FR3128896A1 - Frame for structure made of composite material, and structure made of composite material comprising such a frame - Google Patents

Abstract

TITLE: Reinforcement for structure made of composite material, and structure made of composite material comprising such a reinforcement , and separated from each other by lateral portions of the sheets of fibers, each pocket comprising at least one inflatable bladder, and being open. According to the invention, the side portions surrounding each pocket are extended by a movable end portion between a covering position in which it at least partially covers the opening of the pocket, and a plurality of positions in which part of the end portion at least partially covers the opening of the pocket and another part of the end portion extends in the extension of the side portion and contributes to separating the pocket from a neighboring pocket. The invention also relates to a structure made of composite material comprising such a reinforcement element (1), and to a method for obtaining such a structure. Abstract Figure: Figure 1

Description

Frame for structure made of composite material, and structure made of composite material comprising such a frame

Field of the invention

The present invention relates to the field of structures made of composite materials, consisting of a matrix and reinforcements.

The invention relates in particular to structures made of multilayer composite materials, consisting of several distinct layers of reinforcement, which are assembled together by the matrix.

In particular, the invention relates to such structures made of composite materials defining hollow spaces internal to the structure.

Prior art

Structures made of composite materials are made up of reinforcements, which constitute the reinforcement of the material and which are surrounded by a matrix, which secures the reinforcements together and transmits the mechanical forces to them. In very many structures made of composite materials, the reinforcements consist of fibers, such as for example glass fibers, carbon fibers, etc. The present invention applies particularly to such structures made of composite materials with fibrous reinforcement.

The matrix surrounding these reinforcements is, most often, an organic matrix, which can be, depending on the case, thermosetting or thermoplastic.

In the case of structures made of multilayer composite materials, the reinforcements of a structure made of composite materials are distributed in several layers superimposed on each other and secured together by the matrix. It is known, in certain structures made of multilayer composite materials, that internal layers of the structure have a plurality of empty spaces, to define hollow spaces internal to the structure. Such hollow spaces have the advantage of lightening a composite material structure having a relatively large thickness.

It is particularly common to use a so-called “honeycomb” material structure to form such internal layers comprising hollow spaces. Such a honeycomb material is formed of a plurality of hollow cells juxtaposed to each other and separated by thin walls. These cells often have a hexagonal cross-section. To produce a multilayer composite material structure comprising a layer made of such a honeycomb material, a cutout is generally made of a honeycomb material which has been formed and hardened beforehand, and this material between layers of fibers. These fiber layers are then stiffened by the hardening of a matrix, which also bonds the fiber layers to the honeycomb material with which they are in contact.

The composite material structure obtained, sometimes called a “sandwich” material structure, often has good mechanical characteristics and a relatively low weight. Its manufacture, requiring cutting or machining of the honeycomb material structure, is however long and delicate. Furthermore, the use of such layers of honeycomb materials prohibits the use of certain common manufacturing methods for structures made of composite materials. Thus, if such structures in multilayer materials can be formed using layers of fibers pre-impregnated with a thermosetting organic matrix, it is difficult to manufacture them using the conventional methods of injecting the matrix into the reinforcements. Indeed, such injections would run the risk of filling the cells of the honeycomb material with matrix.

Other methods are known which make it possible to provide hollow spaces inside structures made of composite material. It is thus known to place in the reinforcements of a composite material structure a bladder whose pressure is controlled so that it occupies a desired volume, until the hardening of the matrix coating the reinforcements. After this hardening, the volume occupied by the bladder constitutes an empty space in the composite material structure. The use of such bladders is compatible with composite materials with a thermoplastic or thermosetting organic matrix. The implementation of these bladders, however, greatly complicates the manufacture of the composite material structure. Indeed, each bladder must be put in place at the time of draping the fiber structure and must be connected to an external device allowing control of the internal pressure in the bladder. This pressure must be controlled throughout the matrix injection phase, or the phase of hardening of this matrix by firing.
Objectives of the invention

The present invention aims to overcome these drawbacks of the prior art.

In particular, the object of the present invention is to provide a reinforcement of a structure made of composite material, in particular a structure made of multilayer composite material, which makes it possible to obtain, more easily and in a less constraining manner than with the methods of the prior art, hollow spaces inside the composite material structure.

The invention also aims to provide a framework allowing the manufacture of a composite material structure having a shape, mechanical characteristics and varied dimensions more easily than with the solutions of the prior art.

A particular objective of the invention is to provide a frame allowing easy production of such a structure including inserts.

Another object of the invention is to propose a process for obtaining a composite material structure defining hollow spaces internal to the structure, which can be more easily implemented than the processes of the prior art.

These objectives, as well as others which will appear more clearly subsequently, are achieved with the aid of a reinforcing element for a composite material structure which comprises sheets of fibers forming a plurality of pockets juxtaposed to each other. in an alignment plane and separated from each other by lateral portions of sheets of fibers, which surround the pockets, each of the pockets comprising at least one inflatable bladder and being open in a direction substantially perpendicular to the alignment plane.

