Manufacturing process for a compartmentalized composite material tank

Abstract

Method for manufacturing a compartmentalized composite material tank The present invention relates to a method for manufacturing a compartmentalized composite material tank in which a structure comprising a common bottom precursor is vacuum cured in a tool, and in which domes intended to form the end bottoms are then added and fixed using a thermosetting adhesive. Figure for abstract: Fig. 1.

Description

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

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

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

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

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

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

[0006] The limits of current techniques are even more marked when it comes to integrating reinforcement elements, such as stiffeners, or interface parts into the tank.

[0007] It is therefore desirable to have a method for manufacturing a tank in compartmentalized composite material which addresses all or part of the aforementioned drawbacks. Statement of the invention

[0008] The present disclosure relates to a method of manufacturing a compartmentalized composite material tank, comprising: - obtaining a structure including: (i) a cylinder, precursor of the tank body, made of thermosetting pre-impregnated fibrous material extending along a longitudinal axis, (ii) a molding mandrel comprising two molding portions juxtaposed along the longitudinal axis on which the cylinder is positioned, and (iii) a common bottom precursor, located inside the cylinder and housed between the molding portions, comprising a common bottom zone and at least one thermosetting pre-impregnated fibrous skin defining an intermediate cylindrical junction zone positioned opposite the cylinder, - vacuum curing of the structure during which the cylinder is shaped on the molding mandrel, with the cylinder held in contact with the intermediate cylindrical junction zone and co-curing of the common base precursor with the cylinder to secure the common base to the body, - the extraction, after cooking, of the casting portions through the longitudinal ends of the body, - the positioning, after the extraction of the molding portions, of a dome, precursor of the end bottom of the tank, on each of the longitudinal ends of the body, each dome defining with the common bottom a separate compartment of the tank to be obtained and defining a cylindrical end junction zone made of thermosetting pre-impregnated fibrous material covered with a thermosetting adhesive and positioned opposite the body, and - the shaping of the domes thus positioned by maintaining the cylindrical end junction zones and the adhesive resting on the body and by heating so as to harden the junction zones and the adhesive and thus secure the end bases to the body.

[0009] The method according to the invention makes it possible to obtain a composite material tank in which the common bottom separates two adjacent compartments inside the tank. Co-curing makes it possible to polymerize the thermosetting resin impregnating the cylinder with that impregnating said at least one skin of the common bottom precursor, and to create covalent bonds between the polymer chains present. This joint polymerization leads to a bonding of the common bottom to the body of the composite material tank, without requiring the addition of a third-party adhesive compound. However, it does not go beyond the scope of the invention if a third-party adhesive compound is used on the interfaces of the elements constituting the common base or the body or on the interfaces between the common base and the body, so as to provide additional mechanical strength.

[0010] The invention is also remarkable in that the domes intended to form the end bottoms are only positioned in a second step, which allows the prior extraction of the molding portions through the longitudinal ends of the body left open. In this way, the separation of the molding portions from the baked structure is made much simpler than in the techniques of the prior art where the mold is dismantled and extracted through small openings at the ends of the tank.

[0011] In the following and unless otherwise stated, the word “skin(s)” designates said at least one thermosetting pre-impregnated fibrous skin of the common base precursor.

[0012] In an exemplary embodiment, the common bottom precursor comprises a thermoset composite material frame defining the common bottom area which is covered by said at least one skin and which is configured to allow conformation of said at least one skin on the molding mandrel on the intermediate cylindrical junction area.

[0013] The reinforcement is a thermoset composite material, i.e. one whose matrix has been completely polymerized, so as to give the common base precursor sufficient rigidity to maintain the desired geometry for the common base during the manufacture of the tank, and in particular during vacuum curing. The reinforcement also makes it possible to dispense with the presence of molding tooling on the common base during the manufacture of the tank, thus making it possible to maintain a relatively simple tooling structure. On the other hand, the common base precursor remains sufficiently deformable on the intermediate cylindrical junction zone to allow the deformation of said at least one skin, thus ensuring good joining of the common base to the cylinder. As will be described below, the reinforcement may have various structures making it possible to fulfill this function. The invention does not, however, require the presence of such a reinforcement.According to a variant, the common bottom area, without reinforcement, can be interposed between two molding surfaces, in which case the presence of a molding tool around the common bottom precursor is necessary. The use of a reinforcement is nevertheless preferable because it makes it easier to control the geometry of the common bottom area during curing, without having to manage the gaps between these two molding surfaces by keeping these surfaces as much as possible in contact with the common bottom area being polymerized.

