, for the same level of protection.

[0029] The different stages of a process according to the invention are described in more detail below. Preparation of the fibrous reinforcement:

[0030] Preferably, fabrics are chosen from among those of the 2D or UD type. These fabric weaves exhibit the best ballistic performance. In particular, the satin weave is the most preferred because this type of fabric has fewer warp and weft intersections, which can constitute potential points of weakness in the reinforcement. Among the Q600 to Q660 silica fiber fabrics supplied by Saint-Gobain Quartz, these are preferred because they have a basis weight greater than 350 g / m². Resin preparation:

[0031] The resin mixture is chosen from a resin whose behavior is preferably shear-thinning. In other words, its viscosity decreases as the shear stress increases within a certain range. The following range is particularly suitable for the implementation and production of the damping material according to the invention. The resin preferably exhibits the following rheological behavior, measured using a plane-on-plane rheometer with 20 mm diameter plates and a 1 mm gap, at 50°C: Shear rate (s -1< ) Dynamic viscosity (Pa·s) 100 100 à 300 200 80 à 150 >400 and <500 <80

[0032] To achieve optimal processing conditions for the composite damping material, particularly an optimal impregnation time, the resin preferably exhibits the following rheological behavior, measured using a plane-on-plane rheometer with 20 mm diameter plates and a 1 mm air gap at 50°C by oscillation for 3 hours at a frequency of 2 Hz for a strain of 0.1%: after 3 hours, the resin preferably has a viscosity of less than 400 Pa·s. Preferably, the viscosity variation between 1 and 3 hours is less than 10%, and preferably less than 5%.

[0033] Reinforcement impregnation and pre-impregnation formation: When the reinforcement consists of several layers of textile or several plies of fabric, the resin is generally too viscous at room temperature to be able to impregnate several layers already stacked, it is preferable to pre-impregnate each layer of textile or ply of fabric before being able to stack them.

[0034] The resin mixture is first heated to a processing temperature at which its viscosity is preferably below 400 Pa·s with a shear rate of 200 s⁻¹, preferably at a temperature of around 50°C. A film of the resin mixture is deposited onto a Teflon tray heated to the previous processing temperature. The reinforcement layer, preferably a ply of fabric, is deposited on the tray, and then a second film of resin is deposited on top of the reinforcement layer. Light pressure is applied to the pre-impregnated material to facilitate impregnation of the fabric. The pre-impregnated material is then placed in a sealed bag, which, if necessary, is kept in a freezer before being used for the next step after thawing to promote separation from the Teflon tray.

[0035] This first step can be repeated as many times as there are reinforcement layers to be superimposed in order to form a stack of layers when the reinforcement consists of several layers.

[0036] Preferably, the pre-impregnated preform thus obtained is then placed in a vacuum bag, maintained at less than 1 bar before cooking. Cooking the pre-impregnated product:

[0037] The preform is then placed in an autoclave to apply a temperature and pressure cycle.

[0038] During this curing stage, the initial temperature ramp-up, with a fluidization plateau between 50 and 150°C and a pressure increase up to 2 bar, advantageously facilitates the expulsion of any potential gas release and ensures the most uniform distribution of the resin possible. The subsequent temperature increase beyond the crosslinking temperature of the thermosetting resin allows for resin polymerization and the formation of the matrix encapsulating the reinforcement. Selecting a resin within the claimed viscosity range advantageously yields a damping material according to the invention with a controlled pore volume. Choosing a resin with the workability conditions described above advantageously yields a damping material with a controlled pore width distribution. Impact-resistant plate:

[0039] The impact-resistant plate of the armor plate according to the invention, if present, can be obtained in particular by a process comprising the following steps: a) preparation of a starting charge comprising: at least one powder of silicon carbide particles, a powder including metallic silicon, optionally a powder of a solid phase sintering additive, b) shaping of the starting charge into a preform, c) demolding after hardening or drying, d) optionally, drying of the preform, preferably until the residual moisture is between 0 and 0.5% by weight, e) baking and sintering of the preform under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting charge, preferably at a temperature between 1300 and 1600°C, so as to obtain the sintered product constituting the impact-resistant plate.

[0040] In such a process, at step a) at least one initial silicon carbide powder is used, the median particle diameter of which is between 10 micrometers and 500 micrometers, and preferably between 50 and 300 micrometers. In some advantageous embodiments, a second silicon carbide powder is used, the median particle size of which is at least half that of the first, and preferably the average diameter of which is between 1 and 5 micrometers.

[0041] In step b), the preform can be obtained by pouring or pressing the charge or mixture into a mold, with or without vibration.