According to the invention, this reinforcing element for a composite material structure is characterized in that at least one of the side portions surrounding the pocket is extended by at least one end portion of fiber plies, each of the end portions being movable between a covering position in which this end portion at least partially covers the opening of the pocket and a plurality of positions in which a part of the end portion at least partially covers the opening of the pocket and another part of the end portion extends in the extension of the side portion and contributes to separating the pocket from a neighboring pocket.

The fact that a direction is "substantially perpendicular" to a plane means in the present application that this direction forms an angle of less than 20 degrees with the perpendicular to the plane.

These lateral portions which surround the pocket and these end portions of sheets of mobile fibers make it possible to obtain pockets whose height can vary according to the level of inflation of the pockets. This height depends on the end portions which extend the side portions and form a straight partition between two juxtaposed pockets up to a maximum height.

According to an advantageous embodiment, one of the sheets of fibers is a longitudinal wrapping sheet which wraps at least one partitioning sheet.

Preferably, the partitioning ply is connected to the longitudinal enveloping ply by seams. These seams make it possible to maintain these different layers of fibers together.

According to another embodiment, the side portions of the juxtaposed pockets are interconnected by seams. These seams make it possible to hold the side portions together.

Advantageously, the bladders are closed and contain a solid or liquid material capable of vaporizing at the firing temperature of a thermosetting organic matrix.

The use of this solid or liquid makes it possible, under the effect of heat, to transform this solid or liquid into gas. Thus, this gas exerts pressure on the internal walls of the pockets of the structure, allowing these pockets to expand and change shape.

Preferably, the pockets are aligned in a single direction.

According to another embodiment, the bladders are connected with the outside of the frame by filling means. These filling means allow the user to control the inflation of the bladders and the rigidity of the associated structure.

The invention also relates to a composite material structure consisting of a plurality of layers of fibers solidified by a matrix, at least one of the layers of fibers comprising a reinforcement, solidified so that each of the pockets forms a cell empty.

The presence of pockets contained in the framework makes it possible to obtain empty cells whose size can be chosen by inflating the bladders before hardening. Greater inflation results in more elongated cells. This elongation of the cells thus leads to an increase in the height of the composite material. The distance between the upper and lower layer of this composite material is then increased. The hardening by the matrix makes it possible to maintain and solidify all the fibers at a desired height in order to form the composite material structure.

Preferably, the process for obtaining the composite material structure comprises the following steps: placing the reinforcement in a mould, placing the mold under temperature conditions in which the bladders are capable of inflating to furnish any available space, solidification of the structure by hardening of the matrix surrounding the structure.

According to another embodiment, one of the steps consists in creating the vacuum in the mold to inflate the bladders.

According to another advantageous embodiment, the step consisting in creating a vacuum in the mold is followed by vacuum injection of a matrix in the liquid state. This matrix can be a thermoplastic matrix injected at a temperature at which it is liquid, or an unpolymerized thermosetting matrix.
List of Figures

• La est une vue en perspective d’un élément d’armature de structure en matériau composite selon un mode de réalisation de l'invention.
• La est une vue en perspective de l’élément d’armature de la , dont la nappe d’enveloppement longitudinal est dépliée et dont les poches internes sont vides.

• La est une vue de dessus de la nappe d’enveloppement longitudinal de l’élément d’armature de la dépliée.
• La est une vue de détails de l’élément d’armature tel que représenté par la .
• La est une vue de détails de l’élément d’armature de la , dans une autre configuration.
• La est une vue en perspective de l’élément d’armature de la , dans une autre configuration.
• La est une vue en perspective d’un moule comprenant des éléments d’armature destinés à former l’armature d’une structure en matériau composite.
• La est une représentation, en vue de coupe, d’un moule semblable à celui de la comprenant une armature destinée à former une structure en matériau composite, constituée notamment de plusieurs éléments d’armatures tels que celui représenté par la .
• La est une représentation du moule de la , en vue de coupe, dans laquelle les vessies placées dans les poches des éléments d’armature sont gonflées.
• La est une représentation, en vue de coupe, d’un autre moule présentant une forme différente, comprenant une armature destinée à former une structure en matériau composite, constituée notamment de plusieurs éléments d’armatures tels que celui représenté par la .
• La est une représentation du moule de la , en vue de coupe, dans laquelle les vessies placées dans les poches des éléments d’armature sont gonflées.
• La est une représentation, en vue de coupe, d’un autre moule présentant une forme différente, comprenant une armature destinée à former une structure en matériau composite, constituée notamment de plusieurs éléments d’armatures tels que celui représenté par la .
• La est une représentation du moule de la , en vue de coupe, dans laquelle les vessies placées dans les poches des éléments d’armature sont gonflées.