[0014] In an exemplary embodiment, the common background precursor comprises a first skin covering a first face of the reinforcement and defining a first part of the intermediate cylindrical junction zone which extends towards a first longitudinal end, and a second skin covering a second face of the reinforcement, opposite the first face, and defining a second part of the intermediate cylindrical junction zone which extends towards a second longitudinal end opposite the first longitudinal end.

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

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

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

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

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

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

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

[0022] In an exemplary embodiment, the frame comprises an insulating material configured to thermally insulate the compartments of the tank.

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

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

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

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

[0027] Such a characteristic advantageously makes it possible to further improve the material health of the skin, the cylinder and the skin / cylinder interface in this common bottom stop zone. In addition, this characteristic makes it possible to minimize stress concentrations (at the bottom stop) when the tank is subjected to mechanical stresses (filling, thermal stresses, pressurization, forces applied during takeoff phases and potentially return to Earth, etc.).

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

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

[0030] In particular, the neighboring sectors may have a thinning of thickness on their overlap zone in the direction of their longitudinal edges.

[0031] Thinning the thickness makes it possible to locally avoid thickness jumps and to further minimize misalignments and stress concentrations. By misalignment we mean a local jump on the surface, that is to say that the surface is not smooth, and that the ends of the assembled parts form a step.

[0032] In an exemplary embodiment, the cylinder and said at least one skin are assembled in the half-baked state to form said structure, and the domes are in the half-baked state when assembled with the body.

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

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

[0035] In an exemplary embodiment, the cylinder, said at least one skin and the domes were formed by automatic fiber placement.

[0036] This technique allows access to a wide variety of geometries, in particular compared to winding which does not allow draping in the direction of the longitudinal axis, or automated draping of local excess thicknesses or reinforcements. Automatic fiber placement also makes it possible to obtain elements with low permeability compared to parts obtained by winding, suitable for example for the storage of cryogenic propellants.

[0037] In an exemplary embodiment, the cylinder, said at least one skin and the domes comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

[0038] These fibers are particularly suitable for space launcher applications and cryogenic environments.

[0039] In an exemplary embodiment, the cylinder, said at least one skin and the domes are pre-impregnated with an epoxy resin, for example a class 180 epoxy resin which polymerizes at a temperature between 175°C and 185°C, for example substantially at 180°C.

[0040] This material is particularly suitable for space launcher applications and cryogenic environments, and can be easily reworked after partial polymerization.

[0041] In a preferred embodiment, the cylinder, precursor of the tank body, is directly draped over the molding mandrel.

[0042] In an exemplary embodiment, the cylinder, precursor of the body of the tank, is sectorized and is formed by panels juxtaposed around the longitudinal axis with overlap between the neighboring panels.

[0043] Forming the cylinder from a plurality of panels makes it possible to simplify its manufacture when a very long cylinder is envisaged.

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

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

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

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

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

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

[0050] In particular, the neighboring petals may have a thinning of thickness on their overlap zone in the direction of their longitudinal edges.

