Composite panel and aircraft turbojet engine nacelle comprising such a panel

Abstract

The present disclosure relates to a composite panel having a sandwich structure formed by a central core having a primary cellular structure, for example, of the honeycomb type, sandwiched between two skins. The primary cellular structure includes an array of main cells. The composite panel further includes a plurality of pins, each pin being, on the one hand, arranged to be housed and to cooperate inside a main cell and, on the other hand, formed of a secondary cellular structure having an array of secondary cells.

Claims

1. A non-planar composite panel comprising a sandwich structure formed by a central core having a primary cellular structure of a honeycomb type, sandwiched between two skins, the primary cellular structure comprising an array of main cells, the non-planar composite panel comprising: a plurality of pins, each pin being arranged to be housed and to cooperate inside a main cell of the array of main cells, such that each pin is in contact with and supports side walls of the main cell, and each pin being formed of a secondary cellular structure of a honeycomb type, the secondary cellular structure comprising: an array of secondary cells having cell walls forming a hexagonal-shaped section parallel to the main cells of the primary cellular structure; and at least one area of curvature, wherein the plurality of secondary cell walls are located at said area of curvature such that the secondary cell walls reinforce the primary cellular structure.

2. The non-planar composite panel according to claim 1, wherein the secondary cellular structure has a height substantially equal to a thickness of the primary cellular structure.

3. The non-planar composite panel according to claim 1, wherein at least one of the main cells have a hexagonal-shaped section.

4. The non-planar composite panel according to claim 1, wherein the non-planar composite panel is made of titanium.

5. The non-planar composite panel according to claim 1, wherein the non-planar composite panel forms an acoustic attenuation panel.

6. An inner fixed structure for an aircraft turbojet engine nacelle comprising at least one non-planar composite panel according to claim 1.

7. A nacelle for an aircraft turbojet engine comprising at least one inner fixed structure according to claim 6.

8. A method for manufacturing the composite panel of claim 1, the method comprising: inserting the secondary cellular structure inside the primary cellular structure; and fastening the two skins on opposed sides of the primary cellular structure that is provided with the secondary cellular structure such that the primary cellular structure is sandwiched between the two skins.

9. The method according to claim 8, wherein the step of fastening the skins is performed by soldering.

Description

DRAWINGS

(1) In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIG. 1 is a general representation of a turbojet nacelle for an aircraft to which the teachings of the present disclosure are applied;

(3) FIG. 2 illustrates an exploded view of an inner fixed structure of the nacelle of FIG. 1;

(4) FIG. 3 illustrates a cutaway view of an acoustic panel according to the prior art;

(5) FIG. 4 illustrates a portion of a composite panel according to one form of the present disclosure;

(6) FIG. 5 illustrates a portion of a composite panel according to another form of the present disclosure;

(7) FIG. 6 illustrates a pin cooperating inside a main cell of a primary cellular structure according to one distinct form the present disclosure; and

(8) FIG. 7 illustrates another form of a pin cooperating inside a main cell of a primary cellular structure according to another distinct form of the present disclosure.

(9) The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

(10) The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

(11) As shown in FIG. 1, a nacelle 1 has a substantially tubular shape according to a longitudinal axis X. This nacelle 1 is intended to be suspended from a pylon 2, itself fastened under a wing of an aircraft.

(12) In general, the nacelle 1 comprises a front or an upstream section 3 with an air inlet lip 4 forming an air inlet 5, a median section 6 surrounding a fan of a turbojet engine (not shown) and a rear or downstream section 7. The downstream section 7 comprises an inner fixed structure 8 (IFS) surrounding the upstream portion of the turbojet engine and an outer fixed structure (OFS) 9.

(13) The IFS 8 and the OFS 9 delimit an annular flow path allowing the passage of a main air flow penetrating the nacelle 1 at the air inlet 5.

(14) The nacelle 1 thus includes walls delimiting a space, such as the air inlet 5 or the annular flow path, in which the main air flow penetrates, circulates and is ejected.

