EP0374013A1 - Method of producing composite structures for the absorption of noise, and composite structures, made by this method - Google Patents

Abstract

The subject of the present invention is a method of producing a composite structure and a structure obtained using this method for the absorption of noise, characterised by the following stages: - at least one three-dimensional structure (10) is produced, delimiting spaces between its components; - the said spaces are filled with a plurality of silica-rich volumes (3); - and the said structure (10) and the said volumes (3) are surrounded by a flexible covering skin capable of withstanding great elongation in order to form a deformable or thermoformable structure with a constant volume (4). The invention is applicable to the absorption of noise from noisy land vehicles, sea surface supports and underwater vehicles.

Description

The subject of the present invention is a method of manufacturing composite structures for the absorption of noise and of composite structures obtained by said method.

The technical sector of the invention is that of the means used and finding their application in the absorption of noise and more particularly of noises produced by mechanical devices, in particular vehicles operating in an aquatic environment, such as surface ships or submarines.

Are known, of course, in the context of the means currently used for absorbing noise, complexes comprising one or more layers of natural or artificial fiber materials or even from flexible or rigid synthetic foam.

In general, such materials are used inside the noise-generating enclosure and thus cover the internal face of the compartments in which there are particularly noisy machines such as, for example, air compressor units and Diesel engines.

Such coatings are more particularly used on machines operating in the atmosphere and even in this application, they have the disadvantage of being subject to soiling and to some deterioration due to splashes of oil and / or fuel oil or diesel.

On submerged vehicles, if they can of course be used as for terrestrial equipment in internal lining of engine or other compartments, with the same drawbacks as those stated above, they are not suitable for use outside the hull, especially outside the hull of an underwater vehicle operating at great depths.

We also know the use of double glazing to overcome heat losses and isolate outside noise, such use responding to the application of the principle of the propagation of a wave in a multilayer medium also called random periodic structure .

Such thermal and phonic insulating means are widely used in the building sector and because of their rigid state and the very nature of their components, they are absolutely not suitable for industrial or marine applications such as those which have been given. above.

For the implementation of the composite structures according to the invention, a theoretical principle known as "mechanical quadrupole" is applied by assimilation to electric quadrupoles.

The mechanical quadrupole has been defined as a linear viscoleastic system comprising four "inputs", two of which are displacements and two of which are forces.

From this principle, we have been able to design a composite structure capable of absorbing the energy of the incident wave by dissipation within said structure by intergranular friction.

An imperative for the implementation of such a structure is that the system always remains in the state of a linear viscoelastic system or of a random acoustic wave guide.

If E is posed as being the energy of the propagated wave before it meets said structure;
E1 the energy of the wave dissipated at the heart of it, and E ′, the energy of the residual wave after passing through the structure, we will have: E ′ = E - E1.

This being stated, the objective of the present invention is to produce, from specific materials, composite structures whose assembly is homogeneous and capable of being exposed to the weather or immersed at great depths while retaining their properties of acoustic and / or heat filter.

This objective is achieved by the manufacturing process according to the invention for the absorption of noise, which is characterized by the following stages:
- At least one three-dimensional structure is produced delimiting spaces between its components;
- said spaces are filled with a plurality of volumes rich in silica;
- And said structure and said volumes are surrounded by a flexible covering skin capable of undergoing high elongations to form a deformable or thermoformable structure at constant volume.

In such a method, the three-dimensional structure of which is constituted by a weaving produced by means of synthetic fibers, at least one side of said weaving is covered with a layer of elastomeric resin so as to produce an impermeable covering skin;
- said weaving is filled, until saturation, with glass or silica-rich sand microbeads, so that the microbeads or grains of sand occupy all of the spaces existing between the fibers of said weaving;
- And the other faces of the weave are covered with a layer of said elastomeric resin to produce a closed and sealed composite plate.

In an application of this method from at least two three-dimensional weavings produced by means of synthetic fibers, a core is made up consisting of a layer of synthetic texture capable of undergoing permanent deformation and is applied and secured to each of the faces of this core at least one closed and sealed composite plate comprising a three-dimensional weaving filled with microbeads of glass or sand rich in silica surrounded by a skin of coating of elastomeric resin.

