FR3153015A1 - Manufacturing process of a composite material tank with simplified molding tooling - Google Patents

Abstract

Method for manufacturing a composite tank with simplified molding tooling The present invention relates to a method for manufacturing a composite tank in which an assembly comprising precursor base domes equipped with thermoset reinforcement is implemented so as to simplify the molding tooling. Figure for abstract: Fig. 1.

Description

Manufacturing process for a composite material tank with simplified molding tooling

This description relates to a method for manufacturing a composite material tank using simplified molding tooling to create the ends of the tank. The invention is of particular interest for the manufacture of tanks intended for use on space launch vehicles, although its applications are not limited to this.

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

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

In current manufacturing techniques for composite material tanks, the part is draped onto a rotating mandrel, either by winding or by automated fiber placement (AFP). However, the implementation of these techniques can prove to be relatively complex.

The mandrels must be removable and extractable through small openings in the tank ends. Disassembly can be a delicate operation, with the associated risk of damage to the composite structure (impacts can cause structural damage). This will generate significant costs because complex, specialized tooling must be designed for disassembly through these small openings. Furthermore, in some cases, it is necessary to position a vacuum bag around the part draped over the mandrel and perform vacuum curing. It is then essential to ensure a seal between the various components of the removable mandrel to prevent any impact on the material's integrity.

It is also desirable to reduce the manufacturing cycle time since the draping tooling also serves as polymerization tooling, which requires waiting for the end of this step and the dismantling of the structure before draping can be done again.

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.

It is therefore desirable to have a manufacturing process for a composite material tank that uses simplified tooling and addresses all or part of the aforementioned drawbacks.

This presentation concerns a manufacturing process for a tank made of composite material, comprising:
- the positioning of a precursor assembly of the tank to be manufactured in a vacuum molding tool,
the assembly comprising (i) a cylinder, precursor of the tank body, made of thermosetting pre-impregnated fibrous material extending along a longitudinal axis, and (ii) two domes, precursors of the tank bottom, each of these domes being located on the side of an opposite longitudinal end of the cylinder, each of the domes having an internal surface which delimits with the cylinder an internal volume of the tank to be obtained and an external surface located outside the internal volume, each of the domes comprising a reinforcement made of thermosetting composite material, defining a tank bottom, covered by at least one thermosetting pre-impregnated fibrous skin defining a cylindrical junction zone positioned opposite and inside the cylinder, the reinforcement being configured to allow conformation of said at least one skin against the cylinder on this cylindrical junction zone,
the tooling comprising an internal positioning part lined with an internal vacuum bag, located inside the internal volume, on which the assembly is positioned, and an external molding part, located outside the internal volume, comprising a molded portion of the tank body having a cylindrical shape situated opposite the precursor cylinder, each external surface of the domes being hermetically sealed by an external vacuum bag, and
- vacuum curing of the assembly in the tooling during which the internal vacuum bag applies pressure to conform the assembly to the molding portion, with the junction areas held in contact with the precursor cylinder and co-curing of the domes and the cylinder to bond the bottoms to the body and obtain the tank in composite material.

Co-curing allows the thermosetting resin impregnating the cylinder to polymerize with the resin impregnating at least one layer of the domes, creating covalent bonds between the polymer chains present. This joint polymerization leads to bonding the ends to the body of the composite tank, without requiring the addition of a third-party adhesive. However, the invention remains within the scope of this method if a third-party adhesive is used at the interfaces between the components of the ends and the body, or at the interfaces between the ends and the body, in order to provide additional mechanical strength. Examples of adhesives include: FM® adhesive films marketed by SOLVAY, for example: FM300, FM309-1, FM377, FM209-1; HexBond® adhesive films marketed by HEXCEL, for example: HexBond 322, HexBond 319, HexBond 340, HexBond ST1480; or adhesive films marketed by 3M, for example AF191 or AF3109-2.

The reinforcement is a thermoset composite material, meaning its matrix has been fully polymerized to give the domes sufficient rigidity to maintain the desired geometry of the tank ends during manufacturing, particularly during vacuum curing. The reinforcement also eliminates the need for molding tools on the domes during tank production, thus keeping the tooling structure relatively simple. However, each dome remains sufficiently deformable at its respective cylindrical junction zone to allow for expansion or deformation of at least one skin, ensuring a secure bond between the end and the cylinder. As will be described later, the reinforcement can have various structures to fulfill this function.

In the invention, the molding portion is external to the precursor assembly, and therefore to the resulting composite tank. This external positioning facilitates disassembly compared to the internal molding mandrel of the prior art and makes it easier to guarantee the seal required for vacuuming. Unlike the mandrel of the prior art, the internal portion in the invention serves only a positioning function and not a molding function, and therefore has a much simpler design and is easier to disassemble.

In the following and unless otherwise stated, the word "skin(s)" refers to said at least one pre-impregnated thermosetting fibrous skin which is present within each of the domes.

In one embodiment, the cylinder extends beyond each of the two domes so as to define skirt precursors, and in which each dome comprises a first skin covering a first face of the armature and defining a first part of the cylindrical junction zone which extends towards the other dome, and a second skin covering a second face of the armature, opposite to the first face, and defining a second part of the cylindrical junction zone which extends in a direction opposite to said other dome, the second part of the cylindrical junction zone of each dome being attached to a respective skirt precursor during vacuum cooking.

This feature further improves the conformation of the cylinder's ends, thus enhancing the quality of the connection to the body and reducing the risk of misalignment. Extending the cylinder to form skirts is particularly advantageous for a tank intended for use on an aerospace launch vehicle, as it allows for seamless integration of the skirts with the tank, thereby simplifying the construction of a complete launch vehicle stage.

In particular, each dome may further include a filling material between the first and second parts of the cylindrical junction zone.

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

In one embodiment, the cylindrical junction zone of each dome is at least partly formed by an extension of said at least one skin beyond the framework.