(15) The nacelle 1 ends with an ejection nozzle 10 comprising an outer module 11 and an inner module 12. The inner 12 and outer 11 modules define a flow channel for a hot airflow leaving the turbojet engine.

(16) FIG. 2 illustrates an exploded view of the inner fixed structure 8 of the nacelle 1. In this form, the IFS 8 comprises a barrel 13 composed of two walls 13a, 13b of substantially semi-circular shape, each forming a half of a barrel so that, when assembled, these walls 13a, 13b form the barrel 13 of generally cylindrical shape with a longitudinal axis X.

(17) In addition, the IFS 8 comprises two islets 14, 15 to provide a structural link between the IFS 8 and the OFS 9. One 14, called islet 12H is arranged to be placed vertically above the barrel 13, and the other 15 called islet 6H is arranged to be placed vertically below the barrel 13. Each of these islets 14, 15 is here composed of two sets of parts 14a, 14b 15a, 15b, each being intended to be assembled with one of the walls forming a half-barrel.

(18) The sets of parts composing in particular this IFS 8, as well as many other parts of the nacelle 1, are generally composite panels 20 composed of several parts, namely two skins 22 and a central core 21 having a cellular core structure of the honeycomb type sandwiched between the two skins 22. These composite panels 20 offer weight gain and improved strength.

(19) These composite panels 20 can also be acoustic attenuation panels provided to reduce the noise emissions from the turbojet engines. This type of panel, illustrated in FIG. 3, generally has a sandwich structure comprising:

(20) an outer (oriented towards the source of the noise) air-permeable perforated skin 221, called resistive or acoustic skin, whose role is to dissipate acoustic energy;

(21) a central core 21 having a cellular structure of the honeycomb type; and,

(22) an inner skin 222 formed by a solid skin (opposite to the source of the noise), called structuring skin.

(23) The present disclosure described hereinafter is particularly advantageous in the manufacture of these composite panels intended to equip a nacelle.

(24) FIG. 4 illustrates a portion of a sandwich structure formed by a central core 21 having a primary cellular structure 210 of the honeycomb type. This central core 21 is intended to be sandwiched between two skins to form the composite panel 20.

(25) To make the figure more readable, the skins are not illustrated in this figure.

(26) The primary cellular structure 210 comprises an array of main cells 23, said main cells 23 having a hexagonal-shaped section forming a honeycomb-type structure.

(27) The composite panel 20 comprises a plurality of pins 24, each pin 24 being, on the one hand, arranged to be housed and to cooperate inside a main cell 23 and, on the other hand, formed of a secondary cellular structure 240 comprising an array of secondary cells 25. These secondary cells 25 have also a hexagonal-shaped section forming a honeycomb-type structure.

(28) In this way, by inserting and housing a secondary cellular structure 240 inside the main cell 23, this secondary cellular structure 240 will reinforce structurally the primary cellular structure 210 of the honeycomb type. More precisely here, the secondary cells 25 of the secondary cellular structure 240 are placed, in the inserted position of the pin 24, parallel to the main cells 23 of the primary cellular structure 210.

(29) Moreover, this structural reinforcement is carried out without creating a discontinuity in the primary cellular structure 210 of the honeycomb type. In other words, the sandwich structure formed by the primary cellular structure 210 thus retains its structural integrity and may not present an area of weakness linked to any junction.

(30) In one form, these pins 24 are located together on an area of the panel, defining a reinforcement area of the primary cellular structure 210, that is to say still a reinforcement area of the panel 20.

(31) In this configuration, the primary cellular structure 210 retains its structural integrity and extends continuously beyond this reinforcement area, in particular over the whole extent of the composite panel 20.

(32) Due to the cooperation of the pins 24 with the main cells 23, the latter, in the inserted position, are each in contact and in support with side walls of the main cell 23 which delimits it, the main cells 23 having a closed contour. In this way, the forces exerted on the primary cellular structure 210 will be transmitted to each of the secondary cellular structures 240, that is to say again, to each of the pins 24.

