FR2585445A1 - Method for manufacturing a modular composite material, material produced and component obtained from the said material - Google Patents

Abstract

The invention relates to a method for manufacturing a modular composite material. This method consists a in using balls 2, 3, 4 each comprising a continuous skin situated around a substantially spherical central core, preferably empty, b in positioning the said balls in contact with one another so as to be close to a geometric distribution of the compact crystallographic type, and c in fixing the said balls thus positioned with respect to one another exclusively via their contact zones, so that the said fastenings do not affect the empty spaces between balls. The composite material in accordance with the invention can be used to form working structures, in particular in the aerospace or transport field, for the purpose of combining a low specific mass with excellent mechanical characteristics.

Description

PROCESS FOR PRODUCING A COMPOSITE ATRIAU
MODULAR, TATERIAU REALIZED AND PIECE OBTAINED FROM
DUDIT ATERIAU
The invention relates to a method of manufacturing a new modular composite material. It aims to enable the manufacture of a low specific weight material, having good mechanical characteristics and easily adjustable properties according to each application. The invention extends to the cornposite material manufactured by carrying out the process, as well as mechanical parts produced, usable in various technical sectors, and in particular in the aerospace sector or in that of air or land transport where we are looking for good mechanical characteristics combined with a low specific weight.

 In the aerospace industry, lightweight composite materials known as "honeycombs" have been used for a long time. These are formed by corrugated walls of semi-polygonal section, joined together by welding, gluing, brazing ... to form a material three-dimensional polygonal section. However, such a material has practical limits of use resulting essentially from the anisotropy of its mechanical properties (one of the directions being preferred over others) and its non-moldable and non-formable character without destruction of mechanical properties; for example, such a material compressed in the aforementioned preferred direction (longitudinal direction of the polygonal cells) is the seat of an irreversible buckling which limits the possibilities.This more such a material can not be manufactured without discontinuity if we want to give it properties evolving in space.

 Furthermore, FR Patent No. 1565344 describes a material intended to fill cellular structures with a view to improving the stability of these structures. For this purpose this material is produced by means of a nickel-coated aluminum metal powder, which is carried at high temperature to ensure diffusion of the aluminum through the nickel to the interstices between grains; a material formed of hollow grains is thus obtained, which are fixed in a matrix essentially based on aluminum filling the interstices between grains. This material satisfactorily fulfills its sealing function since the gases are stopped by the interstitial matrix, while by having improved qualities of lightness compared to a solid material of the same nature.However such a material has a much higher specific weight than the composite materials of the honeycomb type Cen because of the presence of the interstitial matrix) and It is totally unthinkable to use it to manufacture aeronautical structures. In fact the use of this material is confined to the filling of small structures which it improves the sealing without significantly modifying the mechanical characteristics but it weighs very substantially; such a material is essentially a filler and can not be used in practice to significantly participate in the mechanical properties of a working structure; it is in fact totally impossible in a material, formed of grains of powders of variable diameters randomly dispersed in the matrix of maintenance, to simultaneously control the shape of the grains, their diameter, their thickness and the distribution of said grains in the interstitial matrix so that the macroscopic mechanical properties of the material match that of the matrix with an unknown reduction coefficient and are incompatible with reliably obtaining high specific mechanical performance.

As is apparent from the aforementioned patent, the interest of such a material lies, therefore, not in its specific mechanical characteristics which are poor and without comparison with the nest of aheille but in its sealing properties combined at a lower density by compared to that of a comparable massive material.

 Furthermore, in the construction field, a cellular material has been proposed, consisting of spherical cells, in particular hollow cells, which are trapped in a mass that serves as a binder (French Patent No. 75.04281); it is stated in this patent that the spherical cells can be made of various materials (ci-ment, p 1 plaster, tre, glass, iron, steel9 copper, bnis, agglomerate, polyester ..) and that the binder is a fluid mass or pasty, solidified, which can be constituted by cement, plaster, lime ... For the reasons already mentioned s, such a material has a specific weight incompatible with use in a mechanical sector including aeronautics (essentially because the presence of the interstitial mass which fills the interstices between cells and makes it possible to fix the latter).

