FR2971233A1 - Multilayer substrate for dampening panel structure of e.g. telecommunication satellite, has skins separated by honeycomb type structure comprising tubular cells, where one of cells is provided with damping element occupying interior of cell - Google Patents

Abstract

The substrate has an upper skin (11) and a lower skin (12) that are separated by a honeycomb type structure comprising a set of tubular cells with a periodic pattern, where the tubular cells have regular or concave hexagonal shape. One of the tubular cells is provided with a damping element (42) occupying an interior of the tubular cell. The damping element is made of polymer material e.g. foam or gel. Each tubular cell has a section in a plane parallel to a main plane of the skins.

Description

The present invention relates to a damping substrate for a satellite structural panel. It applies in particular to the space field, and more specifically to structural panels used in telecommunications, observation and scientific satellites. Satellites typically embark on several structural panels. Some structural panels make up the body of the satellite, that is to say the supporting structure on which the equipment is fixed, others are for example mainly intended for heat dissipation, others for the support of solar generators, or antenna reflectors. There are also structural panels integrating into deployable structures, for example solar generators. The structural panels are subjected to different vibratory levels, of harmonic, random or transient types, in particular caused by launching modes, or by the acoustic environment, or by pyrotechnic shocks, for example due to the stage separation of the launcher , to the expulsion of the satellite, etc., also caused for example to the removal of unfoldable structures. But there is a need for very light structures. In particular, the use of components made of composite materials such as carbon is preferred. These materials are usually very stiff and very resistant, however their damping character is very low, vis-à-vis shocks and vibratory modes. Thus, when vibratory energy is supplied to such components, they render it almost completely. Difficulties arise when these components are excited at their own frequencies, for which resonance and amplification phenomena appear. These phenomena generate very important constraints, and are decisive for the dimensioning of the structures. In addition, especially in the case of pyrotechnic shocks, these components transmit with little loss the shock pulse, which is also difficult, and is also sizing, especially for equipment disposed near the areas where shocks occur. produce, for example near pyrotechnic unlocking systems. The damping of the structures forming the structural panels of satellites thus constitutes a first problem affecting the design thereof. A structural panel architecture commonly used in satellites is defined by two substantially flat and parallel surfaces called "skins" arranged on either side of a structure ensuring in particular the spacing between the skins, and to resume the flow of shear. This structure is typically formed by tubular shaped cells whose section has a shape having a periodic pattern. It is for example customary to use structures of the "honeycomb" type, commonly referred to by the acronym Nida, formed by cells with regular hexagonal section, and made for example in materials such as aluminum. The thickness of the skins allows them to take the flow of significant effort. Both skins are usually formed by an upper skin and a lower skin, the skin surfaces being in contact with the satellite's external environment, or with portions thereof, and capable of accommodating devices, such as modules electronic or electromechanical devices, reflectors, photovoltaic cells, etc. The assembly formed by the two skins and the Nida structure constitutes a substrate whose structure is of the type commonly referred to as a "sandwich". In order to optimize the mass of the substrates as a function of their mechanical strength and their stiffness, the use of thick sandwich-type substrates is in itself known. Such substrates have the main characteristic of being very strong and stiff in bending, for a low mass. Also, for such substrates, the distance maintained between the skins by the Nida structure allows them to resume bending by traction / compression in their main planes. The high thickness of the Nida structure allows the resumption of strong shear flows. In addition, there are certain substrates for satellite panels requiring a specific, relatively large thickness. This is for example the case for substrates hosting antenna reflectors, the thickness of which is dependent on the wavelength of the signals concerned.

For all these substrates of great thickness, a second problem arises, in that the Nida structure tends to be oversized with respect to the function of resumption of shear flows that it provides and thus provides excess surplus weight.