[0042] During firing in step e), the nitrogen from the firing furnace reacts ("reactive sintering") with some of the constituents of the preform, in particular with metallic silicon or even with metallic aluminum if it is present alone or as an alloy with silicon, also with calcined alumina or an aluminum silicate for example clay if these additions are present, to form a matrix and thus bind the grains of the ceramic body.

[0043] In the impact-resistant plate of the armor plate according to the invention, the ceramic grains, preferably silicon carbide and / or boron carbide grains, can be bonded by a matrix comprising a SiAlON phase without the addition of rare-earth compounds and without resorting to a high sintering temperature, i.e., a temperature above 1650°C. In particular, firing a preform comprising metallic aluminum alone or as an alloy with silicon under a nitrogen atmosphere between 1300 and 1500°C for a sufficiently long holding period (>4 hours) makes it possible to obtain an impact-resistant plate made of a sintered material having a residual metallic Al and Si mass content of less than 1%.

[0044] The initial mixture may also include a fraction of an alumina powder with a median diameter between 1 and 10 micrometers, serving as a sintering agent.

[0045] The impact-resistant plate of the armor plate according to the invention is in particular obtained by a process as described above, preferably in the presence of a sintering additive chosen from carbon, boron carbides, titanium, zirconium or zirconium borides, titanium, alone or in mixture.

[0046] In a particularly preferred embodiment, the product is obtained by a process as described above, wherein the sintering additive comprises or consists of boron carbide B4C. The term sintering additive, often simply referred to as "additive" in this description, means a compound commonly known to enable and / or accelerate the kinetics of the sintering reaction. In one embodiment, the starting feed contains a binder and / or a lubricant and / or a surfactant. In another embodiment, the starting feed does not contain a binder.

[0047] The mixing is carried out in such a way as to obtain a good homogeneity of distribution of the different elements, the mixing time being able to be adapted to achieve this result.

[0048] Preferably, the initial reagents are mixed in a jar mill, with a mixing time exceeding 15 hours. A mixing time of 24 hours is well-suited. Once the mixture is obtained, it can be atomized or granulated, for example by freeze granulation, to obtain granules that will be shaped, for example by pressing, to obtain a ceramic preform. Other shaping techniques can be used, such as injection molding or slip casting. After shaping, the preform can be machined.

[0049] The preform is then sintered. Sintering takes place under a nitrogen atmosphere.

[0050] Preferably, the silicon carbide powder has an oxygen content of less than 2%, preferably less than 1.6%, preferably less than 1.4%, preferably less than 1.2%, preferably less than 1%, or even less than 0.7%, or even less than 0.5%, or even less than 0.3% by weight. In one embodiment, the oxygen content of the silicon carbide powder can be reduced before use by any technique known to those skilled in the art, such as acid washing.

[0051] In one embodiment, the aluminum content of the starting charge is less than 1000 ppm, or even less than 500 ppm or even less than 300 ppm, relative to the weight of the starting charge.

[0052] The cooking takes place under a controlled atmosphere, preferably under nitrogen to obtain the nitrided intergranular phase.

[0053] 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:

[0054] Except for example 1, whose damping material is a commercially available composite, each example was constructed using a stack of 18 to 19 layers of resin-impregnated fabric (to maintain a constant surface density), followed by an autoclave heat treatment. This included a holding period at 100°C under 2 bar, followed by a curing stage with a 3-hour holding period at 160°C. The result was two damping plates for each example, each with a surface area of ​​approximately 150 × 150 mm². The thickness was adjusted to allow for comparison of the final shielding plates for all examples, with a surface density of 42 ± 1.5 kg / m². For all examples, each of the damping plates was glued using Elantech 891-892 epoxy glue supplied by the company Elantas onto a SiC ceramic plate with a hardness greater than 10 GPa measured according to the ASTM C1327:03 standard and with dimensions of 100x100x10mm 3< in order to make 2 final shielding plates. Example 1 (comparative):

[0055] In the case of this example, the impact energy dissipation plate is a reference damping material HB26 Dyneema ®< marketed by the company DSM as cited in US2013 / 0220106A1. Example 2 (comparative):

[0056] The damping material in comparative example 2 is made from a fibrous reinforcement in the form of a 500 g / m² fabric composed of Quartzel® yarns. Each single yarn consists of 20 silica fibers with a mass content exceeding 99% SiO₂ and an average equivalent diameter of 9 micrometers. The yarns, with a linear density of 667 tex and a torsion coefficient of Z3, are assembled into a regular satin weave of 8 with a 3 notch, the yarn interlacing being perpendicular.