In addition, such a material has tensile strength characteristics that are mediocre since they are at most equal to that of the binder, with a significant reduction coefficient resulting from the presence of empty cells in the core of this binder.

 The present invention proposes to indicate a method of manufacturing a new mod-ulaire composite material.

 The essential objective of the invention is to provide a structural material which combines a reduced specific weight, compatible in particular with use in the aerospace sector, with excellent mechanical characteristics making it possible to use it as a material constituting a structure hardworking. In particular the invention aims to provide a material with specific mechanical characteristics significantly higher than those of the honeycomb.

 Another objective is to make it possible to manufacture a material capable of preserving good specific mechanical characteristics at high temperature.

 Another objective is to provide a material benefiting from easier operation compared to the honeycomb, by its ability to mold and press forming, which allow to confer any desired shape.

 Another objective is to indicate a process with great flexibility to adapt the properties of the material manufactured to the requirements of the envisaged applications (mechanical properties but also electrical, thermal, magnetic ...).

 Another objective is to provide an isotropic material having no preferred direction and in particular having no direction of buckling or sliding.

For this purpose the method according to the invention for manufacturing a modular composite material consists of
(a) using beads, each comprising a continuous skin located around a substantially spherical central core, said balls having adjacent external diameters greater than 0.6 mm,
(b) positioning said balls in contact with each other so as to approach a geometric distribution of the compact crystallographic type where each ball is in contact with the twelve neighbors with a void ratio of about 26%,
(c) fixing said balls thus positioned to each other by their contact zones, each ball being mechanically attached to the contiguous balls exclusive to its contact areas with the latter and having between these zones of fixing clear zones delimiting empty interstices between balls.

Thus the process of the invention leads to a material which is essentially characterized by
a well-defined compact distribution of balls which individually have thicknesses, diameters and predetermined natures,
a fixing of each ball to the twelve contiguous balls by the twelve contact zones that gives the aforementioned compact distribution,
empty interstices between balls, unaffected by the fastening material.

 Of course, these gaps may optionally be filled by means of a low density material to distribute the compressive forces exerted on the periphery of each ball. But it is important to note that it is not this possible filling material (of low density) which ensures the joining of the balls and the overall cohesion of the material: on the contrary, they are the multiple bindings of the balls between them, which gives its cohesion to the formed network, the mechanical properties of which do not depend substantially on the possible filling material of the interstices; the latter can thus be of very low density so as not to significantly increase the average density of the material, or else be totally absent, the interstices between balls being empty (that is to say occupied by air or where appropriate any other gas). In addition the central core of the balls is preferably empty (filled with air) each ball being formed by a skin or shell, continuous self-supporting. Such beads may in particular be manufactured using the method described in the French patent application filed simultaneously by the applicants.

Such a composite material has a very low specific weight since its only mass element resides in the hulls of the balls, the inner core of these and the external interstices having very low densities, possibly negligible (air). In addition, the mechanical resistance and frigidity of this material are remarkable because of
effects of convex vaults on which the efforts are distributed,
fasteners between balls, the geometric distribution of which results in an equidistribution of forces and allows the crews to work in good conditions to take all the transmitted forces (including tensile and shear forces).

 Experiments have shown that the specific mechanical characteristics of such a material are superior to those of the honeycomb (for identical constituent materials); likewise comparative tests carried out at equal specific weight (nickel-skinned balls, honeycomb aluminum alloy) have observed significantly better compression and shear characteristics in the case of the material of the invention than in that of the aeronautical type nest.

 In addition, the material of the invention has a spherical geometry which confers to it a macroscopic isotropy without privileged direction; in particular the tests have shown that a compression with increasing load generates a progressive plastic deformation of the material without buckling.

 Preferably, beads having an external diameter of between 1 mm and 20 mm and having a skin thickness of between 50 microns and 500 microns are used. These ranges of value make it possible in practice to perfectly control the shape and characteristics of each ball and their arrangement according to the compact distribution mentioned above, while allowing a very strong fixation in the contact areas without affecting the interstitial sites.

 These beads can be manufactured by any method and in particular in the case of empty hollow beads, by the method described in the patent application already mentioned, filed simultaneously with the present application.

