Method for manufacturing a tank made of composite material

Abstract

The present invention relates to a method for manufacturing a tank (1) made of composite material, in which a precursor assembly made of thermosetting pre-impregnated fibrous material is fired under vacuum in a tool (30), the moulding parts of which are external to the assembly in order to facilitate subsequent removal from the mould. The assembly comprises a body-precursor cylinder (100) closed by two bottom-precursor domes (200) which are rigidly connected to the cylinder by co-firing. The invention is of particular interest in the production of large tanks.

Description

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

[0001] The present disclosure relates to a method for manufacturing a composite material tank, particularly suitable for manufacturing a large tank, in particular one of great length. The invention is of particular interest for the manufacture of tanks intended to equip space launchers but is not, however, 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 techniques for manufacturing composite tanks, the part is draped over a rotating mandrel, by winding or by automated fiber placement (AFP). These techniques provide satisfactory results when the tanks have limited dimensions but they can be improved for the manufacture of large tanks, typically having a length of 20 to 30 meters and a diameter of several meters.

[0005] Indeed, particularly long mandrels may not have the required rigidity to maintain their shape during layup, particularly due to bending under their own weight or following the support of a layup robot head. This can cause layup accuracy problems that can lead to defects in the structure.

[0006] The mandrels must be removable and extractable through small openings at the tank ends. This can typically be a mandrel 5 or 6 meters in diameter that must be extracted through an opening 1 meter in diameter or less. The larger the tank, the more complex the disassembly will be, with the associated risks of damage to the composite structure (impacts that can create damage to the structure). This will generate significant costs because complex specific tools will have to be designed for disassembly through these small openings. In addition, it is, in some cases, necessary to position a vacuum cover around the part draped on the mandrel and to carry out vacuum polymerization. It is then necessary to ensure a seal between the different parts constituting the removable mandrel, in order not to affect the material health. However, the longer the tooling, the more joints there will be to seal, with the associated potential problems of air leaks. In addition, the larger the tanks, the more time it will take to carry out the draping and the installation of the vacuum cover, and these operations must be carried out within a certain time period not exceeding the ambient life of the material indicated by the supplier.

[0007] It is also desirable to reduce the manufacturing cycle time since the draping tooling also serves as the curing tooling, which requires waiting for this step to be completed and the structure to be dismantled before draping can be carried out again.

[0008] 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. US 2021 / 245447 discloses a method for manufacturing a high-pressure tank.

[0009] It is therefore desirable to have a method for manufacturing a composite material tank which addresses all or part of the aforementioned drawbacks. Statement of the invention

[0010] The invention relates to a method for manufacturing a composite material tank, comprising: - the positioning of a precursor assembly of the tank to be manufactured in a vacuum molding tool, the assembly being made of thermosetting pre-impregnated fibrous material and comprising (i) a sectored cylinder, precursor of the body of the tank, extending along a longitudinal axis and formed by panels juxtaposed around the longitudinal axis with overlap between the neighboring panels, and (ii) two domes, precursors of the bottom of the tank, 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 junction zone positioned opposite the cylinder and inside the latter, the tooling comprising an internal part coated with a vacuum cover, located inside the internal volume, on which the assembly is positioned, and an external molding part, located outside the internal volume, and comprising (a) a molding portion of the tank body having a cylindrical shape located opposite the precursor cylinder, and (b) molding portions of a dome-shaped tank bottom each located opposite a separate bottom precursor dome, and - vacuum curing of the assembly in the tool during which the vacuum tank applies 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 cylinder to secure the bases to the body and obtain the composite material tank.

[0011] 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 internal portion in the invention only has a positioning function and not a molding function, and therefore has a much simpler design and is more easily disassembled. If necessary, the molding portion of the body can be provided with stiffeners on its face opposite the assembly in order to maintain its shape despite a significant length, without affecting the quality of the molding or the disassembly nature.

[0012] Co-curing allows the thermosetting resin impregnating the panels to polymerize with that impregnating the domes, and to create covalent bonds between the polymer chains present. This joint polymerization leads to a bonding of the bases to the body of the composite material tank, without requiring the addition of a third-party adhesive compound.

[0013] In an exemplary embodiment, the neighboring panels have a thinning in thickness over their overlapping zone towards their longitudinal edges.

[0014] Such a feature helps to further minimize misalignments and stress concentrations in the reservoir.