[0057] The matrix in Example 2 was obtained from an epoxy resin mixture comprising, by mass: 73% of a mixture of 3 different epoxy prepolymers (composed of at least 70% of a digicidyl ether-based prepolymer of bisphenol A) having an average epoxy equivalent weight of 180 grams, 3% of a hardener in the form of a micron-sized dicyandiamide powder, 18% of a reinforcing agent in the form of a polyphenylene ether resin with the formula Poly(2,6-dimethyl-1,4-phenylene ether), and 6% of a modified imidazole catalyst supplied by Curezol®. The dynamic viscosity of the resin measured at 50°C for a shear rate of 200 s⁻¹ under the conditions described above is 50 Pa·s. Example 3 (invention):

[0058] The matrix of Example 3 according to the invention differs from the previous formulation in that the components of the epoxy prepolymer have been modified to incorporate approximately 50% by mass of an epoxy prepolymer obtained from cashew nut shell oil. The new epoxy prepolymer consists of a mixture of two resins having an average equivalent weight of 253 grams of epoxy. The viscosity of the new mixture of the two epoxy resins, measured under the same conditions as before, is 100 Pa·s. Example 4 (comparative):

[0059] Comparative example 4 differs from example 3 according to the invention in that one warp and one weft out of 2 is replaced by an assembled yarn of Lincore ®< flax fibers with a linear mass of 500 tex, the final reinforcement having a basis weight of 500 g / m 2<, 43% of the mass being represented by flax yarns for 57% by pure silica yarns. Example 5 (comparative):

[0060] Comparative example 5 differs from example 3 in that the proportion of matrix has been halved. Example 6 (comparative):

[0061] Comparative Example 6 differs from Example 3 in that the resin exhibits a viscosity greater than 300 Pa·s and less than 500 Pa·s for a shear rate of 200 s⁻¹ at 50°C, measured under the same conditions as before. The ballistic properties of each final armor plate are summarized in Table 1 below. The ballistic performance of the different armor plates was evaluated using measurements of the dynamic deformations on the rear face, which correspond to the elastic deformations of the damping materials during impact. Each armor plate was tested on blocks of Sueur 40 plasticine with a Shore A hardness between 15 and 19 against single impacts fired at their center. The shots were fired at the SiC face of the different armor plates in a stand-alone configuration. The tests were conducted under threat conditions.A 30-06 AP M2 was fired at its nominal velocity of 878 ± 9 m / s from a distance of 15 meters. On each block of plasticine, the depth and diameter of the deformations left by the damping plate at the point of impact were measured using calipers. These indicators characterize the dynamic deformations of the damping plates resulting from the impact. An arithmetic mean was calculated for each example. The presence of a "P" perforation in Table 1 indicates significantly reduced ballistic performance associated with diminished damping capacity.

[0062] The results reported in Table 1 below show that: Compared to those of the commercial material of comparative example 1, the dissipation plates of example 3 according to the invention exhibit, at equivalent surface density, a deformation depth reduced by one third and a deformation diameter increased by 20%, which shows a significantly higher ability to dissipate energy compared to the reference product on the market.

[0063] Example 3, by comparison with examples 2 and 4, shows that the material whose reinforcement and matrix were selected according to the invention, exhibits a higher ability to dissipate energy.

[0064] Comparative example 5 shows that a reinforcement volume ratio exceeding 80% reduces ballistic performance. Comparative example 6 shows that a damping material made with an excessively viscous resin results in excessive porosity and consequently reduced ballistic performance. [Table 1] Comparative Example 1 Comparative Example 2 Example 3 invention Comparative Example 4 Comparative Example 5 Comparative Example 6 Mass distribution (%) of the reinforcement and matrix of the damping material Mass fraction of silica wire (%) N / A 57,6 52,6 28,7 >80 67 Mass fraction of flax fibers (%) 0 0 21,7 0 0 Mass fraction of resin (matrix) (%) 42,4 47,4 49,6 <20 33 Resin viscosity in Pa.s* 50 100 100 100 >300 and <500 equivalent weight of epoxy (g / eq) 180 253 253 253 350 Characteristics of the damping material of the armor plate Average thickness (mm) 14 8,5 9 10 9 9,5 Volumetric fiber reinforcement rate (%) >80 40 36 38 >75 50 Volume percentage of silica fibers in the reinforcement (%) 0 100 100 < 30 100 100 Porosity x of the damping material (%) <2 <2 2<x<5 2<x<5 >5 13 MVA of the damping material (g / cm³) 0,97 1,57 1,63 1,43 > 1,3 1,52 Density of the matrix resin (g / cm³) 0,9-1,3 1,1 1,1 1,1 1,1 1,1 Reinforcement weight (g / m²) NM 500 500 440 500 500 Linear mass of the reinforcement yarns (tex) NM 667 667 667 / 500 667 667 Equivalent average fiber diameter (µm) 17 9 9 9 9 9 Average pore width (µm) NM < 3 3 3 >5 >5 Wire twist rate (Z) Z0 Z3 Z3 Z3 Z3 Z3 Ballistic performance (dimensions in mm) at equal surface density Average deformation depth 24 P 16 P P P Average deformation diameter 60 P 72 P P P NA = not applicable; NM = not measured; P = perforation; *at 50°C and shear of 200s -1<; MVA = apparent density;

[0065] 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.