(33) This amounts to placing inserts having a cellular structure in cells of larger dimensions relative to those of the insert itself. For example, it may be a pin or an insert of the honeycomb type in cells of a honeycomb-type structure forming the core 21 of a composite panel 20.

(34) In one form, as it is the case here, each of the pins 24 has a height substantially equal to a thickness e of the primary cellular structure 210. In other words, each of the two ends of the pins 24 is flush with a surface of the primary cellular structure 210 on which each of the skins will be fastened, for example by soldering, on one side of the central core and on the other opposite side. The distance between these two opposite surfaces of the primary cellular structure 210 defining its thickness e as shown.

(35) In the particular case where the composite panel 20 is intended to form at least a portion of an inner fixed structure 8 for a nacelle 1 of an aircraft turbojet engine, such as an acoustic attenuation panel, the latter is generally made of metal in order to resist the different thermal constraints relating to the use of the turbojet engine of the aircraft.

(36) In this example, the central core 21 formed by the primary cellular structure 210, as well as the pins 24 and the skins 22, are made of titanium. It should be noted, however, that other metals such as aluminum, stainless steel or a nickel alloy may be used.

(37) In this case, the central core 21 and the skins are generally assembled by soldering.

(38) The pins 24 being disposed in the inserted position exclusively inside the main cells 23 of the central core 21, the latter do not interfere with the application of the skins to the central core 21. Moreover, the use of such pins 24 is compatible with such a soldering step.

(39) In general, a method for manufacturing a composite panel 20 as described hereinbefore comprises:

(40) a step of inserting pins 24 into main cells 23, each pin 24 being housed and cooperating within a main cell 23; and

(41) a step of fastening the skins 22 on each side of the primary cellular structure 210 provided with the pins 24 so that the primary cellular structure 210 provided with the pins 24 is sandwiched between two skins 22.

(42) In the particular case where the composite panel 20 is composed of metals, the step of fastening the skins is in one form a soldering step of the primary cellular structure 210 provided with the pins 24 and sandwiched between the two skins 22.

(43) In this case, the soldering step allows the pins to be fastened:

(44) on the one hand at its ends with the skins 22 when each of the pins 24 has a height substantially equal to a thickness e of the primary cellular structure 210; and

(45) on the other hand, laterally between side edges of the pin 24 with the side walls delimiting the associated main cells 23, the latter being in contact. This fastening being permitted during soldering by capillary rise.

(46) Alternatively, in the particular case where the composite panel 20 is made of composite materials, the step of fastening the skins is a step of bonding the skins on the central core 21 formed by the primary cellular structure 210 and provided with the pins 24 so that said central core 21 is sandwiched between the two skins 22.

(47) In this case, the bonding step allows fixing the pins 24 at its ends with the skins 22 located on either side of the central core 21 when each of the pins 24 has a height substantially equal to the thickness e of the primary cellular structure 210. Moreover, each pin 24 cooperating inside a main cell 23, its side edges are in contact with the walls delimiting the associated main cell 23 having a closed contour when they are fitted into said main cells 23, and thus do not require bonding.

(48) The pins 24 being formed of a secondary cellular structure 240 comprising an array of secondary cells 25, its side edges are cut walls of this array of secondary cells 25. The contacts between these side edges of the pin and the walls delimiting the associated main cell 23 are therefore discontinuous along the closed contour of said main cell.

(49) As can be seen in FIG. 2, the composite panels 20 are generally not planar and have areas of curvature. In order to reinforce the composite panels 20 locally, without burdening the inner fixed structure 8 and hence the nacelle more than necessary, the pins 24 are located at these areas of curvature, these areas being the most stressed.

