ITRM20070501A1 - PANEL IN COMPOSITE MATERIALS RESISTANT TO THE FLAME THROUGH AERO, NAVAL AND LAND APPLICATIONS AND ITS LOCKING SYSTEMS. - Google Patents

Description

Description of the invention entitled:

"THROUGH FLAME RESISTANT COMPOSITE MATERIAL PANEL FOR AERO, NAVAL AND LAND APPLICATIONS AND ITS LOCKING SYSTEMS"

DESCRIPTION

Technical sector

The present invention refers in general to the aeronautical industry and specifically concerns fire protection structures on aircraft, ships and land vehicles.

In particular, it concerns a panel made of composite materials, flame resistant, as well as such a panel with an integrated locking system to an aircraft or ship structure.

State of the art

Fire-resistant bulkheads and / or areas where fires can break out inside aircraft must by international law contain the fire so that other areas are not contaminated by the fire.

A typical example are the nacelles or the containers of the engines when external or the areas where the engines are positioned inside modern jets, helicopters, aircraft in general.

The materials that most frequently lend themselves to containing fires are generally thick metal alloys or super alloys as in the case of titanium SPF (super plastic forming). In the case of conventional metal alloys, aluminum alloys are used to contain the passage of a flame at 1100 ° C as required by UNI EN ISO 2685 which must be very thick to meet the requirements and therefore heavy or steel alloys too. they penalize the aircraft due to their weight. In the case of aluminum alloys, strong thicknesses are required as the melting of this material takes place at temperatures close to 600 ° C depending on the type of alloy, while for steels, which have much higher melting temperatures; Lower thicknesses are required, but despite these being reduced, given the high specific weight of the material, they are always heavy for aeronautical applications.

To overcome the problem of weight, a penalizing factor of the payload and consumption, and, more generally of the performance of the aircraft in applications where these requirements are of great importance, the titanium alloy SPF is used which in order to be formed on surfaces in the majority of irregular cases it requires extremely expensive non-recurring equipment and further more complex post-processing in order to control thicknesses: just to cite an example, the manufacture of one of the seven sub-components of the engine bays of a transonic jet in this material requires a sheet metal press molding with an initial thickness of 2 mm, a post electro-erosion to reach the thickness of 1.2 mm (quantity necessary given the geometries in order to contain the flame and guarantee the integrity of the structure for 3 minutes first) and the subsequent assembly with the other sub components to get then to obtain the assembled figure .

From this it is possible to observe and understand the extreme onerousness and laboriousness of the process which exploits the benefits of the Ti SPF alloy in addition to the extremely high cost of the material and its low availability.

Another technique to avoid the passage of the flame is to apply mats of ceramic materials or their derivatives to the planned structure to wait for the containment of any fire.

These structures have the drawback of adding weight to the primary structure and in most cases they are contaminated by liquids often present in the engine containment areas (engine bay, nacelle, external aerodynamic surfaces, in jets where the engines are incorporated in the fuselage) which they need to be replaced.

For the naval sector where the weight, while being important, is not of such great importance as in the aeronautical sector, the methodology used for the manufacture of fireproof bulkheads in GRP boats is to load very thick GRP laminates with alumina oxide which acts from flame retardant agent. With this methodology, in order to guarantee the non-passage of the flame through a GRP laminate in accordance with the UNI EN ISO 2685 standard, a minimum weight of over 25/30 kg / m <2> must be had, which often makes these laminated sheets preferable. of aluminum alloy with thicknesses close to 10 mm. The advantage in favor of this technique (that of loading GRP laminates with alumina oxide) is that of being able to form double-curved molded surfaces.

In any case, it should be noted that the residual mechanical characteristics of the structures responsible for their containment after a fire are almost non-existent.

In the aeronautical case, these structures containing the fire only serve to give the aircraft the possibility to land or to eject the crew.

With regard to the locking devices between a structure (KNS007 type panel, for example) in fire resistant composite materials, or another system that provides for the ablation of the part exposed to fire, the methodology with which to apply the said panel to a part of the fuselage or part serving as a fuselage, or as a fire bulkhead to the main structure, aircraft or ship, just to name a few examples, does not currently exist. Mechanical locking by means of screws, nails, etc., between the primary structure or simply the support to which the fireproof panel is fixed is not possible simply by using metal materials that connect the structure with the panel itself as the thermal conductivity of the materials conventionally used as locking members or metal alloys they have a high thermal conductivity that creates a thermal bridge between the fire and the cold part, canceling the effects caused by internal insulators, and refractories for the first impact to fire that guarantee the survival of the part cold.