[0015] In an exemplary embodiment, the precursor domes have a thinning in thickness on their cylindrical junction zones towards a circumferential edge of the dome.

[0016] Such a feature helps to further minimize misalignments and stress concentrations in the reservoir.

[0017] 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.

[0018] The sectorization of the domes further improves their conformation during sous vide cooking by allowing relative sliding between the petals.

[0019] In particular, neighboring petals may exhibit a thinning of thickness over their overlapping area towards their longitudinal edges.

[0020] Such a feature helps to further minimize misalignments and stress concentrations in the reservoir.

[0021] In an exemplary embodiment, the panels and domes are assembled in the semi-fired state to form the precursor assembly. Thus, the panels and domes, already formed, can be assembled in the semi-fired state to form the precursor assembly, or the panels and petals, intended to form the domes after juxtaposition, can be assembled in the semi-fired state to form the precursor assembly.

[0022] 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).

[0023] 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 very 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.

[0024] In one exemplary embodiment, the panels and domes each include a plurality of stiffeners on a face opposite the molding portions.

[0025] 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.

[0026] In an exemplary embodiment, the method further comprises, prior to positioning the precursor assembly in the molding tool, forming the panels and domes by automatic fiber placement, the panels and domes each being draped over a separate form of the internal positioning portion.

[0027] 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. Automatic fiber placement 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.

[0028] In one exemplary embodiment, the cylinder extends beyond each of the domes so as to define precursors of front and rear skirts.

[0029] 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.

[0030] In particular, each of the domes can define a second cylindrical junction zone opposite a respective skirt precursor and which can be secured to the latter during vacuum cooking.

[0031] In one exemplary embodiment, the panels and domes comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

[0032] These fiber materials are particularly suitable for space launcher applications and cryogenic environments.

[0033] In one embodiment, the panels and 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.

[0034] This material is particularly suitable for space launcher applications and cryogenic environments, and can be easily reworked after partial polymerization. Brief description of the drawings [Fig. 1] Figure 1 represents, schematically in perspective, an example of a panel usable within the framework of the invention. [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 a sectored cylinder. [Fig. 5] Figure 5 represents, schematically and partially, another variant of sectored cylinder. [Fig. 6] Figure 6 represents, schematically and partially, another variant of sectored cylinder. [Fig. 7] Figure 7 represents, schematically and partially, another variant of sectored 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 height 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 height of the dome. [Fig. 12] Figure 12 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. 13] Figure 13 shows, schematically and partially, the stiffeners present on the assembly of Figure 12. [Fig. 14] Figure 14 schematically represents the sous vide cooking of the assembly illustrated in Figure 12. [Fig. 15] Figure 15 schematically represents a detail of a variant of the precursor dome of the bottom. Description of the embodiments

[0035] 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.

[0036] The description below first covers the structure and production of the precursor cylinder of the body, as well as the precursor domes of the bottoms. The details of the vacuum casting tool, inside which the precursor assembly is positioned, as well as the vacuum cooking phase will be discussed in a second step.

[0037] Panels and precursor cylinder of the body

[0038] The precursor cylinder of the body is obtained by juxtaposing thermosetting pre-impregnated fiber panels. Generally, it can comprise at least two fiber panels, or even at least three fiber panels. The example described here concerns the case of a four-panel cylinder.

[0039] 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.

[0040] The panels 10 have an elongated shape along a longitudinal axis X and have a curved shape in cross-section relative to the axis X. The panels 10 define two longitudinal edges 10a, 10b which are intended to be superimposed with a neighboring panel, as will be described below. As indicated above, the invention is of particular interest for the manufacture of very long tanks. Thus, the panels 10 may have a length LO10 of at least 10 meters, for example at least 20 meters, in particular between 20 meters and 30 meters. Figure 1 illustrates an example of a possible structure for the panels 10 which are draped in a female tool, the person skilled in the art will recognize that the panels may alternatively be draped on a male tool without departing from the scope of the present invention.The draping form is not an integral part of the vacuum casting tooling so as to allow parallel operation between draping and curing, thus reducing the manufacturing cycle time.

[0041] 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 raw 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 may 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 may be present over at least the majority (more than 50%), or even at least 80%, of the length LO10 of the panels 10. The panels 10 nevertheless have areas devoid of stiffening elements which will be described below.