Solutions known in themselves aim to solve the first problem mentioned above, relating to vibration amplification phenomena. According to a first known technique, it is possible, for example, to reinforce the structures at the places most affected by shocks or vibrations. This first technique consists of adding mass to the skins, and is implemented at the expense of the mass of structures, and therefore to the detriment of the payload of the satellite. According to a second known technique, the interfaces between the structural panels and the satellite can be modified in the sense of improving the boundary conditions; for example, additional stacking feet can be integrated. Solutions based on this technique, however, have the disadvantage of requiring a mass addition, and make the design of the systems more complex, to the detriment also increased risk of failure. According to a third known technique, the constraints in terms of acceptable excitation levels at the different disturbing frequencies can be relaxed, this level relaxation action being usually referred to as "notching". However, relaxation of the constraints implies negotiations between the subsystem manufacturers, the system integrators and the satellite launching authorities, these negotiations being sometimes delicate, sometimes leading to rejections, and in any case harmful to the time. systems development. According to a fourth known technique, the components most sensitive to shocks and vibrations can be arranged as far as possible from the components that generate them. However, the solutions based on this technique have the disadvantage of requiring a greater complexity of design, and the size of the systems suffers. According to a fifth known technique, active damping devices can be arranged in suitable places, for example on skins, servo loops can advantageously control these devices. The active damping devices may in particular be formed by piezoelectric systems capable of vibrating at determined frequencies, by current or voltage control. The solutions based on this technique however have the disadvantage of being expensive, and the reliability of the systems implementing them is not optimal. In addition, solutions known per se aim at solving the aforementioned second problem, relating to the oversizing of the Nida structure in thick substrates with a sandwich-type structure.

According to a known technique, it is indeed possible to increase the size of the cells of the Nida structure, this increase resulting in a decrease in the total mass of the substrate. Advantageously, the cells of the Nida structure may be chosen smaller in areas where the shear flows are large, and larger in the so-called common areas, where the flows are lower. At the same time, the skins can be more or less thick depending on the zones and the flow of effort exerted on them. However, this technique has the disadvantage of a phenomenon of local buckling, at the level of skin areas reported to large cells. This phenomenon is described in more detail below with reference to FIGS. 2 and 3a to 3c.

An object of the present invention is to overcome at least the disadvantages of existing solutions to solve the two aforementioned problems, by providing a substrate for structural satellite panel with good vibration damping characteristics, and a mass / advantageous bulk, while providing increased robustness.

For this purpose, the subject of the invention is a substrate for a satellite structural panel comprising an upper skin and a lower skin, the two skins being separated by a structure comprising a plurality of tubular cells having a periodic pattern, the substrate being characterized in that at least one of said cells comprises a damping element occupying the interior volume of the cell.

In one embodiment of the invention, a satellite structural panel substrate may comprise an upper portion and a lower portion, each forming a substrate as described above, the upper portion being formed by a top skin and a skin upper intermediate separated by an upper structure of which at least some of the cells comprise a damping element, the lower part being formed by a lower skin and an intermediate lower skin separated by a lower structure of which at least some of the cells comprise a damping element, said parts upper and lower portions being separated by a central structure comprising a plurality of tubular cells having a periodic pattern. In one embodiment of the invention, said structure may be a honeycomb structure, said tubular cells being of regular hexagonal shape.

In one embodiment of the invention, the cells may be auxetic, hexagonal concave. In one embodiment of the invention, the cells of said upper and lower structures may have a section, in a plane parallel to the main plane of the skins, whose area is smaller than that of the section of the cells of said central structure. In one embodiment of the invention, said damping elements may be made of a polymer material, formed by a foam, a gel or a solid particle filler, or a foam or gel comprising a solid particle filler.

Other features and advantages of the invention will appear on reading the description, given by way of example, with reference to the appended drawings which represent:

FIG. 1 is a perspective view illustrating a known sandwich structure substrate; FIG. 2, a perspective view illustrating a sandwich-type structure substrate comprising reinforcement zones, according to a known embodiment; Figures 3a to 3c, sectional views schematically illustrating a local buckling phenomenon; FIG. 4 is a perspective top view illustrating a damping substrate, according to an exemplary embodiment of the invention; Figure 5 is a sectional view schematically illustrating a damping substrate, according to an embodiment of the invention; Figure 6 is a sectional view schematically illustrating a multilayer damping substrate, according to an embodiment of the invention; Figure 7 is a perspective top view illustrating a multilayer damping substrate, according to an alternative embodiment of the invention. Fig. 1 shows a perspective view illustrating a known sandwich structure substrate. A sandwich structure substrate comprises a substantially planar upper skin 11 disposed parallel to a lower skin 12. A structure comprising a plurality of tubular cells having a periodic pattern, for example a Nida structure 10 is disposed between the upper skins 11 and lower 12. The skins 11, 12 are for example made of a composite material, for example carbon, and the structure Nida 10 in an aluminum alloy. Fig. 2 shows a perspective view illustrating a sandwich type structure substrate according to a known improved embodiment. The substrate illustrated in FIG. 2 also comprises upper and lower skins 12 and an intermediate Nida structure. However, the Nida structure 10 consists of different Nida structures of different densities, that is to say whose Nida cells have more or less large surfaces and / or whose aluminum foils usually referred to as "foils". Forming the walls of these cells have more or less significant thicknesses. For example, a first substructure Nida 101 may be formed by larger surface cells than cells of a second substructure Nida 102 disposed in close proximity to an insert 20, the insert 20 allowing the attachment of the substrate to another element that can be the satellite via appropriate interface elements. The area covered by the second sub-structure Nida 102 thus constitutes a reinforcement zone, its higher density conferring on it a better recovery of shear flow. The enlargement of the cells of the first sub-structure Nida 101 thus allows a gain in mass, the large size of the cells not being unacceptable vis-à-vis the resumption of shear flows applying to the structure. Advantageously, the skins 11, 12 may be thicker at the level of the reinforcing zone. Figures 3a to 3c show cross-sectional views showing a synoptic phenomenon of local buckling.

FIG. 3a is a sectional view of the structure illustrated in FIG. 2 and described above, in which the upper and lower skins 11 and lower 12, and the first substructure Nida 101 comprising enlarged cells, are particularly visible, and the second substructure Nida 102 comprising cells of normal size.

Figure 3b shows a structure identical to the structure of Figure 3a, undergoing a bending moment. The bending moment decomposes into a compressional flow applying to the upper skin 11 in its main plane, and a pulling flow applying to the lower skin 12 in its main plane. In this example, the traction flow does not affect the surface condition of the lower skin 12; on the other hand, the compression flow has the consequence of a local buckling phenomenon which can cause the rupture of the upper skin 11. The phenomenon of local buckling can be designated according to the English terminology "Intracell Buckling". The maximum permissible compression stress 6admlB on a skin before appearance of the local buckling phenomenon can be formulated according to the relation: t \ 2 2 _ skin 6adm IB - (-U2) XE skin x \ 1 \ cell / - v denotes the coefficient Poisson de la structure Nida, - Speau means the Young's modulus of the skin, (1), where: - t denotes the thickness of the skin, skin - cDce, denotes the diameter of a Nida cell. FIG. 3c illustrates a substrate with a sandwich structure, comprising a conventional Nida structure 10, in which the Nida cells have a "normal" diameter, for example identical to the diameter of the Nida cells forming the second substructure 102, illustrated in particular in FIGS. Figures 3a and 3b. The use of the Nida structure 10, the cells of which are not enlarged, substantially over the entire structure of the substrate, makes it possible to guard against the risk of buckling by raising the maximum compressive stress admissible on the skins 11, 12. However, as mentioned above, such a structure has the disadvantage of a large mass compared to a structure as shown in FIG. 2.

FIG. 4 is a perspective top view illustrating a damping substrate, according to an exemplary embodiment of the invention. According to a first exemplary embodiment of the invention, a substrate with a sandwich structure similar to the substrate described for example with reference to FIG. 1 may comprise an upper skin 11 and a lower skin 12 between which a Nida structure 10 is arranged.