In fact, the state of the art provides that the junctions between parts subject to flame and primary structures of airplanes, helicopters, ships, etc., are made by inserting thick materials, generally a metal alloy that does not degrade upon exposure to fire. for temperatures around 1000 ° for a time of about 15 minutes covered with covers applied over insulating materials. Therefore, the state of the art does not have solutions for the connection by mechanical members of a panel made of fire resistant composite materials with primary fire resistant structures.

Therefore, an object of the present invention, according to a first aspect thereof, is to provide a sandwich-type panel suitable for containing fires on aircraft, ships and possibly also in terrestrial structures, which is of very low weight, can be made with shapes pleasure, and through materials that are not difficult to find.

In particular, by applying such a panel to aerodynamic surfaces in general, to fuel tanks, to the nacelle of aircraft engines, as fireproof bulkheads, and where it is necessary to limit a fire on an air, land or naval vehicle, a weight is guaranteed very low and a formability at will, also significantly increasing the safety of the vehicle. Therefore, in airplanes in particular, where fire defense remains a problem that is still partially unresolved, especially in the case of emergency landings or fires during the flight, the sandwich panel of the present invention represents a significant step forward in the solution of this problem. for the benefit of an important increase in the “Air Safety” parameter, without influencing the payload.

Another object of the present invention relates to a panel of the aforesaid type, but which incorporates an innovative locking system. The sandwich panel can therefore be locked to the generic structure that houses it, without giving rise to thermal bridges that are dangerous for safety.

The innovative locking system of the panel, integrated into the sandwich panel itself, guarantees the effectiveness of the fastening to the support structure for a period sufficient to ensure, for example, the safety of passengers and / or crew of an airplane, ship, etc. in case of fire.

Description of the invention

The present invention, according to its first aspect, achieves its purposes by providing a fireproof panel made of composite materials and equipped with a sandwich structure, characterized by the fact that it comprises the following layers in order: - a first refractory layer in ceramic material of non-woven fabric (1), of a type already available on the market, located on the "warm side" of the panel;

- a second layer (2) of skins of long fiber fabrics, impregnated in a resin matrix;

- a third layer (3) of structural adhesive;

- a fourth layer (4) with a honeycomb structure designed to receive in its cells a powder of oxidic materials (oxide-based materials: silicon oxide or yttria-stabilized zirconium oxide) with low thermal conductivity;

- a fifth layer (5) of structural adhesive;

- a sixth layer (6), of skins of long fiber fabrics, impregnated in a resin matrix, or formed by a metal sheet, placed on the "cold side" of the panel and with thickness and characteristics according to the expected loads.

Other specific characteristics of the panel are indicated in dependent claims 2 to 15, which define various alternative embodiments.

The present invention, with regard to its second aspect, achieves its purposes by providing a fireproof panel made of composite materials and equipped with a sandwich structure, with a locking system incorporated in the same panel, for locking the panel to a generic structure of support, in which:

- there is an enlargement or excess thickness (7) of the thickness of the cold part, or sixth layer (6), located on the cold side of the panel, the enlargement (7) being made in correspondence with a locking screw (8);

- said locking screw (8) being incorporated, with its head, in the fourth layer (4) of the panel, having a honeycomb structure, in which, the threaded stem of the locking screw (8) protrudes from said side cold of the panel, in order to allow fixing to a support structure, while the head of the locking screw (8) remains hidden inside the panel, inside the honeycomb structure, to avoid direct contact with the flame of a possible fire on the warm side of the panel.

Preferably, the fireproof panel made of composite materials and equipped with a sandwich structure is such that said thickening or excess thickness (7) extends, in the direction parallel to the sides of the panel, for a distance substantially equal to the diameter of the head of the locking screw. (8) or for a distance that is a function of the loads expected to act on the panel.