Such a characteristic corresponds to a possibility of providing flexibility on the cylindrical junction zone by implementing a reinforcement that stops sufficiently early upstream of it.

In one example of an embodiment, the framework of each dome defines a plurality of flexible tabs allowing the conformation of said at least one skin against the cylinder on the cylindrical junction area.

These tabs are flexible enough not to hinder the shaping during sous vide cooking. This arrangement remains functional even if the frame is longer than in the previously described example, due to the presence of a flexible circumferential zone on the side of the cylindrical junction area.

In one embodiment, said at least one skin of each dome has a thinning of thickness on the cylindrical junction area in the direction of a circumferential edge thereof.

This feature advantageously prevents any risk of the tank bridging over any unevenness during vacuum cooking, and further improves the material integrity of the skin, cylinder, and skin/cylinder interface. An unevenness refers to a local surface bump, meaning the surface is not smooth and the ends of the assembled parts form a step. Furthermore, this feature minimizes stress concentrations (at the bottom seam) when the tank is subjected to mechanical stresses (filling, thermal stresses, pressurization, forces applied during takeoff and potential return to Earth, etc.).

In one example of implementation, each skin comprises several sectors juxtaposed around the longitudinal axis.

In this example, each dome is sectorized and comprises several skin sectors distributed along a circumferential direction. Sectorization further improves conformity to the cylinder by allowing the sectors to conform through relative sliding and to assemble with the cylinder without constraint.

In particular, neighboring sectors may exhibit a thinning of thickness in their overlap zone towards their longitudinal edges.

Thinning the thickness helps to avoid local thickness jumps and to further minimize outcrops and stress concentrations.

In one embodiment example, the cylinder and said at least one skin of each dome are assembled in a semi-baked state to form the precursor assembly.

A semi-cured thermosetting material has a partially polymerized resin with a degree of polymerization between 15% and 70%, for example between 25% and 50%. For a given resin, the degree of polymerization can be determined by Differential Scanning Calorimetry (DSC).

A semi-cured material exhibits a certain rigidity at room temperature (20°C), which facilitates handling and simplifies tooling. Its use also reduces constraints related to the material's ambient shelf life, as the polymerization of a semi-cured material changes very little at room temperature. The resin in a semi-cured material regains fluidity when the material is reheated during vacuum curing, allowing the components to soften and conform to the molded portion through relative sliding.

In one embodiment, the process further includes, prior to positioning the precursor assembly in the molding tooling, the formation of the cylinder and said at least one skin of each of the domes by automatic placement of fibers on a distinct form of the internal positioning part.

This technique allows access to a wide variety of geometries, particularly compared to winding, which does not permit draping along the longitudinal axis or the automated draping of localized thicknesses or reinforcements. Automated fiber placement also enables the production of low-permeability components compared to parts obtained by winding, making them suitable, for example, for the storage of cryogenic propellants. Furthermore, the draping tooling is separate from the polymerization tooling, thus reducing the manufacturing cycle time.

In one embodiment, the cylinder and domes comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

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

In one embodiment example, the cylinder 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 approximately 180°C.

This material is particularly suited to space launcher applications and cryogenic environments, and can be easily reworked after partial polymerization.

In one embodiment, the assembly further comprises (iii) a common base precursor located inside the cylinder and between the domes so as to define with each of them a compartment distinct from the internal volume, said common base precursor comprising a common base reinforcement of thermosetting composite material, defining the common base, covered by at least one common base fibrous skin which is pre-impregnated and thermosetting and which defines an intermediate cylindrical junction zone positioned opposite the cylinder, the common base reinforcement being configured to permit a conformation of said at least one common base skin against the cylinder on this intermediate cylindrical junction zone, and wherein there is co-cooking of the common base precursor with the cylinder to bond the common base to the body during vacuum cooking.

In one embodiment, the cylinder, the precursor to the tank body, is segmented and formed by panels placed side by side around the longitudinal axis with overlapping panels. If necessary, the molded portion of the body can be stiffened on its face opposite the assembly to maintain its shape despite its length, without affecting the molding quality or its disassembly.

Forming the cylinder from a plurality of panels simplifies its manufacture when a long cylinder is required.

In particular, neighboring panels may exhibit a thinning of thickness in their overlap area towards their longitudinal edges.

This characteristic helps to further minimize outcrops and stress concentrations in the reservoir.

In one embodiment example, the panels and domes each include a plurality of stiffeners on a face opposite the molding portion.

The external nature of the molding tooling 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 achieve using prior art techniques employing an internal molding mandrel.

Brief description of the drawings
FIG. 1 There FIG. 1 represents, schematically in perspective, an example of a panel that can be used within the framework of the invention to form the cylinder.
FIG. 2 There FIG. 2 represents, schematically and partially, a cross-section of the panel of the FIG. 1 relative to its longitudinal axis.
FIG. 2 There FIG. 2 represents, schematically and partially, the bevel angle of the panel of the FIG. 2 .
FIG. 3 There FIG. 3 represents, schematically in perspective, the overlap of two adjacent panels according to an example of implementation of the invention.
FIG. 4 There FIG. 4 represents, schematically and partially, a variant of a cylinder.
FIG. 5 There FIG. 5 represents, schematically and partially, another variant of the cylinder.
FIG. 6 There FIG. 6 represents, schematically and partially, another variant of the cylinder.
FIG. 7 There FIG. 7 represents, schematically and partially, another variant of the cylinder.
FIG. 8 There FIG. 8 represents, schematically and partially, a cross-sectional view of an example of a dome in a plane containing its axis of revolution.
FIG. 9 There FIG. 9 represents a sector of a first skin intended to be part of the dome of the FIG. 8 .
FIG. 10 There FIG. 10 represents the juxtaposition of several sectors according to the FIG. 9 as part of the dome manufacturing process FIG. 8 .
FIG. 11 There FIG. 11 represents, schematically and partially, a cross-sectional view of a dome variant in a plane containing its axis of revolution.
FIG. 12 There FIG. 12 represents, schematically and partially, a cross-sectional view of another dome variant in a plane containing its axis of revolution.
FIG. 13 There FIG. 13 represents, schematically and partially, a cross-sectional view of another dome variant in a plane containing its axis of revolution.
FIG. 14 There FIG. 14 represents, schematically and partially, a cross-sectional view of another dome variant in a plane containing its axis of revolution.
FIG. 15 There FIG. 15 represents, schematically and partially, a precursor assembly of the tank to be manufactured positioned in a vacuum molding tooling as part of an example of implementation of the invention.
FIG. 16 There FIG. 16 represents, schematically, the vacuum cooking of the assembly illustrated in the FIG. 15 .

