Method for producing a compartmented tank made of composite material

Abstract

The present invention relates to a method for producing a compartmented tank made of composite material, in which an assembly comprising a common base precursor is fired under vacuum in equipment, the moulding parts of which are external to the assembly in order to facilitate subsequent removal from the mould.

Description

Description Title of the invention: Method for manufacturing a compartmentalized composite material tank Technical Field

[0001] The present disclosure relates to a method for manufacturing a compartmentalized composite material tank having a common bottom between two adjacent compartments. The invention is of particular interest for the manufacture of tanks intended to equip space launchers without the invention being limited to this application. Prior art

[0002] Composite materials provide a weight saving compared to metallic materials, which is of particular interest in aerospace and aeronautical applications with a view to improving performance.

[0003] The recent development of reusable launchers is accompanied by the desire to continue developing lighter structures since it is necessary to retain a certain quantity of propellant for the return of the stage to Earth, which leads to the carrying of additional mass.

[0004] In current composite tank manufacturing techniques, the part is draped over a rotating mandrel, by winding or by automated fiber placement (AFP) technique. However, current techniques are limited in achieving a compartmentalized composite structure with a common bottom separating two adjacent compartments inside the tank.

[0005] It is known to add a section of the compartmentalized tank including the common bottom equipped with part of the compartments to be obtained and to connect it to the rest of the tank by gluing circumferential belt strips on the junctions (called "belly belt" in English). However, in this technique, the section must fit perfectly with the rest of the tank and the junction becomes very delicate, even impossible, in the event of a difference in diameter. In addition, the walls of the same compartment are, in this case, cut in the circumferential direction and all the forces (traction / compression / shear) pass through the added / glued belt which ensures the junction of the elements.

[0006] In the particular case where the manufacture of large tanks, typically having a length of 20 to 30 meters and a diameter of several meters, is sought, additional constraints appear, in particular linked to mandrels that are too long and do not have the rigidity required to maintain their shape during draping, to even more difficult disassembly or to the multiplication of junctions to be sealed. US5383566 is known, which discloses a two-chamber composite tank, US2021301094, which discloses a method for manufacturing a molded product made of fiber-reinforced resin, and FR 3 125 739, which discloses a filament winding machine with a rotating support with several winding heads.

[0007] The limitations of current techniques are even more pronounced when it comes to integrating reinforcement elements, such as stiffeners or interface parts, into the tank.

[0008] It is therefore desirable to have a method for manufacturing a compartmentalized composite material tank which addresses all or part of the aforementioned drawbacks. Statement of the invention

[0009] This disclosure relates to a method of manufacturing a compartmentalized composite material tank, comprising: - the positioning of a precursor assembly of the tank to be manufactured in a vacuum molding tool, the assembly comprising: (i) a cylinder, precursor of the tank body, made of thermosetting pre-impregnated fibrous material extending along a longitudinal axis, (ii) two domes, precursors of the end bottom of the tank, made of thermosetting pre-impregnated fibrous material, each of these domes being located on the side of an opposite longitudinal end of the cylinder, the domes delimiting with the cylinder an internal volume of the tank to be obtained, each dome defining a cylindrical end junction zone positioned opposite the cylinder and inside the latter, and (iii) a common bottom precursor located inside the cylinder and between the domes so as to define with each of them a compartment distinct from the internal volume, said common bottom precursor comprising a frame made of thermoset composite material, defining the common bottom, covered by at least one thermoset pre-impregnated fibrous skin defining an intermediate cylindrical junction zone positioned opposite the cylinder, the frame being configured to allow conformation of said at least one skin against the cylinder on this intermediate cylindrical junction zone, and the tooling comprising: (a) a first internal positioning portion coated with a first vacuum cover, located inside a first compartment, a first dome being positioned on a first end of said first portion, and the common bottom precursor being positioned on a second end of said first portion opposite the first end, (b) a second internal positioning portion, coated with a second vacuum cover, positioned in the extension of said first portion along the longitudinal axis and located inside a second compartment, the common bottom precursor being positioned on a first end of said second portion and a second dome being positioned on a second end of said second portion opposite the first end, and (c) an external molding portion, located outside the internal volume, comprising a molding portion of the tank body having a cylindrical shape located opposite the precursor cylinder, and molding portions of a dome-shaped tank bottom each located opposite a separate dome, and - vacuum curing of the assembly in the tool during which the first and second vacuum tanks apply pressure to conform the assembly to the molding portions, with the junction zones held in contact with the precursor cylinder and co-curing of the domes and the common base precursor with the cylinder to secure the bases to the body and thus obtain the compartmentalized composite material tank.

[0010] The method according to the invention makes it possible to obtain a composite material tank in which the common bottom separates two adjacent compartments inside the tank. Co-curing makes it possible to polymerize the thermosetting resin impregnating the cylinder with that impregnating the domes and with that impregnating said at least one skin of the common bottom precursor, and to create covalent bonds between the polymer chains present. This joint polymerization leads to a bonding of the bottoms (end bottoms and common bottom) to the body of the composite material tank, without requiring the addition of a third-party adhesive compound. However, it does not depart from the scope of the invention if a third-party adhesive compound is used on the interfaces of the elements constituting the bottoms or the body or on the interfaces between the bottoms and the body, so as to provide additional mechanical strength.

[0011] The reinforcement is a thermoset composite material, i.e. one whose matrix has been completely polymerized, so as to give the common bottom precursor sufficient rigidity to maintain the desired geometry for the common bottom during the manufacture of the tank, and in particular during vacuum cooking. The reinforcement allows also to avoid the presence of a molding tool on the common bottom during the manufacture of the tank, thus making it possible to maintain a relatively simple tool structure. On the other hand, the common bottom precursor remains sufficiently deformable on the intermediate cylindrical junction zone to allow the expansion or deformation of said at least one skin, thus guaranteeing good attachment of the common bottom to the cylinder. As will be described below, the frame can have various structures making it possible to fulfill this function.

[0012] In the invention, the molding portion is external to the precursor assembly, and therefore to the resulting composite tank. This external positioning makes it easier to disassemble compared to the internal molding mandrel of the prior art and more easily guarantees the seal required for vacuum drawing. Unlike the mandrel of the prior art, the first and second internal portions in the invention only have a positioning function and not a molding function, and therefore have a much simpler design and are more easily disassembled.

[0013] In the following and unless otherwise stated, the word “skin(s)” designates said at least one thermosetting pre-impregnated fibrous skin of the common base precursor.

[0014] In an exemplary embodiment, the common bottom precursor comprises a first skin covering a first face of the frame and defining a first portion of the intermediate cylindrical junction zone which extends towards the first dome, and a second skin covering a second face of the frame, opposite the first face, and defining a second portion of the intermediate cylindrical junction zone which extends towards the second dome.

[0015] Such a feature makes it possible to further improve the conformation of the common base on the cylinder and therefore the quality of the connection to the body, as well as to reduce the risk of misalignment.

[0016] In particular, the common bottom precursor may further comprise a filler material between the first and second portions of the intermediate cylindrical joining area.

[0017] Such a feature makes it possible to further improve the conformation of the common base on the cylinder and therefore the quality of the connection to the body, as well as to reduce the risk of misalignment.

[0018] In an exemplary embodiment, the intermediate cylindrical junction zone is at least partly formed by an extension of said at least one skin beyond the frame.

[0019] Such a characteristic corresponds to a possibility of conferring flexibility on the intermediate cylindrical junction zone by implementing a reinforcement which stops sufficiently early upstream of it.

[0020] Alternatively or in combination, the frame defines a plurality of flexible tabs allowing the conformation of said at least one skin against the cylinder on the intermediate cylindrical junction zone.

[0021] These tabs are sufficiently flexible so as not to hinder conformation during sous vide cooking. This arrangement is functional even if the frame is extended compared to the example previously described due to the presence of a flexible circumferential zone on the side of the intermediate cylindrical junction zone.

[0022] In one exemplary embodiment, the frame comprises an insulating material configured to thermally insulate the first compartment from the second compartment.

[0023] Such a feature further functionalizes the armature and is of particular interest when the application requires compartments in which significantly different temperatures are imposed during operation.