Claims

1. An impact energy dissipation plate for anti-ballistic armor, said dissipation plate consisting of a damping material consisting of a fibrous reinforcement bonded by an organic matrix, said reinforcement comprising inorganic fibers assembled in the form of yarns, said matrix comprising a thermosetting resin, said damping material having the following features: - the volume fraction of fibrous reinforcement of said damping material is between 20% and 70%, the remainder to 100% consisting of said matrix and porosity; - the fibrous reinforcement comprises at least 50% by volume of silica fiber yarns of which SiO2 content by mass is greater than 90%; - the porosity of said damping material is between 2% and 10% by volume.

2. The dissipation plate according to the preceding claim, wherein the bulk density of said damping material is greater than 1.0 g / cm3 and less than 2.0 g / cm3.

3. The dissipation plate according to one of the preceding claims, wherein the linear mass of said yarns is greater than or equal to 500 tex.

4. The dissipation plate according to one of the preceding claims, wherein the average equivalent diameter of the silica fibers constituting said yarns is greater than or equal to 3 micrometers and / or less than or equal to 20 micrometers;5. The dissipation plate according to one of the preceding claims, wherein said fibrous reinforcement consists substantially of said silica yarns.

6. The dissipation plate according to one of the preceding claims, wherein the reinforcement is in the form of at least one layer of a textile, preferably a woven fabric, consisting of a network of parallel warp yarns, with preferably weft yarns running transversely through said network.

7. The dissipation plate according to the preceding claim, wherein the grammage of said textile layer is greater than or equal to 350 g / m2.

8. The dissipation plate according to one of the preceding claims, wherein said matrix has, between said resin and said yarns, pores with an average width of between 10 and 100% of the average equivalent diameter of said fibers.

9. The dissipation plate according to one of the preceding claims, wherein said matrix comprises an epoxy resin.

10. An anti-ballistic armor plate comprising an impact energy dissipation plate according to one of the preceding claims.

11. The armor plate according to the preceding claim, further comprising an anti-impact plate consisting of a material with a hardness greater than that of the damping material, said anti-impact plate having a thickness greater than 2 mm, said anti-impact plate being placed in front of said dissipation plate, with respect to the direction of impact.

12. The armor plate according to the preceding claim, wherein the material of the anti-impact plate has a Vickers hardness greater than 3 GPa.

13. The armor plate according to one of the two preceding claims, wherein the bulk density of the anti-impact plate is less than 10 g / cm3.

14. The armor plate according to one of claims 10 to 13, wherein the material of the anti-impact plate is a sintered material comprising grains of silicon carbide or boron carbide or a mixture of these two carbides.

15. The armor plate according to the preceding claim, wherein the grains of said sintered material are bonded by a matrix comprising a phase of silicon nitride Si3N4 and / or Si2ON2 and / or SiAlON.

16. The armor plate according to one of claims 10 to 15, wherein said anti-impact plate is bonded to said energy dissipation plate by means of an adhesive selected from adhesives based, for example, on polyurethane, epoxy polymers or thermoplastic polymers or elastomers.

17. A method for manufacturing a damping material for a dissipation plate according to one of claims 1-9 or an dissipation plate according to claims 1-9, said method comprising the following steps: 1) preparing, preferably by weaving, at least one fibrous layer comprising yarns of silica fibers with a mass content greater than 90% SiO2 so as to obtain a reinforcement comprising at least 50% by volume of said yarns; 2) preparing a mixture comprising a thermosetting resin of which the viscosity, measured using a 20 mm-diameter plate / plate rheometer with 1 mm air gap, is between 80 and 300 Pa.s for a shear rate of 100 to 200 s-1 at 50°C; 3) impregnating each layer with said mixture, and stacking each layer so as to obtain a preform wherein the volume fraction of fibrous reinforcement of said damping material is between 20% and 70%; 4) curing the preform in an autoclave at controlled pressure and temperature to polymerize and crosslink said resin and form a reinforcement bonded by an organic matrix constituting said damping material.

18. Use of a dissipation plate according to claims 1 to 9 or an armor plate according to claims 10 to 16 as antiballistic protection: - of a person, said protection being selected from a bullet-proof vest, a helmet, or - of a land, sea or air vehicle, or - of a stationary installation chosen from a building, a perimeter wall or a guardhouse, or - of a radome or of detection or communication equipment.

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