WO2015036716A1

WO2015036716A1 - Method for repairing a skin of a composite panel

Info

Publication number: WO2015036716A1
Application number: PCT/FR2014/052290
Authority: WO
Inventors: Arnaud DELEHOUZE; Jean-Philippe MUCHERIE; Emmanuel Anfray; Michel ROGNANT
Original assignee: Aircelle
Priority date: 2013-09-13
Filing date: 2014-09-15
Publication date: 2015-03-19
Also published as: FR3010652A1; FR3010652B1

Abstract

The present invention relates to a method for repairing a skin (3, 4) of a composite panel (1), said skin comprising a group of stacked plies embedded in a matrix. The method comprises steps of: removing the plies and the matrix in a repair zone; installing a group of repair plies, said repair plies being disposed such as to overlap with plies of the skin to be repaired; and curing a material that is intended to form a matrix around the repair plies. The method is characterised in that the repair plies are disposed such as to overlap with the plies of the skin on both sides of the repair zone in relation to a neutral plane of the skin to be repaired.

Description

Method of repairing a skin of a composite panel

The present invention relates to a method for repairing a skin of a sandwich or monolithic composite panel, in particular for an aircraft propulsion unit.

As is known per se, an aircraft propulsion unit conventionally comprises a turbojet engine housed inside a nacelle.

The nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet, a median section intended to surround a fan of the turbojet engine and its casing, and a downstream section intended to surround the combustion chamber of the turbojet engine and sheltering where appropriate. thrust reverser means. It can be terminated by an ejection nozzle whose output is located downstream of the turbojet engine.

In order to reduce mass and increase performance, especially mechanical performance, the aeronautics industry is increasingly using composite materials to produce structural parts and / or panels.

Such elements are generally made from sets of fibrous folds embedded in a polymerized resin matrix. These elements can be monolithic or contain a soul made of another material.

This is the case, for example, acoustic panels used to reduce noise pollution generated by the turbojet, and it is common to equip several parts of the nacelle and / or turbojet.

These parts of the nacelle and / or the turbojet engine may be, for example, an internal surface of the air circulation duct for a double-flow turbojet engine, a nozzle or ejection cone surface, an internal air intake panel air, etc.

Such acoustic panels are in the form of a sandwich-type panel comprising at least one cellular core forming a resonator, for example a honeycomb-type structure, covered with a perforated outer skin (called acoustic skin) and a full inner skin (called skin support or structuring). The skins of these panels may be made of composite material comprising a set of fibers (superposition of fibrous folds) embedded in a polymerized resin.

The skins of these panels, that is to say the folds close to a surface of said panel, are exposed to the flow of air flowing through the propulsion unit and may be damaged, and in particular undergo tears, perforations, delamination, for example at skin interfaces / acoustic honeycomb structure.

It is then necessary to repair the damaged panel so as to restore the panel its properties, especially in terms of structural strength.

Usually, the repair of such a panel is carried out by laying a doubler, that is to say a portion of skin, metal or composite, for example, applied in superposition on the skin to be repaired at the level of the damaged area and secured by rivets. This technique is particularly suitable for metal parts, offers proven mechanical properties but remains unobtrusive once the repair is done. The presence of these reinforcements also disturbs the aerodynamic flow along the panel.

In addition, it should be noted that the doubler adds a certain additional mass to the panel, which is undesirable.

In the case where the use of a doubler is difficult or that these disadvantages are too great, there will be no alternative but to completely replace the damaged panel, which of course is also not desirable.

There are techniques for repairing composite panels that substantially preserve the initial aesthetic and aerodynamic properties of the panel. These techniques are, however, generally limited to small non-structural areas.

These are so-called "scarf", "step" and "offset" type repair techniques.

These techniques include cutting into the damaged skin to remove a portion of said skin at the damaged area and then fill that portion with repair folds to restore the integrity of the panel. In the case of a sandwich panel, the removal of the damaged skin portion provides access to the core of the panel and possibly also remove some if it has been damaged. A repair core portion is then inserted in place of the removed portion.

In the technique called "scarf" (bevel in English), the edges (also called repair interface) of the groove are beveled and the edges of the repair folds have a bevel of complementary slope.

The bevel can be made directly by sanding (followed by a possible depollution and degreasing) or the rectilinear character of the bevel can be provided by a fold, including an adhesive bend, covering the repair folds or the edges of the bleed on the thickness of these. For more details on one way of producing a bevelled surface, reference may be made to US Pat. No. 5,271,145, for example.

In the so-called "step" technique, the edges of the groove are no longer bevelled and rectilinear but the folds of the skin to be repaired are cut so as to be offset from one another and to form a set of steps. The steps can also be done by "step" sanding.

In the technique known as "offset" (English deviation), the edges of the groove are straight and a set of repair plies is added in superposition of the skin to repair so as to cover said bleeding and restore the junction of the skin. The repair plies may be added pyramidal, or to form steps, for example. The skin is thus slightly deflected around the damaged area.

A major disadvantage of this type of repair is the large size of the repair surface extending into a healthy area of the skin to be repaired in relation to the size of the actual surface to be repaired.

