Method for manufacturing tanks made of composite materials

Abstract

The present invention relates to a method for manufacturing a tank made of composite material, wherein a precursor assembly made of a pre-impregnated thermosetting fibrous material is vacuum-cured in a tool located outside the assembly to facilitate subsequent demolding. The assembly comprises a cylinder which is a precursor of a body, closed by two dome-shaped bottom precursors fixed to the cylinder by co-curing. The present invention is of particular interest to the manufacture of large tanks.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a tank made of composite material, and in particular to a method suitable for manufacturing a tank having large dimensions, particularly a large length. The present invention is particularly interested in the manufacture of tanks intended to equip space launch vehicles, but is not limited to this application.

Background Art

[0002] Composite materials offer mass savings compared to metallic materials, which is particularly interesting in terms of performance improvement in the aerospace and aviation fields.

[0003] The recent development of reusable launch vehicles is accompanied by the desire to continue developing lighter structures, since a certain amount of propellant needs to be retained for the return of the stage to Earth, which leads to the loading of additional mass.

[0004] In current techniques for manufacturing composite material tanks, the parts are draped on a rotating mandrel by winding or by means of the automated fiber placement (AFP) technique. These techniques give satisfactory results when the dimensions of the tank are limited, but typically need to be improved for the manufacture of large tanks with lengths of 20 to 30 meters and diameters of several meters.

[0005] Indeed, particularly long mandrels may not have the rigidity required to maintain their shape during draping, particularly due to bending under their own weight or when supporting the head of the draping robot. This can lead to problems of draping accuracy that can result in structural defects.

[0006] The mandrel must be dismantled and removed at its end through a small opening in the bottom of the tank. Typically, a mandrel with a diameter of 5 or 6 meters must be removed through an opening of less than 1 meter in diameter. The larger the tank, the more complex the dismantling process becomes, and the greater the risk of damage to the composite structure (impact that damages the structure) associated with the dismantling. This incurs considerable costs because complex, specific tools must be designed to dismantle through these small openings. Furthermore, in certain cases, it is necessary to position vacuum bags around the draped components on the mandrel and perform vacuum polymerization. In this case, it is necessary to ensure seals between the different components that make up the removable mandrel to avoid affecting the integrity of the material. However, the longer the tools, the more joints there are to seal, leading to the potential problem of associated air leaks. Also, the larger the tank, the longer the time required for draping and vacuum bag installation, and these operations must be performed within a certain time frame that does not exceed the room temperature exposure time of the material indicated by the supplier.

[0007] Furthermore, since the draping tools also serve as polymerization tools, it is desirable to shorten the manufacturing cycle, which requires waiting until the end of this stage and dismantling the structure before it can be draped again.

[0008] The limitations of current technology become even more apparent when reinforcing elements or interface parts, such as reinforcing materials, are integrated into the tank. Patent Document 1 (U.S. Patent Application Publication No. 2021 / 245447) discloses a method for manufacturing a high-pressure tank. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 245447 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, it is desirable to have a method for manufacturing tanks made of composite materials that address all or some of the above-mentioned drawbacks. [Means for solving the problem]

[0011] Furthermore, the present invention relates to a method for manufacturing a tank made of composite material, The aforementioned method, Positioning a precursor assembly of a tank to be manufactured in a vacuum forming machine, wherein the precursor assembly is made of a pre-impregnated thermosetting fibrous material and comprises: (i) a segmented cylinder which is a precursor of the tank body, the cylinder being a segmented cylinder formed by several panels juxtaposed around the longitudinal axis so as to extend along the longitudinal axis and overlap between several adjacent panels; and (ii) two domes which are precursors of the tank bottom, each of which is located on the side of the opposite longitudinal end of the cylinder, the two domes being separated by the volume of the tank to be obtained, and each dome comprising two domes which define a cylindrical joining zone facing the cylinder and inside the cylinder. The vacuum forming tool comprises an inner portion lined with a vacuum bag located within the internal volume where the precursor assembly is positioned, and an outer forming portion located outside the internal volume. The vacuum forming tool comprises (a) a forming portion of a cylindrical tank body facing the cylinder which is a precursor, and (b) a forming portion of a dome-shaped tank bottom facing the dome which is a precursor of a distinct bottom, The present invention relates to a method for obtaining a tank made of composite material, in which, while the vacuum bag applies pressure to shape the precursor assembly on the molding portion, the precursor assembly is vacuum-cured within the vacuum forming tool, the bonding zone in contact with the cylinder which is the precursor is maintained, and the two domes and the cylinder are co-cured, thereby fixing the bottom to the tank body.

[0012] In this invention, the molding section is located outside the precursor assembly and, consequently, outside the resulting composite tank. This external positioning facilitates disassembly with respect to the conventional internal molding mandrel and more easily ensures the tightening required for vacuuming. Unlike the conventional mandrel, the internal section in this invention has only a positioning function and no molding function, resulting in a much simpler design and easier disassembly. If necessary, reinforcing material can be provided on the side of the molding section opposite the assembly to preserve its shape despite its considerable length, without affecting the quality of the molded product or the ability to disassemble it.