 The device of the invention gives all flexibility to achieve the desired properties in each application by adapting the nature of the beads, their diameter and their skin thickness.

 It is possible in particular to use beads whose skin comprises at least one layer of metal or metal alloy with high mechanical, crystalline or amorphous characteristics, in particular nickel and its alloys or oxides, iron and its alloys or oxides, titanium and its alloys or oxides light alloys such as aluminum alloys (Au 4G ..) These beads lead to composite materials that constitute a remarkable compromise specific weight / mechanical performance.

 It is also possible to use beads whose skin comprises at least one layer of refractory material, in particular: refractory steel, cobalt and its alloys or oxides, molybdenum and its alloys or oxides, chromium and its alloys or oxides, tungsten and its alloys or oxides, ceramic ... The composite material obtained retains its specific mechanical properties at very high temperature.

 The method makes it possible, if necessary, to adapt the composite material to give it other specific properties: electrical insulation property by using balls made of insulating material (glass, ceramic, polymeric synthetic material, etc.), thermal insulation properties (use of insulating balls: ceramic), magnetic properties (use of ferromagnetic or ferrimagnetic material: iron oxide), elastic damping property using beads whose skin comprises at least one layer of elastic material (elastomer) ...

 In addition, the balls can be provided with an outer layer of a material resistant to corrosion (metal amorphous, chrone ...).

 Moreover, according to a preferred embodiment, the balls are attached to each other by soldering, by applying a thin film of a solder product around their skin and heating the assembly after positioning the beads. balls at a suitable soldering temperature.

 The brazing product may be deposited either in the form of a powder applied before the positioning of the beads or in the form of a thin layer deposited by any physical or chemical method during the manufacture of the beads. During its fusion, the brazing product concentrates by capillarity around the contact zones and forms a meniscus ensuring the mechanical fixing of the balls together.

 The beads can also be fixed by any other means and in particular by gluing, by coating their skin with a thin film of polymerizable glue and allowing the glue to polymerize after positioning the beads.

 The material according to the invention has the considerable advantage of being moldable and press-formable; it can be molded to manufacture pieces of various predetermined shapes, that is to say parts limited on their periphery by an envelope, or bare parts.

 In the case of a bare part, the process is carried out in a mold of shape corresponding to that of the part, the fixing of the balls together being carried out under conditions suitable for preventing adhesion of the balls to the mold in order to allow to unmold the piece after fixing the balls together. For example, in the case of brazing of the balls, it is possible to coat the mold with a solder inhibitor (or to provide a mold made of a non-brazeable material).

 In the case of a part provided with an envelope on the periphery, the method of the invention is implemented in a mold constituted by this envelope and the peripheral beads are fixed to said envelope by their contact zones with that envelope. this. The fixing of the balls on the envelope can in particular be carried out at the same time as the fixing of the balls together (soldering, gluing, etc.). This gives a piece whose surface state is continuous at the envelope, surface condition that can be adapted to each application.

 From p 1 u-s the character n or 1 ah the composite material according to the invention allows to integrate inside thereof inserts with good transmission of the forces between insert and material.

 Furthermore, according to a first embodiment, the positioning of the balls relative to each other is achieved by placing them in a mold and subjecting said mold to a vibratory movement of small amplitude relative to the diameter of the balls. The beads are thus distributed naturally in a compact stack in which each ball located in the heart is in contact with twelve others. This arrangement is obtained in each volume where the balls are of diameter me and conditions the mechanical properties of the material obtained after fixing the balls by their contact areas.

 It is also possible to position the balls individually in the mold in successive layers so as to obtain the aforementioned geometric distribution. This individual positioning makes it possible, if necessary, to modify the characteristics of the balls according to their position, while keeping them of identical diameters; this distribution, where the balls are different according to the zones considered (skin thickness, nature), makes it possible to produce a material with differentiated properties from one zone to another, in order to respond to non-uniform stresses (mechanical, thermal, electrical stresses). ...).

