FR2616825A1 - Lightweight sandwich panel intended for the production of multilayer structure withstanding impacts and heat attacks - Google Patents

Abstract

A sandwich panel intended for the production of partitions, for example for building, of the type comprising a core 2 placed between two sole plates, outer 1 and inner 3. The outer sole plate 1 consists of a set of at least three layers integrally joined together by welding or adhesive bonding: a first layer 4 made of a composite material, a second layer 5 made of a cellular synthetic material with a low thermal conductivity coefficient, a third layer 6 obtained by lamination of a composite material. The second layer 5 consists of a honeycomb and the composite material of the first 4 and third 6 layers consists of resins reinforced with glass fibres. The resin incorporated into the first layer 4 is chosen from the group consisting of epoxy, polyester, phenolic or vinyl ester resins and the resin incorporated into the third layer 6 is an epoxy resin. The second layer 5 consists of polypropylene, a film 7 made of nonwoven polyester being arranged between the first 4 and second 5 layers and a layer 8 consisting of an aluminium foil is placed between the second 5 and third 6 layers. Application to the production of a wall for building construction.

Description

The technical sector of the present invention is that of sandwich panels providing passive protection, usable in the manufacture of multi-layer walls or partitions.
Sandwich panels are used to make structures with both high rigidity, low mass, possibly high thermal insulation, and self-extinguishing. Their applications are multiple building, aeronautics, aerospace industry, marine construction, transport, armament, etc. Furthermore, the constituent materials can be: metals (aluminum, titanium, steel, etc.), mineral products (cellular concrete, expanded or non-expanded plaster, etc.), or plastic materials (resins, organic composites reinforced with fibers, etc.). .

 In all cases, the sandwich panel is the result of the assembly of two external and internal flanges made of materials with high mechanical resistance and high modulus of deformability, and a core of low density, playing the role sole spacers.

 The two soles are made from metal sheets (Al, Ti, Steel, etc.), or laminates made of a resin + fiber couple (epoxy resins, polyester, phenolics, vinylester, thermoplastic, associated with glass fibers, carbon, kevlar), or extruded and / or calendered sheets (thermoplastics or others), or wood plates (plywood, etc.), or combinations of several of the aforementioned materials (aluminum sheet + plywood for example).

Souls are divided into three main families of materialK:
- expanded or lightened products, such as plastic foams, concretes, etc.,
- honeycomb products, honeycomb type, tubular spacers, or self-supporting ribbed plates, etc.,
- wood (balsa being the typical example).

 The method of manufacturing sandwich panels is characterized by the type of connection between the soles and the core.

Mainly, there are three modes of obtaining the sandwich material
- bonding, bonding, welding, or mechanical attachment, between each sole and the core,
- development of the sole directly in contact with the core, by molding or by stratification in contact (ex.

concrete, resin etc),
- expansion of the core, in situ casting between the two soles (eg: expanded plaster, foams, etc.).

 Given the diversity of the basic products mentioned above, it is possible to develop this or that property of the panel by preferably combining the materials according to their most advantageous properties.

Until now, the various constructions and structures made up of elementary panels were made of various materials, alone or combined, presenting notable drawbacks. Indeed
- thin mechanical sheets show deformation at the slightest impact received perpendicular or not to their surface; moreover, they are not easily repairable, and do not provide any thermal insulation,
- the laminates do not support buckling well; they do not constitute a firewall, and provide only relatively little thermal insulation,
- the thermoplastic sheets do not withstand the rise in temperature, nor with the flames and this for acceptable masses and surface costs,
- honeycombs and other aveolars are not thermal insulators,
- synthetic foams lose their mechanical characteristics when the temperature to which they are subjected rises above 80 to 100 OC.

As an indication, we can refer to patents
EP-A-155 335 and 111 520.

 The present invention aims to fill these gaps using a sandwich panel of low areal mass, and of low cost, capable of providing passive protection.