In another application of said method from at least four three-dimensional weaving, made using synthetic fibers.
- We realize a core consisting of a layer of a fibrous texture of synthetic material, capable of undergoing permanent deformation;
- Is applied and secured, on each of the faces of said core, a first closed and sealed composite plate comprising a three-dimensional weaving filled with microbeads of glass or sand rich in silica surrounded by a skin of elastomeric resin coating;
- And a second closed and sealed composite plate comprising a three-dimensional weaving filled with glass or silica-rich sand microbeads surrounded by an elastomeric resin coating skin is applied and secured to the external face of each of said first plates. .

In another application of said method, several of said closed and sealed composite plates are superimposed and secured on either side of said core. The same number is superimposed and secured on either side of said core said composite plates to produce a symmetrical periodic and anechoic structure.

According to the method and after its realization, the said symmetrical structure is placed in an enclosure and a vacuum is created to both dry the structure and reduce its compressibility in order to improve the granular "coordination" of the glass microbeads or of the grains sand.

In order to obtain, in addition to the absorption of noise but also the dissipation of heat through the plates by thermal conduction, metallic conductive threads extending at least from one side to the other are inserted into the three-dimensional weaving. Another of said plates to obtain, in addition to the absorption of noise, the dissipation of heat through the plates by thermal conduction.

In another embodiment and to obtain the same result as that which has just been stated, or coated, by soaking, the glass microbeads or the grains of sand with a metallic conductive paint.

By implementing the method, a composite structure is obtained capable of absorbing noise from at least three-dimensional weaving made from synthetic fibers, which structure is characterized in that it consists of at least a plate comprising, in addition to said weaving and until saturation, a plurality of microbeads or sand which occupy the totality of the spaces existing between the weaving fibers and an impermeable covering skin which tightly envelops said weaving and the microbeads or sand .

As regards the plates containing microbeads, these are made from silica and have a diameter of between 20 and 80 micrometers.

As regards the plates which contain silica-rich sand, it has a particle size between 80 and 1000 micrometers.

In one embodiment, a structure according to the invention consists of a core constituted by a fibrous synthetic texture capable of undergoing permanent deformation and on each of the faces of which is secured a closed and sealed composite plate comprising a filled three-dimensional weaving glass or silica-rich sand microbeads, which plate has an impermeable coating skin of elastomeric resin.

In another embodiment, said composite structure consists of a core and on either side thereof, several of said closed and sealed composite plates superimposed, the core and the plates being secured to each other using synthetic resin.

Such a structure can consist of said core and on either side of the same number of composite plates to form a symmetrical periodic and anechoic structure.

In order to improve the granular "coordination" of the glass microbeads and the grains of sand, such a composite structure according to the invention is in a compressed state. In this state, the synthetic texture core is permanently deformed.

To obtain, in addition to the absorption of noise but also the dissipation of heat through the plates by thermal conduction, the three-dimensional weaving comprises, in addition to said synthetic fibers, metallic conductive threads which extend at least from one face to the other. of said plates.

To obtain this result and in an alternative embodiment, the glass microbeads or the grains of sand are covered with a conductive metallic paint.

Preferably, said core consists of a texture of carbon fibers or polyester fibers.

The result of the present invention is the production from said materials, the nature of which has just been given, of composite structures whose assembly is of great homogeneity, such structures being liable to be exposed in an aggressive medium, weathering or even submerged at great depths while retaining their acoustic and / or heat filtering properties.

• - la figure 1 est une vue en perspective schématique, partiellement arrachée, illustrant une plaque constituée par une structure composite selon l'invention;
• - la figure 2 est une vue schématique en coupe de la plaque de la figure 1;
• - la figure 3 est une vue en coupe d'une structure composite selon l'invention comportant une âme d'une texture fibreuse et de part et d'autre de laquelle sont assemblées deux plaques superposées, identiques aux plaques des figures 1 et 2.