[0013] Co-curing allows the thermosetting resin impregnated into the panel, while impregnated into the dome, to polymerize, forming covalent bonds between the existing polymer chains. This polymerization of the joint allows the bottom of the composite material tank to be bonded to the tank body without the need for the addition of a third adhesive compound.

[0014] In an exemplary embodiment, several adjacent panels become thinner in their overlapping zone in the direction of their longitudinal edges.

[0015] These characteristics help further minimize misalignment and stress concentration within the tank.

[0016] In one embodiment, the precursor dome becomes thinner in the direction of its circumferential edge in the tubular bonding zone.

[0017] These characteristics help further minimize misalignment and stress concentration within the tank.

[0018] In one embodiment, these precursor domes are each divided and formed by several petal-like parts arranged juxtaposed around a longitudinal axis, with overlaps between several adjacent petal-like parts.

[0019] By partitioning the dome, relative sliding between several petal-shaped parts is enabled, thereby further improving the conformation of the dome during vacuum curing.

[0020] In particular, several adjacent petal-shaped parts may be thinner in their overlapping zones in the direction of their longitudinal edges.

[0021] Such characteristics help to further minimize misalignment and stress concentration within the tank.

[0022] In one embodiment, the panel and the dome are assembled in a semi-cured state to form a precursor assembly. Thus, an already formed panel and dome can be assembled in a semi-cured state to form a precursor assembly, or panels and petal-shaped parts intended to form a dome after juxtaposition can be assembled in a semi-cured state to form a precursor assembly.

[0023] The semi-cured thermosetting material has a partially polymerized resin with a degree of polymerization progress consisting of 15% - 70%, for example 25% - 50%. For a given resin, the degree of polymerization progress can be determined by differential scanning calorimetry (DSC).

[0024] The semi-cured material has a certain rigidity at room temperature (20°C) so that it is easy to handle and tooling can be simplified. Also, due to its use, the polymerization of the semi-cured material hardly changes at room temperature, so that it can be less restricted by the open time of the material at room temperature. The resin of the semi-cured material regains fluidity when the temperature of the material rises during vacuum curing, and the elements soften and can conform to the molded part.

[0025] In an exemplary embodiment, the panel and the dome each comprise a plurality of reinforcing materials on the surface facing the molded part.

[0026] The external properties of the forming tool do not interfere with the presence of reinforcing material. Therefore, the present invention is of particular interest in the manufacture of reinforced tanks, which are relatively difficult to obtain with the techniques of the prior art using an internal forming mandrel.

[0027] In exemplary embodiments, the method further comprises forming panels and domes by automatic fiber placement, which are draped in a different manner from the internal positioning portion, before positioning the precursor assembly within the molding tool.

[0028] This technology allows access to a wide variety of geometric shapes, particularly compared to winding, which does not enable draping in the longitudinal direction, or to automated draping of locally increased thickness or reinforcing members. Furthermore, automated fiber placement makes it possible to obtain elements with lower permeability compared to components obtained by winding, such as those suitable for storing cryogenic propellants. Additionally, since the draping tool is separated from the polymerization tool, the manufacturing cycle time is reduced.

[0029] In one embodiment, the cylinder extends beyond each of the domes to define the front skirt precursor and the rear skirt precursor.

[0030] These characteristics are particularly interesting in relation to tanks intended to carry aerospace launch vehicles, as they allow for the formation of a complete space launch stage in a simplified manner by enabling the skirt to be integrated with the tank.

[0031] In particular, each of the multiple domes can define a second tubular bonding zone that faces its respective skirt precursor and can be fixed to the skirt precursor during vacuum curing.

[0032] In one embodiment, the panel and dome are made of carbon fiber, glass fiber, aramid fiber, or a mixture of the above fibers.

[0033] These fiber materials are particularly suitable for applications in space launch vehicles and cryogenic environments.

[0034] In one embodiment, the panels and dome are pre-impregnated with an epoxy resin, such as a Class 180 epoxy resin that polymerizes at a temperature between 175°C and 185°C, substantially 180°C.

[0035] This material is particularly suitable for applications in space launch vehicles and cryogenic environments, and can be easily reprocessed after partial polymerization. [Brief explanation of the drawing]