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

The examples that will be described below, in connection with the figures, concern an example where a compartmentalized tank is manufactured including a common bottom, but a person skilled in the art will recognize that the invention is not limited to this case and that it can in particular be applied to the manufacture of a non-compartmentalized tank, without a common bottom.

The description below first addresses the structure and production of the precursor cylinder for the body, then the precursor domes for the base. The details of the vacuum molding tooling, inside which the precursor assembly is positioned, as well as the vacuum curing phase, will be detailed later.

Cylinder precursor of the body

The example described here concerns a segmented cylinder obtained by juxtaposing thermosetting pre-impregnated fiber panels, but the invention remains within the scope of this case when the cylinder is formed in a single piece. In this latter case, the cylinder does not contain a continuous circumferential fiber that would impede the increase in diameter, or it comprises segmented circumferential fibers. The circumferential direction corresponds to the direction around the axis of the cylinder, designated as the "X-axis" hereafter.

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

The panels are advantageously manufactured by automated fiber placement, a well-established technique. Each panel comprises a fibrous reinforcement pre-impregnated with a thermosetting resin. The choice of reinforcement material and resin depends on the intended application. For example, the fibrous reinforcement may include carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers. For example, the resin may be an epoxy resin, such as one based on a DGEBA (diglycidyl bisphenol A ether), TGPAP (triglycidyl paraaminophenol), or TGMDA (tetraglycidyl methylenedianiline) monomer, to which an amine-type hardener, such as DDS (diaminodiphenyl sulfone), may optionally be added. The same resin is advantageously used in the different panels, or, failing that, compatible resins.

The panels 10 have an elongated shape along a longitudinal axis X and a curved shape in cross-section with respect to the X axis. The panels 10 define two longitudinal edges 10a, 10b which are intended to overlap with a neighboring panel, as will be described later. FIG. 1 This illustrates an example of a possible structure for the panels 10, which are draped in a female tooling. Those skilled in the art will recognize that the panels can alternatively be draped over a male tooling without departing from the scope of the present invention. The draping form is not an integral part of the vacuum molding tooling, thus allowing for parallel operation between draping and curing, thereby reducing the manufacturing cycle time.

The 10 panels are, in the example of the FIG. 1 , equipped 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-forming of raw flat plates, production of dry preforms, and injection of resin into a mold using a resin transfer molding (RTM) technique. The stiffeners 12 can have any cross-section, for example, Omega, T, J, among other possible shapes. The stiffeners 12 may or may not exhibit local variations in shape or cross-section. As illustrated, the stiffeners 12 can be present over at least the majority (more than 50%) of the LO10 length of the panels 10. The panels 10 nevertheless have areas devoid of stiffening elements, which will be described later.

The illustrated panels 10 are also fitted 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 can have any cross-section, for example, Z, C, F, T, Omega, or J.

The stiffeners 12 and frame sectors 14 may be partially cured, or exhibit complete polymerization, or little or no advanced polymerization.

The panels 10 have circumferential zones 16, intended for attachment to the domes, which are unreinforced. Each zone 16 is located on the opposite longitudinal end of the panel 10. As will be detailed below, the domes will be attached to the tank body at these zones 16. The panels 10 also have an intermediate circumferential zone 16a, intended for attachment to the common bottom in the example considered here, which is also unreinforced. If the manufactured tank does not have a common bottom, there is no zone 16a, but the stiffeners 12 extend into this zone, and the frame sections 14 are also present. Zone 16a is located between zones 16 and interrupts zone 18, which is equipped with stiffeners 12. The panels 10 also have a longitudinal zone 19, located on the side of the longitudinal edge 10b and extending along their entire length LO10, which is devoid of any stiffening element. It should also be noted that, in the illustrated example, the frame sectors 14 extend beyond panel 10 on the side opposite zone 19 (the side of edge 10a), forming an extension 15 of the frame sectors 14. The presence of zone 19 and the extension of the frames 14 result from the arrangement intended for the overlap between adjacent panels 10.

There FIG. 2 This shows the evolution of the thickness e10 of the panels 10 across their width (the dimension between edges 10a and 10b). The panels 10 have a central zone 101 across their width where the thickness e10 is essentially constant, and two lateral zones 103a and 103b, each located on the side of a respective longitudinal edge 10a and 10b, which exhibit a changing thickness. 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 exhibit a thinning of thickness towards their associated longitudinal edge 10a and 10b. The thickness e10 can be strictly decreasing towards the longitudinal edge 10a and 10b. The thickness e10 is minimal at edges 10a and 10b and maximal in the median zone 101. The panels 10 have a bevel at their edges 10a and 10b. In cross-section with respect to the X-axis, the panels 10 have a tapered shape towards their edges 10a and 10b. Zones 103a and 103b together occupy at least 5%, for example, at least 50%, of the width LA10 of the panel 10. Unless otherwise specified, the width LA10 corresponds to the length of the arc connecting edge 10a to edge 10b. The thinning of the thickness leads to a reduction in the thickness e10 of at least 50%, for example, at least 90%. This reduction in the thickness e10 is, for example, between 50% and 95%, or even between 90% and 95%. The FIG. 2 schematically represents a thinning of the thickness of the panel 10 towards a longitudinal edge 10b linked to the presence of a decreasing quantity of superimposed plies PS towards the edge 10b. The bevel angle α, 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 stresses.