 The invention extends, as a new product, to the modular composite material manufactured by implementing the method defined above, as well as to the molded parts obtained with this material. Said material is essentially characterized by the presence of a plurality of balls with external diameters greater than 0.6 nm, by diameters of neighboring balls in elementary volumes of the material, by a geometric distribution of the balls close to the crystallographic type distribution. compact, and by fasteners contiyubs balls to each other exclusively by their contact areas.

The invention is illustrated by the following description with reference to the accompanying drawing; on this drawing
FIG. 1 is a schematic perspective view of a part obtained by implementing the method of the invention,
FIG. 2 schematically represents hollow balls used in the manufacture of said part,
FIG. 3 illustrates the first step of the method described by way of example,
FIG. 4 illustrates the operation of positioning the balls,
FIG. 5 is a sectional view of the part obtained by a plane A,
FIG. 6 is a detailed diagram showing an attachment between balls,
- Figure 7 is a sectional view of a test piece formed by the material according to the invention, which has been subjected to comparative tests.

 The part to be executed represented at 1 in FIG. 1 has the shape of a wing section comprising a peripheral envelope 10. Its optimum filling rate has been defined beforehand by calculation and has made it possible to delimit four elementary volumes z1, Z2, Z3, Z4 to which correspond different diameters of balls.

 FIG. 2 represents said hollow balls 2, 3, 4 whose natures and thicknesses of skin are identical (thickness: 120 microns, nature: nickel). The diameters of the balls are 2.5 minutes, 4 mm and 6 mm. These beads were manufactured by the method described in the patent application already mentioned, filed simultaneously with the present.

They are in a first step coated with a solder powder symbolized at 5 in FIG. 2; the solder used is a nickel base solder available commercially as "LM" manufactured by "WAL-COOLONOY" and bonded by cement ("Nicrobraz 300R").

 The deposition of solder 5 on the balls is carried out in a kneader 6 (FIG. 3) in which the solder, the cement then the balls are successively introduced via conduits 7, 8, 9.

 The amount of solder powder introduced is 3.9 g / dm 2 of ball area. The liquid cement is introduced at a rate of 0.2 ml per gram of powder.

 The mixing is carried out until a uniform recovery of the surface of the balls.

 Figure 4 shows the part 1 in execution. In this example the envelope ln of the room is used as mold. This is placed on a graphite base 1 1 on which has previously deposited a layer of anti-wetting, one open face of the workpiece being in contact with the graphite base, while the other serves as a filling port . The mold formed by the envelope is coated on its inner surface with solder powder and partitioned by three brazing foils 12 delimiting the elementary volumes.

The assembly is placed on a vibrating table 13, the amplitude of vibration is of the order of ten microns.

 The solder-coated balls are introduced through the upper orifice into the respective compartments defined above. The balls 6 mm in diameter are arranged in the compartment corresponding to the volume Z2, the balls of 4 minutes in diameter in the volume Z3, and the balls of 2.5 mm in the volumes Z1 and Z4. These balls are positioned under the effect of their weight and vibrations they come naturally constitute between them a compact stack. This compact stack is obtained almost optimally after 5 minutes and is shown schematically in Figure 5; this stack is found in all elementary volumes and is compact crystallographic type where each ball located in the core of the material is in contact with twelve others, the vacuum coefficient being about 26 S.

The piece is then placed in a vacuum oven. Brazing conditions are as follows
pressure: 3 10-4 millibar
- temperature: 9200 (20 minutes), 10700 (15 minutes)
- rate of rise in temperature: 0.050 C / minute
- duration of the brazing stage: 15 minutes
- cooling: gas pressure 0.3 bar (nitrogen)
After complete cooling of the oven the clamp is extracted and released from the graphite plate.

 Figure 6 shows a soldering detail of the balls together. There appears a meniscus of ~ solder 14 around each contact zone; these meniscuses fix mechanically the balls between them and leave free the interstices between balls.

 This example illustrates the manufacture by molding of a mechanical part of form. The property of modularity of the material is exploited by implementing balls of different diameters in volumes predetermined by the calculation. The compact assemblies obtained in each of these volumes make it possible to approach a macroscopic isotropy of the distribution of the stresses.