Description détaillée de modes de réalisation de l’inventionThe invention will be better understood on reading the following description of preferred embodiments, given by way of a simple figurative and non-limiting example, and accompanied by the figures among which:

• There is a perspective view of a structural reinforcement element made of composite material according to one embodiment of the invention.
• There is a perspective view of the reinforcing member of the , whose longitudinal wrapping ply is unfolded and whose internal pockets are empty.

• There is a top view of the longitudinal wrapping ply of the reinforcement element of the unfolded.
• There is a detail view of the reinforcement element as represented by the .
• There is a detail view of the reinforcement element of the , in another configuration.
• There is a perspective view of the reinforcing member of the , in another configuration.
• There is a perspective view of a mold comprising reinforcement elements intended to form the reinforcement of a structure made of composite material.
• There is a representation, in sectional view, of a mold similar to that of the comprising a reinforcement intended to form a structure of composite material, consisting in particular of several reinforcement elements such as that represented by the .
• There is a representation of the mold of the , in sectional view, in which the bladders placed in the pockets of the frame elements are inflated.
• There is a representation, in sectional view, of another mold having a different shape, comprising an armature intended to form a structure in composite material, consisting in particular of several armature elements such as that represented by the .
• There is a representation of the mold of the , in sectional view, in which the bladders placed in the pockets of the frame elements are inflated.
• There is a representation, in sectional view, of another mold having a different shape, comprising an armature intended to form a structure in composite material, consisting in particular of several armature elements such as that represented by the .
• There is a representation of the mold of the , in sectional view, in which the bladders placed in the pockets of the frame elements are inflated.

Detailed Description of Embodiments of the Invention

There shows in perspective a reinforcement element 1, composed of layers of fibrous reinforcement and intended to form the reinforcement of an internal layer of a structure made of multilayer composite material, this internal layer defining a plurality of cells in the structure.

This reinforcing element is made up of layers of fibers, which can be woven or made up of loose layers of non-woven fibers, called "mat". Such sheets of fibers, very commonly used for the manufacture of composite materials, can be dry, that is to say devoid of matrix, or pre-impregnated with an uncured matrix. When these fibers are dry, they are subsequently impregnated with the matrix which hardens to form the composite material. When these fibers are pre-impregnated, the matrix which impregnates them is subsequently hardened, for example by firing, in order to constitute the composite material. In all cases, these sheets of fibers are flexible during the preparation of the composite material, and are subsequently hardened by the matrix, to form the composite material.

The reinforcement element 1 represented by the is made up of layers of fibers, which define internal pockets intended to form the cells of the composite material structure. These cells are obtained after hardening of a matrix coating the pockets contained in the framework.

This reinforcement element 1 has an elongated shape in a main direction along the x axis, which is subsequently called the “cell alignment direction”. The length of the reinforcing element 1 in this direction of alignment of the cells can be adjusted by cutting this reinforcing element, preferably so as to maintain a whole number of cells therein.

The outer walls of this reinforcement element 1 which extend in the direction of alignment of the cells x are closed by an outer fiber ply called hereinafter the longitudinal wrapping ply 11. This longitudinal wrapping ply 11 has two end strips 114 and 115 whose edges extend in the direction of alignment of the cells x and overlap to form the upper surface of the reinforcement element 1

There is a perspective view of the frame member 1 of the , whose longitudinal wrapping ply 11 is unfolded and placed flat. This figure thus shows the inside of the reinforcement element 1, which contains several layers of fibers called “partitioning layers 2” which separate the internal pockets from each other. In this figure, the internal pockets are empty. Each of the partition layers 2 has two edges extending in the transverse direction, along the z axis, above each of the internal pockets, which overlap to form the upper surface of each of the internal pockets.

To constitute the reinforcement element 1 represented by the , portions of the sheet of fibers are sewn together. Thus, the reinforcement element 1 represented on the has a longitudinal wrapping sheet 11, of substantially rectangular shape, on which are sewn a plurality of partitioning sheets 2, the shape of which is also substantially rectangular, of dimensions smaller than those of the longitudinal wrapping sheet 11.

Of course, those skilled in the art can easily imagine other embodiments of this invention. By way of example, the longitudinal wrapping 11 and partitioning 2 layers can be of different shapes, for example substantially square or substantially triangular. These shapes could for example be chosen by the person skilled in the art to meet specific shape or mechanical strength needs of the reinforcement element 1. Furthermore, the person skilled in the art could also implement other means for assembling the layers of fibers together, for example by gluing.

There shows, in top view, the longitudinal wrapping ply 11 used for the reinforcement element 1 of the .

This longitudinal wrapping ply 11 has a substantially rectangular and elongated shape in the direction of alignment of the cells, along the x axis.