The invention therefore relates to a sandwich panel intended for the production of partitions for example for the building, of the type comprising a core interposed between two external and internal flanges, characterized in that the external flange consists of a set of at least three layers joined together by welding or gluing
- a first layer made of composite material,
- a second layer consisting of a cellular synthetic material with a low coefficient of thermal conductivity,
- a third layer obtained by laminating a composite material.

 The second layer consists of a honeycomb.

 The composite material of the first and third layers consists of resins reinforced with glass fibers.

 The resin incorporated in the first layer is chosen from the group consisting of epoxy, polyester, phenolic or vinylester resins and the resin incorporated in the third layer (6) is an epoxy resin.

 The second layer consists of polypropylene, a non-woven polyester film being placed between the first and second layers.

 A layer consisting of an aluminum film is interposed between the second and third layers.

 The aluminum film is covered with a film-forming thermoplastic film interposed between the second and third layers.

 The aluminum film is placed between a layer of polyethylene applied against the second layer and a layer of cotton fabric applied against the third layer.

 The cells of the second layer are filled with an inert gas, such as argon or nitrogen, or partially evacuated.

 The respective thickness of the first, second and third layers are 0.5 to 3 mm, 5 to 20 mm and 0.5 to 3 mm.

 The core consists of a plate of extruded polystyrene foam, the insole being identical to the outer sole or consisting of a metal plate, for example of aluminum or of a thermoplastic resin.

 According to the method for manufacturing the sandwich panel of the invention, the first and third layers are produced separately or simultaneously by stratification in contact with the second layer, the assembly obtained being compressed before polymerization of the resin of the laminate.

A result of the present invention lies in the fact that the sandwich panel is rigid, light, self-extinguishing, good thermal insulator for prolonged exposure to the sun, and has good resistance to flame, as well as to impact. These characteristics are checked by different tests
- shear test, to check the adhesion of the soles on the core,
- bending test, to check the bending stiffness and the puncture resistance,
- fire resistance test, to simulate the contact of the sandwich material with the flame of a blowtorch, and check the self-extinguishing of the system,
- impact test, to check the impact resistance of the sandwich sole,
- thermal insulation test.

Other advantages of the invention will be better understood on reading the additional description which follows of an embodiment given by way of example in relation to a drawing in which
FIG. 1 illustrates a schematic section of the panel according to the invention,
- Figure 2 illustrates the structure of an exemplary embodiment of the panel according to the invention.

 In Figure 1, there is shown in section a panel comprising a sole 1, a core 2 and a sole 3. - The sole 1 is external, that is to say that it is placed on the side exposed to various attacks likely to intervene. Of course, the insole 3 can be identical to the sole 1. It can be conventional, as shown schematically in this figure, that is to say constituted by a simple metallic skin of the aluminum, steel or titanium type, or else synthetic material of the thermoplastic type such as polyvinyl chloride or a composite such as a polyester resin / glass fiber laminate.

 The core 2 is produced using an extruded polystyrene plate.

 The sole 1 is advantageously a thin multilayer system, for example 5 to 20 mm. It comprises a first layer 4 or outer skin, a second layer 5 and a third layer 6 or inner skin.

 Layer 4, a few millimeters thick, is produced by laminating a thermosetting resin and reinforcements (glass, carbon, kevlar, or other fibers). Thin sheet metal can even be considered, if the problems of impact resistance or possibility of repair do not arise. If on the other hand, the fire resistance is not essential, a thermoplastic resin skin is satisfactory.

 A thickness of between 0.5 and 3 mm and more particularly between 1 and 2 mm will advantageously be chosen. The thermosetting resin is chosen from epoxy, polyester or phenolic resins, optionally tinted in a dark color, for example black, to limit the internal thermal radiation of this layer.

 The second layer 5, from a few millimeters to a few centimeters thick, for example 5 to 40 mm, is made of a material with high compressive strength. Depending on the actual practical application of the material, this layer 5 will be asked to be self-extinguishing, to give off no toxic gas or smoke during its combustion, and to have a low coefficient of thermal conductivity. The layer 5 will therefore be, in this case, a cellular product, of the honeycomb type made of thermoplastic material of the polypropylene type or an acrylonitrile / butadiene / styrene polymer. The cells can advantageously contain an interesting gas (nitrogen, argon, etc.) or placed under partial vacuum.

