ITUD20070117A1 - AIRCRAFT COMPONENT AND PROCEDURE FOR ITS REALIZATION - Google Patents

Description

Description of the invention having as title:

"AERONAUTICAL COMPONENT AND PROCEDURE FOR ITS PRODUCTION"

FIELD OF APPLICATION

The present invention relates to an aeronautical component and to the process for producing it. In particular, the aeronautical component according to the present invention is of the sandwich type, that is composed of a plurality of internal layers of non-metallic materials having different types and / or geometries, externally coated with laminates of composite material, reinforced with carbon fibers. The aeronautical component according to the present invention comprises internally a polymeric syntactic foam and, due to its characteristics of lightness, associated with the high mechanical resistance, it can be used in place of the other additions or columns to the aeronautical components made of metallic material, such as aluminum alloys, or the like. .

STATE OF THE TECHNIQUE

In various fields of the art, components made with "sandwich" technology are known, i.e. composed of a plurality of internal layers, externally coated with laminates in composite material, inside which there is a foam, called foam, made of polymeric material , such as polyurethane foam. These components are particularly widespread and used in the furniture sector, in the "automotive", naval, railway transport sectors and, limited to the interiors of the cabins, also in the aeronautical sector. In particular, it is known to use such sandwich components as internal reinforcement panels, shockproof panels, inserts for the improvement of aerodynamic and hydrodynamic efficiency, at relatively low speeds, ie no higher than a few hundreds of km / hour.

Instead, the aeronautical components, especially the external ones, are normally made of light alloy, usually aluminum-based, by chip removal, with numerical control machines, or by casting. These aeronautical components, in fact, are subject to considerable mechanical stress due to impact with air, at very high speeds, even supersonic, such as, for example, the deflectors, or "strakes", or "chines", installed in particular on each engine nacelle of the aircraft, in order to reduce localized turbulence, which has a negative impact on the efficiency of the turbocharger, especially during take-off.

The production process of these aeronautical metal components has the drawback of being complex and expensive, and generally involves the following work phases: a) realization of the male mold and the female counter-mold in a numerically controlled machining center ; b) surface finishing with machine tools; c) fixing of the mold and counter-mold; d) surface treatment for corrosion protection. Consequently, this makes each known aeronautical component very expensive.

An object of the present invention is to provide an aeronautical component which is much lighter than those made of metal, which, at the same time, resists the considerable mechanical and aerodynamic stresses to which it is subjected and which is also simple and economical to manufacture. Another object of the present invention is to provide a production process for making an aeronautical component in non-metallic material, which includes few and simple processing steps, and which at the same time ensures that the finished product has mechanical characteristics at least not inferior to similar products made with metallic materials.

In order to obviate the drawbacks of the known art and to obtain these and further objects and advantages, the Applicant has studied, tested and implemented the present invention.

EXPOSURE OF THE FOUND

The present invention is expressed and characterized in the independent claims.

The dependent claims disclose other characteristics of the present invention, or variants of the main solution idea.

In accordance with the aforementioned purpose, the aeronautical component according to the present invention comprises a plurality of layers, in a composite fiber-reinforced material, arranged in a sandwich, which define side walls, with a central part, or core, in polymeric foam inside. syntactic.

Advantageously, the aforesaid layers are made with sheets of composite material, reinforced with carbon fibers, kevlar, whiskers, or the like, impregnated, or pre-impregnated, with a resin, or a thermoplastic polymer, or thermosetting (prepreg), for example in epoxy matrix.

The aforementioned syntactic polymer foam is obtained by means of sheets, bars, or granules, of syntactic polymer (called precursor), i.e. a polymer characterized by numerous hollow spheres of glass, polymer, or even ceramic, having a diameter ranging from about 10 microns to about 200 microns, which are capable of expanding, due to the effect of temperature, thus reducing their density, up to 2.5 times the original one.