[0024] In particular, the insulating material may be cellular, for example in the form of a honeycomb or in the form of a filling foam.

[0025] Such a characteristic advantageously makes it possible not to penalize the mass of the structure.

[0026] In an exemplary embodiment, said at least one skin has a thinning of thickness on the intermediate cylindrical junction zone in the direction of a circumferential edge thereof.

[0027] Such a feature advantageously makes it possible to avoid any risk of bridging the tank on a misalignment during vacuum cooking, and to further improve the material health of the skin, the cylinder and the skin / cylinder interface in this common bottom stop zone. By misalignment we are talking about a local surface jump, that is to say that the surface is not smooth, and that the ends of the assembled parts form a step. In addition, this feature makes it possible to minimize stress concentrations (at the bottom stop) when the tank is subjected to mechanical stresses (filling, thermal stresses, pressurization, forces applied during takeoff phases and potentially return to Earth, etc.).

[0028] In an exemplary embodiment, each skin comprises several sectors juxtaposed around the longitudinal axis.

[0029] In this example, the common background precursor is sectorized and comprises several skin sectors distributed in a circumferential direction. The sectorization allows to further improve the conformation to the cylinder by allowing a conformation of the sectors by relative sliding between them and an assembly with the cylinder without constraint.

[0030] In particular, neighboring sectors may exhibit a thinning of thickness over their overlapping area towards their longitudinal edges.

[0031] The thickness reduction makes it possible to locally avoid thickness jumps and to further minimize misalignments and stress concentrations.

[0032] In an exemplary embodiment, the cylinder, said at least one skin and the domes are assembled in the semi-cooked state to form the precursor assembly.

[0033] A semi-cured thermosetting material has a partially cured resin that has a degree of polymerization progress of between 15% and 70%, for example between 25% and 50%. For a given resin, the degree of polymerization progress can be determined by differential scanning calorimetry (DSC).

[0034] A semi-cured material has a certain rigidity at room temperature (20°C) which facilitates its handling, and allows for a simplification of tools. Its use also allows for less constraints on the material's lifespan at room temperature because the polymerization of a semi-cured material changes little at room temperature. The resin of a semi-cured material regains fluidity when the material is raised in temperature during vacuum curing, which allows the elements to soften and conform to the molding portions by relative sliding.

[0035] As indicated below, the cylinder can be sectorized by being formed from a plurality of panels, as well as the domes which can be formed from a plurality of petals. Within the framework of this assembly in the half-cooked state, it will be noted that the different possibilities can be considered: - the cylinder, already formed by juxtaposition of the panels, the domes, already formed by juxtaposition of the petals, and said at least one skin of the common base precursor can be assembled in the half-cooked state to form the precursor assembly, or - the cylinder, already formed by juxtaposition of the panels, the petals, intended to form the domes after juxtaposition, and said at least one skin of the common base precursor can be assembled in the half-cooked state to form the precursor assembly, or - the panels, the domes, already formed by juxtaposition of the petals, and said at least one skin of the common base precursor can be assembled in the half-cooked state to form the precursor assembly, or - the panels, the petals, intended to form the domes after juxtaposition, and the said at least one skin of the common background precursor can be assembled in the half-baked state to form the precursor assembly.

[0036] In an exemplary embodiment, the method further comprises, prior to positioning the precursor assembly in the molding tooling, forming the cylinder, said at least one skin, and the domes by automatic fiber placement, the cylinder, said at least one skin, and the domes each being draped over a separate shape of the first and second positioning portions.

[0037] This technique allows access to a wide variety of geometries, particularly compared to winding, which does not allow draping in the direction of the longitudinal axis, or automated draping of excess thicknesses or local reinforcements. The automatic placement of fibers also makes it possible to obtain elements with low permeability compared to parts obtained by winding, suitable for example for the storage of cryogenic propellants. In addition, the draping tooling is separate from the polymerization tooling, which reduces the manufacturing cycle time.

[0038] In one exemplary embodiment, the cylinder, said at least one skin and the domes comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

[0039] These fibers are particularly suitable for space launcher applications and cryogenic environments.

[0040] In an exemplary embodiment, the cylinder, said at least one skin and the domes are pre-impregnated with an epoxy resin, for example a class 180 epoxy resin which polymerizes at a temperature between 175°C and 185°C, for example substantially at 180°C.

[0041] This material is particularly suitable for space launcher applications and cryogenic environments, and can be easily reworked after partial polymerization.

[0042] In an exemplary embodiment, the cylinder, precursor of the tank body, is sectorized and is formed by panels juxtaposed around the longitudinal axis with overlap between the neighboring panels. If necessary, the molded portion of the body can be stiffened on its face opposite the assembly in order to retain its shape despite a significant length, without affecting the quality of the molding or the disassembly nature.

[0043] Forming the cylinder from a plurality of panels simplifies its manufacture when a long cylinder is envisaged.

[0044] In particular, neighboring panels may exhibit a thinning in thickness over their overlapping area towards their longitudinal edges.

[0045] Such a feature helps to further minimize misalignments and stress concentrations in the reservoir.

[0046] In one exemplary embodiment, the precursor domes have a thinning in thickness on their end cylindrical joining zones towards a circumferential edge of the dome.

[0047] Such a feature helps to further minimize misalignments and stress concentrations in the reservoir.

[0048] In an exemplary embodiment, the precursor domes are each sectorized and formed by petals juxtaposed around the longitudinal axis with overlap between the neighboring petals.

[0049] The sectorization of the domes further improves their conformation during sous vide cooking by allowing relative sliding between the petals.

[0050] In particular, neighboring petals may exhibit a thinning of thickness over their overlapping area towards their longitudinal edges.

[0051] Such a feature helps to further minimize misalignments and stress concentrations in the reservoir.

[0052] In one exemplary embodiment, the panels and domes each include a plurality of stiffeners on a face opposite the molding portions.

[0053] The external nature of the molding tool does not interfere with the presence of the stiffeners. The invention is therefore of particular interest for the manufacture of a stiffened tank which can be relatively difficult to obtain in the techniques of the prior art using an internal molding mandrel.

[0054] In one exemplary embodiment, the cylinder extends beyond each of the domes so as to define precursors of front and rear skirts.

[0055] Such a feature is of particular interest in the context of a tank intended to equip an aerospace launcher, by allowing integration of the skirts in a single piece with the tank, thus making it possible to form a complete launcher stage in a simplified manner.

[0056] In particular, each of the domes can define a second cylindrical end joining zone opposite a respective skirt precursor and which can be secured to the latter during vacuum cooking. Brief description of the drawings [Fig. 1] Figure 1 shows, schematically in perspective, an example of a panel that can be used within the framework of the invention to form the cylinder. [Fig. 2] Figure 2 shows, schematically and partially, a cross-section of the panel of Figure 1 in relation to its longitudinal axis. [Fig. 2A] Figure 2A shows, schematically and partially, the bevel angle of the panel of Figure 2. [Fig. 3] Figure 3 shows, schematically in perspective, the overlapping of two neighboring panels according to an exemplary implementation of the invention. [Fig. 4] Figure 4 represents, schematically and partially, a variant of cylinder. [Fig. 5] Figure 5 represents, schematically and partially, another variant of cylinder. [Fig. 6] Figure 6 shows, schematically and partially, another variant of cylinder. [Fig. 7] Figure 7 shows, schematically and partially, another variant of cylinder. [Fig. 8] Figure 8 represents an example of a petal intended to form a precursor dome of the bottom by juxtaposition with other petals. [Fig. 9] Figure 9 represents the juxtaposition of a second petal on the petal of Figure 8 according to an exemplary implementation of the invention. [Fig. 10] Figure 10 represents, schematically and partially, a sectional view of the dome resulting from the juxtaposition of petals according to figure 8 in a plane containing the axis of revolution of the dome. [Fig. 11] Figure 11 represents, schematically and partially, a sectional view of the dome resulting from the juxtaposition of petals according to figure 8 in a plane perpendicular to the axis of revolution of the dome. [Fig. 12] Figure 12 shows, schematically and partially, a sectional view of an example of a common base precursor in a plane containing its axis of revolution. [Fig. 13] Figure 13 shows a sector of a first skin intended to be part of the precursor of Figure 12. [Fig. 14] Figure 14 represents the juxtaposition of several sectors according to Figure 13 in the context of the manufacture of the precursor of Figure 12. [Fig. 15] Figure 15 shows, schematically and partially, a sectional view of a common base precursor variant in a plane containing its axis of revolution. [Fig. 16] Figure 16 shows, schematically and partially, a sectional view of another variant of common bottom precursor in a plane containing its axis of revolution. [Fig. 17] Figure 17 represents, schematically and partially, another variant of common background precursor in a plane containing its axis of revolution. [Fig. 18] Figure 18 represents, schematically and partially, another variant of common background precursor in a plane containing its axis of revolution. [Fig. 19] Figure 19 represents, schematically and partially, another variant of common background precursor. [Fig. 20] Figure 20 shows, schematically and partially, a precursor assembly of the tank to be manufactured positioned in a vacuum molding tool as part of an example of implementation of the invention. [Fig. 21] Figure 21 shows, schematically and partially, the stiffeners present on the assembly of Figure 20. [Fig. 22] Figure 22 schematically represents the sous vide cooking of the assembly illustrated in Figure 20. [Fig. 23] Figure 23 schematically represents a detail of a variant of the precursor dome of the bottom. Description of the embodiments