The partitioning sheets 2 are assembled to the longitudinal wrapping sheet 11 on a central strip 111 of this longitudinal wrapping sheet 11. This central strip 111 is preferably rectangular in shape and extends over the entire length of the longitudinal wrapping ply 11, in the direction of alignment of the cells, along the x axis. This central strip 111 is intended to form the lower surface of the reinforcement element 1.

The central strip 111 preferably represents approximately 25% of the width of the longitudinal wrapping ply 11. In the embodiment shown, this central strip 111 has a width of approximately 30 mm.

Lateral bands 112 and 113 of the longitudinal wrapping ply 11 extend, over the entire length of the longitudinal wrapping ply 11, on either side of the central band 111. These lateral bands 112 and 113 have , preferably a substantially rectangular shape. They are intended to form the side walls of the reinforcement element 1 by being folded in directions substantially perpendicular to the lower surface of the reinforcement 1 formed by the central strip 111, which extends in a plane called by the continued “alveoli alignment plan”. The fact that these directions are "substantially perpendicular" to this lower surface of the armature 1 means in the present application that these directions form an angle of less than 20 degrees with the perpendicular to the plane of alignment of the cells, along the axis x . In the embodiment shown, these side strips 112 and 113 have a width of approximately 10 mm.

The end strips 114 and 115 respectively extend the side strips 112 and 113 of the longitudinal wrapping ply 11 and surround these side strips 112 and 113 on either side. These end strips 114 and 115 extend over the entire length of this longitudinal wrapping ply 11. These end bands 114 and 115 preferably have a substantially rectangular shape, and their free edges extend substantially along the direction of alignment of the cells, along the x-axis. They are intended to form the upper surface of the frame element 1 by being folded substantially perpendicular to the side strips 112 and 113 of the frame 1.

In the embodiment shown, these end strips 114 and 115 have a width of approximately 20 mm and partially overlap to form the upper surface of the reinforcement element 1. It is possible, in other embodiments embodiment, that these end strips 114 and 115 have a greater width, to overlap more, or on the contrary that they are narrower. In some possible embodiments, these end strips 114 and 115 may not overlap, but each cover a portion of the top surface of the frame member.

The partition layers 2 are intended to separate pockets juxtaposed to each other along the central strip 111 and can be made in different ways.

In the embodiment shown, each of the partition layers 2 has a rectangular shape. By way of illustration, the shows a partitioning layer 202 juxtaposed with two other partitioning layers 201 and 203 which are partially represented. The central portion 211 of the partitioning ply 202 is pressed against the central strip 111 of the longitudinal wrapping ply 11, and is assembled there, preferably by seams 222 and 223. This central portion 211 of each of the partitioning layers 2 is advantageously substantially square in shape, with a side of approximately 30 mm.

The partitioning sheet 202 has lateral portions 212 and 213 surrounding, on each side, the central portion 211. According to a preferred embodiment, represented by the , these side portions 212 and 213 are pressed against the side portions of the adjacent partitioning layers 201 and 203. In the embodiment shown, these lateral portions 212 and 213 are secured to the lateral portions of the neighboring partition layers 201 and 203. By way of example, the lateral portion 212 of the partitioning ply 202 is linked to the lateral portion of the neighboring partitioning ply 201 by the seams 220 and 221. The lateral portions of two neighboring partitioning plies 2, thus assembled, extend substantially perpendicular to the direction of alignment of the x cells, parallel to the y and z axes, and form partitions between the surfaces defined by the central portions 211 of each of these layers, as represented by the . Preferably, these side portions have dimensions allowing these partitions to have a height of about 10 mm.

Each of the partition layers 2 extends, and folds back again on both sides of the side portions 212 and 213, by end portions 214 and 215 which face each other. In the embodiment shown, these end portions 214 and 215 have a width of approximately 20 mm, and partially overlap to form the upper surface of a pocket surrounded by the partitioning ply 2. It is possible, in other embodiments, that these end portions 214 and 215 have a greater width, to overlap more, or on the contrary that they are narrower. In certain possible embodiments, these end portions 214 and 215 may not overlap, but each cover part of the upper surface of the pocket.

To form the frame of the composite material structure according to the invention, the longitudinal enveloping ply 11 and the various partitioning ply 2 therefore together delimit pockets 21 to 26, as shown in . These pockets are juxtaposed to each other in a plane called the cell alignment plane. More precisely, in the embodiment represented, the pockets 21 to 26 are aligned in a plane parallel to the x and z axes. It is however possible, in other embodiments, for pockets juxtaposed in two dimensions, in the plane of alignment of the cells, to form the same reinforcement element.

In the embodiment shown, the lateral bands 112 and 113 of the longitudinal enveloping ply 11 are folded over to extend parallel to the z and y axes and bear against the edge of the lateral portions 212 and 213 of the partitioning ply 2 juxtaposed. Furthermore, the end bands 114 and 115 of the longitudinal wrapping ply 11 are folded over the partitioning ply 2 and extend substantially parallel to the x and z axes. When the layers constituting the frame 1 are thus folded, they define a plurality of empty cells, juxtaposed to each other and each preferably having the shape of a rectangular parallelepiped. The juxtaposed pockets are separated by intermediate partitions which preferably extend substantially perpendicular to the plane of alignment of the cells.

