FR2945338A1 - ENERGY ABSORPTION DEVICE IN SANDWICH COMPOSITE MATERIAL WITH ORIENTED BRIDGES - Google Patents

Abstract

The object of the invention is a protection device against high-energy pressure waves resulting from the blast and / or low energy waves resulting from shocks at low speed, characterized in that it comprises a succession of at least three layers of composite material (31) forming a monolithic part, at least one of these layers comprising: - a skin (51) consisting of a 2D and / or 3D woven reinforcement embedded in a resin, - a core ( 52) of foam, - a skin (53) consisting of a 2D and / or 3D woven reinforcement embedded in a resin, and - bridges made from wires (54), passing through the core (52) and connecting the skins (51,53).

Description

The present invention relates to a power absorbing device of oriented bridge sandwich composite material. It is applicable for example for the protection of vehicles or buildings against attacks of the type blast, impact, crash, shock, accidental explosion ....

A protection solution consists in equipping the structures with an additional protection panel that can resist the forces generated by a mine explosion, a blast, a crash, an impact and / or deforming in order to absorb a part of the energy due to aggression.

Energy absorbing devices equip various types of structures or materials. As an example for vehicles: Military vehicles (armored or non-rolling vehicles, or ships) likely to evolve into hostile territory, on reconnaissance missions for example, are equipped with a protection against the breath, mine and / or or impacts. It is the same for civil vehicles for which a protection absorbing the energy of a crash, a blast and the associated projectiles is used (trams, trains, buses, cars ...) As an example for Materials: Protective enclosures containing dangerous materials (ie ammunition, parcel bombs or pressure vessels), which may be in a place endangering the safety of persons, shall be fitted with protective energy and any projected projectiles. The primary purpose of these devices is to effectively protect against attacks involving high or low pressure waves, including low-speed blast or shock by absorbing the majority of the energy of aggression by deformation and rupture of the device.

State of the art: The current protections for blast-type aggression, explosions, mines are varied and divided into two families of solution. A first solution, described in patents EP0897097, WO2004088238, WO2006105280 is a device consisting of sandwich panels made by insertion of a deformable material such as a thickness of foam, and / or plastic sheets, and / or 2945338 -2- type structure honeycomb, between two rigid metal panels or organic materials (woven reinforcements and matrix for example, or polyurethane). A second solution described in the patents FR2867554, FR2854685 is a device of particular shape to deflect the breath due to the explosion 5 of a mine or other supporting high stresses. These devices are advantageous in the case of directed aggression, mine type but unusable for mufti-directional aggression.

The current protections for impact, crash, and shock attacks are diverse and varied. A first solution, described in the patent EP0955211, is a device for assembling absorbent materials whose absorption capacities are greatly increased with respect to their unit capacity when associated, for example association of ePTFE and a typical elastomer EVA. A second solution, described in EP1404549, is a device 15 of deformable composite material, such as honeycomb structures, which is compressed under impact, impact or crash, crashing.

A major disadvantage of these protection principles is that for each type of aggression (from the strongest to the least important) a device is associated with it. The principles of protection against blast are difficult to adapt for very low energy shocks, and vice versa. Another disadvantage for protection against the breath, mine or explosion is their weight and low maneuverability because they involve metal materials. In particular, the materials constituting these panels as well as their necessary thicknesses give the assembly a significant weight coupled with a lack of flexibility of use. Another disadvantage, directly related to the previous one, lies in the lack of adaptation of these devices to more or less complex forms. Due to the nature of the materials used, forming and forming with radii of curvature is not possible, which limits the possible forms, in particular rounded shapes with small radius are excluded.

Description of the invention: One of the objectives of the invention presented is in particular to overcome the aforementioned drawbacks in terms of: • adaptability of the absorbency to the intensity of the energy to be absorbed 5 • weight reduction • possibility of implementation In this case, the invention adds an excellent capacity for absorbing and dissipating the energy generated by strong energies. low pressures

The subject of the invention is a device for protecting energy absorption, comprising at least three layers of oriented bridge sandwich materials forming a single piece obtained by resin transfer molding. According to one characteristic of the invention, the device is a succession of layers composed of oriented bridges. The basic principle of the energy absorber which is the subject of this patent is based on the energy dissipation by breaking oriented bridges, successive layers. In the first layer the sandwich is for example composed of an assembly of two-dimensional woven fibers, the warp and weft forming between them an angle less than or equal to 90 °, a structural foam core material, of woven fibers in three dimensions. This assembly is secured via a 3D bypass, passing through the foam from one side to the other. In a particular embodiment, the first layer, oriented towards the pressure wave, is composed of aramid fiber fabric and / or glass fibers.

The second sandwich layer is for example composed of woven fibers in two dimensions, the warp and weft forming between them an angle less than or equal to 90 °, positioned on each face of a non-structural foam of core material, assembly is assembled via 3D bridging. The fabrics may be glass fibers. The third sandwich layer is for example composed of woven fibers in two dimensions, the warp and weft forming between them an angle less than or equal to 900, positioned on each side of a structural foam of core material, the assembly is assembled via 3D bridging. The fabrics may be glass fibers.

