FR2988150A1 - ABSORPTION BOX OF ENERGY - Google Patents

Abstract

The invention relates to an energy absorbing buffer box comprising a hollow part (52, 54) made of a composite material and extending in a longitudinal direction, said composite material comprising a matrix of thermoplastic material and a material of fiber reinforcement embedded within said thermoplastic matrix, said hollow part (52, 54) being able to compress irreversibly in said longitudinal direction to absorb shock energy. Said fibrous reinforcement material is a textile material having strands of fibers extended along the three directions of space.

Description

The present invention relates to an energy absorbing buffer box for irreversibly deforming upon impact.

A field of application envisaged is in particular, but not exclusively, that of automobile safety. Energy absorption buffers, commonly known as "crashboxes" under their English name, are well known. They are usually installed at the front of motor vehicles between the side members and the bumper, and when the vehicle encounters an obstacle, the bumper tends to sink while the buffer box deforms and compresses itself. irreversible by absorbing the energy of the shock. Reference can be made to EP 0 361 343, which describes such a buffer box. It comprises two circular section tubes of composite material coaxially engaged one inside the other. These tubes comprise, for example, a matrix made of a thermoplastic material and they have glass or carbon fibers as reinforcing material. The two opposite ends of the tubes are integral, on one side, of the chassis of the vehicle, on the other side, its bumper.

Also, the fibers are embedded in the thickness of the tubes and they extend in a longitudinal direction of the tube. During a frontal collision of the vehicle, the tubes undergo axial stress leading to the destruction of their end. Also, this destruction allows to dissipate energy and to damp, at least partially, the shock.

However, from the first moments of the shock, the deformation of the tube continues, either by folding the tube when the thermoplastic material is not rigid enough, or by a frank break when it is too much, so that the energy dissipation is relatively low. Also, a problem that arises and that aims to solve the present invention is to provide a buffer box including a composite element, which not only the matrix is thermoplastic material, but also allows greater energy dissipation.

For this purpose, the present invention proposes an energy absorption buffer box comprising a hollow part made of a composite material and extending in a longitudinal direction, said composite material comprising a matrix of thermoplastic material and a reinforcing material fibrous material embedded within said thermoplastic matrix, said hollow part being able to irreversibly compress in said longitudinal direction to absorb shock energy. According to the invention, the fibrous reinforcement material is a textile material having strands of fibers extended along the three directions of space.

Thus a feature of the invention lies in the implementation of a three-dimensional textile material, as a reinforcing material and a thermoplastic material as a matrix. A three-dimensional textile material is a textile in which the strands of fibers extend in the three directions of space, that is to say not only following the weft and following the warp of the textile material but also, in a perpendicular direction to the weft and the warp. With this type of material, textile preforms are produced, and after the matrix is used, a composite is obtained whose out-of-plane mechanical properties and crushing behavior is greater than that of the composites obtained using the usual textile materials. two dimensions, which provides benefits that will be described in more detail in the following description. In addition, the use of a thermoplastic material is much easier than the thermosetting polymers epoxy type for example, usually used in the composites, and moreover, it has advantageous possibilities with respect to these thermosetting polymers. Indeed, thermosetting materials are easily reversibly shaped by heating and cooling, while thermosetting polymers are more complex to implement and they crosslink and harden irreversibly. The manufacturing costs of hollow parts using a thermoplastic material are therefore lower. According to a particularly advantageous embodiment of the invention, said textile material has at least two layers of superposed fiber locks and bundles of connecting fibers extending between said at least two layers. Thus, the two layers of superposed fiber strands respectively extend in two perpendicular directions and substantially parallel to each other, while the strands of connecting fibers together connect the two layers and they then extend in a component perpendicular to said two directions perpendicular layers of strands of superimposed fibers. In this way, the fibers of the strands of bonding fibers extend according to the thickness of the textile material, and therefore when the latter is embedded in the thermoplastic matrix, a multiplicity of reinforcement is obtained allowing a progressive rupture of the composite thanks to the multiplication of local breaks. This, of course compared to a conventional textile extending in two dimensions. In addition, the multiplicity of relatively homogeneously oriented fibers in the three directions of the space makes it possible to obtain a composite part having a homogeneous mechanical strength, including out of plane, which is of a nature to avoid unwanted breaks such as delamination out of the area of progressive crushing. When the buffer box is compressed according to a strong acceleration due to a shock, the hollow part of composite material, collapses gradually on itself, and the fiber breaks accompanied by dislocation of the thermoplastic multiply by absorbing large amounts of 'energy. According to a first embodiment of the advantageous invention, said strands of bonding fibers form meshes. Thus, using particular knitting looms, at least two layers of strands of stacked fibers are extended while the strands of fibers of the two layers are connected by means of a mesh. For example, firstly a first layer of strands of fibers is extended in the direction of the warp and a wick layer of fibers perpendicular in the direction of the weft one on the other, and secondly two other layers of cross-fiber wick diagonally. And a mesh is formed enclosing at least three strands of fibers respectively of three different layers. In an alternative embodiment according to this first embodiment, said at least two layers are respectively formed of meshes of said fiber tows. Thus, knitted sandwich textile materials are formed, or the two layers are simultaneously knitted and connected together by a mesh. According to a second embodiment of the invention, said at least two layers are respectively formed of intersecting fiber strands.