Preferably, in correspondence with the head of the locking screw (8) of the locking system, the thickness (9) of the honeycomb structure of said fourth layer (4) of the fireproof panel which covers said head of the locking screw (8 ), is substantially identical to the thickness of the same fourth layer (4) in another region of the firestop panel where there is no locking screw (8), so that the amount of heat reaching the head of the locking screw ( 8) remains lower than that which would cause a dimensional increase such as to slit the hole in which the screw (8) itself is screwed.

Brief description of the drawings

The present invention will now be described in more detail only for illustrative, non-limiting or binding purposes, with reference to the attached drawings which illustrate some of its preferred embodiments, in which:

FIGURE 1 is a schematic sectional view of the various layers of the sandwich panel object of the present invention, before their mutual assembly;

FIGURE 2 is a sectional view of the sandwich panel of Figure 1, but which according to the second aspect of the invention also incorporates the innovative locking system.

Detailed description of some preferred embodiments Some preferred embodiments of the panel of the present invention will be described with reference to Figures 1 and 2, only so that a person skilled in the art can fully understand the invention and possibly reproduce it. Obviously the inventive concept is not limited to these embodiments and therefore a person skilled in the art can make changes without departing, in doing so, from the scope of protection of the present invention.

In a first possible embodiment, the panel comprises (see Fig. 1):

- Hot part, in a refractory material (1): non-woven ceramic fiber fabric weighing 70 g / m;

- long fiber fabrics (2) impregnated with resin: two skins of carbon fiber fabric or alternatively fabric of long fibers such as glass S, glass E, Kevlar with 29 or 49 Twaron count, basalt, and more generally woven of long fibers with a melting temperature higher than 1100 ° C and with warp and weft, or unidirectional of such fibers with crossed skins and with a minimum weight of 120 g / m <2> for each single skin;

- structural adhesive (3): in the form of film or paste with glass transition temperature after its polymerization> 120 ° C;

- honeycomb (4): made of material with a melting temperature above 1000 ° C with a cell of any size of the Nomex type and a minimum thickness of 6 mm or steel alloy; - powder of oxidic materials with thermal conductivity at 1000 ° C equal to 0.09 W / mK for filling the honeycomb cells;

- structural adhesive (5): in the form of film or paste with glass transition temperature after its polymerization> 120 ° C;

- cold part (6) formed by: two skins of carbon fiber fabric or alternatively fabric of long fibers such as glass S, glass E, Kevlar with 29 or 49 Twaron count, basalt, and more generally fabric of long fibers with melting temperature higher than 1100 ° made with a weft and a warp, or unidirectional of these fibers with crossed skins, with a minimum weight of 120 g / m <2> per single skin (note that these fibers are also impregnated with resin such as in the case of layer (2)).

The panel described in its main materials in sequence starting from the part exposed to fire (1) guarantees with a reduced weight of only 3.5 kg / m <2> the non-passage of the flame according to the UNI EN ISO 2685 standard and keeps it intact the cold part (6) in the case of the engine bays of the transonic Jet Trainer M346. After 15 minutes of exposure to the flame as required by the UNI EN ISO 2685 standard, flaking of the part exposed to fire (1) can be observed while the cold part (6) remains intact unless the mechanical characteristics of the laminate in operation deteriorate. of the resin used to manufacture the panel. The higher the TG (glass transition temperature) of the resin used (in the case of thermosetting resins) or the Vickat softening temperature (for thermoplastic resins), the lower their resin content% of the laminate of these resins, and the lower will be the decrease of the admissible loads to be used for the evaluation of the post-fire mechanical characteristics of the cold part.

From the above it is clear that with a very low weight panel that can be made with materials available on the market that for the first time have been assembled together, it is possible to solve the problem of weight in aeronautical structures and more generally in naval structures that have to wait for the containment of fires. . The weight expressed is the minimum with which it is possible to comply with the UNI EN ISO 2685 standard to which all aircraft that want to obtain the certifications to be able to fly must comply.

Even more important is the possibility of customizing according to the loads acting on the cold part which will remain unchanged after the fire unless there is a loss of structural value depending on the type of resin used and its percentage in the context of the laminate in the case of in composite materials or thickness if you want to use a thin sheet of aluminum alloy or steel for the cold part.

