FR2960178A1 - Stiffener web realizing method for stiffened structure i.e. isogrid type structure, utilized to form fuselage of aircraft, involves depositing elongated elements for stiffeners along directions of stiffeners, and twisting central pin - Google Patents

Abstract

The method involves depositing elongated elements (22.1, 24.1, 24.2, 26.1, 26.2) for stiffeners along directions (12.1-12.3) of the stiffeners, where the elements of the stiffeners oriented along different directions crossing in a coverage point are arranged so that the elements are spaced from points on a level of a crossing zone at a side of the coverage point or another side of the coverage point in an alternate way. A central pin (16) on the level of the crossing zone is twisted by the elements of the stiffeners. An independent claim is also included for a stiffened structure comprising a stiffener web.

Description

METHOD FOR REMOVING FIBERS FOR OBTAINING A RAIDIE STRUCTURE AND STRUCTURE THUS OBTAINED

The present invention relates to a method of depositing fibers for obtaining a stiffened structure and a stiffened structure obtained from the process. A stiffened structure generally comprises on the one hand a panel and on the other hand a network of stiffeners attached and secured at at least one of the faces of the panel. An aircraft comprises numerous stiffened structures, the latter being used in particular to form the fuselage. Thus, the stiffened structures are known comprising a first series of stiffeners oriented in a first direction, for example the longitudinal direction of the aircraft, and a second series of stiffeners oriented in a second direction perpendicular to the first. In this case, the area defined by the stiffeners also called pocket has a square or rectangular shape. To reduce the embedded weight, it tends to realize these stiff structures of composite material. By way of example, the document FR-2.901.240 describes such a structure. Strict structures are also known comprising three sets of stiffeners oriented in directions at 60 °. These structures have an isotropic behavior which gives them the desired mechanical characteristics. Thus, the patent application FR-2009/0056286 proposes a method of dimensioning by analytical method such structures.

According to a first embodiment illustrated in FIG. 1A, the structure comprises nodes at which three stiffeners of different directions intersect each other. In this case, all the pockets have an isosceles triangle shape. This structure is also known as "Isogrid".

According to another embodiment illustrated in FIG. 2A, the structure comprises nodes at which only two stiffeners of different directions intersect. In this case, the structure includes triangular pockets and other hexagonal ones. It is known as "Anisogrid".

The "Isogrid" type structure offers better mechanical characteristics, especially with regard to buckling, the hexagonal shaped pockets of an "Anisogrid" type structure providing less stability and tending to reduce the buckling resistance of the structure. The so-called "Isogrid" or "Anisogrid" metallic structures are used in the construction of an aircraft. As for the structures with rectangular or square pockets, it is desired to produce structures called "Isogrid" or "Anisogrid with composite materials. According to one procedure, each stiffener is obtained by the superposition of different layers of elongate elements such as fibers. In the case of an "Isogrid" structure, the superposition of the elongated element layers for each stiffener causes the nodes to superimpose three elongate elements for each layer provided at each stiffener, as illustrated in FIG. 1B. Thus, a superimposition factor of three is obtained for each layer of elongate elements at the stiffeners. In this case, the removal of two layers at each stiffener leads to a superposition of six elongated elements at the node. The height of the stiffeners at the nodes is substantially identical to the height of the stiffeners outside the nodes that leads to obtain for each stiffener a section with a filling rate in elongated elements reduced outside the nodes which restricts the mechanical characteristics of the stiffeners and therefore the structure. In the case of an "Anisogrid" structure, the superposition of the elongated element layers for each stiffener causes the nodes to superimpose two elongate elements for each layer provided at each stiffener. Thus, a superposition factor of two is obtained for each layer of elongate elements at the stiffeners. Therefore, although an "Anisogrid" panel has less mechanical characteristics than those of an "Isogrid" panel with an equivalent filling ratio, this type of structure is preferred when it is made of composite material, in particular because of its lower superposition factor (two instead of three) which makes it possible to obtain stiffeners with better mechanical characteristics because of a higher filling ratio in fibrous elements. The present invention proposes an alternative to existing solutions which tends to reduce the superposition factor at the nodes of a network of stiffeners, in particular of an "Isogrid" type structure.