(50) In this form, the primary cellular structure 210 comprises an array of main cells 23 of size of inch (0.009525 m) and the secondary cellular structure 240 comprising an array of secondary cells 25 of size inch (0.003175 m). These sizes are given by way of example, it is generally understood that the secondary cells 25 are smaller in size than the main cells 23.

(51) FIG. 5 illustrates a portion of a sandwich structure formed by a central core 21 having a primary cellular structure 210 of the honeycomb type, according to another form, this central core 21 being intended to be sandwiched between two skins (not shown here) to form the composite panel 20.

(52) This form differs essentially from that illustrated in FIG. 4 in that the main cells 23 are not hexagonal but generally diamond-shaped. However, they may be of another shape, for example square-shaped.

(53) The reinforcement area, defined by the area where the pins 24 are located in the primary cellular structure 210 is here a substantially diamond-shaped area.

(54) In one form, as illustrated in FIG. 5, the main cells 23 of the primary cellular structure 210 forming a reinforcement area house a pin 24. In other words, a reinforcement area does not present a main cell 23 which would be empty that is to say without pin 24.

(55) FIGS. 6 and 7 each illustrate a pin 24 cooperating inside a main cell 23 of the primary cellular structure 210 according to two distinct forms.

(56) In these two examples, the main cells 23 and the secondary cells 25 have a section of the same shape:

(57) in FIG. 6, the main cell 23 and the secondary cells 25 of the pin 24 have a hexagonal-shaped section; and

(58) in FIG. 7, the main cell 23 and the secondary cells 25 of the pin 24 have a square-shaped section.

(59) Moreover, in these two forms, the pin 24 has a shape that is particularly adapted to the main cell 23 inside which it is housed and cooperates.

(60) More precisely, the ratio of the dimension of the main cell 23 on the dimension of one of the secondary cells 25 of the associated pin 24 is here an integer. In this way, and in the case where the main cells 23 and the secondary cells 25 have a section of the same shape, an envelope circumscribed to the peripheral walls of the pin 24 has a section substantially identical to that of the associated main cell 23. The cooperation of the pins 24 with the main cells 23 is thus improved.

(61) In FIG. 6, for example, the dimensions of the main cell 23 with a hexagonal section are four times larger than those of a secondary cell 25 of the pin 24 also with a hexagonal section, said secondary cells 25 of the pin 24 being, in turn, of the same dimensions. This ratio may vary depending on the desired reinforcement and density. In particular, the greater the desired density, the greater the ratio will be.

(62) In FIG. 7, the dimensions of the main cell 23 with a square section are three times larger than those of a secondary cell 25 of the pin 24 also with a square section, said secondary cells 25 of the pin 24 being, in turn, of the same dimensions.

(63) The contacts between the pin 24 and the walls delimiting the main cell 23 are only surface contacts. This, unlike the form illustrated for example in FIG. 4, where the side edges of the pins 24 are cut walls of its array of secondary cells 25. As a result, the contacts between the pin 24 and the walls delimiting the main cell 23 are essentially linear.

(64) It will be noted that this surface contact is continuous in the case of FIG. 7 and discontinuous in the case of FIG. 6 around the periphery of the pin 24.

(65) Such surface-only contacts between peripheral walls of the array of secondary cells 25 of the pin 24 and the walls delimiting the associated main cell 23 provide a better reinforcement of the composite panel 20.

(66) The present disclosure is described in the foregoing by way of example. It is understood that a person skilled in the art is able to carry out different variants of the present disclosure without departing from the scope of the present disclosure.

(67) For example, it is described that the pins are, in one form, located at an area of curvature to reinforce this area in particular, while maintaining the structural integrity of the panel, in particular at its array of primary cells.

(68) More generally, the pin as described allows consolidating any areas where a force is required, such as the reinforcement of a sandwich panel for example, at the installation of fasteners of a lock, of joining panels, etc.

(69) It will be also noted that the section of the main cells 23 is independent of that of the secondary cells 25. However, a particularly improved strength has been observed for main 23 and secondary 25 cells each with a hexagonal section.

(70) The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.