 It should be noted that, in each elementary volume, the balls have a constant diameter which conditions the compact geometric distribution mentioned above.

However, it is possible to modify in each volume the nature and the thickness of the skin (keeping the external diameter) to give the piece evolutionary properties in different areas of the volume, for example progressive or non-progressive evolution of a face open to the other. Similarly, it is possible when positioning the balls to house an insert in the heart of the material as is often necessary in aeronautics.

 To characterize the composite material from the mechanical point of view, a parallelepipedal specimen 15 delimited by an envelope formed of two parallel sheets 16 and 17 (FIG. 7) was produced.

 This specimen consists of a compact stack of hollow spheres of nickel 6 mm in diameter and 120 microns thick. The manufacture of the test piece was carried out by filling a mold whose two opposite vertical walls are covered by sheets 16 and 17 (made of stainless steel "Z6 CN 18.10" and of thickness 0.4 mm); these sheets are coated with solder powder; the distance between sheets is 15.2 mm. your other two faces and the bottom of the mold are coated with an anti-wrinkling layer.

 Before introduction of the balls into the mold, they are coated with solder powder under the conditions already described.

 In the monent filling, the mold is subjected to a vibratory movement to ensure the positioning of the balls in a compact distribution.

 The mold is then placed in the oven and the brazing is carried out under the conditions already described.

The table below gives the specific mechanical stresses obtained, compared to those of the honeycomb made of light alloy of aeronautical quality of the same specific weight.

<tb><SEP> Constraint
<tb> Material <SEP>: <SEP> Density <SEP>: ---------------------------- <SEP>
<tb><SEP> Compression <SEP>: <SEP> Shear
<tb><SEP><SEP> limit of <SEP> limit <SEP> limit of <SEP> deforma- <SEP>
<tb><SEP> ss <SEP> (bars) <SEP> permanent <SEP> tison
<tb><SEP> (bars) <SEP>
<tb> Nest <SEP> AG3 <SEP> = <SEP> 15
<tb> Bee <SEP>: <SEP> 14.5 <SEP>: <SEP> AC5 <SEP> = <SEP> 21
<tb><SEP> AU4G <SEP> = <SEP> 22.5 <SEP>
<tb> composite <SEP>
<tb> invention <SEP> 0.5 <SEP> 23.5
<tb> Nest
<tb><SEP> (AG3 <SEP> = <SEP> 26
<tb> Bee <SEP> 0.7 <SEP>: Direction <SEP> L <SEP> (AG5 <SEP> = <SEP> 32.5
<tb><SEP> (AU4G <SEP> = <SEP> 30
<tb><SEP> (AG3 <SEP> = <SEP> 16
<tb><SEP> Direction <SEP> W <SEP> (AG5 <SEP> = <SEP> 18.5
<tb><SEP> (AU4G <SEP> = <SEP> 17.5
<tb> Composite
<tb> invention <SEP> 0.7 <SEP> 42
<Tb>

The ranges of values given in the case of
Honeycomb correspond to the three shades of light alloys most used "AU4G", "AG5", "AG3".

 As much in compression as in shear, the specific characteristics obtained are superior or at least equal to that of the honeycomb.

 These tests show the interest of such a modular material, isotropic and moldable whose specific mechanical properties are well suited for use in aeronautics as a structural material.

Claims (23)