For this purpose, the subject of the invention is a process for producing a network of stiffeners for obtaining a stiffened structure comprising at least two series of stiffeners arranged in at least two distinct directions, with zones of cross-section at each of which intersect at least two stiffeners, said method comprising at least one step of depositing for each stiffener elongate elements in the direction of said stiffener, characterized in that the elongate elements of the stiffeners oriented in different directions intersecting in one point of competition are placed in such a way that the elongated elements of each stiffener are separated from the competition point at the crossing zone on one side of the competition point or on the other side of the competition point in such a way that alternately. This solution makes it possible to reduce the superimposition factor at the crossing zones and thus obtain a high filling rate outside these zones. Other features and advantages will become apparent from the following description of the invention, a description given by way of example only, with reference to the appended drawings, in which: FIG. 1A is a perspective view of a stiffened structure of the type "Isogrid"; FIG. 1B is a diagram illustrating the superposition of three elongate elements at a node of an "Isogrid" structure according to the prior art; FIG. 2A is a perspective view of a "Anisogrid" stiffened structure, - Figure 2B is a diagram illustrating the superposition of the elongate elements for a stiffened structure of "Anisogrid" type, - Figures 3 to 9 are diagrams illustrating the various steps of removal of elongate elements at the level of a node to obtain an "Isogrid" type structure according to the invention, and - Figure 10 is a view illustrating in detail a node of an "Isogrid" type structure obtained according to the invention ion. The invention relates to a method of depositing elongated elements in order to obtain a network of stiffeners reported and secured to at least one of the faces of a panel so as to form a stiffened structure. The panel and the method of assembly of the latter with the stiffeners are not described because they are known to those skilled in the art and do not constitute the essential elements of the invention which deals more particularly with the removal of elongated elements to obtain a network of stiffeners. Each stiffener is preferably arranged substantially perpendicular to the panel and has a rectangular section.

According to an embodiment illustrated in FIG. 1A, the structure comprises three series of stiffeners 10.1, 10.2, 10.3, each series comprising stiffeners parallel to one another and spaced at a preferably regular pitch, the stiffeners of the first series being oriented according to a first direction 12.1, the stiffeners of the second series being oriented in a second direction 12.2 and the stiffeners of the third series being oriented in a third direction 12.3. The first, second, third directions form between them an angle of 60 ° for example. The invention relates more particularly to an "Isogrid" type structure. Therefore, the structure comprises nodes 14 at each of which three stiffeners intersect. Each stiffener comprises elongate elements embedded in a resin matrix. Each stiffener is obtained by the successive removal of layers of elongate elements, a layer comprising at least one elongate element. For the remainder of the description, elongated elements are understood to mean an element which has a section whose largest dimension is clearly smaller than its length. Thus, the section can have different forms. In the case of a substantially round section, the elongate member may be a fiber for example. In the case of a rectangular section, the elongate element may be a strip.

In addition, according to the invention, an elongated element may comprise a single distinct element or several separate elements contiguous, deposited at the same time.

According to the applications and according to the desired characteristics, the elongated element is in a suitable material. Thus, the invention is not limited to one type of material. After removal, the elongate members may be embedded in a polymerized resin matrix. However, other embodiments could be envisaged. This phase is not more detailed because it is mastered by the skilled person. In Figures 3 to 10, the invention has been described applied to a single node. Of course, the removal process can be applied to all nodes.

In Figure 3, there is shown a device for removing the elongate elements for the realization of the network of stiffeners. According to the invention, this device comprises a reference surface which may be the panel to be stiffened (corresponding to the plane of the sheet in FIG. 3) and at the level of a node 14 a central pin 16 having a height above the reference surface at least equal to the height of the stiffener to be produced and for each stiffener of the guide wires for orienting the elongate elements in the desired direction on either side of the central pin 16. Preferably, for each stiffener the device comprises a first guide-f il and a second guide-wire diametrically opposite with respect to the central pin 16.

As illustrated in Figure 3, to obtain a stiffener 10.1 of the first series, the device comprises a first wire guide 18.1 and a second wire guide 20.1 diametrically opposed. To obtain a stiffener 10.2 of the second series, the device comprises a first wire guide 18.2 and a second wire guide 20.2 diametrically opposite. To obtain a stiffener 10.3 of the third series, the device comprises a first wire guide 18.3 and a second wire guide 20.3 diametrically opposite.