Such textile materials are obtained using looms. Thus layers of strands of fibers extended parallel, are superimposed and connected together with strands of son of chains that pass through them. For example, interlock woven fabrics having a plurality of layers of fiber locks, the locks of which are oriented alternately in the direction of the warp and the direction of the weft, the layers of fiber lock being interconnected. by strands of fibers passing through them according to the direction of the chain. In this way, a textile material is obtained having spaces which are repeated both longitudinally and transversely, and also according to the thickness of the material. According to an alternative embodiment, the two layers are respectively formed of wicks of fibers intercrossed by braiding. Reinforcements by sewing, stitching or nailing are also provided. Advantageously, the matrix of thermoplastic material is made of polyamide. This material is relatively inexpensive and is easy to implement. In addition, there are many types with different properties. According to other embodiments, the matrix is made of polypropylene or other thermoplastics. According to a preferred embodiment of the invention, the buffer box further comprises two opposite flanges, while said hollow part has two opposite ends respectively engaging in said flanges. The two flanges are for example metallic or even made of a thermoplastic material. When the buffer box is installed on a motor vehicle having spars and at the end a bumper, the two flanges are respectively secured to a spar and the bumper. Preferably, two buffer boxes are respectively installed between the side members and the bumper.

Advantageously, said hollow part is of tubular shape, and for example of elliptical, square cross section or any other. This makes it possible to obtain a relatively rigid piece. According to an alternative embodiment, the buffer box further comprises another hollow part made of a composite material located inside said hollow part. Preferably, the two hollow parts are mounted one in the other concentrically so as to offer greater mechanical strength. In addition, said hollow parts are advantageously of circular symmetry, which makes them easier to produce.

Other features and advantages of the invention will appear on reading the following description of particular embodiments of the invention, given by way of indication but not limitation, with reference to the accompanying drawings, in which: FIG. 1 is a partial schematic perspective view of an element of the buffer box object of the invention, according to a first embodiment; - Figure 2 and a partial schematic perspective view of the element of the buffer box according to a second embodiment; and - Figure 3 and a schematic axial sectional view of a buffer box according to the invention. Figure 1 illustrates in three dimensions and partially a textile material type "Interlock" 10 which extends over three dimensions. This type of material is obtained by means of a suitable loom. It has three layers 12, 14, 16 of strands of fibers 18 oriented in the direction of the chain F and four layers 20, 22, 24, 26 interspersed with strands of fibers 28 crossed and oriented in the direction of the frame T. strands of bonding fibers 30 pass through a vertical component, with respect to the weft direction and the warp direction, the seven layers of strands of fibers 12, 14, 16, 20, 22, 24, 26 forming corrugations in the direction of chain. The bonding fibers 30 hold the fiber wick layers together. In this way, a textile material is obtained having contiguous free spaces 32 between the fiber locks and succeeding both in the direction of the chain F and in the direction of the weft T, but also in a vertical direction V perpendicular to the first two. Thanks to such a textile material 10, a preform is produced which will be described in more detail in the following description and this preform is embedded in a thermoplastic matrix. Also, the thermoplastic material fills all the contiguous free spaces 32 of the textile material. According to another alternative embodiment, illustrated in Figure 2, is carried out here by means of a knitting machine, a textile material with meshes 34 having diagonal frames.