The related production process essentially comprises a single polymerization step inside a mold, in which the compacting of the pre-impregnated composite material sheets and the polymerization, or cure, of the syntactic polymer, takes place simultaneously under the effect of pressure. internal exerted by the same expanding syntactic polymer and the temperature provided both by an external source, such as an oven, or electrical resistances and by the exothermic reaction generated by the expanding syntactic polymer.

Therefore, in the method according to the present invention, no autoclave system is used, not even for a possible post-cure step.

The curing of the resin, for example epoxy, present in the external laminates and the expansion of the syntactic polymer present in the central part, occurs simultaneously at a temperature between about 170 ° C and about 190 ° C and is obtained by heating the molds.

The expansion of the syntactic polymer in the closed mold generates the necessary pressure for compaction of the prepreg layers. This pressure can reach up to about 15 bar and depends on the ratio between the volume of the cavity of the central part, between the walls defined by the layers of composite material, and the original quantity of syntactic polymer (precursor), not yet foamed.

The molds used to make the aeronautical component according to the present invention and to carry out both the curing and the post-curing of the thermosetting polymer contained in the prepregs and of the syntactic polymer, can be of various kinds: composite, metal, fiberglass, ceramic, or other. , integrated with suitable heat exchangers, such as electric resistances for heating, integrated coil circuit for cooling and / or thermal regulation systems.

The heat generated, for example by the passage of current, is necessary to trigger the expansion of the syntactic polymer and activate the cure of the thermosetting polymer.

The use of fiberglass for the realization of the molds is possible and advantageous in consideration of the relative thermal resistance and its low cost. It is therefore evident how the use of fiberglass, for the realization of the molds, further and considerably reduces both the cost of the molds themselves, and their weight, allowing an easy transportability of the equipment for carrying out the process according to the present invention, and a consequent ease of carrying out the process, even for small production batches.

The advantages of the innovative method according to the present invention are both technical and economic and can be summarized as follows: - reduction of intensive work;

- no surface treatment required;

- no risk of corrosion;

- significant weight reduction;

- high reproducibility of the product.

ILLUSTRATION AND DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become clear from the following description of a preferential embodiment, given by way of non-limiting example, with reference to the attached drawings in which:

- fig. 1 is a perspective view of an aeronautical component according to the present invention, mounted on an engine nacelle of an aircraft;

- fig. 2 is a side view of the aeronautical component of fig. 1, inserted in a mold, during its manufacturing process;

- fig. 3 is a section along the line III-III of fig. 2;

fig. 4 is a first enlarged detail (A) of fig. 3;

fig. 5 is a second enlarged detail (B) of fig. 3;

figs. 6a to 6f schematically show six steps of the manufacturing process of the aeronautical component of fig. 1;

fig. 7 is a first graph, which represents the trend of the expansion coefficient of a given syntactic polymer, as a function of the temperature;

fig. 8 is a second graph, which represents the trend of the internal pressure generated by a given syntactic polymer, as a function of the temperature;

fig. 9 is a third graph, which represents the trend of the internal pressure generated by a given syntactic polymer, as a function of the filling percentage of the cavity, or part, central of the aeronautical component of fig. 1;

- fig. 10 is a fourth graph, which represents the average volume of the individual cells of a given syntactic polymer, as a function of the filling percentage of the cavity, or part, central of the aeronautical component of fig. 1;

- fig. 11 is a fifth graph, which represents the shear strength value of the aeronautical component of fig. 1, as a function of the average volume of the individual alveoli;

- fig. 12 is a sixth graph, which represents a cycle of curing, or polymerization, of the resin and of the syntactic polymer in relation to the temperature and the heat that develops inside a mold in a process according to the present invention.

DESCRIPTION OF A PREFERENTIAL FORM OF

REALIZATION OF THE FOUND

With reference to fig. 1, an aeronautical component according to the present invention is, in this case, a deflector 10, or fluid-dynamic insert called strake, which is mounted on a nacelle 11 of an aircraft engine, of any known type.