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

[0052] In an exemplary embodiment, the method comprises, after the extraction of the molding portions, the positioning of stiffeners on an internal surface of the body covered with a second thermosetting adhesive facing the body, the second adhesive being hardened during the heating carried out during the shaping of the domes so as to secure the stiffeners to the body. Brief description of the drawings [Fig.l] [Fig.l] represents, schematically and partially, an example of a panel usable within the framework of the invention to form the cylinder taken in cross section relative to its longitudinal axis. [Fig.lA] [Fig.lA] represents, schematically and partially, the bevel angle of the panel of [Fig.l]. [Fig.2] [Fig.2] represents, schematically and partially, a variant of cylinder. [Fig.3] [Fig.3] represents, schematically and partially, another variant of cylinder. [Fig.4] [Fig.4] represents, schematically and partially, another variant of cylinder. [Fig.5] [Fig.5] represents, schematically and partially, another variant of cylinder. [Fig.6] [Fig.6] represents an example of a petal intended to form a precursor dome of end bottom by juxtaposition with other petals. [Fig.7] [Fig.7] represents the juxtaposition of a second petal on the petal of [Fig.6] according to an exemplary implementation of the invention. [Fig.8] [Fig.8] represents, schematically and partially, a sectional view of the dome resulting from the juxtaposition of petals according to [Fig.6] in a plane containing the axis of revolution of the dome. [Fig.9] [Fig.9] represents, schematically and partially, a sectional view of the dome resulting from the juxtaposition of petals according to [Fig.6] in a plane perpendicular to the axis of revolution of the dome. [Fig. 10] [Fig. 10] schematically and partially represents a sectional view of an example of a common bottom precursor in a plane containing its axis of revolution. [Fig. 11] [Fig. 11] represents a sector of a first skin intended to be part of the precursor of [Fig. 10]. [Fig. 12] [Fig. 12] represents the juxtaposition of several sectors according to [Fig. 11] in the context of the manufacture of the precursor of [Fig. 10]. [Fig. 13] [Fig. 13] schematically and partially represents a sectional view of a common base precursor variant in a plane containing its axis of revolution. [Fig. 14] [Fig. 14] schematically and partially represents a sectional view of another variant of common bottom precursor in a plane containing its axis of revolution. [Fig. 15] [Fig. 15] schematically and partially represents another variant of a common background precursor in a plane containing its axis of revolution. [Fig. 16] [Fig. 16] schematically and partially represents another variant of a common background precursor in a plane containing its axis of revolution. [Fig. 17] [Fig. 17] schematically and partially represents another variant of common background precursor. [Fig. 18] [Fig. 18] schematically and partially represents a structure comprising a body precursor cylinder and a common bottom precursor according to an exemplary implementation of the invention. [Fig. 19] [Fig. 19] represents, in a schematic and partial manner, the vacuum cooking of the structure of [Fig. 18]. [Fig.20] [Fig.20] represents, in a schematic and partial manner, the assembly obtained after extraction of the molding portions following the cooking carried out in connection with the [Fig.19], [Fig.21] [Fig.21] represents, in a schematic and partial manner, the conformation of the domes positioned at the longitudinal ends so as to obtain the compartmentalized tank. Description of the embodiments

[0053] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0054] The description below firstly addresses the structure and production of the precursor cylinder of the body, the precursor domes of the bottoms and the common bottom precursor. The details of the molding installation, as well as the cooking phases will be detailed in a second step.

[0055] Precursor cylinder of the body

[0056] The example described here concerns a sectored cylinder obtained by juxtaposition of thermosetting pre-impregnated fiber panels, but it does not depart from the scope of the invention when the cylinder is formed in a single piece. In the latter case, the cylinder may contain continuous circumferential fibers or sectored circumferential fibers. The circumferential direction corresponds to the direction around the axis of the cylinder, referred to as the “X axis” in the following.

[0057] The precursor cylinder of the body is here obtained by juxtaposition of thermosetting pre-impregnated fiber panels. Generally speaking, it may comprise at least two fiber panels, or even at least three fiber panels. The example described here concerns the case of a cylinder with four panels.

[0058] The panels are advantageously produced by automatic placement of fibers, which constitutes a technique known per se. The panels 10 each comprise a fiber reinforcement pre-impregnated with a thermosetting resin. The choice of the reinforcing material and the resin depends on the intended application. For example, the fiber reinforcement comprises carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers. For example, the resin is an epoxy resin, for example based on a monomer DGEBA (diglycidyl ether of bisphenol A), TGPAP (triglycidyl paraaminophenol), or TGMDA (tetraglycidyl methylenedianiline), to which an amine-type hardener, for example DDS (diaminodiphenyl sulfone), may optionally be added. The same resin is advantageously used in the different panels, or, failing that, compatible resins.