[0036] [Figure 1] Figure 1 schematically shows an example of a panel that can be used in relation to the present invention. [Figure 2] Figure 2 schematically shows a partial cross-section of the panel in Figure 1 with respect to its longitudinal axis. [Figure 2A] Figure 2A schematically and partially shows the bevel angle of the panel in Figure 2. [Figure 3] Figure 3 is a schematic perspective view showing the overlap of two adjacent panels according to an embodiment of the present invention. [Figure 4] Figure 4 schematically and partially shows a modified embodiment of the segmented cylinder. [Figure 5] Figure 5 schematically and partially shows another modified embodiment of the segmented cylinder. [Figure 6] Figure 6 schematically and partially shows another modified embodiment of the segmented cylinder. [Figure 7] Figure 7 schematically and partially shows another modified embodiment of the segmented cylinder. [Figure 8] Figure 8 shows an example of a petal-like structure that attempts to form a dome, which is a precursor to the base, when placed alongside other petal-like structures. [Figure 9] Figure 9 shows the juxtaposition of a second petal-like portion on the petal-like portion of Figure 8, according to an embodiment of the present invention. [Figure 10] Figure 10 schematically and partially shows a cross-sectional view of the dome resulting from the juxtaposition of the petal-like parts as shown in Figure 8, in a plane that includes the height of the dome. [Figure 11] Figure 11 schematically and partially shows a cross-sectional view of the dome resulting from the juxtaposition of the petal-like parts shown in Figure 8, in a plane perpendicular to the height of the dome. [Figure 12] Figure 12 schematically and partially shows a precursor assembly of a tank to be manufactured, positioned within a vacuum forming tool, in relation to an embodiment of the present invention. [Figure 13] Figure 13 schematically and partially shows the reinforcing materials present in the assembly shown in Figure 12. [Figure 14] Figure 14 schematically shows the vacuum curing of the assembly shown in Figure 12. [Figure 15] Figure 15 schematically shows the details of the deformation embodiment of the dome, which is the precursor of the bottom. [Modes for carrying out the invention]

[0037] The present invention will now be illustrated with reference to the figures. These figures are provided for illustrative purposes to illustrate specific embodiments of the present invention and should not be construed as limiting.

[0038] The following explanation will first describe the structure and acquisition of the cylinder, which is a precursor to the tank body, and the dome, which is a precursor to the bottom. Next, the details of the vacuum forming tool in which the precursor assembly is located, and the vacuum curing process will be described.

[0039] The cylinder is a precursor to the panel and the main body. The cylinder, which is a precursor to the main body, is obtained by the juxtaposition of pre-impregnated thermosetting fiber panels. Generally, the cylinder, which is a precursor to the main body, may comprise at least two fiber panels, or even at least three fiber panels. The example described here concerns a cylinder consisting of four panels.

[0040] The panels are advantageously manufactured by automated fiber arrangement, which constitutes a known technique. Each panel 10 comprises a fiber reinforcement pre-impregnated with a thermosetting resin. The choice of reinforcement and resin depends on the intended application. For example, the fiber reinforcement comprises carbon fibers, glass fibers, aramid fibers, or mixtures of the above fibers. For example, the resin is an epoxy resin, based on, for example, bisphenol A bisphenol diglycidyl ether (DGEBA) monopolymer, triglycidyl-para-aminephenol (TGPAP) monopolymer, or tetraglycidyl methylenedianiline (TGMDA) monopolymer, to which an amine-type curing agent, such as diaminodiphenyl sulfone (DDS), may be optionally added. Advantageously, the same resin is used for different panels, or otherwise, a corresponding resin is used.

[0041] Panel 10 has an elongated shape along the longitudinal axis, the X-axis, and a curved shape in cross-section with respect to the X-axis. Panel 10 defines two longitudinal edges 10a, 10b intended to be superimposed with adjacent panels, as described below. As shown above, the present invention has found particular interest in the manufacture of tanks of considerable length. Thus, panel 10 has a length LO10 of at least 10 meters, for example, at least 20 meters, and particularly 20 to 30 meters. Figure 1 shows an example of a possible structure of panel 10 draped in a female tool. Those skilled in the art will recognize that the panel can be alternatively draped on a male tool without exceeding the technical scope of the present invention. Since draping is not an integral part of the vacuum forming tool, draping and curing can be performed simultaneously, thereby reducing the manufacturing cycle time.

[0042] Panel 10, in the example shown in Figure 1, includes longitudinal stiffeners 12 made of a thermosetting composite material. 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 mold, or stamping in a press of a flat green plate to create a dry preform, and then by injecting resin into the mold using resin transfer molding (RTM) technology. The stiffeners 12 may have any cross-section, such as omega, T, or J shapes, among other possible shapes. The stiffeners 12 may or may not have localized variations in shape or section (cross-section). As shown, the stiffeners 12 may be present in at least a large portion (more than 50%), or even at least 80%, of the length LO 10 of panel 10. Nevertheless, panel 10 has zones lacking the stiffener elements described below.

[0043] The illustrated panel 10 is also provided with a circumferential frame section 14 made of a thermosetting composite material. With respect to the reinforcing member 12, the frame section 14 is formed by a known method. The frame section 14 may have any cross-section, such as Z-shaped, C-shaped, F-shaped, T-shaped, omega-shaped, or J-shaped.

[0044] The reinforcing material 12 and the frame section 14 may be partially cured, or may have complete polymerization, or may have little or no polymerization.

[0045] Panel 10 has circumferential zones 16 intended for connection to the bottom, which lacks reinforcing elements. These zones 16 are located on the opposite longitudinal end side of panel 10 and on either side of zone 18, which has reinforcing members 12 and frame sections 14. As detailed below, the bottom is fixed to the tank body over these zones 16. Panel 10 also has a longitudinal zone 19 located on the longitudinal edge 10b side and extending along the entire length LO 10, which lacks reinforcing elements. Note that in the illustrated example, the frame section 14 protrudes from panel 10 on the opposite side of zone 19 (the edge 10a side), forming an extension 15 of the frame section 14. The presence of zone 19 and the extension of the frame 14 is a result of the assumed arrangement for overlaps between several adjacent panels 10.