[0057] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0058] The description below firstly covers the structure and production of the body precursor cylinder, the base precursor domes and the common base precursor. The details of the vacuum casting tooling, inside which the precursor assembly is positioned, as well as the vacuum curing phase will be detailed in a second step.

[0059] Precursor cylinder of the body

[0060] The example described here relates to a sectored cylinder obtained by juxtaposition of thermosetting pre-impregnated fiber panels, but it does not depart from the scope of the invention when the cylinder is formed in a single piece. In the latter case, the cylinder does not contain a continuous circumferential fiber which hinders the increase in diameter or comprises sectored circumferential fibers. The circumferential direction corresponds to the direction around the axis of the cylinder, designated by "axis X" in the following.

[0061] The precursor cylinder of the body is obtained here by juxtaposition of thermosetting pre-impregnated fiber panels. Generally speaking, it can comprise at least two fiber panels, or even at least three fiber panels. The example described here concerns the case of a cylinder with four panels.

[0062] The panels are advantageously produced by automatic placement of fibers, which constitutes a technique known per se. The panels 10 each comprise a fiber reinforcement pre-impregnated with a thermosetting resin. The choice of the reinforcing material and the resin depends on the intended application. For example, the fiber reinforcement comprises carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers. For example, the resin is an epoxy resin, for example based on a monomer DGEBA (diglycidyl ether of bisphenol A), TGPAP (triglycidyl paraaminophenol), or TGMDA (tetraglycidyl methylenedianiline), to which an amine-type hardener, for example DDS (diaminodiphenyl sulfone), may optionally be added. The same resin is advantageously used in the different panels, or, failing that, compatible resins.

[0063] The panels 10 have an elongated shape along a longitudinal axis X and have a curved shape in cross-section relative to the X axis. The panels 10 define two longitudinal edges 10a, 10b which are intended to be superimposed with a neighboring panel, as will be described below. Figure 1 illustrates an example of a possible structure for the panels 10 which are draped in a female tooling, the person skilled in the art will recognize that the panels can alternatively be draped on a male tooling without departing from the scope of the present invention. The draping form is not an integral part of the vacuum molding tooling so as to allow parallel operation between draping and curing, and thus reduce the manufacturing cycle time.

[0064] The panels 10 are, in the example of Figure 1, provided with longitudinal stiffeners 12 made of thermosetting composite. These stiffeners 12 are formed by conventional means known to those skilled in the art, for example by manual or automated draping, draping in a shaped mold or press stamping of green flat plates, production of dry preforms and injection of resin into a mold by a resin transfer molding technique (“Resin Transfer Molding”; “RTM”). The stiffeners 12 can have any cross-section, for example Omega, T, J, among other possible shapes. The stiffeners 12 may or may not have a local variation in shape or cross-section. As illustrated, the stiffeners 12 can be present over at least the majority (more than 50%) of the length LO10 of the panels 10. The panels 10 nevertheless have areas devoid of stiffening elements which will be described below.

[0065] The illustrated panels 10 are also provided with circumferential frame sectors 14 made of thermosetting composite. As with the stiffeners 12, the frame sectors 14 are formed in a manner known per se. The frame sectors 14 may have any cross-section, for example Z-shaped, C-shaped, F-shaped, T-shaped, Omega-shaped or J-shaped.

[0066] The stiffeners 12 and frame sectors 14 may be half-baked, or have complete, or little or no advanced polymerization.

[0067] The panels 10 have circumferential zones 16, intended for docking with the end bottoms, which are devoid of stiffening element. The zones 16 are each located on the side of an opposite longitudinal end of the panel 10 in question. As will be detailed below, the end bottoms will be secured to the body of the tank on these zones 16. The panels 10 also have an intermediate circumferential zone 16a, intended for docking with the common bottom, which is also devoid of stiffening element. The zone 16a is located between the zones 16 and interrupts the zone 18 provided with stiffeners 12. The panels 10 also have a longitudinal zone 19, located on the side of the longitudinal edge 10b and extending over their entire length LO10, which is devoid of stiffening element.It will also be noted that, in the example illustrated, the frame sectors 14 protrude from the panel 10 on the side opposite the zone 19 (on the side of the edge 10a), and form an extension 15 of the frame sectors 14. The presence of the zone 19 as well as the extension of the frames 14 are the result of the arrangement envisaged for the overlap between neighboring panels 10.

[0068] Figure 2 shows the evolution of the thickness elO of the panels 10 over their width (dimension between the edges 10a and 10b). The panels 10 have a middle zone 101 of their width where the thickness elO is substantially constant, and two lateral zones 103a and 103b each located on the side of a respective longitudinal edge 10a, 10b which have an evolving thickness. The zone 101 is located between the zones 103a, 103b. The zone 103a connects the zone 101 to the edge 10a, and the zone 103b connects the zone 101 to the edge 10b. More precisely, the zones 103a, 103b have a thinning of thickness in the direction of the associated longitudinal edge 10a, 10b. The thickness elO may be strictly decreasing in the direction of the longitudinal edge 10a, 10b. The thickness elO is minimal on the edges 10a, 10b and maximal on the median zone 101. The panels 10 have a bevel on their edges 10a, 10b.The panels 10 have, in cross-section relative to the X axis, a tapered shape towards their edges 10a, 10b. The zones 103a and 103b jointly occupy at least 5%, for example at least 50%, of the width LA10 of the panel 10. Unless otherwise stated, the width LA10 corresponds to the length of the arc of the curve. connecting the edge 10a to the edge 10b. The thinning of thickness leads to a reduction in the thickness elO of at least 50%, for example at least 90%. This reduction in the thickness elO is for example between 50% and 95%, or even between 90% and 95%. Figure 2A schematically represents a thinning of the thickness of the panel 10 in the direction of a longitudinal edge 10b linked to the presence of a decreasing quantity of superimposed folds PS in the direction of the edge 10b. The bevel angle a, corresponding to the angle taken locally on the edge 10b, can advantageously be less than or equal to 1.5°, so as to further improve the smoothing of the forces.

[0069] The panels 10 which have just been described include stiffening elements but it is not outside the scope of the invention if they are devoid of them. The following describes, in connection with Figures 3 to 7, the juxtaposition of these panels 10 to form the cylinder 100 which is, in the example considered, a precursor of the body of the tank but also of front and rear skirts which extend beyond the end bottoms.