According to one embodiment, each wire guide comprises two pins spaced a distance adapted to the desired width of the stiffener between which the elongated elements pass. In Figure 4, there is illustrated the removal of a first elongated element 22.1 oriented in a first direction 12.1 to obtain a stiffener 10.1 of the first series. At the node, the first elongate element 22.1 bypasses the central pin 16 so as to deviate from the point of competition A of the different directions 12.1 to 12.3. Advantageously, the first elongate element 22.1 is guided by the wire guides 18.1 and 20.1 upstream and downstream of the central pin 16 so as to be correctly oriented in the first direction 12.1 on either side of the central pin 16. By following , as illustrated in FIG. 5, a second elongate element 24.1 oriented in a second direction 12.2 is deposited in order to obtain a stiffener 10.2 of the second series. At the level of the node, the second elongate element 24.1 bypasses the central pin 16 so as to deviate from the competition point A. Advantageously, the second elongate element 24.1 is guided by the wire guides 18.2 and 20.2 upstream and downstream of the central pin 16 so as to be correctly oriented in the second direction 12.2 on either side of the central pin 16.

Following, as shown in Figure 6, is deposited a third elongate member 26.1 oriented in a third direction 12.3 to obtain a stiffener 10.3 of the third series. At the level of the node, the third elongate element 26.1 bypasses the central pin 16 so as to deviate from the competition point A. Advantageously, the third elongate element 26.1 is guided by the wire guides 18.3 and 20.3 upstream and downstream of the central pin 16 so as to be correctly oriented in the third direction 12.3 on either side of the central pin 16.

Following, as illustrated in Figure 7, is deposited a fourth elongate element 22.2 superimposed on the first element 22.1 oriented in the first direction 12.1 to obtain a stiffener 10.1 of the first series. At the nceud, the fourth element 22.2 bypasses the central pin 16 so as to deviate from the competition point A opposite the first elongate element 22.1. As for the first elongate element 22.1, the fourth elongated element is guided by the son-guides 18.1 and 20.1. Following, as illustrated in Figure 8, is deposited a fifth elongate member 24.2 superimposed on the second member 24.1 oriented in the second direction 12.2 to obtain a stiffener 10.2 of the second series. At the level of the node, the fifth element 24.2 bypasses the central pin 16 so as to deviate from the competition point A at the opposite of the second elongate element 24.1. As for the second elongate element 24.1, the fifth elongate element 24.2 is guided by the son-guides 18.2 and 20.2.

Following, as shown in Figure 9, is deposited a sixth elongated member 26.2 superimposed on the third member 26.1 oriented in the third direction 12.3 to obtain a stiffener 10.3 of the third series. At nceud, the sixth element 26.2 bypasses the central pin 16 so as to deviate from the competition point A opposite the third elongate element 26.1.

As for the third elongate element 26.1, the sixth elongate element 26.2 is guided by the son-guides 18.3 and 20.3. According to this procedure, it can be seen that for two layers of elongated elements 22.1 and 22.2 or 24.1 and 24.2 or 26.1 and 26.2 at the level of the stiffeners outside the zone of the node, the zone of the node comprises twelve superpositions 28.1 to 28.12 of two elongated elements distributed around the central pin, said superpositions being offset in the plane of deposition, parallel to the panel, as illustrated in FIG.

Thus, according to the invention, a superimposition factor of 2 is obtained for two layers, ie a superimposition factor of 1 for a layer at the level of the stiffeners. If the overlays are not sufficiently spaced out, they are not arranged in the same plane but slightly offset in height so that in the worst case we obtain a superposition ratio of 3 for two layers, ie a superposition factor of 1.5 for a layer at the stiffeners. Thus, the invention makes it possible to obtain a filling ratio in elongate elements at the level of the stiffeners outside the zone of the nodes greater than that of an "Anisogrid" type structure while preserving the mechanical properties related to a structure of Isogrid type with isotropic behavior. The central pin 16 must have a suitable diameter. Indeed, if the central pin has too large a diameter the isotropic nature of the structure can be altered and / or the volume and thus the mass of the structure can be increased significantly. Conversely, if the central pin has a too small diameter, the overlays are not sufficiently spaced which tends to increase the superimposition factor and thus reduce the filling rate of the stiffeners.

To obtain a good compromise, the central pin has a diameter adapted to the section of elongate elements between 2 and 25 mm. Advantageously, the distance separating the center of the central pin and each wire guide must be greater than 10 mm in order to limit the possible mechanical stresses applied to the elongated elements because of the interlacing.