Other advantages and characteristics of the invention will emerge on reading the following description of such composite structures and their manufacturing process with reference to the appended drawing in which:

• - Figure 1 is a schematic perspective view, partially broken away, illustrating a plate formed by a composite structure according to the invention;
• - Figure 2 is a schematic sectional view of the plate of Figure 1;
• FIG. 3 is a sectional view of a composite structure according to the invention comprising a core of a fibrous texture and on either side of which two superimposed plates are assembled, identical to the plates of FIGS. 1 and 2.

Referring to the drawing, FIG. 1 represents a composite structure according to the invention taking the form of a plate 1.

For the implementation of such a plate 1 and according to the manufacturing method according to the invention, at least one three-dimensional structure 2 is produced, delimiting spaces 2f between its components; said spaces are filled with a plurality of volumes rich in silica 3 and said structure 2 and said volumes 3 are surrounded by a flexible covering skin 1a to 1e capable of undergoing high elongations of the order of 200%.

The product obtained by said process is thus a flexible plate comprising a closed and sealed envelope and which can be used alone for example to cover the internal faces of an engine compartment or of an air compressor or even to enter into the composition of 'A complex structure comprising for example four superposed plates 1 integral in pairs and fixed on either side of a core of fibrous texture as illustrated in Figure 3, such a structure can for example be used to cover outside, the hull of a surface ship or submarine operating in an aquatic environment at great depths to protect it from sonar sound wave detection devices.

According to the invention, the three-dimensional structure is constituted by a weaving produced by means of deformable synthetic fibers, for example polyester.

The waterproof coating skin which constitutes the formed and waterproof envelope is produced from an elastomeric resin, for example chosen from the family of butyls or silicones;
For the implementation of a plate 1, a three-dimensional weaving 2 is used, made of synthetic fibers, for example polyester, and comprising a weft 2a formed of fibers extending regularly sinuously to form vertices 2b / 2c coming substantially facing each other and a warp 2d, formed from fibers of the same kind and extending substantially perpendicular to the weft 2a. Said weaving 2 also includes a third fiber thread 2e which connects the tops 2b / 2c of weft threads.

The upper face of the weaving 2 is coated with a layer of elastomeric resin so as to produce an impermeable covering skin which constitutes the upper face 1a of the plate 1.

The underside of said weaving 2 is also coated with a layer of elastomeric resin in order to produce a skin of waterproof coating which constitutes the lower face 1b of said plate.

The spaces 2f existing between the threads of weaving fibers, glass microbeads or silica-rich sand 3 are then filled to saturation, so that said microbeads or the sand occupy all of the spaces 2f.

For example, the diameter of said microbeads is between 20 and 80 micrometers, the sand is, for example, of a particle size between 80 and 1000 micrometers.

Finally, the other side faces 1c / 1d / 1e of the plate 1 are coated with elastomeric resin to form a closed and sealed envelope.

Figure 2 of the drawing gives in section the composition of the plate of Figure 1, which thus consists of a three-dimensional weaving 2, as described above, and whose spaces 2f, delimited by the son of polyester fibers are filled to saturation with glass or silica-rich sand 3.

The weaving 2 and the microbeads or the sand 3 are closely surrounded by an envelope and skin of closed and waterproof coating 1a / 1b / 1d of elastomeric resin.

A composite structure according to the invention 4 is shown in cross section in FIG. 3 comprising several plates 5/6/7/8, identical to that which has just been described with reference to FIGS. 1 and 2.

For the implementation of such a structure, a core 9 is first produced consisting of a layer of a texture comprising synthetic fibers capable of undergoing permanent deformation. For example, the core 9 is made from carbon fibers or polyester fibers.

A first plate 5 is applied and secured or by means of a synthetic resin on the upper face 9a of the core 9 and on the upper face 9b, another first plate 6.

Said first plates 5 and 6 are identical to plate 1 in Figures 1 and 2 and are for example filled to saturation with glass microbeads.

On the outer face 5a / 6a of said first plates 5/6, a second composite plate 7/8 identical to plate 1 of FIGS. 1 and 2 is applied and secured by means of synthetic resin, which plates 7 and 8 are by example saturated with silica-rich sand.