[0070] Figure 3 illustrates the juxtaposition of two neighboring panels 10 around the X axis. The two illustrated panels 10 have the same structure and the same references are retained with respect to what has just been described. The panels 10 partially overlap here. The panels have a thinning of thickness on their overlap zone, that is to say that the zone 103b of the first panel 10 is covered by the zone 103a of the second neighboring panel 10. The edge 10b of the first panel 10 is superimposed with the second neighboring panel 10, and the edge 10a of the second panel 10 is superimposed with the first panel. The stiffeners 12 and frame sectors 14 of the second panel 10 cover the area 19 of the first panel 10. The extension 15 of the frame sectors 14 of the second panel 10 extends over the area 101 of the first panel and is positioned adjacent to and in line with the frame sectors 14 of the first panel.The extension 15 of the second panel 10 is assembled with the frame sectors 14 of the first panel 10 by techniques known per se, for example by overlapping, jockeying or splicing. Furthermore, the zones 16 of the first panel 10 come in the extension of the zones 16 of the second panel 10, and the zone 16a of the first panel 10 in the extension of the zone 16a of the second panel 10.

[0071] The arrangement just described can be applied to each pair of neighboring panels 10 juxtaposed to form the sectored cylinder. Generally speaking, the overlapping areas between neighboring panels can occupy at least 5%, for example at least 30% of the perimeter of the sectored cylinder. Having spread overlapping areas makes it possible to further improve the mechanical properties of the resulting tank. In particular when all the panels are assembled to form the cylinder sectorized, the meeting of the zones 16 forms a 360° circumferential zone devoid of any stiffening element. In addition, the meeting of the frame sectors 14 of each of the panels defines a plurality of 360° circumferential frames distributed along the length of the cylinder.

[0072] Figures 4 to 7 show different variants of juxtaposition of the panels 10 to form the sectored cylinder 100. The cylinder 100 extends along the X axis with panels juxtaposed around this axis.

[0073] In the variant of Figure 4, the cylinder 100 is formed by tiling all the panels 10, that is to say that each of the panels has a first longitudinal edge 10b covering (above) a first neighboring panel, and a second longitudinal edge 10a, opposite the first edge 10b, covered (below) by a second neighboring panel, opposite the first neighboring panel. In particular, the thinning of the thickness of the neighboring panels 10 over their overlapping zone ZR10 in the direction of their longitudinal edges 10a, 10b is noted.

[0074] In the variant of figure 5, there is tiling except for panel 10 at the bottom right of the figure which covers its two neighboring panels.

[0075] The variants of Figures 6 and 7 show cases where there is no tiling which are also covered by the present invention.

[0076] The part just described concerns the panels and their juxtaposition to form the precursor body cylinder. The following concerns the precursor end-bottom domes which are intended to be secured to the cylinder to delimit the internal volume of the composite material tank to be obtained.

[0077] End-bottom precursor domes

[0078] Figure 8 shows a petal 20, which has the shape of a dome sector, draped in shape. According to this example, each base precursor dome is obtained by juxtaposition of thermosetting pre-impregnated fibrous petals 20. Generally, each of the domes may comprise at least two petals 20, or even at least three petals 20. The example described here concerns the case of domes each having four petals 20.

[0079] As for the panels 10, the petals 20 are advantageously made by automatic placement of fibers. The petals 20 each comprise a fiber reinforcement pre-impregnated with a thermosetting resin. The choice of the reinforcement material and the resin depends on the intended application. The reinforcement and the resin of the petals 20 may be as described above for the panels 10. A resin identical to that of the panels 10, or failing that compatible with it, will advantageously be chosen for the petals 20. In a similar manner to the panels 10, the petals 20 may be draped over a male or female tooling, and on a draping form not forming an integral part of the vacuum casting tooling.

[0080] As for the panels 10, the petals 20 define two edges 20a, 20b each extending along a longitude, called longitudinal edges, which are intended to be superimposed with a neighboring petal. The longitudinal edges 20a, 20b are intended to extend along the longitudinal axis X of the cylinder 100 in the precursor assembly which will be described below. The petals 20 define two edges 20c, 20d each extending along a latitude (or circumferential) which are transverse to the edges 20a, 20b. Each of the edges 20c, 20d connects the edge 20a to the edge 20b. The edge 20c has a first curvilinear length, and the edge 20d has a second curvilinear length which is greater than the first curvilinear length.

[0081] In a similar manner to the panels 10, and to the illustration of FIG. 2, the petals 20 have a thickness that varies between the edges 20a and 20b. The petals 20 thus have a median zone 201 where the thickness is substantially constant, and two lateral zones 203a and 203b each located on the side of a respective edge 20a, 20b which have a thickness that varies. Area 203a is bounded by edge 20a and longitude 21 and area 203b by edge 20b and longitude 23. Area 201 is located between areas 203a and 203b, or between longitudes 21 and 23. The description provided above relating to areas 103a, 101 and 103b applies respectively to areas 203a, 201 and 203b mutatis mutandis.

[0082] The petals 20 define a sector 203d of a cylindrical end junction zone which is intended to come opposite the precursor cylinder of the body, and more particularly opposite the docking zone 16 which was described above. The sector 203d corresponds to a circumferential zone delimited by the edge 20d and by a latitude 25. In the example described here and as illustrated in FIG. 10, the petals 20 have a thinning of thickness on their sector 203d in the direction of the edge 20d.

[0083] The petals 20 are juxtaposed at their edges 20a, 20b with overlap between neighboring petals, in a manner similar to what was described above for the panels 10. Thus, Figure 9 represents the positioning of a second petal 20 in partial overlap with the first petal 20, it being understood that two other petals are juxtaposed to form the complete dome 200 in the example considered. Figure 11 schematically shows the juxtaposition of these four petals 20. The neighboring petals 20 here have a thinning of thickness e20 on their overlap zone ZR20 in the direction of their longitudinal edges 20a, 20b.

[0084] As illustrated in Figure 10, the dome 200 has a bottom zone 205 located between the edge 20c and the latitude 25. The dome 200, and in particular the zone 205, has a shape of revolution. The meeting of the sectors 203d forms a 360° cylindrical junction zone 210 which extends the zone 205 to the edge 20d. Figure 10 shows the thinning of the thickness e20 of the petals 20 (or of the dome 200) in the direction of the edge 20d, at the level of the sectors 203d or of the zone 210. The evolution of the radius R of the dome 200 is also visible with a radius R strictly increasing between the edge 20c and the latitude 25, and substantially constant over the zone 210.

[0085] It will also be noted that the petals 20 may be provided with thermosetting composite stiffeners. The description given above for these stiffeners in connection with the panels 10 is applicable. A possible illustration for these stiffeners is provided in Figure 22 which will be described below.

[0086] A possible structure for the cylinder 100 and the domes 200 has just been described. The following describes different possible examples for the common bottom precursor which allows the compartmentalization of the tank.

[0087] Common background precursor

[0088] Figure 12 illustrates an example of a common base precursor 300. The precursor 300 comprises a reinforcement 302 made of thermoset composite material. The reinforcement 302 thus comprises a fibrous reinforcement densified by an organic matrix obtained after polymerization of a thermosetting resin. The resin of the reinforcement 302 is completely polymerized.

[0089] The example of precursor 300 considered comprises a thermosetting pre-impregnated fibrous skin on each of the faces of the reinforcement 302. Each of the skins is here formed by a juxtaposition of sectors 304, 306 around the X axis. The skins or sectors 304, 306 can be produced by automatic placement of fibers. The skins or sectors 304, 306 each comprise a fibrous reinforcement pre-impregnated with a thermosetting resin. The example considered comprises first sectors 304 which cover a first face 3024 of the frame 302, and second sectors 306 which cover a second face 3026 of the frame 302 opposite the first face 3024. The first sectors 304 are juxtaposed circumferentially, like the second sectors 306. The frame 302 is housed between the first 304 and second 306 sectors.The frame 302 here has a dome shape and comprises an internal circumferential edge 3021 capable of cooperating with the tooling to position the precursor 300, and an external circumferential edge 3023 intended to be positioned on the side of the cylinder 100 in the assembly. The cooperation between the internal circumferential edge of the frame and the tooling will be described below.

[0090] The draping of the sectors 304 and 306 is similar to the draping of the petals 20 described above to obtain the domes 200. The second sectors 306 are however draped with a folded shape in the illustrated example to form a portion 312 of the intermediate cylindrical junction zone 310.