In the configuration represented by the , these end portions 214 and 215 are in a so-called "covering" position, in which they extend entirely above the central portion 211 of the partitioning ply 202.

In other configurations, these end portions 214 and 215 can take a plurality of positions in which a part of each end portion 214 and 215 extends in the extension of the partitions formed by the side portions 212 and 213, substantially parallel to the y and z axes, and another part extends above the central portion 211 of the partitioning sheet 202, substantially parallel to the x and z axes.

• une partie 2141 de la portion d’extrémité 214 s’étend dans le prolongement de la portion latérale 212,
• une autre partie 2142 de la portion d’extrémité 214 s’étend au-dessus de la portion centrale 211,
• une partie 2151 de la portion d’extrémité 215 s’étend dans le prolongement de la portion latérale 213,
• une autre partie 2152 de la portion d’extrémité 215 s’étend au-dessus de la portion centrale 211.

Thus, the represents a configuration in which

• a part 2141 of the end portion 214 extends in the extension of the side portion 212,
• another part 2142 of the end portion 214 extends above the central portion 211,
• a part 2151 of the end portion 215 extends in the extension of the side portion 213,
• another part 2152 of the end portion 215 extends above the central portion 211.

In such a configuration, the height, in the direction of the y axis, of the pocket defined by the partitioning layer 202 is increased, which increases the volume of this pocket. It should be noted that, the end portions 214 and 215 not being linked to each other, they do not close the pocket, which remains open in the direction of the y axis. This opening is only covered, partially or totally, by the end portions 214 and 215.

In the configuration represented by the , the end strips 114 and 115 of the longitudinal enveloping ply 11 are in a so-called “covering” position, in which they extend entirely above the partitioning ply.

In other configurations, these end strips 114 and 115 can take a plurality of positions in which a part of each end strip extends in the extension of the side strips 112 and 113, substantially parallel to the x and y axes. , and another part extends above the partition layers, substantially parallel to the x and z axes.

• une partie 1141 de la bande d’extrémité 114 s’étend dans le prolongement de la bande latérale 112,
• une autre partie 1142 de la bande d’extrémité 114 s’étend au-dessus de la bande centrale 111,
• une partie 1151 de la bande d’extrémité 115 s’étend dans le prolongement de la bande latérale 113,
• une autre partie 1152 de la bande d’extrémité 115 s’étend au-dessus de la bande centrale 111.

Thus, the represents a configuration in which

• a part 1141 of the end band 114 extends in the extension of the side band 112,
• another part 1142 of the end strip 114 extends above the central strip 111,
• a part 1151 of the end band 115 extends in the extension of the side band 113,
• another part 1152 of the end strip 115 extends above the central strip 111.

In such a configuration, the height, in the direction of the axis y, of the structural element defined by the longitudinal wrapping ply 11 is increased, which allows this structure to contain pockets whose height is itself - even augmented, like the pocket represented by the . It should be noted that, the end strips 114 and 115 not being linked to each other, they do not close the pockets of the reinforcement element 1, which remain open in the direction of the y-axis. The partitioning layers 2, which delimit the pockets, are only covered, partially or totally, by the end bands 114 and 115 of the longitudinal wrapping layer 11.

It should be noted that the reinforcing element 1 shown in the figures is only one example of assembling layers of fibers to form a plurality of pockets 21 to 26 juxtaposed to each other. A person skilled in the art will be able without difficulty to imagine variants of such an embodiment.

There shows, in schematic cross-sectional view, a mold in which is arranged a reinforcement element 1, similar to that represented by the . On the , this reinforcement element defines four successive pockets, extending in the direction of the x axis. Each of these pockets 21 to 24 contains a bladder, respectively 31 to 34, which is inflatable and able to expand. Such inflatable bladders 31 to 34 are well known to those skilled in the composites art and are commonly used to provide hollow spaces in a composite part.

Bladders 31-34 are initially in a deflated configuration. Depending on their degree of filling, the bladders 31 to 34 grow and exert more or less strong pressure against the walls of the pockets 21 to 24 in which they are located. Thus, the shapes of the pockets 21 to 24 change and these extend in height, in the direction of the y axis and, to a lesser extent, the pockets extend parallel to the x axis.

When the bladders 31 to 34 grow, they make it possible to adjust the height of the reinforcement element 1 formed by the folding of the longitudinal enveloping plies 11 and the partitioning 2, as shown according to one embodiment on the .

In the embodiment shown, which constitutes a preferred solution, the various inflatable bladders 31 to 34 are closed bladders. These are not connected outside the room. Each of these bladders 31 to 34 is inflated, before it is closed, by a predetermined volume of air.