Preferably, the distance separating the center from the central pin and each wire guide must be less than or equal to min (a1,... A1, ... a6) / 8, with the distance separating the center of the central pin considered with the center of an adjacent central pawn (see Figure 1B). This arrangement makes it possible to obtain a distance L where the elongated elements are grouped between two adjacent nodes, greater than or equal to 75% of the distance separating said two nodes so as not to alter the isotropic nature of the structure too much. After removal of the elongate members, the central pin 16 and the wire guides are removed. An arrangement as shown in FIG. 10 is obtained. The void created by the removal of the central pin can be used as a housing for an insert. Although described applied to an "Isogrid" type structure, the invention is not limited to this type of structure. Thus, it may be suitable for structures of the "anisogrid", "orthogrid" or other type. In general, the deposition method can be applied to all structures each comprising at least two sets of stiffeners arranged in at least two distinct directions, with crossing zones of the stiffeners at each of which at least two intersect each other. stiffeners. Although the preferred embodiment describes the use of central pin 16 and wire guide, the removal method can be realized without these elements. Thus, according to the invention, the elongate elements of the stiffeners oriented in different directions intersecting at a competition point are deposited in such a way that the elongate elements in the same direction are separated from the competition point at the level of the zone. crossing a first side of the competition point or the other side of the competition point alternately (the first elongated element being separated from one side, the second from the other side, the next 25 from the first side , and so on ). Preferably, the spacing between the two elongate elements oriented in the same direction and spaced apart at the point of competition is between 2 and 25 mm.

Advantageously, the elongated elements are successively deposited according to the different directions (in the first direction, in the second direction, according to the nth direction, in the first direction, in the second direction, ..., along the nth direction, and in the case of n directions), Preferably, the elongate elements are deposited successively always in the same order. Although the invention provides for several elongated elements, these elongate elements can in fact constitute the sections of a single and single elongated element.

Claims (10)

REVENDICATIONS1. Process for producing a stiffener network (10.1, 10.2, 10.3) for obtaining a stiffened structure comprising at least two series of stiffeners arranged in at least two distinct directions (12.1, 12.2, 12.3), with zones crossing at each of which intersect at least two stiffeners (10.1, 10.2, 10.3), said method comprising at least one step of depositing for each stiffener (10.1, 10.2, 10.3) elongate elements (22.1, 22.2, 24.1). , 24.2, 26.1, 26.2) according to the direction of said stiffener, characterized in that the elongated members (22.1, 22.2, 24.1, 24.2, 26.1, 26.2) of the stiffeners oriented in different directions intersecting at a point of competition are deposited from such that the elongated members (22.1, 22.2, 24.1, 24.2, 26.1, 26.2) of each stiffener are spaced apart from the competition point at the crossover area on one side of the contest point or on the other side of the competition point alternately. 2. A method of producing a network of stiffeners according to claim 1, characterized in that it consists in using a central pin (16) at the crossing zone bypassed by the elongate elements (22.1, 22.2, 24.1, 24.2, 26.1, 26.2). 3. A method of producing a network of stiffeners according to claim 2, characterized in that it consists in using for each stiffener two son-guides (18, 20) diametrically opposed relative to the central pin (16). 4. A method of producing a network of stiffeners according to claim 3, characterized in that the distance separating the central pin and each wire guide is such that the distance L where the elongated elements are grouped between two adjacent nodes is greater or equal to 75% of the distance separating said two nodes. 5. A method of producing a network of stiffeners according to claim 3 or 4, characterized in that each wire guide comprises two pins between which pass the elongated elements. 6. A method of producing a network of stiffeners according to any one of the preceding claims, characterized in that the spacing between the elongate elements of the same stiffener spaced at the point of competition is between 2 and 25 mm . 7. A method of producing a network of stiffeners according to any one of the preceding claims, characterized in that the elongate elements (22.1, 22.2, 24.1, 24.2, 26.1, 26.2) are deposited successively in different directions. 8. A method of producing a network of stiffeners according to claim 6, characterized in that the elongated elements (22.1, 22.2, 24.1, 24.2, 26.1, 26.2) are deposited successively always in the same order. 9. A method of producing a network of stiffeners according to any one of the preceding claims for obtaining a stiffened structure of "Isogrid" type comprising three sets of stiffeners arranged in three distinct directions (12.1, 12.2, 12.3). , with crossing zones at each of which three stiffeners (10.1, 10.2, 10.3). 10. A stiffened structure comprising a stiffener network obtained from the method according to any one of the preceding claims.