According to a specificity of the present invention, a plurality of cells of the Nida structure 10 may contain a damping element 42. The remaining cells of the Nida structure 10 are "empty" cells 41, i.e. similar to the cells. previously described. It is also conceivable that all the cells of the Nida structure 10 contain a damping element 42. The damping element 42 may be made of polymer material. For example, the damping element 42 may be formed by a polymer foam, or a polymer gel, a load of solid particles may for example be included in the foam or the polymer gel; the damping element 42 may also be formed by a charge of solid particles. Advantageously, the damping element 42 may be formed by a polymer gel initially in liquid phase, and able to change phase to pass to the solid phase, with the addition of an additive or by temperature treatment. In this way, the damping element 42 can, during the manufacturing process, be easily inserted into the cells of the Nida structure 10. Advantageously, only the cells of the Nida structure 10 located in the zones most stressed by deformation may contain a damping element 42, as shown in Figure 5 described below. In the example illustrated in Figure 5, a device 50 is disposed on the upper skin 11. The equipment 50 may constitute a source of shock. It is for example possible to fill with a damping element 42, the cells of the structure Nida 10 which are located around the equipment 50, the rest of the cells of the structure Nida 10 being empty cells 41. In the example 5. The damping elements 42 are arranged over the entire thickness of the cells of the Nida structure 10, that is to say that they extend from the upper skin 11 to the lower skin 12. Advantageously, and according to another specificity of the present invention, the substrate may be formed by a multilayer sandwich structure, as is illustrated in FIG. 6 described below.

FIG. 6 is a cross-sectional view schematically illustrating a multilayer damping substrate according to an exemplary embodiment of the invention. In the example illustrated in FIG. 6, the substrate comprises an upper skin 11 and a lower skin 12. Intermediate skins parallel to the upper 11 and lower 12 skins may be between the two upper and lower skins 11, 12. upper intermediate skin 61 may be disposed at a determined distance from the upper skin 11, and a lower intermediate skin 62 may be disposed at a determined distance from the lower skin 12. In this way, the upper skin 11 and upper intermediate skin 61 form a sandwich type structure, an upper Nida structure 601 can be disposed therebetween. In the same way, the lower and lower intermediate skins 62 form another sandwich-type structure, a lower Nida structure 62 being able to be disposed between them. Finally, a central Nida structure 600 may be disposed between the upper intermediate 61 and lower 62 skins, the assembly also forming a sandwich-type structure. A first advantage provided by such a multilayer structure is that it is possible to arrange the damping elements 42 in smaller volumes. In other words, the substrate comprises an upper portion comprising the upper skin 11, the upper intermediate skin 61 and the upper Nida structure 601, and a lower portion comprising the lower skin 12, the lower intermediate skin 62 and the Nida structure 10 lower part 602, the upper and lower parts being in themselves similar to the substrate presented previously with reference to FIG. 4. In the example illustrated in FIG. 6, a device 50 is in a manner similar to FIG. 11. It is possible to have the damping elements 42 for example only around the equipment 50 to be damped. Therefore, the damping elements 42 may be arranged only in the cells of the upper Nida structure 601, without their damping power is affected. In this way, the mass penalty provided by the damping elements 42 is low. A second advantage provided by a multilayer structure is that it allows a considerable reduction of the local buckling phenomenon described above, without implying a significant mass penalty. Indeed, the deformations for example due to shocks and vibrations, mainly affect the upper and lower parts of the substrate. For example, the upper part of the substrate is affected by compression-type stresses, while the lower part of the substrate is affected by tensile-flux type stresses, or vice versa. If the upper part of the substrate is subjected to a compression flow, then in a multilayer structure, mainly the upper skin 11 is subject to local buckling phenomena. To a lesser extent, the upper intermediate skin 61 is too. The multilayer structure makes it possible, for example, to reduce the diameter of the cells of the upper Nida structures 601 and lower 602 in order to reduce the effect of local buckling phenomena. In addition, it is possible to increase the cell diameter of the central Nida structure 600, the local buckling phenomenon being of little influence in the central part of the substrate. Thus, even if the intermediate skins 61, 62 and the upper Nida 601 and lower 602 structures represent a mass contribution compared to a conventional sandwich type Nida structure, the latter is compensated by the enlargement of the diameter of the cells of the structure Nida central 600. Even on thick panels, such a structure can allow a reduction of the total mass, compared to a conventional sandwich type structure. The example illustrated in FIG. 6 is not limiting of the present invention: it is for example possible to design multilayer substrates in which the diameters of the cells of the different Nida structures are not homogeneous within a given Nida structure . For example, it is possible to densify the upper Nida structures 601 and lower 602 at defined zones. Also, it is advantageously possible to design Nida structures formed by cells of alternative shapes, as illustrated by FIG. 7 described below.