These closed bladders 31 to 34 can be inflated by varying different parameters. In particular, these bladders 31 to 34 can be placed under vacuum. In response to this vacuum, these bladders 31 to 34 expand to fill the space in which they are contained. During this inflation, the bladders 31 to 34 push layers of fibers which surround them, until they are pressed against the internal surface of a mold or against another bladder. The inflation of the bladders 31 to 34 then has the effect of extending the volume of the bladders, and of the pockets which contain them, in a direction substantially perpendicular to the direction of alignment of the cells and parallel to the axes y and z.

It is also possible, according to other embodiments, for these different bladders 31 to 34 to be connected, by suitable connection means, such as pipes, to a pressure control system located outside the reinforcing element 1. The pressure that the bladders 31 to 34 exert on the longitudinal enveloping 11 and partitioning 2 plies is controlled by the level of inflation. Thus, the user can adjust the height of the reinforcement element 1 formed by the folding of the longitudinal wrapping 11 and partitioning 2 layers by increasing or decreasing the inflation.

It is also possible, according to variants, for the bladders 31 to 34 to be closed and filled with components other than air.

By way of example, these bladders 31 to 34 can be filled with another gas, or with a solid or liquid material capable of vaporizing under the effect of heat. The pressure that the bladders 31 to 34 exert on the various wrapping layers is controlled by the level of inflation, which is itself controlled by the temperature and/or by the pressure of the atmosphere surrounding the bladders. When the bladder is filled with a liquid, heating the structure to a temperature above the boiling point of the liquid transforms this liquid into gas, and inflates the bladders 31 to 34.

According to another possible embodiment, the bladders 31 to 34 can contain capsules capable of releasing a gas. In this embodiment, the release of this gas allows the expansion and inflation of the bladders 31 to 34.

To form a multilayer composite material structure, a reinforcement element 1 as described above can be placed in a mold, between other reinforcing layers. The composite material structure can also contain several juxtaposed reinforcement elements 1 which can, together, constitute a layer of a multilayer composite material structure.

There represents a mold formed of two shells 402 and 403, at the bottom of which is placed at least one lower layer of fibers 302 intended to form a wall of a composite part. This lower ply of fibers 302 is covered by a plurality of reinforcement elements 1 as described in FIGS. 1 and 6. Such reinforcement elements 1 are advantageously juxtaposed to each other over the entire surface of the ply of lower fibers 302. Thus, in the embodiment shown, four reinforcing elements 1 are placed next to each other, above the lower layer of fibers 302.

These reinforcement elements 1 can have different lengths and be shortened in the direction of alignment of the cells. All of these reinforcement elements 1 are then covered by a second layer of upper fibers 303 intended to form the outer wall of the part made of composite material.

In the embodiments represented below by FIGS. 8 to 13, the various pockets represented in each figure may belong indiscriminately to the same reinforcement element according to the invention, such as for example that represented by the , or to reinforcement elements juxtaposed to each other.

Of course, those skilled in the art will be able without difficulty to imagine other embodiments of the mold and of the reinforcing layers encompassing the reinforcement elements. By way of example, the reinforcing layers can be of different thicknesses. These thicknesses could, for example, be chosen by those skilled in the art to meet specific needs in terms of shape or mechanical strength of the structure made of multilayer composite material.

It should be noted that it is possible to place in a mold several superposed layers each consisting of reinforcement elements 1 juxtaposed to each other. In this case, advantageously, the different layers of reinforcement elements according to the invention can be separated by an intermediate layer of fibers. It is thus possible to use the reinforcement elements according to the invention to form parts of composite material having a significant thickness.

The upper shell 403 of the mold has an internal surface, not shown on the , which may be flat or have irregularities such as cavities.

According to a preferred embodiment, the part made of composite material can be formed according to a known vacuum resin injection process. According to this method, suction equipment can create a vacuum in the mold, by sucking the air present there. Once this vacuum has been created, liquid resin can be injected. This resin can be a thermosetting resin, which is hardened by baking after it is injected. This resin can also be a hot injected thermoplastic resin, which is thus made malleable by heat, able to take the shape of a mould, and which subsequently cools and hardens. A thermoplastic resin is considered hot if its temperature allows it to be in a completely fluid and homogeneous form. The vacuum produced in the fibrous reinforcements helps the resin to penetrate into all the interstices located between these fibrous reinforcements and in a substantially homogeneous manner.

When the vacuum is created in the mold containing the reinforcement element 1 according to the invention, the bladders 31 to 34 which are partially inflated at temperature and at ambient pressure, inflate to occupy all the space available in the mold. This inflation does not cause any significant displacement of the partitions formed by the side portions 212 and 213 separating two juxtaposed pockets 21 to 24. In fact, the bladders located in two neighboring pockets inflate in the same way, pressing against these partitions formed by the side portions 212 and 213. The inflating bladders 31 to 34 tend to push the end bands 114 and 115 of the longitudinal enveloping sheet 11 as well as the end portions 214 and 215 of the partitioning sheets 2 constituting the upper wall in folded form.