Therefore, it is clear from the above that it is sufficient to protect a structure as follows from the passing flame (second possible realization):

* non-woven ceramic fiber fabric weighing 70 g / m <2>;

* two skins of carbon fiber fabric or alternatively long fiber fabric of the type S glass, E glass, Kevlar with 29 or 49 Twaron count, basalt, and more generally long fiber fabric with melting temperature higher than 1100 ° C and with warp and weft, or unidirectional of such fibers with crossed skins, with a minimum weight of 120 g / m <2> for each single skin;

* structural adhesive in the form of film or paste with a glass transition temperature after its polymerization> 120 ° C;

* honeycomb made of material with a melting temperature above 1400 ° C with a cell of any size of the Nomex type and a minimum thickness of 6 mm;

* powder of oxidic materials with thermal conductivity at 1100 ° C equal to 0.09 wm / k to fill the honeycomb cells; * structural adhesive in film or paste form with glass transition temperature after its polymerization> 120 ° C.

The last missing point compared to the previous table which as an example could be represented by 3 skins of carbon fabric (of the type 8552S37% / AGP280 in which 8552S is the epoxy resin system used, 37% is the quantity of resin present in the laminate and AGP 280 is the weight of the fabric equal to 280 g / m, it has been suitably tested for its application as a substitute for the Ti SPF alloy in the manufacture of the engine bays of the transonic jet called M346.

The last missing point compared to the previous table being the temperature found on the cold skin after 15 minutes around 300 ° C could also be represented by a sheet of metal alloy of your choice. Provided it has a higher melting temperature equal to 300 ° C.

In its second aspect, the present invention relates - in one of its preferred embodiments - to the same panel described above with reference to Fig. 1, in any of its possible preferred embodiments indicated above, but with a locking system integrated therein clearly represented in section in Fig. 2.

As shown in Fig. 2, in order to lock the panel of the present invention to a generic support (not shown) which accommodates it, in the case of a fireproof bulkhead, the partition ordinate between the engine compartment and the cockpit of a jet or of a generic aircraft, it is necessary to take advantage of the system indicated which foresees to thicken the cold part (6) which remains intact after exposure to the flame, with an excess thickness (7) in relation to the diameter of the locking screw (8), and the loads acting on the panel and cover it with the same amount (9) in height of honeycomb filled with oxide materials and covered with lamination (see Fig. 1) and then the refractory (1) which is exposed to the part hot. In this way, the amount of heat that reaches the screw head is> 300 ° C which does not entail a dimensional increase for certain metal alloys which would slit the passage hole, making the locking of the panel on its support structure ineffective. We want the temperature taken as a reference of 300 ° C to be observed to be the maximum temperature reached by the cold part after 15 minutes of exposure to fire according to the UNI EN ISO 2685 test procedure.

Note that in Fig. 2, for the sole purpose of simplifying the drawing, the various layers 1, 2, 3 and 5, 6 of Fig. 1 have been represented only by two relative layers whose faces 1 and 6 correspond respectively to the side exposed to fire (hot side) 1 and to the cold side 6.

In addition, note that the refractory 1 joins (on the left in Fig. 2) to the cold part (at the edge of the panel), protecting the honeycomb 4 which is inside.

The formability of the panel of the present invention obviously means that the flat shape of the panel, shown in Figures 1 and 2, is obviously only exemplary and that any shape could be used depending on the shape of the support structure and the installation conditions and the application.

The present invention has been described in detail exclusively by way of non-binding example and various modifications may come to mind to a person skilled in the art while always remaining within the scope of the same inventive concept.

Claims (19)