The deflector 10 (figs. 3, 4 and 5) comprises a plurality of layers 12, made of fiber-reinforced composite material, arranged in a sandwich, which define side walls 13 and a bottom wall 15, with a central part inside, o core, 16 in syntactic polymer foam. The side walls 13 and the bottom wall 15 constitute the external structural envelope of the deflector 10.

The method according to the present invention for making the deflector 10 comprises a first phase (fig. 6a), in which a mold is made essentially composed of three parts 20, 21 and 22 (figs. 2, 3 and 6e), suitable to be coupled together to define a cavity 23 (Figs. 4, 5 and 6a) which has the negative shape of the deflector 10 to be made.

Inside the cavity 23, a separating or releasing agent of a type known per se, for example of the PVA type (polyvinyl alcohol), or the like, is first applied to facilitate the removal of the deflector from the mold.

Subsequently, as an optional step, using the well-known IMC (In Mold Coating) technique, a layer of protective varnish, advantageously of the polyurethane type, with a high molecular weight, anti-wear and anti-scratch, is deposited and polymerized for about one now at about 80 ° C (fig. 6a). The thickness of the aforementioned polyurethane varnish will be adjusted between about 300 microns and about 500 microns.

The sheets of pre-impregnated composite material are then cut and the resulting sandwich layers 12 are arranged to form a laminate which defines the side walls 13 and the bottom wall 15 (Fig. 6b). The layers 12 of prepreg are arranged on the internal surface of the parts 20 and 21 of the mold according to the desired configuration. The resin of the prepreg is, for example, type HexPly 8552 / AS4-8HS from Hexcel Composites.

Then sheets, bars, or granules, of expandable syntactic polymer are inserted into the cavity defined by the layers 12, in such a quantity that, at the end of expansion, the expanded structure is of the type with "cells, or closed alveoli", distributed in a homogeneous way in the expanded mass. The expandable syntactic polymer is, in this case, epoxy-based, such as Core Foam AF3024, or similar, marketed by the 3M company, and is compatible with the resin of the pre-impregnated.

Without prejudice to the degree of expansion of the syntactic polymer, the average size of the "cells, or closed alveoli" basically depends on the ratio between the volume of the syntactic polymer at the origin (VO), deposited in the cavity to be filled, and the volume of the cavity itself (Vf). Precisely, when said ratio tends to l, the size of the cells is zeroed and the pressure tends to the maximum value of the range of variation (1-15 bar).

The flaps 25 (figs. 3, 4 and 6d) of the layers 12 which come out of the mold are advantageously turned up, overlapped and placed inside the central part 16.

The method according to the present invention also provides for the optional integration of a conductive surface layer 26 (Figs. 4 and 5), consisting of a pre-impregnated product having the same epoxy matrix as the aforesaid resin, reinforced with an aluminum mesh. The surface layer 26 has the function of "anti-lightning", that is to distribute (dissipate) any concentrated electrostatic charges, mainly induced by lightning, over the entire surface of the aircraft, in order to avoid local damage. The three parts 20, 21 and 22 of the mold are tightened together by means of a connection with "head" type clamps, of a known type, or suitably designed for the purpose, to facilitate and speed up the operations of closing, molding, opening and extraction of the deflector 10 (figs. 6e and 6f).

After closing, the parts 20, 21 and 22 of the mold are heated and brought to the curing temperature of the syntactic polymer, of about 180 ° C. The heating can take place in the oven, or the heat produced by the Joule effect of the passage of current in electrical resistances inserted in the parts 20, 21 and 22 of the mold itself can be exploited. This last technology is more flexible as it allows to release the production from the useful size of the oven.