[0046] Figure 2 shows the variation in the thickness e10 of panel 10 across its width (the dimension between edge 10a and edge 10b). Panel 10 has an intermediate zone 101 in the width of panel 10 where the thickness e10 is substantially constant, and two lateral zones 103a and 103b located on the sides of the respective longitudinal edges 10a and 10b, which have varying thicknesses. Zone 101 is located between zones 103a and 103b. Zone 103a connects zone 101 to edge 10a, and zone 103b connects zone 101 to edge 10b. More precisely, zones 103a and 103b become thinner in the direction of the corresponding longitudinal edges 10a and 10b. The thickness e10 can decrease precisely in the direction of the longitudinal edges 10a and 10b. The thickness e10 is minimum at the edges 10a and 10b and maximum in the intermediate zone 101. Panel 10 has bevels in cross-section at its edges 10a and 10b, and panel 10 has a shape that tapers toward its edges 10a and 10b with respect to the X axis. Zones 103a and 103b together occupy at least 5%, e.g., at least 50%, of the width LA10 of panel 10. Unless otherwise stated, the width LA10 corresponds to the arc length of the curve connecting edge 10a to edge 10b. The thickness reduction results in a reduction of at least 50%, e.g., at least 90%, of thickness e10. This reduction in thickness e10 consists of, for example, between 50% and 95%, or even between 90% and 95%. Figure 2A schematically shows the thickness reduction of panel 10 in the direction of the longitudinal edge 10b, related to the presence of a reduction in overlapping folds PS in the direction of edge 10b. The bevel angle α corresponding to the locally measured angle on the edge 10b can, advantageously, be 1.5° or less, resulting in further improvement in force smoothing.

[0047] Although the panel 10 described above is equipped with reinforcing elements, the absence of these elements does not exceed the scope of the present invention. Referring to Figures 3 to 7, the following describes arranging these panels 10 side by side to form a segmented cylinder 100, which in the embodiment of the present invention is a precursor to the tank body, but is also a precursor to the front skirt and rear skirt that extend beyond the bottom.

[0048] Figure 3 shows the juxtaposition of two adjacent panels 10 around the X-axis. The two illustrated panels 10 have the same structure, and the same reference numbers are maintained with respect to what has just been described. The panels 10 partially overlap here. The panels are thinner in their overlapping zones. That is, zone 103b of the first panel 10 is covered by zone 103a of the adjacent second panel 10. The adjacent second panel 10 overlaps the edge 10b of the first panel 10, and the first panel overlaps the edge 10a of the second panel 10. The reinforcing members 12 and frame divisions 14 of the second panel 10 cover zone 19 of the first panel 10. The extension 15 of the frame division 14 of the second panel 10 extends across zone 101 of the first panel and is positioned adjacent to the frame division 14 of the first panel at the extension. The extension 15 of the second panel 10 is assembled together with the frame section 14 of the first panel 10 by techniques known to themselves, such as overlapping, joggling, or splicing. Furthermore, the zone 16 of the first panel 10 is located within the extension of the zone 16 of the second panel 10.

[0049] The configuration described above can be applied to each pair of adjacent panels 10 that are juxtaposed to form a partitioned cylinder. Generally, the overlapping zone between adjacent panels can occupy at least 5%, for example, at least 30%, of the perimeter of the partitioned cylinder. The wider the overlapping zone, the better the mechanical properties of the resulting tank can be. In particular, when all the panels are assembled to form a partitioned cylinder, the joints of zone 16 form a 360° circumferential zone without any reinforcing elements. In addition, the joints of the frame divisions 14 of each panel define multiple 360° circumferential frames distributed along the length of the cylinder.

[0050] Figures 4 to 7 show different modified embodiments of the juxtaposition of panels 10 to form a segmented cylinder 100. The cylinder 100 extends along the X-axis with several panels juxtaposed around this axis.

[0051] In the modified embodiment shown in Figure 4, the cylinder 100 is formed by stacking all the panels 10 in a tile-like manner. That is, each of these panels has a first longitudinal edge 10b that overlaps (above) with a first adjacent panel, and a second longitudinal edge 10a that overlaps (below) with a second adjacent panel opposite to the first adjacent panel and opposite to the first adjacent panel. It is noteworthy that, in particular, the thickness of adjacent panels 10 is thinned across the overlapping zone ZR10 of the panels 10 in the direction of the longitudinal edges 10a, 10b of the panels 10.

[0052] In the modified embodiment shown in Figure 5, the panels are stacked in a tile-like fashion, except for panel 10 in the lower right of the figure, which overlaps with two adjacent panels.

[0053] The modified embodiments shown in Figures 6 and 7 illustrate cases where there is no overlap of the present invention.

[0054] The parts already described concern panels for forming the cylinder, which is a precursor to the tank body, and their arrangement. The remainder concerns a dome, which is a precursor to the bottom, intended to be fixed to the cylinder to limit the internal volume of the composite tank to be obtained.