 The definition of layer 6 is the same as that of layer 4. The face of layer 6 opposite layer 4 radiates energy towards the latter. It is therefore advantageous to increase the thermal emission coefficient of this face, by placing, for example, an aluminum film at the interface between layer 5 and layer 6. The absorption of thermal radiation from the layer 6 is thus greatly reduced, and it therefore remains cold longer.

 As a variant, the aluminum film can be coated with a film-forming thermoplastic material which is welded by hot compression on the layer 5.

 Another variant consists in providing a three-layer polyethylene / aluminum / cotton film, the polyethylene layer being made adherent to layer 5.

 All the layers 4, 5, 6 and the aluminum film are assembled by gluing or welding, the whole forming the sole 1.

 The insole 3 can be a multilayer sole, made like the sole 1, or a conventional single skin, metallic or not as indicated above.

 The two soles 1 and 3 are fixed on either side of the friend 2, of the alveolar type, about 5 centimeters thick. The connection is also made by gluing or welding.

EXAMPLE OF IMPLEMENTATION
In Figure 2, there is shown a sandwich panel whose various layers are assembled by first making the sole l, from the outside to the inside. This order is not imperative and can be obviously modified by a person skilled in the art.

 This outer sole 1 is in the form of a multilayer structure formed by layers 4, 5 and 6.

Layer 4 is made of composite material, consisting of epoxy resin and glass fibers with a thickness of the order of 1.5 mm. Layer 5 is a 10 mm thick polypropylene honeycomb, the face of which, on layer 4 side, is coated with a film 7 of non-woven polyester.

 Layer 4 is laminated directly in contact with honeycomb layer 5, on the side of layer 7 of non-woven polyester. The connection of layer 4 with layer 5 is thus immediate.

 On the other side of the honeycomb layer 5, a three-layer polyethylene / aluminum / cotton film 8 is thus deposited by welding. By welding, a bond is created between the polypropylene of the honeycomb and the polyethylene of the film 8.

 Then layer 6 is made of epoxy resin / glass fiber composite. The stratification is done directly on the cotton canvas of the three-layer film 8.

- soul 2
The core 2, 30 mm thick, consists of an extruded polystyrene plate. It is deposited on the stratification of layer 6 before polymerization of the epoxy resin. By compression and after polymerization, the friend 2 becomes integral with the layer 6.

- insole 3
Finally, we stick. on the other face of friend 2, a 1 mm thick sheet of aluminum alloy, thus constituting the inner face.

Such a panel has a surface mass of less than 10 kg / m2 and has characteristics of
- rigidity,
- temperature resistance,
- reduction of the heat exchange between the external environment and the soul,
- shock resistance of the sole,
- flame resistance of the sole,
- resistance to punching of the sole,
- limitation of combustion on contact with flames,
- reduction in the time required to stop ignition, during combustion, significantly improved.

 On a panel conforming to FIG. 2, bending, shearing, fire behavior, impact, thermal insulation, sunshine and flammability tests were carried out, showing the advantage of this type of structure. .

BENDING TEST
A panel 750 mm long and 400 mm wide resting on two cylinders with a radius of 50 mm is subjected to compression in the middle. The minimum breaking load obtained is approximately 11,000 N, which is higher than the conventional standard of 8,000 N.

SHEAR TEST
The panel is immobilized at the core and a traction is exerted using a jaw on one of the soles with a speed of 4.2.10 4 m / s. The shear breaking stress obtained is 3.105 Pa, which is higher than the standard standard of 105 Pa.

FIRE BEHAVIOR
A flame at 1000 OC is applied perpendicular to a 600x600 mm panel, for 72 seconds. After removing the flame, the extinction time, which is less than 10 seconds, is measured.