Figure 7 shows a top view in perspective, illustrating a multilayer damping substrate, according to an alternative embodiment of the invention. The substrate shown in the example illustrated in FIG. 7 is substantially of the same structure as the substrate shown in FIG. 6. Thus, the substrate comprises two upper skins 11 and lower skins 12, as well as two upper intermediate skins 61 and lower skins 62. A central Nida structure 600 is disposed between the upper intermediate skin 61 and the lower intermediate skin 62. In a similar manner, an upper structure 701 may be disposed between the upper skin 11 and the upper intermediate skin 61. A lower structure 702 may similarly be disposed between the lower skin 12 and the lower intermediate skin 62. However, the upper 701 and lower 702 structures may be formed by structures alternative to a Nida type structure. In the example illustrated in FIG. 7, the upper 701 and lower 702 structures may be formed by cells of hexagonal concave or "diabolo" shape. Such cells are said to be auxetic, that is, they have a negative Poisson's ratio; auxetic cells have the particular property to see their volume vary significantly more than "normal" cells when they are stressed in tension or compression in one direction. A consequence of the properties of auxetic cells, is a pumping effect on a material that they contain. This pumping effect is particularly advantageous if the cells contain a damping element 42 as described above. A multilayer substrate structure as shown in Fig. 7, wherein the upper 701 and lower 702 structures are formed by auxetic cells, some or all of which contain a damping element 42, the remaining cells, if any, being cells voids 71, thus has a significant advantage in terms of damping compared to a conventional sandwich-type structure, for a total mass remaining quite acceptable.

Claims (11)

CLAIMS 1- Satellite structural panel substrate, comprising an upper skin (11), a lower skin (12), the two skins (11, 12) being separated by a structure (10) comprising a plurality of tubular cells having a periodic pattern , the substrate being characterized in that at least one of said cells comprises a damping element (42) occupying the interior volume of the cell. 2- satellite structural panel substrate comprising an upper portion and a lower portion, each forming a substrate according to claim 1, the upper portion being formed by an upper skin (11) and an upper intermediate skin (61) separated by a structure (601) upper of which at least some of the cells comprise a damping element (42), the lower part being formed by a lower skin (12) and a lower intermediate skin (61) separated by a lower structure (602) of which at least some cells comprise a damping element, said upper and lower portions being separated by a central structure (600) comprising a plurality of tubular cells having a periodic pattern. The satellite structural panel substrate according to any one of the preceding claims, wherein said structure is a honeycomb structure (10), said tubular cells being of regular hexagonal shape. The substrate for a satellite structural panel according to claim 1, wherein said cells are auxetic, hexagonal concave. The satellite structural panel substrate according to claim 2, wherein the cells of said upper (601) and lower (602) structures are auxetic, hexagonal concave. The structural satellite panel substrate according to any one of claims 2, 4 and 5, wherein the cells of said upper (601) and lower (602) structures have a section, in a plane parallel to the main plane of the skins ( 11, 12, 61, 62), whose area is smaller than that of the section of the cells of said central structure (600) The substrate for a structural satellite panel according to any of the preceding claims, wherein said damping elements (42) are made of a polymeric material. The substrate for a structural satellite panel according to claim 7, wherein the polymeric material is a foam. The substrate for a structural satellite panel according to claim 7, wherein the polymeric material is a gel. 10. The structural satellite panel substrate according to any one of claims 7 to 9, wherein the polymeric material contains a solid particle charge. The satellite structural panel substrate according to any one of claims 1 to 6, wherein said damping elements (42) are formed by a charge of solid particles.