[0055] The dome is a precursor to the bottom. Figure 8 shows petal-like portions 20 having the shape of a dome section formed by draping. In this example, each dome precursor is obtained by juxtaposing petal-like portions 20 of pre-impregnated thermosetting fibers. Generally, each dome may comprise at least two petal-like portions 20, or at least three more petal-like portions 20. The example described here concerns the case of a dome having four petal-like portions 20, each having four petal-like portions 20.

[0056] With respect to panel 10, the petal-shaped portions 20 are advantageously produced by automatic fiber arrangement. Each petal-shaped portion 20 comprises a fiber-reinforced member pre-impregnated with a thermosetting resin. The selection of the reinforcement and resin depends on the intended application. The reinforcement and resin of the petal-shaped portions 20 can be those described above for panel 10. Advantageously, the same resin as that of panel 10 is selected for the petal-shaped portions 20, or otherwise, a corresponding resin is selected. Similar to panel 10, the petal-shaped portions 20 can be draped on a male or female tool and in a draping form that is not an integral part of a vacuum forming tool.

[0057] With respect to panel 10, the petal-shaped portion 20 defines two edges 20a and 20b that extend along longitude, called longitudinal edges, and these edges are intended to overlap with several adjacent petal-shaped portions. The longitudinal edges 20a and 20b are intended to extend along the X-axis, which is the longitudinal axis of the cylinder 100 in the precursor assembly described later. The petal-shaped portion 20 defines two edges 20c and 20d that extend along latitude (or circumferential direction) that intersects with the edges 20a and 20b, respectively. Each edge 20c and 20d connects edge 20a to edge 20b. Edge 20c has a first curved length, and edge 20d has a second curved length that is greater than the first curved length.

[0058] In a similar manner to panel 10, as shown in Figure 2, the petal-like portion 20 has a thickness that varies between the edges 20a and 20b. Thus, the petal-like portion 20 has an intermediate zone 201 with substantially constant thickness and two lateral zones 203a and 203b, respectively, located on the sides of the respective edges 20a and 20b, which have varying thicknesses. Zone 203a is demarcated by the edge 20a and longitude 21, and zone 203b is demarcated by the edge 20b and longitude 23. Zone 201 is located between zones 203a and 203b, or between longitude 21 and longitude 23. The above description of zones 103a, 101 and 103b applies to zones 203a, 201 and 203b, respectively, and the relevant variations are made.

[0059] The petal-like portion 20 is intended to face the cylinder, which is a precursor of the main body, and defines a tubular joining zone section 203d that faces the joining zone 16 described above. Section 203d corresponds to a zone that is separated by the edge portion 20d and circumferentially divided by latitude 25. In the example described here and shown in Figure 10, the petal-like portion 20 has a thickness that decreases in the direction of the edge portion 20d in its section 203d.

[0060] The petal-like portions 20 are juxtaposed at their edges 20a, 20b so as to overlap between several adjacent petal-like portions, in a manner similar to that described above for panel 10. Thus, Figure 9 shows the positioning of the second petal-like portion 20 partially overlapping the first petal-like portion 20, and it is understood that in the example considered, the two other petal-like portions are juxtaposed to form a complete dome 200. Figure 11 schematically shows the juxtaposition of these four petal-like portions 20, where several adjacent petal-like portions 20 have a thickness e20 that decreases across their overlapping 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 latitude 25. The dome 200, and in particular zone 205, have an orbital shape. The joining of these sections 203d forms a 360° tubular joining zone 210 that extends zone 205 to the edge 20d. Figure 10 shows the decrease in the thickness e20 of the petal-like portion 20 (or dome 200) in section 203d or zone 210 in the direction of the edge 20d. Also, the change in the radius R of the dome 200 appears to be substantially constant across zone 210, with the radius R increasing precisely between the edge 20c and latitude 25. The radius R of the dome 200, measured from the edge 20d, can be 1 meter or more, for example, 2.5 meters or more.

[0062] It should also be noted that the petal-shaped portion 20 may be provided with reinforcing materials made of thermosetting composite material. The above description applies to these reinforcing materials in relation to the panel 10. Figure 13 below shows possible examples of these reinforcing materials.

[0063] Possible structures for cylinder 100 and dome 200 have been described. Their assembly and positioning in a vacuum forming tool are described below.

[0064] Assembly of vacuum forming tools, and positioning of precursor assemblies in these tools. Here, the kinematics of the vacuum forming tool 30 assembly and the positioning of the precursor assembly will be described in detail with reference to Figure 12. In this figure, as in Figure 14, not only the spacing between different elements but also the relative thicknesses are not strictly observed for the sake of readability.

[0065] First, the vacuum bag 34 is placed on the positioning section 32. The positioning section 32 is a much simpler design than the mandrel used in the prior art, as it is not used as a molding surface and does not need to be sealed. Therefore, it can be disassembled more easily. The positioning section 32 is supported by a shaft 36 that extends along the longitudinal axis, the X-axis. The X-axis corresponds to the longitudinal axis of the panel 10 and the cylinder 100 described above. The positioning section 32 may have an aerated structure, for example, a lattice structure, or it may have a plurality of retractable positioning elements fixed to the shaft. The positioning section 32 may generally have the shape of the tank to be obtained, as shown in the figure. The bag 34 covers the positioning section 32. The bag 34 is made of an elastomer material, which can be optionally reinforced and constitute a known element of its own.