The panels 10 described above include stiffening elements, but their absence does not depart from the scope of the invention. The following section describes, with reference to Figures 3 to 7, the juxtaposition of these panels 10 to form the cylinder 100, which, in the example considered, is the precursor to the tank body as well as to the front and rear skirts that extend beyond the bottoms formed by the domes.

There FIG. 3 This illustrates the juxtaposition of two adjacent panels 10 around the X-axis. The two panels 10 shown have the same structure, and the same references are maintained with respect to what has just been described. The panels 10 partially overlap here. The panels exhibit a thinning of thickness at their overlapping area; that is, area 103b of the first panel 10 is covered by area 103a of the second adjacent panel 10. Edge 10b of the first panel 10 is superimposed on the second adjacent panel 10, and edge 10a of the second panel 10 is superimposed on the first panel. The stiffeners 12 and frame sectors 14 of the second panel 10 overlap area 19 of the first panel 10. The extension 15 of the frame sectors 14 of the second panel 10 extends into 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 joined to the frame sectors 14 of the first panel 10 using techniques known per se, for example, by lap, splicing, or joining. Furthermore, the areas 16 of the first panel 10 are in line with the areas 16 of the second panel 10, and area 16a of the first panel 10 is in line with area 16a of the second panel 10.

The arrangement just described can be applied to each pair of adjacent panels 10 placed side-by-side to form the sectorized cylinder. Generally, the overlap areas between adjacent panels can occupy at least 5%, for example, at least 30% of the perimeter of the sectorized cylinder. Having these overlap areas further improves the mechanical properties of the resulting tank. In particular, when all the panels are assembled to form the sectorized cylinder, the combined areas 16 form a 360° circumferential zone without any stiffening elements. Furthermore, the combined frame sectors 14 of each panel define a plurality of 360° circumferential frames distributed along the length of the cylinder.

Figures 4 to 7 show different variations of juxtaposing the panels 10 to form the sectorized cylinder 100. The cylinder 100 extends along the X axis with panels juxtaposed around this axis.

In the variant of the FIG. 4 The cylinder 100 is formed by overlapping all the panels 10, meaning that each panel has a first longitudinal edge 10b overlapping (above) a first neighboring panel, and a second longitudinal edge 10a, opposite the first edge 10b, overlapped (below) by a second neighboring panel, opposite the first neighboring panel. Note in particular the thinning of the thickness of the neighboring panels 10 in their overlapping zone ZR10 towards their longitudinal edges 10a, 10b.

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

The variants in figures 6 and 7 show cases where there is no tiling which are also covered by the present invention.

The section just described concerns the panels and their juxtaposition to form the precursor cylinder of the body. The following section concerns the precursor domes of the base, which are intended to be attached to the cylinder to define the internal volume of the composite material tank to be produced.

Precursor domes of the background

There FIG. 8 illustrates an example of a 300 dome, a precursor to a tank bottom, intended to be positioned at one longitudinal end of the cylinder as will be illustrated in connection with the FIG. 15 The dome 300 comprises a 302 reinforcement made of thermosetting composite material. The 302 reinforcement thus includes a fibrous reinforcement densified by an organic matrix obtained after polymerization of a thermosetting resin. The resin of the 302 reinforcement is completely polymerized.

The dome 300 example under consideration includes a thermosetting pre-impregnated fibrous skin on each face of the frame 302. Each skin is formed by a juxtaposition of sectors 304, 306 around the X-axis. The skins or sectors 304, 306 can be produced by automated fiber placement. Each skin or sector 304, 306 comprises a fibrous reinforcement pre-impregnated with a thermosetting resin. The example under consideration includes first sectors 304 that cover a first face 3024 of the reinforcement 302, and second sectors 306 that cover a second face 3026 of the reinforcement 302 opposite the first face 3024. The first sectors 304 are circumferentially juxtaposed, as are the second sectors 306. The reinforcement 302 is housed between the first 304 and second 306 sectors. The reinforcement 302 includes an internal circumferential edge 3021 adapted to cooperate with the tooling to position the precursor 300, and an external circumferential edge 3023 intended to be positioned on the side of the cylinder 100 in the assembly. The cooperation between the internal circumferential edge of the reinforcement and the tooling will be described later.

The following section details a possible draping method to obtain the 300 dome.

Sectors 304, 306 can be draped onto a male or female tooling, and onto a draping form not forming an integral part of the vacuum molding tooling.

In the example considered, the second sectors 306, which have a more complex shape, can first be draped, then the reinforcement 302 can be positioned on the draped second sectors 306, and then the first sectors 304 can be draped over the resulting assembly to obtain the dome 300. The reinforcement 302 has been fully polymerized beforehand, prior to its assembly with the sectors 304 and 306. An adhesive film can be positioned at the interfaces between the reinforcement 302 and the sectors 304 and 306. The first face 3024 of the reinforcement 302 is covered over 360° by the first sectors 304, and the second face 3026 of the reinforcement 302 is covered over 360° by the second sectors 306. Figures 9 and 10, which will be described below, detail the draping of the first sectors 304, it being understood that the draping of the second sectors 306 is made in a similar way.

The sectors 304 each define two edges 304a1, 304b1, each extending along a longitude, called longitudinal edges, which are intended to be superimposed with a neighboring sector. The edges 304a1, 304b1 are intended to extend along the longitudinal X-axis of the cylinder 100 in the precursor assembly that will be described below. The sectors 304 define two edges 304c1, 304d1, each extending along a latitude (or circumferential edges), which are transverse to the edges 304a1, 304b1. Each of the edges 304c1, 304d1 connects the edge 304a1 to the edge 304b1. The edge 304c1 has a first curvilinear length, and the edge 304d1 has a second curvilinear length that is greater than the first curvilinear length.