[0042] 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.

[0043] The stiffeners 12 and frame sectors 14 may be half-baked, or have complete, or little or no advanced polymerization.

[0044] The panels 10 have circumferential zones 16, intended for docking with the bottoms, which are devoid of stiffening elements. The zones 16 are each located on the side of an opposite longitudinal end of the panel 10 in question and on either side of a zone 18 provided with stiffeners 12 and frame sectors 14. As will be detailed below, the bottoms will be secured to the body of the tank on these zones 16. 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 elements. 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.

[0045] 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. Zone 101 is located between zones 103a, 103b. Zone 103a connects zone 101 to edge 10a, and zone 103b connects zone 101 to edge 10b. More Specifically, the zones 103a, 103b have a thinning in thickness towards the associated longitudinal edge 10a, 10b. The thickness elO may be strictly decreasing towards 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 thickness thinning 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.

[0046] 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 sectored 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 bottoms.

[0047] 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. covering, splinting or splicing. In addition, the zones 16 of the first panel 10 are an extension of the zones 16 of the second panel 10.

[0048] The arrangement just described can be applied to each pair of neighboring panels 10 juxtaposed to form the sectored cylinder. Generally speaking, the overlap zones between neighboring panels can occupy at least 5%, for example at least 30% of the perimeter of the sectored cylinder. Having spread overlap zones makes it possible to further improve the mechanical properties of the resulting tank. In particular when all the panels are assembled to form the sectored cylinder, the joining of the zones 16 forms a 360° circumferential zone devoid of any stiffening element. Furthermore, the joining of the frame sectors 14 of each of the panels defines a plurality of 360° circumferential frames distributed along the length of the cylinder.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The variants of Figures 6 and 7 show cases where there is no tiling which are also covered by the present invention.

[0053] The part just described concerns the panels and their juxtaposition to form the precursor body cylinder. The following concerns the precursor bottom domes which are intended to be secured to the cylinder to delimit the internal volume of the composite material tank to be obtained.

[0054] Background precursor domes

[0055] Figure 8 shows a petal 20, which has the shape of a dome sector, draped in shape. According to this example, each bottom 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.

[0056] As for the panels 10, the petals 20 are advantageously produced 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 tool, and over a draping form that is not an integral part of the vacuum molding tool.

[0057] 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.

[0058] 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.

[0059] The petals 20 define a sector 203d of a cylindrical 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.

[0060] 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.

[0061] 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 revolution shape. The union 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 latitude 25, and substantially constant over the zone 210. The radius R of the dome 200, taken on the edge 20d, can be greater than or equal to 1 meter, for example greater than or equal to 2.5 meters.

[0062] 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 13 which will be described below.

[0063] A possible structure for the cylinder 100 and the domes 200 has just been described. The following describes their assembly and positioning in the vacuum molding tool.

[0064] Mounting the vacuum casting tool and positioning the precursor assembly in this tool

[0065] The kinematics of mounting the vacuum molding tool 30 and positioning the precursor assembly will now be detailed in connection with figure 12. In this figure, as well as in figure 14, the relative thicknesses as well as the spacings between the different elements have not been strictly respected for reasons of readability.

[0066] A vacuum cover 34 is initially placed over a positioning portion 32. The portion 32 is of much simpler design than the mandrel implemented in prior art techniques in that it is not used as a molding surface and does not need to be sealed. It is, therefore, more easily removable. The part 32 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 part 32 may have an aerated structure, for example a lattice, or comprise a plurality of retractable positioning elements fixed to the shaft. The part 32 may, as illustrated, generally have the shape of the tank to be obtained. The tarpaulin 34 covers the part 32. The tarpaulin 34 may be made of elastomeric material, reinforced or not, and constitutes an element known per se.

[0067] The petals 20 are then positioned on the part 32 at its two opposite longitudinal ends 321 and 323. The petals 20 are juxtaposed in the manner described above to form two precursor domes 200 at the opposite ends 321, 323. The bottom zones 205 of the domes 200 each define an orifice 206, here in the general shape of a disc, through which the shaft 36 extends. The domes 200 may have a general shape of revolution around the axis X.