The central layer plays the role of energy absorber. The other two layers assume the role of force distributor to increase the performance of energy absorption.

Each layer comprises a stack of materials, the number of layers of fabric and the thickness of the core depending on the desired thickness. In a particular embodiment, the thickness of the third layer is half the thickness of the first layer. The thickness of the second layer 15 is at least three times the thickness of the third layer. The density of bridges, the orientation and the height of the bridges is dependent on the energy to be absorbed. The number of total layers is dependent on the energy to be absorbed. The minimum number is three. Depending on the energy this minimum number is increased by a multiple of 2 layers. For example, for a stack of five layers, the first three are those described above to which is added a fourth layer close to the second layer described. The fifth layer will be close to the third described. The materials of the 3D bypasses may be glasses or flax fibers. Advantageously, the resin may be a phenolic resin.

Other features and advantages of the invention will become apparent from the following description made with reference to the accompanying drawings which show: FIG. 1a and 1b, an example of an energy absorption panel according to the prior art previous; FIG. 2, an example of assembly of panels of the type of FIG. 1 to form a protective structure; FIG. 3, an exemplary possible embodiment of a protection device according to the invention; FIGS. 4, an illustration of the principle of producing a three-dimensional weave; FIGS. 5, an illustration of the principles of realization of a 3D bridging assembly; Figure 6 is an illustration of the principles of making an N-layer 3D bridge assembly;

Figure la shows an example of energy absorbing panel (1) according to the prior art. This panel comprises several layers 11, 12, 13, 14 juxtaposed, 10 fixed together by adhesive layers of adhesive 10 or studs 15, FIG. The outer layer is for example ceramic material material while the layer 12 is made of steel, the layer 13 of metal sandwich type material or foam, the layer 14 of composite type material. Depending on the thickness, in particular of this layer 12, the panel is more or less heavy.

In all cases of application, its weight is an obstacle. The layers 11, 12 may also during the impact of the projected elements produce rear effects such as splinters. These effects are generally harmful or even dangerous for the environment, especially for people.

FIG. 2 shows an assembly of panels 1 of the type of FIG. 1 for an application of a material 21. The assembled assembly marries as much as possible the shape of this material 21, but in a non-optimal manner. The two panels are interconnected at their slices forming a projecting angle 22 because of the adopted contour.

FIG. 3 shows an exemplary possible embodiment of an energy absorption device according to the invention. The device is represented by a partial sectional view. The part shown is flat but it can advantageously take all kinds of other forms. The panel of FIG. 3 is formed of a stack of monoblock sandwich composite material comprising three integral layers 31, 32, 33 made in the same mold.

The first layer 31 is disposed on the side of the threat, in this case the arrival of the pressure wave 30. This first may be a sandwich layer 2945338 -6- for example, composed of fibers woven in three and / or two dimensions, composed for example of aramid fibers, glass or polypropylene embedded in resin. The fibers are previously dry woven according to a weave in three and / or two dimensions. A foam core spaced apart the woven reinforcements and is necessary to obtain the desired thickness of the resin transfer molded layer 31, as will be described later. Figure 4 illustrates the principle of making a three-dimensional weave, respectively by a sectional view. Classically, meshes cross in three dimensions. The figure shows an example where the warp and weft threads intersect perpendicularly in the plane of the reinforcement thickness. The weaving where the threads cross at an angle of 90 °, in the horizontal plane. Figure 5 illustrates the principle of making a 3D bridging assembly. A thread 54 of fibrous material binds the woven reinforcements 51, for example illustrated in FIG. 4, and the reinforcements 53 through the foam core 52. This thread is composed of several filaments. The material may be, for example, glass, basalt, aramid, flax or polypropylene. The filament density may be for example of the order of 600 to 3000 TeX. The density of bridges and their inclination as well as the distribution of the desired pressure can be determined a priori in order to obtain the desired absorption. The inclination of the bridges can be oriented at an angle less than or equal to 90 °, for example between 45 ° and 90 °.

This first layer may also be, for example composed of woven fibers in three and / or two dimensions, composed for example of aramid fibers, glass or polypropylene embedded in the resin. The fibers are previously dry woven according to a weave in three and / or two dimensions. The stack of reinforcements is necessary to obtain the desired thickness of the layer 31 obtained by resin transfer molding, as will be described later.

The number of superposed reinforcements with or without the thickness of the foam to obtain the desired thickness can be determined a priori. The thickness of the layer 31 may be less than or equal to 20 mm, for example between 5 mm and 20 mm. This first layer makes it possible to distribute the pressure wave, it absorbs a part of the energy. It contains the elements projected by the pressure wave.