The sectors 304 exhibit a changing thickness between the edges 304a1 and 304b1. The sectors 304 thus have a median zone 3041 where the thickness is substantially constant, and two lateral zones 3043a and 3043b each located on the side of an edge 304a1, 304b1 respectively which exhibit a changing thickness. Zone 3043a is bounded by boundary 304a1 and longitude 305, and zone 3043b by boundary 304b1 and longitude 307. Zone 3041 is located between zones 3043a and 3043b, or between longitudes 305 and 307. The description provided above relating to zones 103a, 101 and 103b applies respectively to zones 3043a, 3041 and 3043b mutatis mutandis .

The sectors 304 define a sector 3043d of a portion 311 of the intermediate cylindrical junction zone 310, which is intended to be positioned opposite the precursor cylinder of the body, and more specifically opposite a berthing zone 16 described above. The sector 3043d corresponds to a circumferential zone delimited by the edge 304d1 and by a latitude 309. The sectors 304 may exhibit a thinning of thickness in the sector 3043d towards the edge 304d1.

The 304 sectors are juxtaposed at their edges 304a1, 304b1 with overlap between neighboring sectors. Thus, the FIG. 10 represents the positioning of an additional sector 304 partially overlapping the initial sector 304, it being understood that two other sectors are juxtaposed to form the first skin. The sectors 304 are thus juxtaposed circumferentially.

As mentioned above, the draping of the second sectors 306 is done in a similar manner to that of the first sectors 304. It should be noted however that, in the illustrated example, the second sectors 306 are folded back on the side of the edge 3023 of the frame 302 so as to form a second part 312 of the zone 310. The second part 312 extends in a direction opposite to the direction of extension of the first part 311. The part 312 is also intended to come opposite the precursor cylinder of the body, opposite one of the berthing zones 16.

Generally, sectors can be draped over the armature in their raw state with a raw pre-impregnated clay, or in a semi-fired state with a pre-impregnated clay that has been partially fired before draping. When draped in a semi-fired state, a single-layer architecture of sectors can be preferred, draped directly over the armature, or a two-layer architecture with the two layers joined beyond the armature.

In the example of the FIG. 8 The skins each extend beyond the reinforcement 302 (beyond the end 3023) so as to define the first 311 and second 312 parts of the cylindrical junction zone 310. More precisely, the skins are directly assembled beyond the end 3023 on an assembly region 308 up to a separating edge 305, from which they separate to define the first 311 and second 312 parts. This separation defines a space that can be filled by a filler material 320 distinct from the skins. The material 320 is present between the first 311 and second 312 parts. The material 320 can be chosen from: cellular materials, including foam cores and honeycombs. Foams can be from the PU (Polyurethane), PVC (Polyvinyl Chloride), PMI (Polymethacrylate Imide), PEI (Polyether Imide), and PAI (Polyamide Imide) families; PAEK (PolyArenyl Ether Ketone) foams such as PEEK (PolyetherEtherKetone) and PEKK (PolyetherKetoneKetone); or even metallic foams, carbon foams, and so on. For honeycomb structures, examples include Nomex® honeycomb (made from aramid fibers and phenolic resin), aluminum honeycomb, Kevlar® honeycomb, carbon honeycomb, and others. The 320 material may or may not be fiber-reinforced.

Extending the skins beyond the reinforcement ensures they can conform to the cylinder during the vacuum curing stage. Thus, the possibility of conformation is guaranteed here by the absence of reinforcement—that is, of a completely rigid, polymerized material—in zone 310. However, other reinforcement configurations are possible to achieve the desired skin conformation, as will be described below.

The choice of reinforcing material and resin depends on the intended application. For the skins, a resin identical to that used for the panels 10 is chosen, or failing that, a compatible one. The reinforcement and resin for the skins can be as described above for the panels. Although not illustrated, it should be noted that the 300 dome may or may not be fitted with stiffeners or supports.

Figures 11 to 14 represent dome variants usable within the framework of the invention.

There FIG. 11 represents a 300a dome with a structure similar to that of the FIG. 8 , comprising a 302a reinforcement interposed between first 304a and second 306a skin sectors. The first 304a and second 306a sectors extend beyond the 302a reinforcement and are specifically assembled directly onto an assembly region 308a. Unlike the FIG. 8 This assembly region 308a extends to the cylindrical junction zone 310a. Therefore, in this example, there is no filler material between the first 311a and second 312a parts of zone 310a.

There FIG. 12 Figure 300b represents a dome comprising a reinforcement 302b interposed between first 304b and second 306b skin sectors. The first 304b and second 306b sectors extend beyond the reinforcement 302b and are specifically assembled directly onto an assembly region 308b. Unlike the domes in Figures 8 and 11, the first 304b and second 306b sectors extend in the same direction to form the cylindrical junction zone 310b. Note that a similar structure can be obtained with a single layer of sectors, or with a single-piece cap-shaped skin rather than a sectored structure. In the latter case, the skin either does not contain a continuous circumferential fiber that would impede the increase in diameter or comprises sectored circumferential fibers.

There FIG. 13 represents a 300c dome with a structure similar to that of the FIG. 12 The difference is that it features a reinforcement extension. A reinforcement 302c1 is interposed between the first 304c and second 306c skin sectors. The dome 300c includes a reinforcement extension 302c2 that extends beyond the first reinforcement 302c1 to prevent a sudden change in radius during skin forming in the vacuum curing stage. The extension 302c2 is localized and covers only a fraction of the first reinforcement 302c1 near its end 302c1a. This ensures proper pressurization of the skin sectors 306c located between the two reinforcements 302c1 and 302c2 during curing. The reinforcement 302c1 and its extension 302c2 stop early enough to allow the skins to bond together. In an unillustrated variant and preferably, the 302c2 frame can also be covered with a skin going in the opposite direction to that along which the skins formed from sectors 304c, 306c extend.