During the heating and during the cure time, the precursor, ie the syntactic polymer, expands until it touches the internal surface of the laminate, ie of the layers 12, towards which it exerts the necessary pressure to compress its constituent sheets. The regularity of expansion even in components with a complex shape produces a uniform pressure on the entire external composite cladding (walls 13 and 15), or skin, guaranteeing high quality and repeatability of the final result.

After cooling and extraction, the deflector 10 thus made is ready for its use.

The graphs of figures 7 to 11 illustrate with sufficient approximation the performance of the aforementioned syntactic polymer (foam).

In particular, in fig. 7 shows the behavior of the foam, which is determined by the following simplified formula:

Vf = V0 * (1 Ce * ln (Tc / Ta)),

where is it :

Vf = Final volume

V0 = Initial volume

Ce = Expansion constant typical of the foam in question (in the case Ce = 0,8)

Tc = Curing temperature

Ta = Ambient temperature.

The graphic representation of fig. 8 derives from the following simplified formula:

Pf = PO * Ce * ln (Tc / Ta) * (At / Ta)

where is it

Pf = Final pressure

PO = Initial pressure (atmospheric)

At = Difference between the cure temperature and the ambient temperature (Tc - Ta)

Ce = Expansion constant typical of the foam in question (in the case Ce = 0,8)

In order to achieve a significant structural contribution of the syntactic polymer constituting the core 16 of the sandwich structure of the deflector 10, the dimensions of the "closed cells or alveoli" will be comprised in an average diameter between 0.5 mm and 3 mm. The quantity of precursor (syntactic polymer) is defined as a function of the final design density of the core 16, the minimum pressure to be exerted on the side 13 and bottom 15 walls (approximately 3 bar), the temperature and cure time of the polymer matrix , sufficient for the expansion to be complete.

The graphs of figures 9, 10 and 11 indicate approximately some parameters useful for the manufacturing and care process, and for the structural requirements consistent with those of the design.

In particular, the graph of fig. 9 comes from the following simplified formula:

Pf = P0 * Ce * ln (Tc / Ta) * (At / Ta) * ((Vr / Vc) <Λ> (3/2)), where:

Pf = Final pressure

PO = Initial pressure (atmospheric)

At = Difference between the cure temperature and the ambient temperature (in the case Tc - Ta = 180-20 = 160 ° C, this implies At / Ta = 160/20 8)

Ce = Expansion constant typical of the foam in question (in the case Ce = 0,8)

Vr = Volume of foam occupied (% of filling) Ve = Total volume of the cavity

For simplification, the formation of the individual cells in the expansion phase of the foam is assumed to be of the spherical type, with closed cells, i.e. not communicating with the next or adjacent ones.

The graph of fig. 10 illustrates the behavior of the foam, in terms of size / volume of the cells, as a function of the filling percentage of the mold cavity.

The graph of fig. 11 indicates how the shear strength of the foam, and therefore of the deflector 10, is strictly linked to the volume of the alveoli after curing at 180 ° C.

The graphs illustrated in Figures 7 to 11 are derived from the approximate formulas indicated above, and represent parameters related to the ideal conditions of treatment.

Furthermore, the typical thermal behavior of the chosen foam involves the generation of heat from an exothermic reaction. This thermal energy can be appropriately absorbed / exploited in the component care cycle, as shown in the graph in fig. 12. This exothermic reaction can increase the temperature inside the mold up to about 280 ° C. The amount of thermal energy that develops depends exclusively on the amount of syntactic polymer disposed in the aforementioned central part. This energy, specially controlled by temperature regulators of the mold heating / cooling system, can be absorbed / exploited in the curing cycle of the pre-impregnated composite material layers.

It is clear that modifications or additions of parts or phases can be made to the aeronautical component and to the manufacturing process described up to now, without thereby departing from the scope of the present invention.

It is also clear that, although the present invention has been described with reference to only one specific example of an aeronautical component, a person skilled in the art will be able to realize many other forms of aeronautical components, having the characteristics expressed in the claims and therefore all falling within the scope of protection defined by them.