The second layer 32 is a sandwich layer, for example composed of two-dimensional woven fibers, composed for example of aramid fibers, glass or polypropylene embedded in resin. The fibers are previously dry woven according to a two-dimensional weave. A foam core spaced apart the woven reinforcements and is required to obtain the desired thickness of the resin transfer molded layer 32, as will be described later. The embodiment of the 3D bridging assembly of the layer 32 is shown in FIG. The filament density may be for example of the order of 300 to 2000Tex. The density of bridges and their inclination to obtain the desired absorption can be determined a priori. The inclination of the bridges can be oriented at an angle less than or equal to 90 °, for example between 20 ° and 90 °. The number of superimposed reinforcements and the thickness of the foam to obtain the desired thickness can be determined a priori. This first layer makes it possible to distribute the pressure wave, it absorbs a part of the energy. It contains the elements projected by the pressure wave. This second layer has a preponderant role insofar as it absorbs the majority of the energy of the pressure wave. Regarding the thickness, it is also adapted to the amplitude of the pressure wave and in particular to its energy. A thickness in the range of 20 to 50 millimeters may be necessary.

The third layer 33 may be a sandwich layer for example composed of two-dimensional woven fibers, composed for example of aramid fibers, glass or polypropylene embedded in resin. The fibers are previously dry woven according to a weave in three and / or two dimensions. A foam core spaced the woven reinforcements and is necessary to obtain the desired thickness of the layer 33 obtained by resin transfer molding, as will be described later. FIG. 5 illustrates the principle of making an assembly with 3D bridging. The filament density may be for example of the order of 600 to 3000 TeX. The density of bridges and their inclination as well as the distribution of the desired pressure can be determined a priori, in order to obtain the desired absorption. The inclination of the bridges can be oriented at an angle (relative to the horizontal plane of the layer) less than or equal to 90 °, for example between 45 ° and 90 °.

This third layer may also be, for example composed of woven fibers in three and / or two dimensions, composed for example of aramid fibers, glass or polypropylene embedded in the resin. The fibers are previously dry woven according to a weave in three and / or two dimensions. The stack of reinforcements is necessary to obtain the desired thickness of the layer 33 obtained by resin transfer molding, as will be described later.

The number of superposed reinforcements with or without the thickness of the foam to obtain the desired thickness can be determined a priori. This last layer makes it possible to distribute the pressure wave, it absorbs a part of the energy. In particular, this third layer 33 cash the residual deformation, 20 stops the pressure wave. It brings in particular the resistance with the continuity of the material, by dissipation of the mechanical stresses in all the back face. The third layer 33 has for example a thickness of the order of half the thickness of the second layer 31. The thicknesses of the layers are adapted to the desired level of protection. Other layers may be added by superimposition to the three layers 31, 32, 33 to adapt the protection to the desired level of protection. Figure 6 illustrates the principle of making a n-layer 3D bridging assembly. The minimum number of layers is three, Figure 3. The layer 61 may be composed by the same principle as the layer 32, illustrated in Figure 5. The layer 33 is added to the layer 61 to close the stack. For example, a stack of five layers will increase the level of protection. The addition of a layer 6n associated with a layer 33 makes it possible to adapt the level of protection. The layer 6n may be composed by the same principle as the layer 32, illustrated in FIG. 5. The technique of implementation for the manufacture of the composite box which is the subject of this patent application uses technology wet way ". The principle of the technique consists of impregnating dry reinforcements with a liquid resin (viscosity that can vary). This impregnation can be performed by RTM injection (with or without vacuum assistance), by infusion (in the plane or transverse), by compression or manual stratification.

The resin used may be epoxy resin or phenolic resin or any other type of resin depending on the desired properties. In the overall assessment of the mass of a device according to the invention, the management of the ratio of reinforcement rate, resin content is a key element in the search for energy absorption. Such a structure provides a very significant weight gain while ensuring good absorbency as demonstrated by the tests and numerical simulations performed by the applicants.

Claims (4)

REVENDICATIONS1. Device for protection against pressure waves CLAIMS1. Protective device against high-energy pressure waves resulting from blast and / or low energy waves resulting from shocks at low speed, characterized in that it comprises a succession of at least three layers of composite material (31, 32,33) forming at least one of these layers comprising: a skin (51) consisting of a 2D and / or 3b woven reinforcement embedded in a resin, a foam core (52), a skin (53) consisting of a 2D and / or 3D woven reinforcement embedded in a resin, and - bridges made from wires (54), passing through said core (52) and connecting the skins (51,53) . 2. Protective device according to claim 1, characterized in that the bridges made from wires (54) are through and inclined at an angle of between 20 ° and 90 °. 3. Protection device according to claim 1 or 2, characterized in that the bridges are made with son (54) of density between 300 and 3000 Tex. 4. Protection device according to any one of the preceding claims, characterized in that it comprises three layers (31,32,33) with each a skin (51), a foam core (52) and a skin (53). ) and bridges made from wires (54), with the thickness of the third layer which is half of the thickness of the first layer and the thickness of the second layer which has a thickness equal to at least three times the thickness of the third layer. Protective device according to any one of claims 1 to 4, characterized in that it comprises five layers with the first three layers (31, 32, 33) each having a skin (51 ), a foam core (52) and a skin (53) and bridges made from wires (54), the fourth layer being substantially identical to the second layer and the fifth layer being substantially identical to the third layer.