[0066] Next, the petal-shaped portion 20 is positioned on the positioning portion 32 at its two opposing longitudinal ends 321 and 323. The petal-shaped portion 20 is then positioned side by side in the manner described above to form two dome precursors 200 at the opposite ends 321 and 323. The bottom zones 205 of the dome 200 each define an orifice 206, which in this case is in the shape of a disk through which the shaft 36 passes. The dome 200 may have a general rotational shape about the X-axis.

[0067] Next, the molded portions 38 are positioned. Each of these portions 38 has a dome shape and is shaped like the bottom of the tank to be obtained. The illustrated example shows two symmetrical portions 38, but of course, this does not exceed the scope of the invention. The domes 200 are located inside the internal volume defined between the portions 38. Each dome 200 is held in place by its respective portion 38. Each dome 200 is inserted between the portion 38 and the vacuum bag 34 (or portion 32). As shown, the portion 38 covers the bottom zone 205 but does not cover the tubular joining zone 210. Those skilled in the art will recognize that other modified embodiments are also possible. For example, the domes 200 can first be positioned on the portion 38, and then this assembly can be positioned on the ends 321, 323 of the positioning portion 32. The shaft 36 precisely positions the portions 38 and holds them in place. According to the modified embodiment, all petal-like parts are first draped on the dome tool, and the dome can then be semi-cured before being assembled on the positioning part 32 or part 38.

[0068] In the example shown in Figure 12, a second vacuum bag 35 and a third vacuum bag 35 are then positioned to form the front skirt and rear skirt, respectively, as described below. The second bag 35 and the third bag 35 may have the same properties as the first bag 34.

[0069] Next, the positioning ring 40 is positioned on the ends 361, 363 of the shaft 36, which define a cylindrical positioning surface 42 whose function is described below.

[0070] Next, the panel 10 is positioned and juxtaposed in the manner described above to form a cylinder 100, which is a precursor to the tank body. The cylinder 100 is positioned around the dome 200. In the illustrated example, the dome 200 is located inside the cylinder 100. The cylinder 100 extends from one dome 200 to the other. Generally, the length LO10 of the panel, 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. Length LC substantially corresponds to the length of the tank body to be obtained. In the illustrated example, the cylinder 100 extends beyond the dome 200, forming a front skirt precursor 110 and a rear skirt precursor 120, which are positioned opposite the second bag 35 and the third bag 35, respectively. 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 dome 200. Length LR substantially corresponds to the length of the composite tank to be obtained. However, the invention does not extend to cases where the cylinder does not form such a skirt by stopping at the dome 200.

[0071] Thus, after positioning panel 10, a precursor assembly of the tank to be manufactured is obtained, comprising a cylinder 100 and a dome 200, each located on the longitudinal end opposite to the cylinder 100. The dome 200 separates the internal volume V of the tank to be produced from the cylinder 100. The dome 200 closes the cylinder 100 on each side of its longitudinal end. The cylinder 100 and the dome are each made of a pre-impregnated thermosetting fibrous material. Panel 10 is positioned facing zone 210 so that its bottom can be fixed to the body during co-curing, which is described below. In particular, zone 210 faces zone 16 of panel 10, lacks reinforcing elements, and is as described above.

[0072] A precursor assembly can be formed by assembling the panel 10 and the dome 200 (or petal-shaped part 20) in a semi-cured state. The panel 10 and the dome 200 can each be draped in a semi-cured state during their manufacture, or they can be draped in an unprocessed state, i.e., a state with a lower degree of polymerization than semi-cured, and then subjected to partial polymerization heat treatment to reach a semi-cured state. The dome 200 (or petal-shaped part 20) and the panel 10 can be assembled after this partial polymerization.

[0073] Next, the molded portion 60 of the tank body is positioned, which is the shape of the tank body to be obtained and surrounds the cylinder 100 along its entire length. The cylinder 100 is located inside the molded portion 60. This molded portion 60 is located around the cylinder 100. This molded portion 60 makes it possible to hold the panel 10 in place. It can be assumed that the panel 10 is indexed onto the portion 60. Similar to the panel 10, the portion 60 can be segmented and formed by several segments assembled together to form a 360° molded portion. As shown in the figure, the portion 60 extends from one ring 40 to the other ring 40. The portion 60 is positioned on the positioning surface 42 to avoid having to support the weight of this external tool on the panel 10. Despite its considerable length, the portion 60 has high rigidity without bending and thus may be equipped with reinforcing materials (not shown) on the surface facing the panel 10 to maintain the same shape. The inner surface S1 of the precursor assembly is located on the side of the bag 34 (and separates the internal volume portion V of the tank), and the outer surface S2 of the assembly is located on the side of portions 38 and 60.