[0068] The molding portions 38 are then positioned. These portions 38 each have the shape of a dome and are in the shape of the 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 the vacuum tank 34 (or the part 32). As illustrated, the portions 38 cover the bottom area 205 but do not cover the cylindrical junction area 210. The person skilled in the art will recognize that other variants are possible. Thus, the domes 200 can first be positioned on the portions 38 and then this assembly can then be placed on the ends 321, 323 of the part 32. The precise positioning of the portions 38 as well as their maintenance can be ensured by the shaft 36.Alternatively, all petals may first be draped over a dome tool, and then the dome may be half-baked before assembly on portion 32 or portion 38.

[0069] In the example considered in Figure 12, a second and a third empty tarpaulins 35 are then placed respectively for the formation of the front and rear skirts which will be described below. The second and third tarpaulins 35 may have the same nature as the first tarpaulin 34.

[0070] 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.

[0071] The panels 10 are then positioned and juxtaposed, in the manner described above, so as to form the cylinder 100 precursor of the body of the tank. The cylinder 100 is located around the domes 200. In the illustrated example, the domes 200 are located inside the cylinder 100. The cylinder 100 extends from one dome 200 to another. Generally speaking, the length LO10 of the panels, which also corresponds to the length of the cylinder 100, is greater than or equal to the length LC, measured along the X axis, which corresponds to the distance separating the two zones 205. The length LC corresponds substantially to the length of the body of the tank to be obtained. 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 second and third tarpaulins 35.Thus in this example the length LO10 is greater than the length LR, measured along the X axis, which corresponds to the distance between the orifices 206 of the domes 200. The length LR corresponds substantially to the length of the composite tank to be obtained. However, it does not depart from the scope of the invention if the cylinder does not form such skirts by stopping at the level of the domes 200.

[0072] Thus, after positioning the panels 10, a precursor assembly of the tank to be manufactured is obtained, which comprises the cylinder 100 and the domes 200 each located on the side of an opposite longitudinal end of the cylinder 100. The domes 200 delimit with the cylinder 100 an internal volume V of the tank to be obtained. The domes 200 close the cylinder 100 on the side of each of its longitudinal ends. The cylinder 100 and the domes are each made of thermosetting pre-impregnated fibrous material. The panels 10 are positioned opposite the zones 210 so as to allow the bases to be secured to the body during the co-firing which will be described below. In particular, the zones 210 are opposite the zones 16 of the panels 10 devoid of stiffening elements which have been described above.

[0073] The panels 10 and domes 200 (or petals 20) 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 polymerization progress 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) and the panels 10 may be assembled after this partial polymerization.

[0074] 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 crown 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 can 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. An internal surface SI of the precursor assembly is located on the side of the tank 34 (and delimits the internal volume V of the tank), and an external surface S2 of the assembly is located on the side of the portions 38, 60.

[0075] Figure 13 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 zone 210, or if the domes are devoid of stiffeners.

[0076] The seals 52 between the tarpaulins 34, 35 and the molding portions 38, 60 are then made.

[0077] The precursor assembly is thus positioned in the vacuum molding tool 30. In particular, the cylinder 100 is interposed between the cover 34 and the molding portion 60, and each dome 200 is interposed between the cover 34 and a respective molding portion 38. The portion 32 is located inside the precursor assembly, that is to say is 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.

[0078] Vacuum curing of the precursor assembly in the tooling and disassembly

[0079] The sous vide cooking phase is illustrated in Figure 14. This cooking phase can be carried out with or without additional pressure.

[0080] The heating applied leads to a fluidification of the resin(s) present. The vacuuming of the tool 30 causes the tarpaulin 34 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 are pressed against the panels 10 thanks to the slight relative displacement / separation of the petals 20, separation 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 temperature and pressure, the petals 20 move apart to conform to the internal surface of the panels. It is essentially the zone 210 which will dock with the panels 100. The tarpaulins 35 apply pressure to the skirt precursors 110 and 120.

[0081] 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 (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 co-curing step.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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 bottoms 2000. The skirts 1100 and 1200 are monolithic with the rest of the tank 1. Figure 15 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.

[0086] Thus, the dome 200 of FIG. 15 defines a second cylindrical junction zone 310 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 310 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 310 extends outside this volume V.

[0087] The second zone 310 is defined by a toroidal-shaped part 300 which is attached to the zone 205. More particularly, the part 300 comprises a zone 305 for joining to the dome 200 taking the shape of the zone 205 and secured to the latter, the zone 310 opposite the skirt precursor 120 and a folded intermediate zone 307 connecting the zone 305 to the zone 310.