[0091] A draping possibility to obtain precursor 300 is now detailed.

[0092] The sectors 304, 306 can be draped onto male or female tooling, and onto a draping form not forming an integral part of the vacuum casting tooling.

[0093] In the example considered, the second sectors 306, which have a more complex shape, can first be draped, then the reinforcement 302 can be positioned on the second sectors 306 thus draped and then the first sectors 304 can be draped on the assembly obtained in order to obtain the precursor 300. The reinforcement 302 has been completely polymerized beforehand, before its assembly with the sectors 304, 306. An adhesive film can be positioned at the interfaces between the reinforcement 302 and the sectors 304, 306. The first face 3024 of the reinforcement 302 is covered over 360° by the first sectors 304 and the second face 3026 of the reinforcement 302 is covered over 360° by the second sectors 306. Figures 13 and 14 which will be described below detail the draping of the first sectors 304, it being understood that the draping of the second sectors 306 is made in a similar way.

[0094] The sectors 304 each define two edges 304al, 304bl each extending along a longitude, called longitudinal edges, which are intended to be superimposed with a neighboring sector. The edges 304al, 304bl are intended to extend along the longitudinal X axis of the cylinder 100 in the precursor assembly which will be described below. The sectors 304 define two edges 304cl, 304dl each extending along a latitude (or circumferential) which are transverse to the edges 304al, 304bl. Each of the edges 304cl, 304dl connects the edge 304al to the edge 304bl. The edge 304cl has a first curvilinear length, and the edge 304dl has a second curvilinear length which is greater than the first curvilinear length.

[0095] The sectors 304 have a thickness that varies between the edges 304al and 304bl. The sectors 304 thus have a median zone 3041 where the thickness is substantially constant, and two lateral zones 3043a and 3043b each located on the side of a respective edge 304al, 304bl which have a thickness that varies. Area 3043a is bounded by edge 304al and longitude 305 and area 3043b by edge 304bl and longitude 307. Area 3041 is located between areas 3043a and 3043b, or between longitudes 305 and 307. The description provided above relating to areas 103a, 101 and 103b applies respectively to areas 3043a, 3041 and 3043b mutatis mutandis.

[0096] The sectors 304 define a sector 3043d of a portion 311 of the intermediate cylindrical junction zone 310 which is intended to come opposite the precursor cylinder of the body, and more particularly opposite the docking zone 16a which has been described above. The sector 3043d corresponds to a circumferential zone delimited by the edge 304dl and by a latitude 309. The sectors 304 may have a thinning of thickness on the sector 3043d in the direction of the edge 304dl.

[0097] The sectors 304 are juxtaposed at their edges 304al, 304bl with overlap between neighboring sectors, in a manner similar to what was described above for the petals 20. Thus, Figure 14 represents the positioning of an additional sector 304 in partial overlap with the first initial sector 304, it being understood that two other sectors are juxtaposed to form the first skin. The sectors 304 are thus juxtaposed circumferentially.

[0098] As indicated above, the draping of the second sectors 306 is done in a similar manner to that of the first sectors 304. It will nevertheless be noted that, in the illustrated example, the second sectors 306 are folded back on the side of the edge 3023 of the frame 302 so as to form a second part 312 of the zone 310. The second part 312 extends in a direction opposite to the direction of extension of the first part 311. The part 312 is also intended to come opposite the precursor cylinder of the body, and more particularly opposite the docking zone 16a.

[0099] Generally speaking, the sectors can be draped onto the reinforcement in the raw state with a raw prepreg, or in the semi-cured state with a prepreg previously semi-cured before draping. In the case where they are draped in the semi-cured state, a single-layer architecture of sectors can be preferred, which will be draped directly onto the reinforcement, or a two-layer architecture with the two layers joining beyond the reinforcement.

[0100] In the example of Figure 12, the skins each extend beyond the frame 302 (beyond the end 3023) so as to define the first 311 and second 312 parts of the intermediate cylindrical junction zone 310. More specifically, the skins are directly assembled beyond the end 3023 on an assembly region 308 up to a separation edge 305 from which they separate to define the first 311 and second 312 parts. This separation defines a space which can be filled by a filling material 320 distinct from the skins. The material 320 is present between the first 311 and second 312 parts. The material 320 can be chosen from: cellular materials including filling foams (“foam core” in English) as well as honeycombs (or NIDA or “honeycomb” in English). Foams can be foams from the PU (Polyurethane), PVC (Polyvinyl Chloride) family, PMI (PolyMethacrylate Imide), PEI (PolyEther Imide), PAI (Polyamide Imide), foams from the PAEK (PolyArenylEtherKetone) family such as PEEK (PolyEtherEtherKetone), PEKK (PolyEtherKetoneKetone), or metal foams, or carbon foams, etc. For honeycombs we can have for example Nomex® honeycombs (based on aramid fibers and phenolic resin), aluminum honeycombs, Kevlar® honeycombs, carbon honeycombs, etc. The 320 material may or may not be loaded with fibers.

[0101] The extension of the skins beyond the reinforcement ensures that they can conform against the cylinder during the vacuum curing step. Thus, the possibility of conformation is ensured here by the absence of reinforcement, i.e. of completely rigid polymerized material, at the level of zone 310. Nevertheless, other reinforcement configurations are conceivable to allow the desired conformation of the skins as will be described below.

[0102] The choice of the reinforcing material and the resin depends on the intended application. For the skins, a resin identical to that of the panels 10 is chosen, or failing that, compatible therewith. The reinforcement and the resin of the skins may be as described above for the panels. Although not illustrated, it will be noted that the precursor 300 may or may not be provided with stiffeners or supports.

[0103] Figures 15 to 17 represent common background precursor variants usable in the context of the invention.

[0104] Figure 15 shows a common base precursor 300a of similar structure to that of Figure 12, comprising a reinforcement 302a interposed between first 304a and second 306a skin sectors. The first 304a and second 306a sectors extend beyond the reinforcement 302a and are in particular assembled directly on an assembly region 308a. Unlike Figure 12, this assembly region 308a extends to the intermediate cylindrical junction zone 310a. There is therefore no filling material in this example between the first 311a and second 312a parts of the zone 310a.

[0105] Figure 16 shows a common bottom precursor 300b of similar structure to that of Figure 12, comprising a frame 302b interposed between first 304b and second 306b skin sectors. In this example, the frame 302b is formed from an insulating material configured to thermally insulate one compartment from the other. The insulating material may be housed in the frame or arranged on at least one of its faces. The insulating material may be a cellular material, for example in the form of a honeycomb or filling foam. The nature of the insulating material depends on the intended application and will be chosen by the person skilled in the art depending on the objective sought.

[0106] Figure 17 shows a common bottom precursor 300c, comprising a reinforcement 302c interposed between first 304c and second 306c skin sectors. The first 304c and second 306c sectors extend beyond the reinforcement 302c and are in particular assembled directly on an assembly region 308c. Unlike the precursors of Figures 12, 15 and 16, the first 304c and second 306c sectors extend on the same side to form the intermediate cylindrical junction zone 310c. It will be noted that a similar structure can be had with a single layer of sectors, or a one-piece cap-shaped skin rather than a sectored structure. In the latter case, the skin does not contain a continuous circumferential fiber that hinders the increase in diameter or comprises sectored circumferential fibers.

[0107] Figure 18 shows a common base precursor 300d with a structure similar to that of Figure 17, except that it has a reinforcement extension. A reinforcement 302dl is interposed between first 304d and second 306d skin sectors. The precursor 300d comprises a reinforcement extension 302d2 which extends beyond the first reinforcement 302dl so as to avoid the formation of a sudden variation in radius during the shaping of the skins during the vacuum cooking step. The extension 302d2 is local and only covers a fraction of the first reinforcement 302dl in the vicinity of the end 302dla of the latter. This guarantees good pressurization of the skin sectors 306d located between the two reinforcements 302dl and 302d2 during cooking. The 302dl frame and its 302d2 extension stop early enough to allow the skins to be joined.In a variant not illustrated and preferably, the frame 302d2 can also be covered with a skin going in a direction opposite to that along which the skins formed from the sectors 304d, 306d extend.