[0074] Figure 13 shows details relating to the reinforcing members 12 of panel 10 and the reinforcing members 202 of the assembled dome 200. The reinforcing members 202 here have a curved shape that follows the respective longitudes of the dome 200. The reinforcing members 202 and 12 are located on the surface of the precursor assembly opposite to sections 38, 60. In the illustrated example, when the cylinder 100 is assembled with the dome 200, the reinforcing members 202 extend beyond the dome 200 along the panel. The reinforcing member 202 is joined to the reinforcing member 12 in the joining zone 212 by techniques known to the present invention, such as edge-to-edge joining, jogging, and splicing. The invention is not limited to cases where the dome reinforcing members do not extend beyond zone 210, or where the dome lacks reinforcing members.

[0075] Next, a seal 52 is created between the bags 34 and 35 and the molded parts 38 and 60.

[0076] The precursor assembly is therefore positioned within the vacuum forming tool 30. In particular, the cylinder 100 is interposed between the bag 34 and the forming portion 60, and each dome 200 is interposed between the bag 34 and the respective forming portion 38. This positioning portion 32 is located inside the precursor assembly, i.e., inside the internal volume V of the tank to be obtained. The assemblies of the forming portions 60 and 38 are located outside this internal volume and form the outer portion of the assembly for forming the tank.

[0077] Vacuum curing and disassembly of precursor assemblies within tools The vacuum curing stage is shown in Figure 14, and this curing stage can be performed with or without additional pressure.

[0078] The applied heat fluidizes the present resin(s). When tool 30 is placed under vacuum, bag 34 is pressed against cylinder 100 and dome 200 so as to press the dome against sections 38, 60 and conform them to the desired shape. The dome 200 is pressed against panel 10 by slight relative displacement / spacing of petal-like sections 20, which is made possible by the low viscosity of the resin with respect to temperature and creep between some of the petal-like sections. During assembly with panel 10, under the influence of temperature and pressure, some of the petal-like sections 20 move away to conform to the inner surface of the panel. Essentially, this is the zone 210 that bonds with panel 100. Bag 35 applies pressure to skirt precursors 110 and 120.

[0079] Once all the components are in place, heating completes the polymerization process, which involves the formation of bonds in the polymer chains (creation of a three-dimensional network), and the interface and overall shape of the tank structure freeze. Polymerization of the thermosetting material is completed after the co-curing stage.

[0080] Vacuum curing can be performed in a heated chamber such as an oven or autoclave. An oven allows for vacuum polymerization, while an autoclave provides additional pressure beyond the vacuum. In a modified embodiment, or in combination, this curing can be performed using a molding tool equipped with a heating element (not shown). The temperature imposed during vacuum curing depends on the resin used and can be, for example, 150°C or higher, and can range from, for example, between 175°C and 185°C, and is close to 180°C.

[0081] A tool 30 made of a composite material can be used to reduce the phenomenon of differential expansion between the tool and the tank. In a modified embodiment, the tool 30 may be made of metal, such as Invar or steel. In the case of steel, it may be advantageous to minimize stress during cooling, for example, by breaking the vacuum in the vacuum bag at the end of the polymerization stage, or by providing a partial opening in part 60.

[0082] Next, the tool 30 is disassembled, which is facilitated by the positioning of the molded outer part of the tank and the simplified design of the inner part.

[0083] The tank 1 described above has a front skirt 1100 and a rear skirt 1200 that extends the main body 1000 beyond the bottom 2000. The skirts 1100 and 1200 are one piece with the rest of the tank 1. Figure 15 shows a modified embodiment relating to the use of the donut-shaped (toroidal) section described here, which gives the dome an additional joint on the skirt side.

[0084] Therefore, it is understood that the dome 200 in Figure 15 defines a second cylindrical junction zone 310 facing the skirt precursor 120, and a similar structure exists on the side of the skirt precursor 110. The second zone 310 is located on the opposite side from the first zone 210. The first zone 210 demarcates the internal volume V of the tank to be obtained, and the second zone 310 extends outside this internal volume V.

[0085] The second zone 310 is defined by a donut-shaped portion 300 attached to zone 205. More specifically, the donut-shaped portion 300 has a zone 305 for joining a dome 200 that takes the shape of zone 205 and is integrated with this zone, zone 310 faces the skirt precursor 120, and a folded intermediate zone 307 connects zone 305 to zone 310.

[0086] Several donut-shaped sections 300 are manufactured separately. Similar to the base section 200, the donut-shaped sections 300 may consist of several juxtaposed sections formed from a partially overlapping, pre-impregnated thermosetting fibrous material. The donut-shaped sections 300 can be manufactured by automated fiber placement, or manually if the "fold" radius is too small to be produced by AFP draping. Advantageously, the donut-shaped sections 300 are semi-cured after draping and before assembly of the base section 200 and panel 10.

[0087] The donut-shaped portion 300 is positioned on the bottom portion 200 once its bottom portion is positioned on the positioning portion 32. Then, once portion 38 is positioned in a predetermined position, it is positioned to have a shape that conforms to the presence of the donut-shaped portion 300. In a modified embodiment, the donut-shaped portion 300 is first positioned on portion 38, then the bottom portion 200 is positioned on portion 38, and the assembly is positioned on the positioning portion 32.