It is specified that such a structure may comprise only two 5/6 plates, for example fixed on either side of the core 9 or even be composed of several superimposed plates and assembled on either side of the core 9, the number of these plates thus being greater than four to take as a reference the example illustrated in FIG. 3.

Similarly, in the embodiment of a structure comprising at least four plates, the arrangement of the plates filled with microbeads or sand could be reversed.

However, in order to obtain a periodic and anechoic composite structure and in a preferred embodiment, the same number of plates 5/7 and 6/8 is superimposed and secured on either side of the core 9 to result in a symmetrical structure, an example of which has been described above with reference to FIG. 3.

In order to improve the granular "coordination" of the glass microbeads or of the grains of sand 3, the plate 1 or the complex 4 is placed in an enclosure and a depression is created therein for both drying said plate 1 or said complex 4, and to reduce its compressibility.

In the compressed state of the structure 4, the core 9 is permanently deformed due to its composition from synthetic fibers, for example carbon or polyester.

According to one embodiment, and in order to obtain a composite structure as described with reference to FIGS. 1 and 2 or to FIG. 3, which in addition to the absorption of noise allows the dissipation of heat by thermal conduction, the weaving is inserted three-dimensional 2/10 metallic conductor wires, for example copper or aluminum.

Such threads are associated with synthetic fiber threads which make up the three-dimensional weavings and more particularly with threads 2e which connect the tops 2b / 2c of said weavings.

To obtain this same result and as a variant, said glass beads or the grains of sand are covered with a conductive metallic paint.

This operation is for example carried out by soaking the microbeads or sand in a bath of metallic paint, preferably but not limited to a silver-based paint.

Of course and without departing from the scope of the invention, the parts which have just been described by way of example with reference to FIGS. 1 to 3 may be replaced by a person skilled in the art by equivalent parts filling the same function.

Claims (21)