There FIG. 14 illustrates a dome variant in which the armature is extended compared to the examples just described.

There FIG. 14 This illustrates a dome 300d comprising at least one skin 306d assembled to a spider-like reinforcement 302d, which includes a rigid portion 3025d located on the circumferential edge side 3021d and a plurality of flexible tabs 3027d extending from the portion 3025d to the circumferential edge 3023d. The flexibility of the tabs 3027d allows the skin to bond to the cylinder despite the increased length of the reinforcement. The tabs 3027d are not in direct contact with the cylinder panels during final polymerization, with the skin 306d coming into contact at the interface between the reinforcement and the cylinder. The tabs 3027d may stop before the circumferential edge 306d1 of the skin 306d, as illustrated, or alternatively extend to this edge in the cylindrical junction zone.

We have just described the various constituent elements of the assembly. An example of the kinematics of the assembly of the vacuum molding tooling 30 and the positioning of the precursor assembly will now be detailed in relation to the FIG. 15 On this figure, as well as on the FIG. 16 The relative thicknesses and spacing between the different elements have not been strictly respected for reasons of readability.

Assembly of the vacuum molding tooling and positioning of the precursor assembly within this tooling

A first internal vacuum bag 341 is initially placed on a first internal positioning portion 321. The first portion 321 is of a much simpler design than the mandrel used in prior art techniques, since, within the scope of the invention, it is not used as a molding surface and does not need to be watertight. It is, therefore, more easily disassembled. The first portion 321 is supported by a shaft 36 extending along a longitudinal axis X. The axis X corresponds to the longitudinal axis of the panels 10 and the cylinder 100 described previously. The first portion 321 may have an open structure, for example, a lattice structure, or comprise a plurality of retractable positioning elements attached to the shaft. The first portion 321 may, as illustrated, generally have the shape of a first compartment C1 of the tank to be obtained. The first tarpaulin 341 covers the first portion 321. The first tarpaulin 341 can be made of elastomeric material, reinforced or not, and constitutes a known element in itself.

A first dome 300a can then be positioned on the portion 321 at a first longitudinal end 3211. The bottom of the dome 300a defines an opening 206, here generally disc-shaped, through which the shaft 36 extends. The dome 300a can have a general shape of revolution around the X-axis. The illustrated example implements the embodiment of dome 300a according to the FIG. 11 However, domes with a different structure can, of course, be used. The dome 300a extends circumferentially around the X-axis. The dome 300a may have a general shape of revolution around the X-axis. The dome 300a extends with a non-zero component along a radial direction R, perpendicular to the X-axis, between a first internal end 3051a located on the side of the X-axis and the shaft 36, and a second external end 3053a opposite to the first end located on the side of the cylinder 100. The first 311a and second 312a parts extend from the second end 3053a so as to form the cylindrical junction zone 310a intended to allow the dome 300a to be joined to the cylinder 100 during sous vide cooking. More specifically, the first part 311a of the dome 300a extends towards the other dome which will be positioned on the opposite end of the cylinder, and the second part 312a extends in the opposite direction to said other dome.

The 302a reinforcement is present on the first end 3051a and, more generally, on the bottom area. Thus, the 302a reinforcement eliminates the need for molding tools on the bottom, thereby simplifying the structure used for molding, and gives the 300a dome sufficient rigidity to maintain its shape during vacuum cooking.

The 302a reinforcement can extend beyond the skins at the 3051a end in a manner similar to that illustrated in the FIG. 8 so as to cooperate with the shaft 36 to position the dome 300a in the tooling. In one embodiment, the end 3051a is housed in a circumferential support tooling 362 attached around the shaft 36, for example in the form of a ring. The cover 341, as well as the cover 35 discussed later, are fixed watertight onto the tooling 362. The tooling 362 may, as illustrated, have chamfered axial ends to facilitate sealing. Those skilled in the art will recognize that other solutions are possible for positioning the dome 300a; the illustrated possibility is only one example among various possible embodiments. In the illustrated example, the frame 302a stops upstream of the second end 3053a to give sufficient flexibility to the parts 311a, 312a and thus allow their shaping and their joining to the cylinder 100 during vacuum cooking.

In the illustrated example, a common base precursor 400a is then positioned at a second longitudinal end 3213 of the portion 321 which is opposite the first end 3211. In the illustrated example, the precursor 400a has the same structure as the dome 300a and the elements having a similar function bear an identical reference except that it begins with the number 4. The precursor 400a is intended to form a common base separating the compartments C1 and C2 in the resulting tank. The precursor 400a extends with a non-zero component along a radial direction R, perpendicular to the X-axis, between a first internal end 4051a located on the side of the X-axis and the shaft 36, and a second external end 4053a opposite the first end located on the side of the cylinder 100. The first 411a and second 412a portions extend from the second end 4053a so as to form an intermediate cylindrical junction zone 410a intended to secure the precursor 400a to the cylinder during vacuum cooking. The end 4051a is housed in a circumferential support tool 362 attached around the shaft 36 in a manner similar to that described above for the dome 300a.

The second portion 322, covered by the second internal vacuum bag 342, is then positioned in line with the first portion 321 along the X-axis. The second portion 322 is of a much simpler design than the mandrel used in prior art techniques, as it is not used as a molding surface and does not need to be airtight. It is, therefore, more easily disassembled. The second portion 322 is supported by the shaft 36. The second portion 322 may have an open structure, for example, a lattice structure, or include a plurality of retractable positioning elements attached to the shaft. The second portion 322 can, as illustrated, generally be shaped like a second compartment C2 of the tank to be obtained. The second bag 342 may have the same characteristics as the first bag 341 described above.