[0108] Figure 19 illustrates a common base precursor variant in which the armature is extended compared to the examples just described.

[0109] Figure 19 illustrates a common base precursor 300e comprising at least one skin 306e assembled to a “spider” type frame 302e which comprises a rigid portion 3025e located on the side of the circumferential edge 3021e and a plurality of flexible tabs 3027e extending from the portion 3025e to the circumferential edge 3023e. The flexibility of the tabs 3027e allows the skin to be secured to the cylinder despite an increased length of the frame. The tabs 3027e are not in direct contact with the panels of the cylinder during the final polymerization, the skin 306e coming to the interface between the frame and the cylinder. The tabs 3027e can stop before the edge 306el circumferential of the skin 306e as shown, or alternatively extend to this edge on the intermediate cylindrical junction area.

[0110] The various constituent elements of the assembly have just been described. An example of the kinematics of mounting the vacuum molding tool 30 and positioning the precursor assembly will now be detailed in connection with Figure 20. In this figure, as well as in Figure 22, the relative thicknesses and the spacings between the various elements have not been strictly respected for reasons of readability.

[0111] Mounting the vacuum casting tool and positioning the precursor assembly in this tool

[0112] A first vacuum cover 341 is initially placed on a first internal positioning portion 321. The first portion 321 is of a much simpler design than the mandrel implemented in the techniques of the prior art insofar as it is not, in the context of the invention, used as a molding surface and does not need to be sealed. It is, therefore, more easily removable. The first portion 321 is supported by a shaft 36 which extends along a longitudinal axis X. The axis X corresponds to the longitudinal axis of the panels 10 and the cylinder 100 which was described previously. The first portion 321 may have an aerated structure, for example a lattice structure, or comprise a plurality of retractable positioning elements fixed to the shaft. The first portion 321 may, as illustrated, generally have the shape of a first compartment C1 of the tank to be obtained. The first cover 341 covers the first portion 321.The first tarpaulin 341 may be made of elastomeric material, reinforced or not, and constitutes an element known per se.

[0113] The petals 20 can then be positioned on the portion 321 at a first longitudinal end 3211. The petals 20 are juxtaposed in the manner described above to form a precursor dome 200 at the bottom on the first end 3211. The bottom area 205 of the dome 200 defines an orifice 206, here in the general shape of a disc, through which the shaft 36 extends. The dome 200 can have a general shape of revolution around the axis X.

[0114] The common bottom precursor 300a is then positioned at a second longitudinal end 3213 of the portion 321 which is opposite the first end 3211. The illustrated example implements the precursor embodiment 300a according to FIG. 15 but common bottom precursors having a different structure can, of course, be used. The precursor 300a extends circumferentially around the X axis. The precursor 300a may have a general shape of revolution around the X axis. The precursor 300a may comprise a zone 305a, dome-shaped in the illustrated example, which is intended to form a common bottom separating the compartments C1 and C2 in the obtained reservoir. The precursor 300a extends with a non-zero component along a radial direction R, perpendicular to the axis X, between a first internal end 3051a located on the side of the axis X and the shaft 36, and a second external end 3053a opposite the first end located on the side of the cylinder 100. The first 311a and second 312a parts extend from the second end 3053a so as to form the intermediate cylindrical junction zone 310a intended to allow the precursor 300a to be secured to the cylinder 100 during vacuum cooking.

[0115] The frame 302a is present on the first end 3051a and, more generally, on the zone 305a. Thus, the frame 302a makes it possible to dispense with the presence of a molding tool on the common base and gives the precursor 300a sufficient rigidity so that it substantially retains its shape during vacuum cooking. The zone 305a defines an orifice, here in the general shape of a disc, through which the shaft 36 extends. The frame 302a can extend beyond the skins at the end 3051a in a manner similar to that illustrated in FIG. 12, so as to cooperate with the shaft 36 to position the precursor 300a in the tooling. In the example illustrated, the frame 302a stops upstream of the second end 3053a to provide sufficient flexibility to the parts 311a, 312a and thus allow them to be shaped and secured to the cylinder 100 during vacuum cooking.

[0116] The second portion 322 covered with the second vacuum cover 342 is then positioned in the extension of the first portion 321 along the X axis. The second portion 322 is of a much simpler design than the mandrel implemented in the techniques of the prior art insofar as it is not used as a molding surface and does not need to be sealed. It is, therefore, more easily removable. The second portion 322 is supported by the shaft 36. The second portion 322 may have an aerated structure, for example a lattice, or comprise a plurality of retractable positioning elements fixed to the shaft. The second portion 322 may, as illustrated, generally have the shape of a second compartment C2 of the tank to be obtained. The second cover 342 may have the same characteristics as the first cover 341 described above.

[0117] The precursor 300a, and in particular its zone 305a, is interposed between the first 321 and second 322 portions. In an exemplary embodiment, the end 3051a is housed in a circumferential support tool 362 attached around the shaft 36, for example in the form of a ring. The second portion 322 comprises an end 3221 on the side of which the cover 342 is fixed in a sealed manner on an axial end of the tooling 362. The first portion 321 comprises an end 3213 on the side of which the tarpaulin 341 is fixed in a sealed manner on the other axial end of the tooling 362. The tooling 362 may, as illustrated, have beveled axial ends facilitating the creation of seals at the ends 3213 and 3221. The person skilled in the art will recognize that other solutions are possible for positioning the precursor, the illustrated possibility being only one example among different possible embodiments. The two tarpaulins 341 and 342 thus do not need to be in contact to create the seal in the positioning zone of the precursor 300a. The ends 3221 and 3213 may, as illustrated, take on the shape of the precursor 300a and the axial ends of the tooling 362.The petals 20 can then be positioned on the portion 322 at a second longitudinal end 3223 so as to form the dome 200, in a manner similar to that described above. The zone 205 defines an orifice 206, here in the general shape of a disc, through which the shaft 36 extends. The dome 200 can have a general shape of revolution around the axis X. The orifices 206 are concentric with the orifice of the precursor 300a along the axis X.

[0118] The molding portions 38 can then be positioned. These portions 38 each have the shape of a dome and are shaped like the end bottoms of the tank to be obtained. The illustrated example shows two symmetrical portions 38 but it is, of course, within the scope of the invention if this is not the case. The domes 200 are located inside the interior volume defined between the portions 38. Each dome 200 is held in place by a respective portion 38. Each dome 200 is interposed between a portion 38 and a vacuum tank 341 or 342 (or the portions 321 and 322). As illustrated, the portions 38 cover the bottom area 205 but do not cover the end cylindrical junction area 210. Those skilled in the art will recognize that other variants are possible. Thus, the domes 200 can first and preferably be positioned on the portions 38 and then this assembly can then be placed on the ends 3211 and 3223. The precise positioning of the portions 38 as well as their maintenance can be ensured by the shaft 36.Alternatively, all the petals can first be draped over a dome tool, then the dome can be half-baked before assembly on portion 321 or 322, or portion 38. One could also start by positioning the precursor 300a first on the shaft 36 then the portions 321 and 322 on each side of the precursor 300a, and then the domes 200, already in the portions 38, on the ends 3211 and 3223. Placing the common bottom first on the shaft allows access to both faces of the bottom during positioning, which is useful for making the assembly even more reliable.

[0119] In the example considered in Figure 20, a third and a fourth empty tarpaulins 35 are then placed respectively for the formation of the front and rear skirts which will be described below. The third and fourth tarpaulins 35 may have the same characteristics as the first and second tarpaulins 341, 342.

[0120] Positioning crowns 40 are then positioned at the ends 361, 363 of the shaft 36 which define a cylindrical positioning surface 42 whose function will be described below.

[0121] The panels 10 can then be positioned and juxtaposed, in the manner described above, so as to form the precursor cylinder 100 of the tank body. The cylinder 100 is located around the domes 200 and the precursor 300a. The cylinder is positioned on the first 321 and second 322 portions. The cylinder extends between the end 3223 and the end 3211, possibly extending beyond them to form the front and rear skirts as illustrated. The domes 200 are located inside the cylinder 100. The precursor 300a is located inside the cylinder 100. The cylinder 100 extends from one dome 200 to another. In the illustrated example, the cylinder 100 extends beyond the domes 200 to form front 110 and rear 120 skirt precursors positioned respectively opposite the third and fourth tarpaulins 35.However, it does not go beyond the scope of the invention if the cylinder does not form such skirts by stopping at the level of the domes 200.