CLAIMS 1. Fireproof panel made of composite materials and equipped with a sandwich structure, characterized by the fact that it includes the following layers in the order: - a first refractory layer in ceramic material of non-woven fabric (1), of a type already available on the market, located on the "warm side" of the panel; - a second layer (2) of skins of long fiber fabrics, impregnated in a resin matrix; - a third layer (3) of structural adhesive; - a fourth layer (4) with a honeycomb structure designed to receive in its cells a powder of oxide materials with low thermal conductivity; - a fifth layer (5) of structural adhesive; - a sixth layer (6), of skins of long fiber fabrics, impregnated in a resin matrix, or formed by a metal sheet, placed on the "cold side" of the panel and with thickness and characteristics according to the expected loads. 2. Fire-resistant panel made of composite materials and provided with a sandwich structure according to claim 1, wherein said structural adhesive constitutes a film or a paste with a glass transition temperature after its polymerization> 120 ° C. 3. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to any one of the preceding claims, characterized in that said skins of long fiber non-woven fabric, which make up said second layer (2) and possibly said sixth layer ( 6), have a melting temperature higher than 1100 ° C. 4. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to claim 3, in which said skins of non-woven fabric in long fibers have weft and warp, for example balanced according to the angles 0 ° and 90 °, or they are unidirectional with crossed skins. 5. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to claim 3 or 4, in which the long fibers are selected from at least one of the following components of the following group of fibers: carbon fibers, glass-type fibers 5 . glass E, Kevlar with title 29 or 49 Twaron, basalt. 6. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to any one of claims 3, 4 or 5, in which the minimum weight of a fabric skin comprised in said second layer (2) and possibly in said sixth layer (6) is equal to about 120 g / m <2>. 7. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to any one of claims 1 or 3-6, characterized in that said resin which impregnates said long fibers of the second layer (2) or of the sixth layer (6) is chosen from the following group: epoxy resin, phenolic resin, thermoplastic resin or polyester. 8. Fireproof panel made of composite materials and equipped with a sandwich structure, according to any of the previous claims, in which the honeycomb structure of said fourth layer (4) is formed by Nomex. 9. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to claim 8, in which said powders of oxidic materials which fill the honeycomb structure have a thermal conductivity equal to about 0.09 W / mK a 1000-1 100 ° C. 10. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to claim 8, in which the honeycomb structure is formed of Nomex material with a melting temperature higher than 1400 ° C and a cell of any size, and with a minimum thickness of 6 mm. 11. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to any one of the preceding claims, in which said long-fiber fabric skins relating to the second layer (2) and possibly to the sixth layer (6) if the latter it is not a metal sheet, there are two in number for the second layer (2), and two or three for the sixth layer (6). 12. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to any one of the preceding claims, in which said first refractory layer in ceramic material of non-woven fabric (1), of a type already available on the market, consists of ceramic fiber and has a weight of 70 g / m <2>. 13. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to any one of the preceding claims, wherein the panel has a minimum weight of approx. 3.5 kg / m <2>. 14. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to any one of the preceding claims, in which, if said sixth layer (6) is a metal sheet, or a metal alloy, its melting temperature is higher or equal to about 300 ° C. 15. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to any one of the preceding claims, in which said sixth layer (6) is formed by three skins in carbon fiber fabric impregnated with epoxy resin, and in which the percentage of epoxy resin present in the sixth layer (6) is approximately 37%, while the weight of the carbon fiber fabric is equal to 280 g / m <2>. 16. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to any one of the preceding claims, characterized in that it also presents a system for locking the panel to a support structure, the locking system being incorporated in the panel itself and formed as follows: - thickening or over-thickness (7) of the thickness of the cold part, or sixth layer (6), located on the cold side of the panel, Γ enlargement (7) being made in correspondence with a locking screw (8); - said locking screw (8) being incorporated, with its head, in the fourth layer (4) of the panel, having a honeycomb structure, in which, the threaded stem of the locking screw (8) protrudes from said side cold of the panel, in order to allow fixing to a support structure, while the head of the locking screw (8) remains hidden inside the panel, inside the honeycomb structure, to avoid direct contact with the flame of a possible fire on the warm side of the panel. 17. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to claim 16, wherein said thickening or excess thickness (7) extends, in the direction parallel to the sides of the panel, for a distance substantially equal to the diameter of the head of the locking screw (8) or for a distance that is a function of the loads expected to act on the panel. 18. Fire-resistant panel made of composite materials and provided with a sandwich structure, according to claim 17, wherein at the head of a locking screw (8) of the locking system, the thickness (9) of the honeycomb structure bee of said fourth layer (4) of the fire panel covering said head of the locking screw (8), is substantially identical to the thickness of the same fourth layer (4) in another region of the fire panel where no screw is present. locking (8), so that the amount of heat reaching the head of the locking screw (8) remains lower than that which would cause a dimensional increase such as to slit the hole in which the screw (8) is screwed. 19. Fire-resistant panel made of composite materials and equipped with a sandwich structure, according to claim 18, in which the maximum temperature reached by the cold part (6) and the head of the locking screw (8) after 15 minutes of exposure to fire is equal to about 300 ° C.