Indeed, the realization of a bevel, steps or the application recovery recovery folds implies an expansion of the repair area that extends to the healthy zone.

In addition, the addition of repair plies in a shape substantially pyramid or cone, alters the symmetry of the skin and induces a shift of the neutral plane of said skin.

There is therefore a need for a process for repairing composite skins that makes it possible to solve all or part of these problems. To this end, the present invention provides a method of repairing a skin of a composite panel, said skin comprising a set of superimposed folds embedded in a matrix, the method comprising the steps of:

remove the folds and the matrix of the skin at a repair zone,

- Set up at the level of the repair area thus released a set of repair folds, said repair folds being arranged to overlap with folds of the skin to be repaired,

- curing a material intended to form a matrix around the repair folds,

the method being characterized in that the repair folds are arranged to overlap the folds of the skin on either side of the repair zone with respect to a neutral plane of the skin to be repaired.

Thus, by providing to apply the repair plies on both sides of the skin at the area to be repaired, the overlap range of the folds can be greatly reduced. A repair according to the invention makes it possible to obtain a better distribution of the forces on either side of the repaired skin, and finally a better mechanical strength of the repaired zone compared to the repairs according to the known methods.

Advantageously, the repair plies are applied on both sides of the repair zone in a substantially symmetrical manner. This keeps the neutral line of the skin to repair. This also makes it possible to substantially halve the overlap distance of the folds with respect to the repair zone.

The material, in particular of the resin type, intended to form the matrix around the repair plies, may be applied ad hoc or may already be present on the plies in the case of use of pre-impregnated plies.

According to a first variant embodiment, the repair plies are applied on both sides of the skin on an overlapping surface that is at least partially bevelled. This corresponds to a "scarf" type repair. According to a second variant embodiment, the repair plies are applied on either side of the skin on a surface forming steps. This corresponds to a step repair.

According to a third embodiment, the repair plies are applied on both sides of the skin on a so-called offset overlapping surface. This corresponds to an "offset" type repair.

Preferably, the material intended to form the matrix is identical to the material forming the original matrix of the panel.

Advantageously, the matrix is a resin.

According to a first embodiment, the repair plies are non-pre-impregnated dry plies.

According to a second embodiment, the repair folds are pre-impregnated folds of the material intended to form the matrix.

According to a preferred embodiment, the panel is a sandwich panel comprising a core, in particular a cellular core.

The present invention also relates to a composite panel comprising at least one skin, the skin comprising a set of superimposed folds embedded in a matrix, the panel being characterized in that it is obtained by a repair method according to the invention.

The present invention will be better understood on reading the detailed description which follows with reference to the appended drawing in which:

FIG. 1 is a schematic representation of a composite sandwich panel repair according to a method of the prior art, according to the "scarf" method,

FIG. 2 is a diagrammatic representation in longitudinal section of a known method of repairing a skin of a composite panel, according to a step method,

FIG. 3 is a diagrammatic representation in longitudinal section of a repair method according to the invention, according to a so-called scarf method,

FIG. 4 is a diagrammatic representation in longitudinal section of a repair method according to the invention, according to a so-called step method, - Figure 5 is a schematic representation in longitudinal section of a repair method according to the invention, according to a method called offset ("offset").

On all of these figures, identical references designate elements or sets of identical or similar elements.

FIG. 1 is a schematic representation of a repair of one of the skins of a composite panel 1, in the example an acoustic sandwich panel, the repair being in accordance with a method of the prior art, according to the method called " scarf "(bevel).

The composite panel 1 comprises a honeycomb-like honeycomb core 2 comprised between an upper skin 3 and a lower skin 4.

One of the upper skins 3 and lower 4 may be a perforated skin, called acoustic, while the other skin will generally be a non-perforated structural skin, called full.

Each upper and lower skin 3 is made of composite material and comprises a set of superposed fibrous folds embedded in a matrix of hardened resin type.

The fibrous folds may in particular be made of carbon fibers, Kevlar, etc. They can also be woven or non-woven.

As can be seen in FIG. 1, the upper skin 3 and the alveolar core 2 have been partially damaged and must be repaired.

To this end, and in accordance with the prior art, a repair zone 5 is defined in which a damaged portion of the alveolar core 2 is removed, as are the folds and the matrix of the upper skin 3.

The edges of the repair zone 5 located at the level of the upper skin 3 are prepared according to the "scarf" method, that is to say in bevel.

Thus, a surface surrounding the repair zone 5 is cut or abraded so as to expose a section of each fold of said upper skin 3.

The core portion 2 which has been removed is replaced by a repair portion 6. The repair portion 6 is fixed with the aid of adhesive films 6a, in this case arranged laterally and on a lower surface of the portion of the repair 6.

Of course, other means of maintaining the repair portion are possible and left to the choice of the skilled person.

The upper skin 3 is then repaired in the following manner. A set of repair plies 7 is set up at the repair area 5, said repair plies being arranged to conform to the bevel shape of the rim of the repair area.