[0122] Thus, after positioning the panels 10, a precursor assembly of the tank to be manufactured is obtained, which comprises the cylinder 100, the domes 200 each located on the side of an opposite longitudinal end of the cylinder 100 and the common bottom precursor 300a located between the domes 200. As indicated above, the precursor 300a defines the intermediate cylindrical junction zone 310a positioned opposite the cylinder 100 which is intended to be secured to the latter during vacuum cooking. In the example considered, the skin sectors 304a, 306a extend beyond the frame 302a so as to define the zone 310a.More specifically, first skin sectors 304a juxtaposed around the X axis define a first portion 311a of the area 310a extending towards a first dome 200, and second skin sectors 306a juxtaposed around the X axis define a second portion 312a of the area 310a extending towards a second dome 200 opposite the first dome. The first portion 311a rests on the first portion 321 and the second portion 312a rests on the second portion 322. The area 310a extends over both the first 321 and second 322 portions.

[0123] In the example illustrated, the precursor 300a is located substantially equidistant from the domes, but it is not outside the scope of the invention when this is not the case depending on the relative volume desired for the compartments C1 and C2. The domes 200 delimit with the cylinder 100 an internal volume V of the reservoir to be obtained. The precursor 300a delimits with the first dome 200 a first compartment C1. The precursor 300a delimits with the second dome 200 a second compartment C2 distinct from the first compartment. The domes 200 close the cylinder 100 on the side of each of its longitudinal ends. The cylinder 100, the domes 200 and the skins of the precursor 300a are each made of thermosetting pre-impregnated fibrous material.

[0124] The panels 10 are positioned opposite the zones 210 and 310a so as to allow the end bottoms and the common bottom to be secured to the body during the vacuum cooking which will be described below. In particular, the zones 210 are opposite the zones 16 of the panels 10, and the zone 310a is opposite the zone 16a. The zones 16 and 16a are devoid of any stiffening element and have been described above.

[0125] The panels 10, domes 200 (or petals 20) and skins (or sectors 304a, 306a) may be assembled in the semi-baked state to form the precursor assembly. They may each be draped, during their manufacture, in the semi-baked state, or alternatively be draped in the raw state, that is to say with a degree of advancement of polymerization lower than that of the semi-baked state and then undergo a partial polymerization heat treatment to bring them to the semi-baked state. The domes 200 (or petals 20), skins (or sectors 304a, 306a) and panels 10 may be assembled after this partial polymerization.

[0126] The molding portion 60 of the tank body is then positioned, which is in the shape of the tank body to be obtained and which surrounds the cylinder 100 over its entire length. The cylinder 100 is located inside the portion 60. The portion 60 is located around the cylinder 100. The portion 60 makes it possible to hold the panels 10 in place. It is possible to consider indexing the panels 10 on the portion 60. Like the panels 10, the portion 60 can be sectorized and formed by several sectors assembled together to form a 360° molding portion. As illustrated, the portion 60 extends from one ring 40 to the other. It is positioned on the surface 42, which avoids having the weight of this external tooling supported on the panels 10.The portion 60 may include stiffeners (not shown) on its face opposite the panels 10 in order to present significant rigidity and thus retain the same shape, without flexing, despite a significant length if a very long tank is desired. An internal surface SI of the precursor assembly is located on the side of the tanks 341 and 342 (and delimits the volume. V internal surface of the tank), and an external surface S2 of the assembly is located on the side of the portions 38, 60.

[0127] Figure 21 shows a possible detail relating to the stiffeners 12 of the panels 10 and to the stiffeners 202 of the assembled domes 200. The stiffeners 202 have a curved shape, here following longitudes of each of the domes 200. The stiffeners 202 and 12 are located on a face of the precursor assembly opposite the portions 38, 60. In the illustrated example, the stiffeners 202 protrude from the domes 200 to extend along the panels when the cylinder 100 is assembled with the domes 200. The stiffeners 202 are joined to the stiffeners 12 at junction zones 212, by techniques known per se, for example by edge-to-edge joining, joisting or splicing. It is not outside the scope of the invention if the stiffeners of the domes do not extend beyond the zone 210, or if they are not aligned with the stiffeners 12, or if they are not joined with the stiffeners 12, or if the domes are devoid of stiffeners.

[0128] The seals 52 between the tarpaulins 341, 342 and 35 and the molding portions 38, 60 are then produced.

[0129] The precursor assembly is thus positioned in the vacuum molding tool 30. In particular, the cylinder 100 is interposed between the tarpaulins 341, 342 and the molding portion 60, and each dome 200 is interposed between the tarpaulin 341 or 342 and a respective molding portion 38. The parts 321, 322 are located inside the precursor assembly, that is to say located inside the internal volume V of the tank to be obtained. The meeting of the portions 60 and 38 is located outside this internal volume and forms a part external to the assembly, intended for molding the tank.

[0130] Vacuum curing of the precursor assembly in the tooling and disassembly

[0131] The sous vide cooking phase is illustrated in Figure 22. This cooking phase can be carried out with or without additional pressure.

[0132] The applied heating leads to a fluidification of the resin(s) present. The vacuuming of the tool 30 causes the tarpaulins 341, 342 to be pressed against the cylinder 100 and the domes 200 so as to press the latter against the portions 38, 60 and to conform them to the desired shape. The domes 200 come to be pressed against the panels 10 thanks to the slight relative displacement / spacing of the petals 20, a spacing made possible thanks to the low viscosity of the resin at temperature and the creep between petals. During assembly with the panels 10, under the effect of the temperature and the pressure, the petals 20 move apart to conform to the internal surface of the panels. It is essentially the zone 210 which will come into contact with the panels 100. Tl

[0133] Similarly, the tarpaulins 341, 342 press against the precursor 300a, on either side of the frame 302a, on the parts 311a, 312a which then conform against the cylinder 100. The first tarpaulin 341 presses the part 311a against the cylinder 100 and the second tarpaulin 342 presses the part 312a against the cylinder 100, during vacuum cooking. The conformation of the parts 311a, 312a is done without deformation of general shape since the frame 302a is completely polymerized. The tarpaulins 35 apply pressure to the skirt precursors 110 and 120.

[0134] Once all the parts are in place, heating allows the resin to finish polymerizing with the creation of bonds at the level of the polymer chains of the resins (creation of a three-dimensional network), freezing the interfaces and the overall shape of the tank structure. The polymerization of thermosetting materials is complete after the vacuum curing step.

[0135] Vacuum curing can be carried out in a heating chamber, such as an oven or an autoclave. The oven will allow polymerization under vacuum, the autoclave will provide additional pressure in addition to the vacuum. Alternatively or in combination, a molding tool equipped with heating elements (not shown) can be used to carry out this curing. The temperature imposed during vacuum curing depends on the resin used and can, for example, be greater than or equal to 150°C, and for example, be between 175°C and 185°C, for example, close to 180°C.

[0136] A tool 30 made of composite material may be used to reduce the phenomenon of differential expansion between the tool and the tank. Alternatively, the tool 30 may be metallic, for example made of Invar, or steel. In the latter case, it may be advantageous to minimize stresses during cooling, for example by breaking the vacuum in the vacuum tank at the end of the polymerization stage, or by providing a half-opening of the portion 60.

[0137] The tooling 30 is then dismantled, which is facilitated by the positioning of the molding portions outside the tank, and by the simplified design of the internal part.

[0138] The resulting tank 1 which has just been described has a front skirt 1100 and a rear skirt 1200 extending the body 1000 beyond the end bottoms 2000. It also has a common bottom 3000 which separates the tank into two separate compartments C1 and C2. The skirts 1100 and 1200 are monolithic with the rest of the tank 1.