1. Method of manufacturing a composite structure (1/4) for noise absorption, characterized by the following steps:
- At least one three-dimensional structure (2/10) is produced delimiting spaces (2f) between its components;
- said spaces (2f) are filled with a plurality of volumes (3) rich in silica;
- And surrounding said structure (2/10) and said volumes (3) by a flexible covering skin (1a to 1e) capable of undergoing strong elongations to form a deformable or thermoformable structure at constant volume (1/4). Method according to Claim 1, in which the said three-dimensional structure consists of a weaving (2) produced by means of synthetic fibers, characterized by the following operations:
- At least one side of said weaving (2) is covered with a layer of elastomeric resin (1a) so as to produce an impermeable coating skin;
- said weaving (2) is filled to saturation with glass or silica-rich sand microbeads (3), so that the microbeads or grains of sand occupy all of the spaces (2f) existing between the fibers of said weaving (2);
- And the other faces of the weaving are covered with a layer of said elastomeric resin (1a to 1e) to produce a closed and sealed composite plate (1). 3. Method according to any one of claims 1 and 2 implemented from at least two three-dimensional weavings (2) produced by means of synthetic fibers, characterized by the following operations:
- a core (9) is produced, consisting of a layer of synthetic texture capable of undergoing permanent deformation,
- And we apply and secure on each of the faces (9a / 9b) of this core, at least one closed and sealed composite plate (5/6) comprising a three-dimensional weaving (2) filled with glass or sand microbeads enriched with silica (3) surrounded by an elastomeric resin coating skin (1a to 1e). 4. Method according to any one of claims 1 and 2, implemented from at least four three-dimensional weavings (2), produced by means of synthetic fibers, characterized by the following operations:
- A core (9) is made up consisting of a layer of a fibrous texture of synthetic material capable of undergoing permanent deformation;
- applying and securing on each of the faces (9a / 9b) of said core (9) a first closed and sealed composite plate (5/6) comprising a three-dimensional weaving (2) filled with glass or sand-rich microbeads silica (3) surrounded by an elastomeric resin coating skin (1a to 1e);
- And is applied and secured on the outer face (5a / 6a) of each of said first plates (5/6) a second closed and sealed composite plate (7/8) comprising a three-dimensional weaving (2), filled with microbeads glass or sand rich in silica (3) surrounded by an elastomeric resin coating skin (1a to 1e). 5. Method according to any one of claims 3 and 4, characterized in that it is superimposed and joined together and other of said core (9) several of said closed and sealed composite plates (1/5/6/7/8). 6. Method according to claim 5, characterized in that the same number of said composite plates (5 / 7-6 / 8) are superimposed and secured on either side of said core (9) to produce a structure symmetric periodic and anechoic (4). 7. Method according to any one of claims 1 to 6, characterized in that after its completion, said symmetrical structure (4) is placed in an enclosure and what creates a depression, to both dry the structure and reduce its compressibility in order to improve the granular "coordination" of the glass or sand grain microbeads (3). 8. Method according to any one of claims 1 to 7, characterized in that there is inserted into the three-dimensional weaving (2), metallic conductive son extending at least from one face (1a) to the other ( 1b) of said plates to obtain, in addition to the absorption of noise, the dissipation of heat through the plates by thermal conduction. 9. Method according to any one of claims 1 to 7, characterized in that the glass microbeads or the grains of sand (3) are coated by soaking with a conductive metallic paint to obtain, in addition to noise absorption , heat dissipation through the plates (1/5/6/7/8) by thermal conduction. 10. Composite structure for noise absorption, comprising at least three-dimensional weaving made from synthetic fibers (2), characterized in that it consists of at least one plate (1) comprising, in addition to said weaving (2 ) and until saturation, a plurality of microbeads or sand (3) which occupy all of the spaces (2f) existing between the weaving fibers and an impermeable covering skin (1a to 1e) which tightly envelops said weaving (2) and microbeads or sand (3). 11. Structure according to claim 10, characterized in that the microbeads (3) are made from silica and have a diameter between 20 and 80 micrometers. 12. Structure according to claim 10, characterized in that the sand (3) is rich in silica and has a particle size between 80 and 1000 micrometers. 13. Structure according to any one of claims 10 to 12, characterized in that the covering skin (1a to 1e), which envelops the weaving (2) and the microbeads or the sand (3) is made of elastomeric resin. 14. Structure according to any one of claims 10 to 13, characterized in that it consists of a core (9) constituted by a fibrous synthetic texture capable of undergoing permanent deformation and on each of the faces (9a / 9b ) which is secured a closed and sealed composite plate (5/6) comprising a three-dimensional weaving (2) filled with glass or silica-rich sand microbeads (3), which plate (5/6) comprising a coating skin waterproof in elastomeric resin. 15. Structure according to any one of claims 10 to 13, characterized in that it consists of said core (9) and on either side thereof of several of said closed and waterproof composite plates superimposed (5 / 7-6 / 8) the core (9) and the plates (5 to 8) being secured to each other by means of a synthetic resin. 16. Structure according to claim 15, characterized in that it consists of said core (9) and on either side thereof of the same number of composite plates (5 / 7-6 / 8) to constitute a periodic and anechoic symmetrical structure (4). 17. Structure according to any one of claims 10 to 16, characterized in that it is in a state pure tablet to improve the granular "coordination" of glass microbeads or grains of sand (3). 18. Structure according to any one of claims 14 to 17, characterized in that by being compressed from the structure (4), the core of synthetic texture (9) is permanently deformed. 19. Structure according to any one of claims 10 to 18, characterized in that the three-dimensional weaving (2) comprises, in addition to said synthetic fibers (2a / 2d / 2e), metallic conductive wires which extend at least one facing (1a) to the other (1b) of said plates to obtain, in addition to the absorption of noise, the dissipation of heat through the plates by thermal conduction. 20. Structure according to any one of claims 10 to 18, characterized in that the microbeads or grains of sand (3) are covered with a conductive metallic paint to obtain, in addition to the absorption of noise, the dissipation of heat through the plates by thermal conduction. 21. Structure according to any one of claims 14 to 16 and 18, characterized in that said core (9) consists of a texture of carbon fibers or polyester fibers.

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