The set of repair plies 7 may, where appropriate, comprise one or more filling plies 8 intended to ensure contact with the repair portion 6 of the core 2 and the leveling of the repair plies. The set of repair plies 7 may also comprise one or more additional cover plies 9 intended to ensure complete recovery of the repair zone 5.

The bevelled portion of the repair plies 7 and, if appropriate, the filling ply 8 and the cover ply 9 can be made as for the rim of the repair zone 5, by controlled abrasion or cutting.

The rectilinear character of the bevel can also be provided by an interface ply 10, and more particularly an adhesive ply allowing the maintenance of repair plies 7.

The set of repair folds 7 is set up so that each repair fold comes in continuity with the fold which it repairs and overlaps it partially (more precisely, in this case it overlaps its end portion). bevel). Of course, it is possible to provide several folds of repair for a fold to repair (see Figure 2), in this case we refer to all these folds, taken from the fold to repair.

The repair plies 7 thus put in place, a material intended to form a matrix is added and polymerized so as to restore the matrix of the upper skin 3.

In the case of a step-type repair, the repair interface is prepared in such a way that a flat portion (and no longer beveled) of each fold is discovered (see FIG. half of the repair zone 5 is shown). Thus, each repair fold 7 and overlap overlaps the adjacent fold, and no longer the repaired fold in the continuity of which it is installed.

As seen in Figure 2, the clearance required by each fold or layer of the upper skin 3 is relatively large, and so as to have a sufficient overlap surface, to ensure the proper transmission of efforts between the folds of the parent skin to the folds of repairs. Thus, the repair zone 5 extends over a much larger area than the damaged area.

According to the present application, the repair method comprises a step of arranging the repair folds on either side of the repair zone with respect to a neutral plane (or plane of symmetry) of the skin to be repaired.

Thus, by arranging the repair folds on both sides of the repair zone, the overlapping surface of said folds no longer extends on one side of the skin, but can be made on both sides of this skin. . The overlapping surface can thus be shortened and the size of the repair area is reduced accordingly. The reduction of the repair area reduces the work required to prepare this area as well as the increase in mass related to the repair. In addition, this reduction of the repair zone makes it possible to limit the reduction in acoustic performance in the case where the skin to be repaired is an acoustic-type skin whose acoustic perforations can not generally be kept in the repair zone.

Advantageously, the repair folds are arranged symmetrically with respect to a neutral plane of the skin to be repaired. In this way, the fraction of the repair zone dedicated to the placement of the repair plies can be divided substantially by two, the overlapping surface being distributed substantially equally on both sides of the skin of the composite panel 1.

Figures 3 to 5 illustrate this repair method with bevel (Figure 4), step (Figure 3) and offset (Figure 5) repair methods. Only half of the repair zone 5 is shown in FIGS. 3 and 4.

According to the present application, the repair plies 7 are arranged so as to overlap the folds of the skin, on either side of the repair zone with respect to a neutral plane of the skin to be repaired (median fold ).

It will be noted that in FIGS. 3 and 4, two repair plies 7 per repaired fold are provided.

Advantageously, the repair plies 7 and, where appropriate, the cover plies 9 and the filling plies 8 are applied from and other of the repair zone substantially symmetrically with respect to a neutral plane (or median fold) of the skin.

It should be noted that for an offset-type repair (FIG. 5), the portion of the plies of the panel 3 and of the matrix which has been removed at the level of the repair zone is filled with a filling material 10. which may be a composite fiber / resin replacement material.

Although the invention has been described with a particular embodiment, it is obvious that it is in no way limited and that it includes all the technical equivalents of the means described and their combinations if they enter into the scope of the invention.

Claims

1. A method of repairing a skin of a composite panel, said skin comprising a set of superimposed folds embedded in a matrix, the method comprising the steps of:

remove the folds and the matrix of the skin at a repair zone,

- curing a material intended to form a matrix around the repair folds,

2. A method of repairing a panel according to claim 1, characterized in that the repair plies are applied on both sides of the repair zone substantially symmetrically.

3. Method according to any one of claims 1 or 2, characterized in that the repair plies are applied on either side of the skin of the panel on an overlapping surface at least partially bevelled.

4. Method according to any one of claims 1 to 2, characterized in that the repair plies are applied on both sides of the skin on a surface forming steps.

5. Method according to any one of claims 1 to 2, characterized in that the repair folds are applied on either side of the skin on a so-called offset overlapping surface.

6. Method according to any one of claims 1 to 5, characterized in that the material for forming the matrix is identical to the material forming the original matrix of the skin.

7. Method according to any one of claims 1 to 6, characterized in that the matrix is a resin.

8. Method according to any one of claims 1 to 7, characterized in that the repair plies are non-preimpregnated dry plies.

9. Method according to any one of claims 1 to 7, characterized in that the repair plies are prepreg plies of the material intended to form the matrix.

10. Method according to any one of claims 1 to 9, characterized in that the panel is a sandwich panel comprising a core, in particular a cellular core.

1 1. Composite panel comprising at least one skin, the skin comprising a set of superposed folds embedded in a matrix, the panel being characterized in that it is obtained by a repair method according to any one of claims 1 to 10.