[0059] The panels 10 have an elongated shape along a longitudinal axis X and have a curved shape in cross-section relative to the axis X. The panels 10 define two longitudinal edges 10a, 10b which are intended to be superimposed with a neighboring panel, as will be described below. [Fig.l] illustrates an example of a possible structure for the panels 10. The panels 10 can be draped in a female tool or in a male tool.

[0060] [Fig. 1] shows the evolution of the thickness elO of the panels 10 over their width (dimension between the edges 10a and 10b). The panels 10 have a middle zone 101 of their width where the thickness elO is substantially constant, and two lateral zones 103a and 103b each located on the side of a respective longitudinal edge 10a, 10b which have an evolving thickness. The zone 101 is located between the zones 103a, 103b. The zone 103a connects the zone 101 to the edge 10a, and the zone 103b connects the zone 101 to the edge 10b. More precisely, the zones 103a, 103b have a thinning of thickness in the direction of the associated longitudinal edge 10a, 10b. The thickness elO may be strictly decreasing in the direction of the longitudinal edge 10a, 10b. The thickness elO is minimal on the edges 10a, 10b and maximal on the median zone 101. The panels 10 have a bevel on their edges 10a, 10b.The panels 10 have, in cross-section relative to the X axis, a tapered shape towards their edges 10a, 10b. The zones 103a and 103b jointly occupy at least 5%, for example at least 50%, of the width LA10 of the panel 10. Unless otherwise stated, the width LA10 corresponds to the length of the arc of the curve connecting the edge 10a to the edge 10b. The thinning of the thickness leads to a reduction in the thickness elO of at least . 50%, for example at least 90%. This reduction in thickness el0 is for example between 50% and 95%, or even between 90% and 95%. [Fig.lA] schematically represents a thinning of the thickness of the panel 10 in the direction of a longitudinal edge 10b linked to the presence of a decreasing quantity of superimposed folds PS in the direction of the edge 10b. The bevel angle a, corresponding to the angle taken locally on the edge 10b, can advantageously be less than or equal to 1.5°, so as to further improve the smoothing of the forces.

[0061] Figures 2 to 5 describe the juxtaposition of these panels 10 to form the cylinder 100, precursor of the body of the tank.

[0062] [Fig. 2] illustrates a possible juxtaposition of two neighboring panels 10 around the X axis. The two panels 10 illustrated have the same structure and the same references are retained with respect to what has just been described. The panels 10 partially overlap here. The panels have a thinning of thickness on their overlap zone, that is to say that the zone 103b of the first panel 10 is covered by the zone 103a of the second neighboring panel 10. The edge 10b of the first panel 10 is superimposed with the second neighboring panel 10, and the edge 10a of the second panel 10 is superimposed with the first panel. In the variant of [Fig.2], the cylinder 100 is formed by tiling all the panels 10, that is to say that each of the panels has a first longitudinal edge 10b covering (above) a first neighboring panel, and a second longitudinal edge 10a, opposite the first edge 10b, covered (below) by a second neighboring panel, opposite the first neighboring panel. In particular, the thinning of the thickness of the neighboring panels 10 over their overlapping zone ZR10 in the direction of their longitudinal edges 10a, 10b is noted.

[0063] Generally speaking, the overlapping areas between neighboring panels can occupy at least 5%, for example at least 30% of the perimeter of the sectored cylinder. Having spread overlapping areas makes it possible to further improve the mechanical properties of the resulting tank.

[0064] In the variant of [Fig.3], there is tiling except for panel 10 at the bottom right of the figure which covers its two neighboring panels.

[0065] The variants of Figures 4 and 5 show cases where there is no tiling which are also covered by the present invention.

[0066] The part which has just been described concerns the panels and their juxtaposition to form the precursor cylinder of the body. The following concerns the precursor domes of the end bottoms which are intended to be secured to the body to delimit the internal volume of the composite material tank to be obtained.

[0067] End bottom precursor domes

[0068] [Fig.6] shows a petal 20, which has the shape of a dome sector, draped in shape. According to this example, each background precursor dome is obtained by juxta position of thermosetting pre-impregnated fibrous petals 20. Generally speaking, each of the domes may comprise at least two petals 20, or even at least three petals 20. The example described here concerns the case of domes each having four petals 20.