Claims (17)

CLAIMS 1. Aeronautical component, characterized by the fact that it comprises a plurality of layers (12), made of fiber-reinforced composite material and arranged in a sandwich, defining one or more side walls (13), and a central part, or core (16) in syntactic polymer foam. 2. Aeronautical component as in claim 1, characterized in that said layers (12) are made with sheets of composite material, reinforced with carbon fibers, kevlar, whiskers, or the like, impregnated, or pre-impregnated, with a resin, or a thermoplastic polymer, or thermosetting (prepreg). 3. Aeronautical component as in claim 1 or 2, characterized in that said syntactic polymeric foam is obtained by means of sheets, bars, or granules, of syntactic polymer. 4. Aeronautical component as in any one of the preceding claims, characterized in that it also comprises a protective paint layer, of the polyurethane type, with a high molecular weight, anti-wear and anti-scratch. 5. Aeronautical component as in claim 4, characterized in that the thickness of the protective paint layer is comprised between about 300 microns and about 500 microns. 6. Aeronautical component as in any one of the preceding claims, characterized in that the flaps (25) of said layers (12) are turned up, overlapped and placed inside said central part (16). 7. Aeronautical component as in any one of the preceding claims, characterized in that it further comprises a conductive surface layer (26), consisting of a pre-impregnated having the same epoxy matrix as said resin, reinforced with aluminum mesh. 8. Process for manufacturing an aeronautical component, comprises a first phase in which a mold is made consisting of a plurality of parts (20, 21, 22), capable of being coupled together to define a cavity (23) having the shape negative of said aeronautical component to be made, characterized in that it also comprises a second phase in which a plurality of layers (12), in fiber-reinforced composite material, impregnated, or pre-impregnated, with a resin, or a thermoplastic polymer, or thermosetting, are sandwiched in said cavity (23), to define one or more side walls (13) of said aeronautical component, a third phase in which a syntactic polymer is used to define a central part, or core (16) , of said aeronautical component, and a fourth polymerization phase in which both said resin, or said thermoplastic or thermosetting polymer, and said syntactic polymer are polymerized in said mold . 9. Process as in claim 8, characterized in that said layers (12) are made with sheets of composite material, reinforced with carbon fibers, kevlar, whiskers, or the like. 10. Process as in claim 8 or 9, characterized in that said syntactic polymer comprises hollow spheres of glass, polymer, or even ceramic, having a diameter ranging from about 10 microns to about 200 microns, which are capable of expanding, due to the effect of the temperature, thus reducing their density, up to 2.5 times the original one. 11. Process as in claim 8, 9 or 10, characterized in that said polymerization, as well as the expansion of said syntactic polymer, occur simultaneously at a temperature between about 170 ° C and about 190 ° C, obtained by heating said mold. 12. Process as in claim 11, characterized in that said expansion of said syntactic polymer in said closed mold generates a pressure for compacting said layers (12) comprised between about 3 bar and about 15 bar and depends on the ratio between the volume of the cavity of said central part and the original quantity of said syntactic polymer. 13. Process as in any one of claims 8 to 12, characterized in that said parts (20, 21, 22) of said mold are made of composite material, metal, fiberglass, and / or ceramic. 14. Process as in any one of claims 8 to 13, characterized in that in one or more of said parts (20, 21, 22) there are heating and / or cooling means, possibly associated with thermal regulation means . 15. Process as in any one of claims 8 to 14, characterized in that between said first and said second phase, a separating or releasing agent is applied inside said cavity (23) to facilitate the demoulding of said aeronautical component from said mold. 16. Process as in any one of claims 8 to 15, characterized in that it also comprises a fifth step in which a conductive surface layer (26) is formed, with an "anti-lightning" function and consisting of a pre-impregnated having the same epoxy matrix as said resin, reinforced with aluminum mesh. 17. Aeronautical component and process for making it, substantially as described, with reference to the attached drawings.