Also, the textile material 34 has two superimposed layers 36, 38 of diagonal weft fibers 40, 42 and meshes 44 of strands of warp fibers 46, for connecting together the weft fibers diagonally 40, 42. In the same way, a three-dimensional textile material having a smaller thickness than the textile material 10 illustrated in FIG. 1 is obtained. However, it has contiguous spaces 48 in which the thermoplastic matrix is able to be housed. . The fibers of the fiber locks may be carbon, fiberglass, aramid or other technical fibers. The fiber locks may be totally or partially twisted Other types of textile materials have strands of fibers extended in the three directions of space. For example sewn materials, where layers of fibers consisting of interlaced fiber locks are matched and sewn together. The strands of stitch fibers then extend in a component perpendicular to the two plies. Mention may also be made of textile materials obtained by braiding fiber locks, which braiding may have a plurality of layers of fiber locks, the fiber lock layers being interconnected by strands of fibers passing from one layer to another. another, following the example of interlock braids. Thanks to these textile materials in three dimensions, preforms are made to be inserted inside molds corresponding to the part to be produced. Then, we just inject a thermoplastic material inside the mold. This thermoplastic material, for example polyamide of a suitable grade, then drowns the textile preform and is introduced into its free spaces. The nature of the thermoplastic material will be chosen, depending on the conditions of implementation but also as a function of the mechanical properties of the part to be produced and its behavior over time. For example, with regard to these conditions of implementation, it is chosen as a function of the temperature of its melting point and its viscosity at this same melting point. As regards the methods of implementation, mention may be made, for example, of the RTM method, which stands for "Resin Transfer Molding". It is also possible to use other means of embedding the textile preform with the thermoplastic, for example by introducing into the textile preform thermoplastic fibers or wicks of comelated materials, that is to say containing reinforcing fibers intimately bound together. with the proper amount of thermoplastic. The composite is consolidated by wearing the preform at a temperature above the melting point of the thermoplastic yarns and applying pressure, which allows the thermoplastic to fill the free spaces of the textile preform. A buffer box 50 according to the invention will now be described with reference to FIG. It comprises two tubular hollow pieces 52, 54 of circular section, an inner tubular hollow part 54 engaged inside an outer tubular hollow part 52. Also, they are made in a suitable cylindrical mold having a core, and from two preforms in the form of sleeves of three-dimensional textile material of the aforementioned type, which sleeves were placed inside the mold around the core. Then the thermoplastic material was injected so as to obtain, after cooling, a cylindrical hollow piece of circular symmetry. In this case, the sleeves of textile material are obtained by braiding. The fiber locks are oriented partly in the axis of the hollow tubular pieces 52, 54. The other fiber locks are oriented at an angle of between 0 ° and 90 ° relative to the axis of the hollow tubular pieces 52 54. At least a portion of the locks allow the different wick layers to be bonded through the thickness of the composite. The inside diameter of the outer tubular hollow part 52 is equal to the functional clearance close to the outside diameter of the inner tubular hollow part 50.