[0069] As for the panels 10, the petals 20 are advantageously made by automatic placement of fibers. The petals 20 each comprise a fiber reinforcement pre-impregnated with a thermosetting resin. The choice of the reinforcement material and the resin depends on the intended application. The reinforcement and the resin of the petals 20 may be as described above for the panels 10. A resin identical to that of the panels 10, or failing that compatible with it, will advantageously be chosen for the petals 20. In a similar manner to the panels 10, the petals 20 may be draped over male or female tooling.

[0070] As for the panels 10, the petals 20 define two edges 20a, 20b each extending along a longitude, called longitudinal edges, which are intended to be superimposed with a neighboring petal. The longitudinal edges 20a, 20b are intended to extend along the longitudinal axis X of the cylinder 100 in the precursor assembly which will be described below. The petals 20 define two edges 20c, 20d each extending along a latitude (or circumferential) which are transverse to the edges 20a, 20b. Each of the edges 20c, 20d connects the edge 20a to the edge 20b. The edge 20c has a first curvilinear length, and the edge 20d has a second curvilinear length which is greater than the first curvilinear length.

[0071] In a similar manner to the panels 10, and to the illustration of [Fig.l], the petals 20 have a thickness that varies between the edges 20a and 20b. The petals 20 thus have a median zone 201 where the thickness is substantially constant, and two lateral zones 203a and 203b each located on the side of a respective edge 20a, 20b which have a thickness that varies. Area 203a is bounded by edge 20a and longitude 21 and area 203b by edge 20b and longitude 23. Area 201 is located between areas 203a and 203b, or between longitudes 21 and 23. The description provided above relating to areas 103a, 101 and 103b applies respectively to areas 203a, 201 and 203b mutatis mutandis.

[0072] The petals 20 define a sector 203d of a cylindrical end junction zone which is intended to come opposite the precursor cylinder of the body. The sector 203d corresponds to a circumferential zone delimited by the edge 20d and by a latitude 25. In the example described here and as illustrated in [Fig.8], the petals 20 have a thinning of thickness on their sector 203d in the direction of the edge 20d.

[0073] The petals 20 are juxtaposed at their edges 20a, 20b with overlap between neighboring petals, in a manner similar to what was described above for the panels 10. Thus, [Fig.7] represents the positioning of a second petal 20 in partial overlap with the first petal 20, it being understood that two other petals are juxtaposed to form the complete dome 200 in the example considered. [Fig.9] schematically shows the juxtaposition of these four petals 20. The neighboring petals 20 here have a thinning of thickness e20 on their overlap zone ZR20 in the direction of their longitudinal edges 20a, 20b.

[0074] As illustrated in [Fig. 8], the dome 200 has a bottom zone 205 located between the edge 20c and the latitude 25. The dome 200, and in particular the zone 205, may have a general shape of revolution. The union of the sectors 203d forms a 360° cylindrical junction zone 210 which extends the zone 205 to the edge 20d. [Fig. 8] shows the thinning of the thickness e20 of the petals 20 (or of the dome 200) in the direction of the edge 20d, at the level of the sectors 203d or of the zone 210. The evolution of the radius R of the dome 200 is also visible with a radius R strictly increasing between the edge 20c and the latitude 25, and substantially constant over the zone 210.

[0075] A possible structure for the cylinder 100 and the domes 200 has just been described. The following describes different possible examples for the common bottom precursor which makes it possible to ensure the compartmentalization of the tank.

[0076] Common background precursor

[0077] [Fig. 10] illustrates an example of a common base precursor 300. The precursor 300 comprises a reinforcement 302 made of thermoset composite material. The reinforcement 302 thus comprises a fibrous reinforcement densified by an organic matrix obtained after polymerization of a thermosetting resin. The resin of the reinforcement 302 is completely polymerized.