SHOCK TEST
We drop a 3 kg ball from a height of 2 m on a panel resting on a wooden frame. After numerous tests, no deformation or delamination is observed at the location of the impacts.

THERMAL INSULATION TEST
An insulating box is made using a panel which is exposed to the sun for a day. It is found that the temperature inside the panel remains below the temperature of use of the material. On the other hand, the temperature inside the box does not change significantly, which makes it possible to appreciate the insulating power of the panel.

SUNLIGHT TEST
During exposure to the sun, layer 4, directly subjected to radiation absorbs energy and therefore heats up. On the other hand, it radiates energy in proportion to its temperature.

 The part of the radiation emitted towards the inside of the panel passes through the honeycomb 5, and is reflected on the aluminum of the film 8. This radiation is absorbed again by the layer 4.

 In this way, layer 4 radiates outwards, while layer 6 stays cold. The temperature of the foam constituting layer 5 remains significantly lower than its operating temperature (750C). The only heat exchange towards the inside of the panel is by convection. The use of a gas with low thermal conductivity such as nitrogen or argon, therefore improves the system.

FLAMMABILITY TEST
When exposed to a blowtorch, the resin in layer 4 burns, as does the polypropylene honeycomb in layer 5.

 Combustion is stopped by the aluminum film.

Layer 6 is therefore not deteriorated. The foam of the core 2 made of polystyrene shrinks with heat. Combustion stops completely by itself. The system is then repairable.

The panel according to the invention can be used in any type of construction,
- modular intervention hospital walls,
- frame panels,
- light rigid structures,
- various decking and panels for engineering crossing equipment.

Claims (12)

- CLAIMS  1 - Sandwich panel intended for the production of partitions for example for the building, of the type comprising a core (2) interposed between two external (1) and internal (3) footings, characterized in that the external footing (1) is consisting of a set of at least three layers joined together by welding or gluing  a first layer (4) made of composite material,  - a second layer (5) consisting of a cellular synthetic material with a low coefficient of thermal conductivity,  - a third layer (6) obtained by laminating a composite material.  2 - Panel according to claim 1, characterized in that the second layer (5) consists of a honeycomb.  3 - Panel according to claim 2, characterized in that the composite material of the first (4) and third (6) layers consists of resins reinforced with glass fibers.  4 - Panel according to claim 3, characterized in that the resin incorporated in the first layer (4) is chosen from the group consisting of epoxy, polyester, phenolic or vinylester resins and that the resin incorporated in the third layer ( 6) is an epoxy resin.  5 - Panel according to any one of claims 1 to 4, characterized in that the second layer (5) consists of polypropylene, a film (7) of woven m2m polyester being disposed between the first (4) and second ( 5) cassettes.  6 - Panel according to any one of claims 1 to 5, characterized in that a layer (8) consisting of an aluminum film is interposed between the second (and third (6) layers.  7 - Panel according to claim 6, characterized in that the aluminum film is covered with a film-forming thermoplastic film interposed between the second (5) and third (6) layers.  8 - Panel according to claim 6, characterized in that the aluminum film is disposed between a layer of polyethylene applied against the second layer (5) and a layer of cotton fabric applied against the third layer (6).  9 - Panel according to any one of claims 1 to 8, characterized in that the cells of the second layer (5) are filled with an inert gas, such as argon or nitrogen, or partially evacuated.  10 - Panel according to any one of the preceding claims, characterized in that the respective thickness of the first (4), second (5) and third (6) layers are 0.5 to 3 mm, 5 to 20 mm and 0 , 5 to 3 mm.  11 - Panel according to any one of the preceding claims, characterized in that the core (2) is constituted by a plate of extruded polystyrene foam, the internal sole (3) being identical to the external sole (1) or constituted a metal plate, for example aluminum or a thermoplastic resin.  12 - Process for manufacturing a sandwich panel according to any one of the preceding claims, characterized in that the first (4) and third (6) layers are produced separately or simultaneously by laminating in contact with the second layer (5) , the assembly obtained being compressed before polymerization of the resin of the laminate.