These longitudinal enveloping 11 and partitioning 2 layers can be held together by adhesive tapes having low resistance, which unhook to allow the layers to extend with ease when the bladders 31 to 34 inflate. The end strips 114 and 115 of the longitudinal wrapping ply and the end portions 214 and 215 of the partitioning ply 2 are then pushed until they come into contact with the upper fiber ply 303 which is itself in contact with the upper shell 403.

Each of the bladders 31 to 34, by occupying all the space that is available, tends to deform the cell in a single direction, parallel to the y axis, causing it to occupy all the available height. This inflation makes it possible to fill the void between the upper layer of fibers 303 and the shell 403 of the mould, whatever the shape of the internal surface of the shell 403 and the irregularities present on this internal surface.

According to an embodiment shown in Figures 8 and 9, the inner surface of the shell 403 has a relatively flat surface. There shows the initial state in which the bladders 31 to 34 are partially inflated and the pockets 21 to 24 preferably have a similar rectangular shape between them.

In this embodiment, during inflation, the bladders 31 to 34 inflate in an equivalent manner. This inflation causes the extension of each pocket 21 to 24 in a direction substantially perpendicular to the direction of alignment of the cells, parallel to the y axis. Nevertheless, the juxtaposition of the pockets 21 to 24, contained in the partition layers 2, does not allow the extension of these pockets 21 to 24 in a direction parallel to the direction of alignment of the cells.

Thus, when the bladders 31 to 34 are inflated as shown in the , the pockets 21 to 24 are pressed against the upper layer of fibers 303 while maintaining similar rectangular shapes between them. In this way, the upper layer of fibers 303 matches the entire shell 403, and the empty space 501 between the shell 403 and the upper layer of fibers 303 is filled.

There shows that after inflation, the intermediate partitions between the pairs of cells retain a similar height and remain oriented in directions substantially perpendicular to the plane of alignment of the cells and parallel with the axes y and z.

According to another embodiment shown in Figures 10 and 11, the shell 403 may have a non-planar surface. There shows the initial state in which the bladders 31 to 34 are partially inflated and the pockets 21 to 24 have rectangular shapes similar to each other.

In this embodiment, the inflation of the bladders 31 to 34 allows the pockets 21 to 24 to fill the empty space 501 between the shell 403 and the upper layer of fibers 303. The shows the state of the cells after this inflation.

This inflation causes the extension of each pocket 21 to 24 in a single direction parallel to the axis y, perpendicular to the direction of alignment of the cells x. After inflation, the pockets 21 to 24 have a more or less elongated shape, depending on the height available between the shells 402 and 403 of the mould.

The top of the pockets 21 to 24 thus hugs the surface of the shell 403, which allows the upper layer of fibers 303 to stick to this shell 403 despite its non-planar shape. Thus, this upper layer of fibers 303 is attached to the shell 403 regardless of the shape of the shell 403 of the mold and the empty space 501 between the shell 403 and the layer of fibers 303 is filled.

There shows that after swelling the intermediate partitions between the pairs of juxtaposed cells remain oriented in directions perpendicular to the direction of alignment of the cells, parallel to the y and z axes. On the other hand, all of these partitions have different heights. There shows that after swelling the intermediate partition between the pockets 22 and 23 has a greater height, along the y axis, than the partitions separating the other neighboring pockets. This greater deformation of the pockets 22 and 23 makes it possible to press the upper sheet of fibers 303 against the shell 403 despite the presence of a larger cavity on the internal surface of this shell.

Figures 12 and 13 show a variant of the embodiment represented by Figures 10 and 11, in which the shells 402 and 403 approach each other, near one of their ends, to form a fine portion of the composite structure, without empty space. At the level of the transition zone between the thick portion of the composite structure and its thin portion there is a pocket 25, having a triangular shape and a smaller volume than the pockets 21 to 24. This pocket 25 can belong to an element of armature according to the invention, adapted to have this particular shape, and contains a bladder 35, which advantageously has an initial volume smaller than that of the bladders 31 to 34.

The shape and arrangement of this pocket 25 advantageously allows it to perfectly fill the transition space between the thick portion and the thin portion of the composite structure, when the bladders 31 to 35 are inflated.

When the bladders 31 to 35 are inflated, resin is injected into the reinforcements represented by FIGS. 9, 11 or 13. If this resin is thermoplastic, it is injected at a temperature at which it is liquid. Its subsequent cooling leads to its hardening. If this resin is thermosetting, the entire mold containing the resin can subsequently be subjected to heat allowing the resin to harden. The hardening of this resin makes it possible to form the rigid composite part, in which the pockets of the reinforcement form cells.