[0078] The example of precursor 300 considered comprises a thermosetting pre-impregnated fibrous skin on each of the faces of the reinforcement 302. Each of the skins is here formed by a juxtaposition of sectors 304, 306 around the X axis. The skins or sectors 304, 306 can be produced by automatic placement of fibers. The skins or sectors 304, 306 each comprise a fibrous reinforcement pre-impregnated with a thermosetting resin. The example considered comprises first sectors 304 which cover a first face 3024 of the frame 302, and second sectors 306 which cover a second face 3026 of the frame 302 opposite the first face 3024. The first sectors 304 are juxtaposed circumferentially, like the second sectors 306. The frame 302 is housed between the first 304 and second 306 sectors.The frame 302 here has a dome shape and comprises an internal circumferential edge 3021, and an external circumferential edge 3023 intended to be positioned on the side of the cylinder 100 in the assembly.

[0079] The draping of the sectors 304 and 306 is similar to the draping of the petals 20 described above to obtain the domes 200. The second sectors 306 are however draped with a folded shape in the illustrated example to form a portion 312 of the intermediate cylindrical junction area 310.

[0080] A draping possibility to obtain precursor 300 is now detailed.

[0081] In the example considered, it is first possible to drape the second sectors 306, which have a more complex shape, then position the reinforcement 302 on the second sectors 306 thus draped and then drape the first sectors 304 on the assembly obtained in order to obtain the precursor 300. The reinforcement 302 has been completely polymerized beforehand, before its assembly with the sectors 304, 306. An adhesive film can be positioned at the interfaces between the reinforcement 302 and the sectors 304, 306. The first face 3024 of the reinforcement 302 is covered over 360° by the first sectors 304 and the second face 3026 of the reinforcement 302 is covered over 360° by the second sectors 306. Figures 11 and 12 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 carried out in a similar manner.

[0082] The sectors 304 each define two edges 304al, 304bl each extending along a longitude, called longitudinal edges, which are intended to be superimposed with a neighboring sector. The edges 304al, 304bl are intended to extend along the longitudinal axis X of the cylinder 100 in the precursor assembly which will be described below. The sectors 304 define two edges 304cl, 304dl each extending along a latitude (or circumferential) which are transverse to the edges 304a 1, 304b 1. Each of the edges 304c 1, 304dl connects the edge 304a 1 to the edge 304b 1. The edge 304c 1 has a first curvilinear length, and the edge 304dl has a second curvilinear length which is greater than the first curvilinear length.

[0083] The sectors 304 have a thickness that varies between the edges 304al and 304b 1. The sectors 304 thus have a median zone 3041 where the thickness is substantially constant, and two lateral zones 3043a and 3043b each located on the side of a respective edge 304al, 304b 1 which have a thickness that varies. Area 3043a is bounded by edge 304al and longitude 305 and area 3043b by edge 304bl and longitude 307. Area 3041 is located between areas 3043a and 3043b, or between longitudes 305 and 307. The description provided above relating to areas 103a, 101 and 103b applies respectively to areas 3043a, 3041 and 3043b mutatis mutandis.

[0084] The sectors 304 define a sector 3043d of a portion 311 of the intermediate cylindrical junction zone 310 which is intended to come opposite the precursor cylinder of the body. The sector 3043d corresponds to a circumferential zone delimited by the edge 304dl and by a latitude 309. The sectors 304 may have a thinning of thickness on the sector 3043d in the direction of the edge 304dl.

[0085] The sectors 304 are juxtaposed at their edges 304al, 304bl with re covering between neighboring sectors, in a similar manner to what was described above for the petals 20. Thus, [Fig. 12] represents the positioning of an additional sector 304 in partial overlap with the first initial sector 304, it being understood that two other sectors are juxtaposed to form the first skin. The sectors 304 are thus juxtaposed circumferentially.

[0086] As indicated above, the draping of the second sectors 306 is done in a similar manner to that of the first sectors 304. It will nevertheless be noted that, in the example illustrated, 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.

[0087] Generally speaking, the sectors can be draped onto the reinforcement in the raw state with a raw prepreg, or in the semi-cured state with a prepreg previously semi-cured before draping. In the case where they are draped in the semi-cured state, it will be possible to favor an architecture with a single layer of sectors which will be draped directly onto the reinforcement or a two-layer architecture with the two layers joining beyond the reinforcement.