The outer tubular hollow part 52 has a first outer end 56 having a first edge 58 and opposite a second outer end 60 having a first mechanical weakening 62 to initiate crushing or collapse. This first mechanical weakening 62 may be achieved by singularizing the shape of the second outer end 60, by removal of material or from the shaping of the tube, to give it a shape having sharp edges or salient points, such as a chamfer , saw teeth, a variation of the section of the tube or a combination of its patterns. Alternatively or in addition, this mechanical weakening 62 can be achieved by modifying the constitution of the composite at the first edge 58, by modifying the quantity or the orientation of the reinforcing fibers or by the deliberate introduction of manufacturing defects such as only foreign bodies or porosities in the plastic. The inner tubular hollow part 54 has, opposite to the first outer end 56, an inner first end 64 having a second edge 66 and, on the opposite side, a second inner end 68 having a second mechanical weakening 70 which also makes it possible to initiate crushing or collapse. This second mechanical weakening 70 is also achieved by singularizing the shape of the second inner end 68. The two tubular hollow parts 52, 54 are offset substantially axially so that the outer 60 and inner 60 outer ends 68 respectively protrude at each end. In addition, the buffer box 50 comprises two opposed flanges, a male flange 72 inside which are fitted the first outer end 56 and the second inner end 68 and a female flange 74 which are themselves fitted inside the second outer end 60 and the first inner end 64. The male flange 72 has a bottom 76 and, spaced radially, an inner shoulder 78. The second inner end 68 is then resting against the bottom 76 while the first edge 58 takes support flat against the inner shoulder 78. In contrast, the female flange 74 has a first outer shoulder 80 and spaced radially, a second outer shoulder 82. The second edge 66 then bears flat against the first outer shoulder 80 , while the second outer end 60 bears against the second outer shoulder 82. In this way, the second ends 62, 70 constitute rupture initiation zones which allow their axial collapse, when the buffer box 50 is subjected to compression, axial or substantially off-axis, exceeding a predefined threshold value. The flanges 72, 74, made of metal or plastic, can promote a progressive crushing tubular hollow parts 52, 54, managing the evacuation of dust produced. The three-dimensional structure of the textile materials of the tubular hollow parts 52, 54 makes it possible to prevent the propagation of a delamination which would bring about a rupture of the structure with a low energy dissipation. The structure of the textile material is chosen in such a way as to be able to multiply the fiber breaks in this crushing zone, which makes it possible to dissipate a maximum of energy. The thermoplastic matrix is chosen to absorb energy during crushing, and to ensure the integrity of the structure until crushing. The flanges 72, 74 are designed to allow, by plastic deformation, a deflection between the axis of the hollow tubular pieces 52, 54 and that of the flanges 72, 74. The three-dimensional structure of the textile materials of the hollow tubular pieces 52, 54 makes it possible to preserve the behavior sought at deformation, when the impact is no longer frontal but occurs with some incidence. Such a buffer box makes it possible to manufacture, from simple and therefore potentially inexpensive elements, an energy absorber capable of dissipating the energy of a severe automobile shock, of the frontal impact type at 65km / h, in a small space and reliably. Other designs are provided in which the tubular hollow parts 52, 54 are conical, or replaced by a single axially open profile capable of coming collapse on a single flange.

Moreover, similar buffer box devices are used in the field of aeronautics, for example for helicopter floors, or in the railway field. The manufacture of an energy absorber inexpensive and effective in relation to its weight can therefore find application.

In general, all mechanical applications where a stop-type safety system is required which can absorb energy when necessary may be a field of application of the box-object of the invention. .

Claims (10)

REVENDICATIONS1. An energy absorbing buffer box comprising a hollow piece (52, 54) made of a composite material and extending in a longitudinal direction, said composite material comprising a thermoplastic matrix and a fibrous reinforcing material (10; 34) embedded within said thermoplastic matrix, said hollow part (52, 54) being able to irreversibly compress in said longitudinal direction to absorb shock energy; characterized in that said fibrous reinforcing material (10; 34) is a textile material having fiber locks (18, 28, 30; 40,42,46) extended along the three directions of the space. Buffer box according to claim 1, characterized in that said textile material (10; 34) has at least two layers (12, 14, 16, 20, 22, 24, 26, 40, 42) of fiber locks. superimposed and strands of bonding fibers (30; 46) extending between said at least two layers. Buffer box according to claim 2, characterized in that said strands of bonding fibers (46) form meshes. 4. buffer box according to claim 2 or 3, characterized in that said at least two layers are respectively formed of meshes of said fiber locks. 5. The buffer box according to claim 2 or 3, characterized in that said at least two layers are respectively formed of intersecting strands of fibers. 6. Box-buffer according to any one of claims 1 to 5, characterized in that matrix of thermoplastic material is made of polyamide. 7. A buffer box according to any one of claims 1 to 6, characterized in that it further comprises two opposing flanges (72, 74), while said hollow piece (52, 54) has two opposite ends (56). , 60; 64, 68) respectively engaging said flanges. 8. Box-buffer according to any one of claims 1 to 7, characterized in that said hollow part (52, 54) is tubular. 9. The buffer box of claim 8, characterized in that it further comprises another hollow part (54) made of a composite material located inside said hollow part (52). 10. The buffer box according to claim 8 or 9, characterized in that said hollow parts (52, 54) are of circular symmetry.