More specifically, this resin hardening makes it possible to obtain intermediate partitions formed of layers of solidified fibers whose height depends on the height of the mould. Thus, these layers of fibers solidified after the inflation of the bladders 31 to 34 allow the pockets 21 to 24 to form empty cells.

In the preferred embodiment, the mold is placed under vacuum before injecting the resin, and this vacuum causes the bladders 31 to 34 to swell.

According to another embodiment, the inflation of these bladders 31 to 34 can be triggered by heating them. This regulation of the level of inflation is possible, for example, by filling the bladders with a non-gaseous material, which vaporizes under the effect of heat.

According to another embodiment, the bladders 31 to 34 can be connected to inflation means outside the mould, which makes it possible to control the inflation of the bladders 31 to 34 after they have been placed in the pockets 21 to 24 of the reinforcement element 1. By way of example, the bladders 31 to 34 can be equipped with pipes making it possible to bring an external fluid to the reinforcement element 1.

According to another embodiment of the invention, the pockets formed in the reinforcement element 1 are open at their two ends, in the same direction substantially perpendicular to the plane or to the direction of alignment of the pockets. Each of the openings can, in this case, be at least partially covered by end portions of the side portions of sheets of fibers surrounding the pockets.

Thus, when the inflatable bladders contained in the pockets are inflated, each pocket can extend in two opposite directions, in order to increase its length in a direction substantially perpendicular to the plane or to the direction of alignment of the pockets.

In the embodiment represented by the , the reinforcement element 1 forms pockets which are aligned with each other in a single alignment direction. It is however possible, according to a variant of the invention, for a reinforcement element to form pockets aligned one beside the other in two directions, to form a plate. The plane formed by such a plate, when the latter is placed flat, is then the plane of alignment of the pockets of the reinforcement element.

Claims (11)

Reinforcement element (1) for composite material structure,
said reinforcement comprising sheets of fibers (11, 2) forming a plurality of pockets (21, 22, 23, 24)

• juxtaposed to each other in an alignment plane, and
• separated from each other by lateral portions (212, 213) of said layers of fibers (11, 2), which surround said pockets (21, 22, 23, 24),

each of said pockets (21, 22, 23, 24) comprising at least one inflatable bladder (31, 32, 33, 34), and being open in a direction substantially perpendicular to said plane of alignment,
characterized in that
at least one of the side portions (212, 213) surrounding said pocket (21, 22, 23, 24) extending by at least one end portion (214, 215) of said fiber layers (11, 2),
each of said end portions (214, 215) being movable between:

• a covering position in which this end portion (214, 215) at least partially covers the opening of said pocket (21, 22, 23, 24), and
• a plurality of positions in which a part of said end portion (214, 215) at least partially covers the opening of said pocket (21, 22, 23, 24), and another part of said end portion ( 214, 215) extends in the extension of said lateral portion (212, 213) and contributes to separating said pocket (21, 22, 23, 24) from an adjacent pocket.

Reinforcing element (1) for a composite material structure according to Claim 1, characterized in that one of the said layers of fibers (11, 2) is a longitudinal wrapping layer (11) which wraps at least one partitioning layer (2). Reinforcing element (1) for a composite material structure according to the preceding claim, characterized in that said partitioning ply (2) is connected to said longitudinal enveloping ply (11) by seams (222, 223). Reinforcing element (1) for a composite material structure according to claim 1, characterized in that the lateral portions (212, 213) of the said juxtaposed pockets (21, 22, 23, 24) are interconnected by seams (220 , 221). Reinforcing element (1) for a composite material structure according to any one of the preceding claims, characterized in that the said pockets (21, 22, 23, 24) are aligned in a single direction. Reinforcing element (1) for a structure made of composite material according to any one of the preceding claims, characterized in that the said bladders (31, 32, 33, 34) are closed and contain a solid or liquid material capable of vaporizing at the curing temperature of a thermosetting organic matrix. Reinforcing element (1) for a composite material structure according to any one of Claims 1 to 5, characterized in that the said bladders (31, 32, 33, 34) are connected with the exterior of the said reinforcement by means filling. A composite material structure consisting of a plurality of layers of fibers solidified by a matrix, at least one of the said layers of fibers comprising a reinforcement element (1) according to any one of the preceding claims, solidified so as to that each of said pockets (21, 22, 23, 24) forms an empty cell. Process for obtaining a composite material structure according to the preceding claim, characterized in that it comprises the following steps:

• placement of the reinforcement element (1) in a mould,
• swelling of said bladders (31, 32, 33, 34),
• solidification of the structure by hardening of the matrix surrounding said structure.

Process for obtaining a composite material structure according to the preceding claim, characterized in that the said inflation step consists in creating a vacuum in the mold to inflate the bladders (31, 32, 33, 34). Process for obtaining a composite material structure according to the preceding claim, characterized in that the said swelling step is followed by vacuum injection of a matrix in the liquid state.