[0088] In the example of [Fig. 10], the skins each extend beyond the frame 302 (beyond the end 3023) so as to define the first 311 and second 312 parts of the intermediate cylindrical joining zone 310. More specifically, the skins are directly assembled beyond the end 3023 on an assembly region 308 up to a separation edge 305 from which they separate to define the first 311 and second 312 parts. This separation defines a space which can be filled by a filling material 320 distinct from the skins. The material 320 is present between the first 311 and second 312 parts. The material 320 can be chosen from: cellular materials including filling foams (“foam core” in English) as well as honeycombs (or Nida or “honeycomb” in English).Foams can be foams from the PU (Polyurethane), PVC (Polyvinyl Chloride), PMI (PolyMethacrylate Imide), PEI (PolyEther Imide), PAI (Polyamide Imide) family, foams from the PAEK (PolyArenylEtherKetone) family such as PEEK (PolyEtherEtherKetone), PEKK (PolyEtherKetoneKetone), or metal foams, or carbon foams, etc. For honeycombs we can have for example Nomex® honeycombs (based on aramid fibers and phenolic resin), aluminum honeycombs, Kevlar® honeycombs, carbon honeycombs, etc. The 320 material may or may not be loaded with fibers.

[0089] The extension of the skins beyond the frame ensures that they can conform against the cylinder during the vacuum cooking step. Thus, the possibility conformation is here ensured by the absence of reinforcement, that is to say of completely rigid polymerized material, at the level of zone 310. Nevertheless, other reinforcement configurations are possible to allow the desired conformation of the skins as will be described below.

[0090] The choice of the reinforcing material and the resin depends on the intended application. For the skins, a resin identical to that of the panels 10 is chosen, or failing that, compatible with it. The reinforcement and the resin of the skins may be as described above for the panels.

[0091] Other common background precursor variants can be used within the scope of the invention.

[0092] [Fig. 13] shows a common base precursor 300a of similar structure to that of [Fig. 10], comprising a reinforcement 302a interposed between first 304a and second 306a skin sectors. The first 304a and second 306a sectors extend beyond the reinforcement 302a and are in particular assembled directly on an assembly region 308a. Unlike [Fig. 10], this assembly region 308a extends to the intermediate cylindrical junction zone 310a. There is therefore no filling material in this example between the first 311a and second 312a parts of the zone 310a.

[0093] [Fig. 14] shows a common base precursor 300b of similar structure to that of [Fig. 10], comprising a frame 302b interposed between first 304b and second 306b skin sectors. In this example, the frame 302b is formed from an insulating material configured to thermally insulate one compartment from the other. The insulating material may be housed in the frame or arranged on at least one of its faces. The insulating material may be a cellular material, for example in the form of a honeycomb or filling foam. The nature of the insulating material depends on the intended application and will be chosen by the person skilled in the art according to the intended objective.

[0094] [Fig. 15] shows a common bottom precursor 300c, comprising a reinforcement 302c interposed between first 304c and second 306c skin sectors. The first 304c and second 306c sectors extend beyond the reinforcement 302c and are in particular assembled directly on an assembly region 308c. Unlike the precursors of FIGS. 10, 13 and 14, the first 304c and second 306c sectors extend on the same side to form the intermediate cylindrical junction zone 310c. It will be noted that a similar structure can be had with a single layer of sectors, or a one-piece cap-shaped skin rather than a sectored structure. In the latter case, the skin does not contain a continuous circumferential fiber that hinders the variation in diameter or comprises sectored circumferential fibers.

[0095] [Fig. 16] shows a common base precursor 300d of similar structure to that of [Fig. 15], except that it has a reinforcement extension. A reinforcement 302dl is interposed between first 304d and second 306d skin sectors. The precursor 300d comprises a reinforcement extension 302d2 which extends beyond the first reinforcement 302dl so as to avoid the formation of a sudden variation in radius during the shaping of the skins during the baking step. The extension 302d2 is local and only covers a fraction of the first reinforcement 302dl in the vicinity of the end 302dla of the latter. This guarantees good pressurization of the skin sectors 306d located between the two reinforcements 302dl and 302d2 during baking. The 302dl frame and its 302d2 extension stop early enough to allow the skins to be joined.In a variant not illustrated and preferably, the frame 302d2 can also be covered with a skin going in a direction opposite to that along which the skins formed from the sectors 304d, 306d extend.