[0139] Figure 23 illustrates an alternative embodiment which fits into this framework in which the dome has an additional junction on the skirt side thanks to the use of a toric part which will now be described.

[0140] Thus, the dome 200 of figure 23 defines a second cylindrical junction zone 410 opposite the skirt precursor 120, it being understood that a similar structure is present on the side of the skirt precursor 110. The second zone 410 is located on the side opposite the first zone 210. The first zone 210 delimits the internal volume V of the reservoir to be obtained, and the second zone 410 extends outside this volume V.

[0141] The second zone 410 is defined by a toroidal-shaped part 400 which is attached to the zone 205. More particularly, the part 400 comprises a zone 405 joining the dome 200 taking the shape of the zone 205 and integral with the latter, the zone 410 opposite the skirt precursor 120 and a folded intermediate zone 407 connecting the zone 405 to the zone 410.

[0142] The part 400 is produced separately. In the same way as the base 200, it can be made up of juxtaposed sectors, formed by a thermosetting pre-impregnated fibrous material, which partially overlap. The part 400 can be produced by automatic fiber placement, or manually in the case where the “fold” radius is too small to be produced by automated AFP draping. Advantageously, the part 400 is half-baked after draping and before assembly with the base 200 and the panels 10.

[0143] The part 400 is positioned on the bottom 200 once the latter is positioned on the positioning portion. Then once in place, the portion 38 is positioned which has a shape adapted to the presence of the part 400. Alternatively, the part 400 is first positioned on the portion 38, then the dome 200 is positioned on this portion 38 and the assembly is placed on the positioning portion.

[0144] Part 400 may or may not be stiffened. The stiffeners may be as described above and are positioned in the tooling prior to layup.

[0145] The space 250 between the dome 200 and the part 400 can be filled with a filling material, possibly loaded with fibers.

[0146] As with the tank bottom, during vacuum curing, the toroidal part will soften under the action of temperature (reduction in the viscosity of the resin). Under the action of pressure, applied by the tarpaulins 35, the diameter of the toroid will slightly increase in diameter (relative spacing of the toroid sectors) and come to conform to the interior surface of the panels. Once completely polymerized, the toroidal part is integral with the bottom and the panels, and ensures a connection of the bottoms to the front and rear skirts.

[0147] The manufacture of a two-compartment tank has just been described, but those skilled in the art will recognize that the principle of the invention can be applied in a similar manner to form a tank having three or more compartments. It is thus possible align three positioning portions with two common bottom precursors and two end domes to form a three-compartment tank.

[0148] The invention which has just been described is suitable for the manufacture of tanks for the main stage of space launchers (lower stage in English). The invention also applies to tanks for upper stages. In operation, the composite tank can be filled, for example and in a non-limiting manner, with liquid methane, liquid hydrogen or refined kerosene (such as RP-1 for example) or a combination of these compounds in a first compartment, and liquid oxygen in a second compartment. The tank can be used in a cryogenic environment.

[0149] The field of the invention is however not limited to a tank for integration into an aerospace launcher but can find an application in the aeronautical field or, more generally, in any application requiring a compartmentalized tank integrating a common bottom.

[0150] The expression "between ... and ..." must be understood as including the limits.

Claims

Claims

1. Method for manufacturing a tank (1) made of compartmentalized composite material, comprising: - positioning a precursor assembly of the tank to be manufactured in a vacuum molding tool (30), the assembly comprising: (i) a cylinder (100), precursor of the body (1000) of the tank, made of thermosetting pre-impregnated fibrous material extending along a longitudinal axis (X), (ii) two domes (200), precursors of the bottom (2000) of the end of the tank, made of thermosetting pre-impregnated fibrous material, each of these domes being located on the side of an opposite longitudinal end of the cylinder, the domes delimiting with the cylinder an internal volume (V) of the tank to be obtained, each dome defining a zone (210) of cylindrical end junction positioned opposite the cylinder and inside the latter, and (iii) a common bottom precursor (300; 300a - e) located inside the cylinder and between the domes so as to define with each of them a separate compartment (C1; C2) of the internal volume, said common bottom precursor comprising a reinforcement (302; 302a - c; 302dl; 302d2; 302e) made of thermoset composite material, defining the common bottom, covered by at least one thermoset pre-impregnated fibrous skin (304; 304 ae; 306; 306 ad) defining an intermediate cylindrical junction zone (310; 310a; 310c) positioned opposite the cylinder, the reinforcement being configured to allow conformation of said at least one skin against the cylinder on this intermediate cylindrical junction zone, and the tooling comprising: (a) a first internal positioning portion (321) covered with a first tarpaulin (341) vacuum, located inside a first compartment (Cl), a first dome being positioned on a first end (3211) of said first portion, and the common bottom precursor being positioned on a second end (3213) of said first portion opposite the first end, (b) a second internal positioning portion (322), covered with a second tarpaulin (342) vacuum, positioned in the extension of said first portion along the longitudinal axis and located inside a second compartment (C2), the common bottom precursor being positioned on a first end (3221) of said second portion and a second dome being positioned on a second end (3223) of said second portion opposite the first end, and (c) an external molding part, located outside the internal volume, comprising a molding portion (60) of the tank body having a cylindrical shape located opposite the precursor cylinder, and molding portions (38) of a dome-shaped tank bottom each located opposite a separate dome, and - vacuum curing of the assembly in the tool during which the first and second vacuum tanks apply pressure to conform the assembly to the molding portions, with the junction zones resting on the precursor cylinder and co-curing of the domes and the common base precursor with the cylinder to secure the end bases and the common base to the body and thus obtain the compartmentalized composite material tank.

2. The method of claim 1, wherein the common bottom precursor (300; 300a-b) comprises a first skin (304; 304a-b) covering a first face (3024) of the armature (302; 302a-b) and defining a first portion (311; 311a) of the intermediate cylindrical junction zone which extends towards the first dome (200), and a second skin (306; 306a-b) covering a second face (3026) of the armature, opposite the first face, and defining a second portion (312; 312a) of the intermediate cylindrical junction zone which extends towards the second dome (200).

3. The method of claim 2, wherein the common bottom precursor (300; 300b) further comprises a filler material (320) between the first (311) and second (312) portions of the intermediate cylindrical junction area.

4. Method according to any one of claims 1 to 3, in which the intermediate cylindrical junction zone (310; 310a; 310c) is at least partly formed by an extension of said at least one skin beyond the reinforcement.

5. Method according to any one of claims 1 to 4, in which the frame (302e) defines a plurality of flexible tabs (3027e) allowing the conformation of said at least one skin (306e) against the cylinder (100) on the intermediate cylindrical junction zone.

6. A method according to any one of claims 1 to 5, wherein the frame (302b) comprises an insulating material configured to thermally insulate the first compartment (Cl) from the second compartment (C2).

7. A method according to any one of claims 1 to 6, wherein said at least one skin (304) has a thinning in thickness on the intermediate cylindrical junction zone towards a circumferential edge thereof.

8. Method according to any one of claims 1 to 7, in which each skin comprises several sectors (304) juxtaposed around the longitudinal axis (X).

9. Method according to claim 8, in which the neighboring sectors have a thinning of thickness on their overlap zone in the direction of their longitudinal edges (304al; 304bl).

10. A method according to any one of claims 1 to 9, wherein the cylinder (100), said at least one skin (304; 304 ae; 306; 306 ad) and the domes (200) are assembled in the half-baked state to form the precursor assembly.

11. A method according to any one of claims 1 to 10, wherein the method further comprises, prior to positioning the precursor assembly in the molding tooling (30), forming the cylinder (100), said at least one skin (304; 304 ae; 306; 306 ad) and the domes (200) by automatic fiber placement, the cylinder, said at least one skin and the domes each being draped over a separate shape of the first (321) and second (322) positioning portions.

12. A method according to any one of claims 1 to 11, wherein the cylinder (100), said at least one skin (304; 304 ae; 306; 306 ad) and the domes (200) comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

13. Method according to any one of claims 1 to 12, in which the cylinder (100), said at least one skin (304; 304 ae; 306; 306 ad) and the domes (200) are pre-impregnated with an epoxy resin.

Images