A second 300a dome, with the same structure and attachment to the shaft as described above, is then positioned. The illustrated example shows two 300a domes with a symmetrical structure, but this does not, of course, depart from the scope of the invention if this is not the case.

In the example considered, a third and fourth external vacuum tarpaulins 35 are then placed respectively to form the front and rear skirts, which will be described later. The third and fourth tarpaulins 35 can have the same characteristics as the first and second tarpaulins 341, 342.

Next, positioning rings 40 are positioned at the ends 361, 363 of the shaft 36 which define a cylindrical positioning surface 42 whose function will be described below.

The panels 10 can then be positioned and placed side by side, as described above, to form the precursor cylinder 100 of the tank body. Cylinder 100 is located around the domes 300a and the precursor 400a. Cylinder 100 is positioned on the first 321 and second 322 sections. The cylinder extends from end 3223 to end 3211, and may optionally extend beyond these ends to form the front and rear skirts as illustrated. The domes 300a are located inside cylinder 100. The precursor 400a is located inside cylinder 100. Cylinder 100 extends from one dome 300a to another. In the illustrated example, the cylinder 100 extends beyond the domes 300a to form precursors of the front skirt 110 and rear skirt 120, positioned respectively opposite the third and fourth tarpaulins 35. However, the invention remains within the scope of this design if the cylinder does not form such skirts by stopping at the level of the domes 300a. Each of the domes 300a has an internal surface SI which, together with the cylinder 100, defines an internal volume of the tank to be obtained, and an external surface SE located outside the internal volume and which is hermetically sealed by the third or fourth tarpaulin 35, depending on the dome in question. The tarpaulins 35 are located outside the internal volume, while the tarpaulins 341 and 342 are located inside the internal volume.

After positioning the panels 10, a precursor assembly of the tank to be manufactured is obtained, comprising the cylinder 100, the domes 300a located on opposite sides of the cylinder 100's longitudinal ends, and the common base precursor 400a situated between the domes 300a in the illustrated example. The precursor 400a, together with the first dome 300a, defines a first compartment C1, and the precursor 400a, together with the second dome 300a, defines a second compartment C2, distinct from the first compartment. The domes 300a close the cylinder 100 on each of its longitudinal ends. The cylinder 100, the skins of the domes 300a, and the skins of the precursor 400a are each made of thermosetting pre-impregnated fibrous material.

The panels 10 are positioned opposite zones 310a and 410a to allow the bases to be bonded to the body during the sous-vide cooking process described below. Specifically, zone 310a is aligned with zone 16 of panels 10, and zone 410a with zone 16a. Zones 16 and 16a are unsupported and have been described above.

Next, the molded portion 60 of the tank body, which is shaped to match the desired tank body, is positioned and encircles the cylinder 100 along its entire length. The cylinder 100 is located inside portion 60. Portion 60 is positioned around the cylinder 100. Portion 60 holds the panels 10 in place. The panels 10 can be indexed onto portion 60. Like the panels 10, portion 60 can be divided into sections and assembled to form a 360° molded portion. As illustrated, portion 60 extends from one ring 40 to the other. It is positioned on surface 42, which avoids placing the weight of this external tooling on panels 10. Portion 60 may include stiffeners (not shown) on its face opposite panels 10 to provide significant rigidity and thus maintain the same shape, without deflection, despite its considerable length if a long tank is desired. An internal surface S1 of the precursor assembly is located on the side of the tarpaulins 341 and 342 (and delimits the internal volume V of the tank), and an external surface S2 of the assembly is located on portion 60.

The 52 sealing joints are then made.

The precursor assembly is thus positioned in the vacuum molding tooling 30. In particular, the cylinder 100 is interposed between the molding plates 341, 342 and the molding portion 60, and each dome 300a is interposed between the molding plate 341 or 342 and a respective molding plate 35. The parts 321, 322 are located inside the precursor assembly, that is, within the internal volume V of the tank to be produced. The portion 60 is located outside this internal volume and forms an external part of the assembly, intended for molding the tank.

Vacuum cooking of the precursor assembly in the tooling and disassembly

The sous vide cooking phase is illustrated in the FIG. 16 This cooking phase can be carried out with or without additional pressure.

The applied heat leads to the fluidization of the resin(s) present. Vacuuming the tooling 30 causes the tarpaulins 341 and 342 to be pressed against the cylinder 100, thus pressing the latter against the portion 60 and conforming it to the desired shape. The domes 300a are pressed against the panels 10 at the level of the zones 310a, and the precursor 400a is pressed against the level of the zone 410a. The parts 311a and 411a, 411b thus conform to the desired shape without any overall deformation, since the reinforcement is completely polymerized. The tarpaulins 35 apply pressure to the skirt precursors 110 and 120 and to the parts 312a to press them against the skirts 110 and 120. The tarpaulins 35 also apply pressure to the SE surface of each of the domes 300a during sous vide cooking.

Once all the parts are in place, heating allows the resin to finish polymerizing, creating bonds at the polymer chains (forming a three-dimensional network), thus solidifying the interfaces and the overall shape of the reservoir structure. The polymerization of thermosetting materials is complete after the vacuum curing stage.

Vacuum curing can be performed in a heated chamber, such as an oven or autoclave. The oven allows for vacuum polymerization, while the autoclave provides additional pressure beyond the vacuum. Alternatively, or in combination with other methods, molding tools equipped with heating elements (not shown) can be used for this curing process. The temperature required during vacuum curing depends on the resin used and can, for example, be greater than or equal to 150°C, or between 175°C and 185°C, or close to 180°C.

A composite tooling 30 can be used to reduce the differential expansion between the tooling and the reservoir. Alternatively, the tooling 30 can 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 bag at the end of the curing period, or by providing a gap in the portion 60.

The tooling 30 is then dismantled, a process facilitated by the positioning of the molded portion outside the tank and by the simplified design of the internal part. The tank 1 is then demolded. It features, in particular, thermoset composite reinforcements covered by one or more thermoset composite skins at each of its longitudinal ends, defining the bottoms 3000 of the tank 1.