[0088] The donut-shaped portion 300 may or may not be reinforced. The reinforcing material may be as described above and is placed inside the tool before draping.

[0089] The space 250 between the dome 200 and the donut-shaped portion 300 can be filled with a filler material, which optionally contains fibers.

[0090] At the bottom of the tank, during vacuum curing, the donut-shaped portion softens due to the effect of temperature (decrease in resin viscosity). Then, under the effect of pressure, when applied by bag 35, the diameter of the torus increases slightly (relative spacing of the torus segments), allowing it to conform to the inner surface of the panel. Once completely polymerized, the donut-shaped portion becomes integrated with the bottom and panel, ensuring connections to the front and rear skirts of the bottom.

[0091] The present invention described above is particularly suited to the manufacture of tanks of considerable or very considerable length, which may be encountered in the case of tanks for the main stage (lower stage) of a space launcher, or tanks for the powder accelerator stage (booster). The present invention also applies to upper stage tanks. In operation, the composite material tank may be filled with liquid methane, liquid hydrogen, or liquid oxygen, or a combination of these compounds. The tank can be used in cryogenic environments.

[0092] However, the field of the present invention is not limited to tanks for integration into aerospace launch vehicles, but can find applications in the aerospace field, or more generally, in any application requiring a large tank.

[0093] The expression "comprised between ... and ..." should be understood as having a boundary.

Claims

1. In a method for manufacturing a tank (1) made of composite material, The aforementioned method, Positioning a precursor assembly of a tank to be manufactured in a vacuum forming tool (30), wherein the precursor assembly is made of a pre-impregnated thermosetting fibrous material and comprises: (i) a segmented cylinder (100) which is a precursor of the tank body (1000), the cylinder (100) being formed by several panels (10) arranged around the longitudinal axis so as to extend along a longitudinal axis (X) and overlapping between several adjacent panels; and (ii) two domes (200) which are precursors of the tank bottom (2000), each of which is located on the side of the opposite longitudinal end of the cylinder, the two domes being separated by the volume (V) of the tank to be obtained, and each dome being a segmented cylinder (200) which defines a cylindrical joining zone (210) facing the cylinder and inside the cylinder. The vacuum forming tool comprises an inner portion (32) lined with a vacuum bag (34) located within the internal volume portion in which the precursor assembly is positioned, and an outer forming portion located outside the internal volume portion, wherein the vacuum forming tool comprises (a) a forming portion (60) of a cylindrical tank body facing the cylinder which is the precursor, and (b) a forming portion (38) of a dome-shaped tank bottom facing the dome which is the precursor of a distinct bottom, A method for obtaining a tank made of composite material, in which, while the vacuum bag applies pressure to shape the assembly on the molded portion, the assembly is vacuum-cured within the vacuum forming tool, the bonding zone in contact with the precursor cylinder is held, and the two domes and the cylinder are co-cured together, thereby fixing the bottom to the tank body.

2. The method according to claim 1, wherein several adjacent panels (10) have thinner portions (e10) in the direction of their longitudinal edges (10a, 10b) on their overlapping zone (ZR).

3. The method according to claim 1 or 2, wherein the precursor dome (200) has a thinner portion (e20) on a cylindrical bonding zone (210) toward the circumferential edge (20d) of the dome.

4. The method according to any one of claims 1 to 3, wherein the precursor dome (200) is divided and formed by several petal-like parts (20) arranged around the longitudinal axis (X) so as to overlap between several adjacent petal-like parts.

5. The method according to claim 4, wherein several adjacent petal-like portions (20) have thinner portions (e20) on their overlapping zone (ZR20) in the direction of their longitudinal edges (20a, 20b).

6. The method according to any one of claims 1 to 5, wherein the panel (10) and the dome (200) are assembled in a semi-cured state to form a precursor assembly.

7. The method according to any one of claims 1 to 6, wherein the panel (10) and the dome (200) each have a plurality of reinforcing members (12; 202) on the surface facing the molded portion (38; 60).

8. The method according to any one of claims 1 to 7, further comprising forming the panel (10) and dome (200), which are draped in a different manner from the internal positioning section (32), by automatic fiber arrangement before positioning the precursor assembly within the vacuum forming tool (30).

9. The method according to any one of claims 1 to 8, wherein the cylinder (100) extends beyond each of the dome (200) to define a front skirt precursor (110) and a rear skirt precursor (120).

10. The method according to claim 9, wherein each of the domes (200) defines a second tubular bonding zone (310) that faces each of the skirt precursors (110;120) and is fixed to each of the skirt precursors (110;120) during vacuum curing.

11. The method according to any one of claims 1 to 10, wherein the panel (10) and the dome (200) comprise carbon fiber, glass fiber, aramid fiber, or a mixture of the carbon fiber, glass fiber, or aramid fiber.

12. The method according to any one of claims 1 to 11, wherein the panel (10) and the dome (200) are pre-impregnated with epoxy resin.

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