[0088] The part 300 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 300 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 300 is half-baked after draping and before assembly with the base 200 and the panels 10.

[0089] The part 300 is positioned on the base 200 once the latter is positioned on the part 32. Then, once in place, the portion 38 is positioned, which has a shape adapted to the presence of the part 300. As a variant, the part 300 is first positioned on the portion 38, then the base 200 is positioned on this portion 38 and the assembly is placed on the part 32.

[0090] Part 300 may or may not be stiffened. The stiffeners may be as described above and are positioned in the tooling prior to layup.

[0091] The space 250 between the dome 200 and the part 300 can be filled with a filling material, possibly loaded with fibers.

[0092] 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). And 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.

[0093] The invention which has just been described is particularly suitable for the manufacture of long, or even very long, tanks, which can be found in the case of tanks for the main stage of space launchers ("lower stage" in English), or in the case of tanks for powder acceleration stages ("boosters" in English). The invention also applies to upper stage tanks. In operation, the composite tank can be filled with liquid methane, liquid hydrogen or liquid oxygen, or a combination of these compounds. The tank can be used in a cryogenic environment.

[0094] 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 large tank.

[0095] The expression "between ... and ..." must be understood as including the limits.

Claims

Claims

1. Method of manufacturing a tank (1) made of composite material, comprising: - positioning a precursor assembly of the tank to be manufactured in a vacuum molding tool (30), the assembly being made of thermosetting pre-impregnated fibrous material and comprising (i) a sectored cylinder (100), precursor of the body (1000) of the tank, extending along a longitudinal axis (X) and formed by panels (10) juxtaposed around the longitudinal axis with overlap between the neighboring panels, and (ii) two domes (200), precursors of the bottom (2000) of the tank, 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 cylindrical junction zone (210) positioned opposite the cylinder and inside the latter, the tool comprising an internal part (32) coated with a vacuum cover (34), located inside of the internal volume, on which the assembly is positioned,and an external molding portion, located outside the internal volume, and comprising (a) a molding portion (60) of the tank body having a cylindrical shape located opposite the precursor cylinder, and (b) molding portions (38) of a dome-shaped tank bottom each located opposite a separate bottom precursor dome, and, - vacuum curing of the assembly in the tool during which the vacuum tank applies 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 cylinder to secure the bases to the body and obtain the composite material tank.

2. Method according to claim 1, in which the neighboring panels (10) have a thinning of thickness (elO) on their overlapping zone (ZR) in the direction of their longitudinal edges (10a; 10b).

3. Method according to claim 1 or 2, in which the precursor domes (200) have a thinning of thickness (e20) on their cylindrical joining zones (210) towards a circumferential edge (20d) of the dome.

4. Method according to any one of claims 1 to 3, in which the precursor domes (200) are each sectorized and formed by petals (20) juxtaposed around the longitudinal axis (X) with overlap between the neighboring petals.

5. Method according to claim 4, in which the neighboring petals (20) have a thinning of thickness (e20) on their overlapping zone (ZR20) in the direction of their longitudinal edges (20a; 20b).

6. A method according to any one of claims 1 to 5, wherein the panels (10) and domes (200) are assembled in a semi-baked state to form the precursor assembly.

7. A method according to any one of claims 1 to 6, wherein the panels (10) and domes (200) each comprise a plurality of stiffeners (12; 202) on a face opposite the molding portions (38; 60).

8. A method according to any one of claims 1 to 7, wherein the method further comprises, prior to positioning the precursor assembly in the molding tooling (30), forming the panels (10) and domes (200) by automatic fiber placement, the panels and domes each being draped over a separate form of the internal positioning portion (32).

9. A method according to any one of claims 1 to 8, wherein the cylinder (100) extends beyond each of the domes (200) so as to define precursors (110; 120) of front and rear skirts.

10. Method according to claim 9, in which each of the domes (200) defines a second cylindrical junction zone (310) opposite a respective skirt precursor (110; 120) and which is secured to the latter during vacuum cooking.

11. A method according to any one of claims 1 to 10, wherein the panels (10) and domes (200) comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

12. A method according to any one of claims 1 to 11, wherein the panels (10) and domes (200) are pre-impregnated with an epoxy resin.

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