 1 / A method of manufacturing a modular composite material, characterized in that it consists  (a) using beads, each comprising a continuous skin located around a substantially spherical central core, said beads having adjacent external diameters greater than 0.6 mm,  (b) positioning said balls in contact with each other so as to approach a geometric distribution of the compact crystallographic type where each ball is in contact with the twelve neighbors with a void ratio of about 26%,  (c) fixing said balls thus positioned one to the other by their contact zones, each ball being mechanically fixed to the contiguous balls exclusively by its zones of contact with the latter and having between these fixing zones open areas delimiting empty interstices; between balls.  2 / A method according to claim 1, characterized in that (a) one uses beads of outer diameter between 1 min and 20 mm, having a skin thickness of between 50 microns and 500 microns.  3 / A method according to one of claims 1 or 2, characterized in that (a) one uses beads having an empty central core and a self-supporting continuous skin.  4 / A method according to one of claims 1, 2 or 3, characterized in that (a) is used beads whose skin comprises at least one layer of metal or metal alloy with high mechanical properties.  5 / A method according to one of claims 1, 2, 3 or 4, characterized in that (a) is used beads whose skin comprises at least one layer of refractory material.  6 / A method according to one of claims 1, 2, 3, 4 or 5, characterized in that (a) is used beads whose skin comprises at least one layer of an insulating material on the electrical plane.  7 / A method according to one of claims 1, 2, 3, 4, 5 or 6, characterized in that (a) is used beads whose skin comprises at least one layer of a thermally insulating material .  8 / A method according to one of s-s claims 1, 2, 3, 4, 5, 6 or 7, characterized in that (a) one uses beads whose skin comprises at least a layer of ferro material -nagnetic, or ferrimagnetic.  9 / A method according to one of claims 1 2, 3, 6, 7, characterized in that (a) one uses beads whose p e ti c o m e d at least one layer of elastic material.  10 / A method according to one of claims 1, 2, 3 or 4, characterized in that (a) is used multilayer skin beads composed of at least two different layers, each according to one of claims 6, 7, 8 or 9 for the purpose of determining the properties of said layers.  11 / A method according to one of claims 1, 2, 3, & 5, 6, 7, 8, 9 or 10, characterized in that (b) the bill-es are positioned by placing them in a mold and submitting said mold has a vibratory movement of small amplitude relative to the diameter of the balls.  12 / A method according to one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, characterized in that (b) the balls are positioned in a mold by an individual implementation an successive layers so as to obtain the aforementioned geometric distribution.  13 / A method according to one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, characterized in that (c) the balls are fixed to each other by soldering , by applying a thin film of a solder around their skin and heating the assembly after positioning the balls 9 at a suitable soldering temperature.  14 / A method according to one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, characterized in that (c) the balls are fixed to each other by gluing , by coating their skin with a thin film of polymerizable glue and allowing the glue to polymerize after positioning the beads.  15 / A method according to one of the preceding claims, characterized in that, after fixation of the balls, (d) one fills the empty interstices between balls by means of a low density material, able to distribute the compression forces exercising on the periphery of each ball.  16 / A method according to one of the preceding claims for producing a material having differentiated properties from one area to another, characterized in that, during their positioning (b), the balls are distributed so as to constitute several contiguous zones, the balls used in one zone being different from those used in another zone.  17 / A method of manufacturing a piece of predetermined shape, made of modular composite material and limited on its periphery by a casing (10) characterized in that:  the method according to one of claims 11 or 12 is implemented in a mold constituted by the envelope (10) mentioned above,  and the peripheral beads are fixed to said envelope by their areas of contact therewith.  18 / manufacturing method according to claim 17, characterized in that the fixing of the balls on the casing is performed at the same time as the fixing of the balls together, by brazing or gluing.  19 / A method of manufacturing a naked piece of predetermined shape, made of modular composite material, characterized in that  the method according to one of claims 11 or 12 is implemented in a mold of shape corresponding to that of the part, the fixing of the balls together being carried out under conditions suitable for preventing adhesion of the balls to the mold,  the part obtained is then demolded.  20 / modular composite material made by implementing the method according to one of claims 1 to 16, characterized by the presence of a plurality of balls (2, 3, 4) with external diameters greater than 0.6 mm, the diameter of the balls being close in elementary volumes of the material (Z1, Z22 Z3 Z4), said balls being geometrically arranged in a distribution close to the compact crystallographic type distribution, and being fixed to each other exclusively by their contact zones (14).  21 / A modular composite material according to claim 20 wherein each ball is hollow and formed by a skin self-supporting at least one layer.  22. The modular composite material according to claim 21, wherein each layer of the skin of each ball is made of a material of the group: nickel, iron, titanium, chromium, molybdenum, tungsten, cobalt, or their alloys or oxides, crystallized or amorphous. , aluminum alloy, refractory steel, ceramic, synthetic material, elastomers.  23 / molded piece of a modular composite material according to one of claims 20, 21 or 22.