The resulting tank 1, as described above, has a front skirt 1100 and a rear skirt 1200 extending the body 1000 beyond the bottoms 3000. In the illustrated example, it also features a common bottom 4000 that divides the tank into two separate compartments, C1 and C2; however, the presence of this common bottom 4000 is optional, as mentioned earlier. The skirts 1100 and 1200 are monolithic with the rest of tank 1.

The invention described above is suitable for manufacturing the tanks of the lower stage of space launch vehicles. The invention also applies to the tanks of the upper stages. In operation, the composite tank can be filled, for example, but not limited to, with liquid methane, liquid hydrogen, or refined kerosene (such as RP-1), or a combination of these compounds, in a first compartment, and with liquid oxygen in a second compartment. The tank can be used in a cryogenic environment.

In an unillustrated variant, the tank is not compartmentalized, and the precursor assembly is positioned on a single internal positioning section, extending from one dome to the other, lined with an internal vacuum bag. In this latter case, the tank can be used in a solid rocket booster stage in addition to the applications just mentioned.

The scope of the invention is not limited to a tank for integration into an aerospace launcher but can find application in the aeronautical field or, more generally, in any application requiring a tank made of composite material.

The expression "between ... and ..." should be understood as including the boundaries.

Claims (13)

Method for manufacturing a tank (1) made of composite material, comprising:
- the positioning of a precursor assembly of the tank to be manufactured in a vacuum molding tool (30),
The assembly comprises (i) a cylinder (100), precursor to the body (1000) of the tank, made of thermosetting pre-impregnated fibrous material extending along a longitudinal axis (X), and (ii) two domes (300a), precursors to the tank bottom, each of these domes being located on the side of an opposite longitudinal end of the cylinder, each domes having an internal surface (SI) which, together with the cylinder, delimits an internal volume of the tank to be obtained and an external surface (SE) located outside the internal volume, each of the domes comprising a reinforcement (302a) made of thermosetting composite material, defining a tank bottom, covered by at least one thermosetting pre-impregnated fibrous skin (304a; 306a) defining a cylindrical junction zone (310a) positioned opposite and inside the cylinder, the reinforcement being configured to allow a conformation of said at least a skin against the cylinder at this cylindrical junction area,
the tooling comprising an internal positioning portion (321; 322) covered with an internal vacuum cover (341; 342), located inside the internal volume, on which the assembly is positioned, and an external molding portion, located outside the internal volume, comprising a cylindrical molding portion (60) of the tank body situated opposite the precursor cylinder, each external surface of the domes being hermetically sealed by an external vacuum cover (35), and
- vacuum curing of the assembly in the tooling during which the internal vacuum bag applies pressure to conform the assembly to the molding portion, with the junction areas held in contact with the precursor cylinder and co-curing of the domes and the cylinder to bond the bottoms to the body and obtain the tank in composite material.
A method according to claim 1, wherein the cylinder (100) extends beyond each of the two domes (300a) so as to define skirt precursors (110; 120), and wherein each dome comprises a first skin (304a) covering a first face of the frame and defining a first part (311a) of the cylindrical junction zone extending towards the other dome, and a second skin (306a) covering a second face of the frame, opposite to the first face, and defining a second part (312a) of the cylindrical junction zone extending in a direction opposite to said other dome, the second part of the cylindrical junction zone of each dome being attached to a respective skirt precursor during vacuum cooking. Method according to claim 2, wherein each dome (300) further comprises a filling material (320) between the first (311) and second (312) parts of the cylindrical junction zone (310). A method according to any one of claims 1 to 3, wherein the cylindrical junction zone (310a) of each dome is at least partly formed by an extension of said at least one skin (304a; 306a) beyond the frame (302a). A method according to any one of claims 1 to 4, wherein the frame (302d) of each dome (300d) defines a plurality of flexible tabs (3027d) allowing the shaping of said at least one skin (306d) against the cylinder on the cylindrical junction area. A method according to any one of claims 1 to 5, wherein said at least one skin (304a; 306a) of each dome (300a) has a thinning in thickness on the cylindrical junction area (310a) in the direction of a circumferential edge thereof. A method according to any one of claims 1 to 6, wherein each skin comprises several sectors (304) juxtaposed around the longitudinal axis (X). Method according to claim 7, wherein the neighboring sectors exhibit a thinning of thickness on their overlap zone in the direction of their longitudinal edges (304a1; 304b1). A method according to any one of claims 1 to 8, wherein the cylinder (100) and said at least one skin (304a; 306a) of each dome (300a) are assembled in the semi-baked state to form the precursor assembly. A method according to any one of claims 1 to 9, wherein the method further comprises, prior to positioning the precursor assembly in the molding tooling, the formation of the cylinder (100) and of said at least one skin (304a; 306a) of each of the domes (300a) by automatic placement of fibers on a distinct form of the internal positioning part (321; 322). A method according to any one of claims 1 to 10, wherein the cylinder (100) and the domes (300a) comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers. A method according to any one of claims 1 to 11, wherein the cylinder (100) and the domes (300a) are pre-impregnated with an epoxy resin. A method according to any one of claims 1 to 12, wherein the assembly further comprises (iii) a common base precursor (400a) located inside the cylinder and between the domes so as to define with each of them a distinct compartment (C1; C2) of the internal volume, said common base precursor comprising a common base reinforcement of thermosetting composite material, defining the common base, covered by at least one common base fibrous skin which is pre-impregnated and thermosetting and which defines an intermediate cylindrical junction zone (410a) positioned opposite the cylinder, the common base reinforcement being configured to permit a conformation of said at least one common base skin against the cylinder on this intermediate cylindrical junction zone, and wherein there is co-cooking of the common base precursor with the cylinder to bond the common base to the body during vacuum cooking.