[0096] [Fig. 17] illustrates a variant of a common base precursor in which the armature is extended compared to the examples just described.

[0097] [Fig. 17] illustrates a common base precursor 300e comprising at least one skin 306e assembled to a “spider” type frame 302e which comprises a rigid portion 3025e located on the side of the circumferential edge 3021e and a plurality of flexible tabs 3027e extending from the portion 3025e to the circumferential edge 3023e. The flexibility of the tabs 3027e allows the skin to be secured to the cylinder despite an increased length of the frame. The tabs 3027e are not in direct contact with the panels of the cylinder during the final polymerization, the skin 306e coming to the interface between the frame and the cylinder. The tabs 3027e may stop before the circumferential edge 306el of the skin 306e as shown, or alternatively extend to this edge on the intermediate cylindrical joining area.

[0098] The various elements used in the manufacture of the tank have just been described. Figures 18 to 21, which will now be described, illustrate a sequence of possible steps for obtaining the tank from these elements.

[0099] A common base precursor 300a, for example of the type illustrated in [Fig. 13], is positioned between two molding portions 401, 402 of a molding mandrel 400. The portions 401, 402 are juxtaposed along the X axis. The precursor 300a defines an intermediate cylindrical junction zone 310a which here comprises a first part 311a positioned on a first portion 401, and a second part 312a positioned on a second portion 402 distinct from the first portion 401. The precursor 300a extends circumferentially around the X axis. The precursor 300a may have a general shape of revolution around the X axis. precursor 300a may comprise a zone 305a which is intended to form a common bottom separating the compartments C1 and C2 in the resulting reservoir. The precursor 300a extends with a non-zero component along a radial direction R, perpendicular to the axis X, between a first internal end located on the side of the axis X, and a second external end 3053a opposite the first end intended to be on the side of the cylinder. The first 311a and second 312a parts extend from the second end 3053a so as to form the intermediate cylindrical junction zone 310a intended to allow the precursor 300a to be secured to the cylinder 100 during vacuum cooking. The frame 302a is present on the first end 3051a and, more generally, on the zone 305a.Thus, the frame 302a makes it possible to dispense with the presence of a molding tool on the common base and gives the precursor 300a sufficient rigidity so that it substantially retains its shape during vacuum cooking. In the example illustrated, the frame 302a stops upstream of the second end 3053a to give sufficient flexibility to the parts 311a, 312a and thus allow their conformation, and their attachment to the cylinder 100 during vacuum cooking. The precursor 300a, and in particular its zone 305a, is interposed between the first 401 and second 402 portions. The area 305a may, as illustrated, be interposed between two molding surfaces 401a, 401b forming part of the portions 401, 402 respectively. A seal is produced at the surfaces 401a, 401b by a vacuum cover 345 fixed to an internal surface of the portions 401, 402. Seals 347 are produced on this internal surface.

[0100] The cylinder 100 is then positioned around the mandrel 400 which can be draped directly onto the mandrel or formed from a juxtaposition of panels 10 as described above. The precursor 300a is located inside the cylinder 100 and the zone 310a is positioned opposite the cylinder. Generally speaking, the panels 10 and skins (or sectors 304a, 306a) can be assembled in the semi-baked state. They can each be draped, during their manufacture, in the semi-baked state, or alternatively be draped in the raw state, that is to say with a degree of progress of polymerization lower than that of the semi-baked state and then undergo a partial polymerization heat treatment to bring them to the semi-baked state. The elements can then be assembled after this partial polymerization.

[0101] A vacuum cover 341 is then placed around the cylinder 100. The cover may be made of elastomeric material, reinforced or not, and constitutes an element known per se. The cylinder 100 is interposed, in a sealed manner, between the cover 341 and the mandrel 400. The cover 341 is fixed on an external surface of the portions 401, 402 and sealing gaskets 343 are provided on these.

[0102] Vacuum cooking is then carried out as illustrated in [Fig. 19]. This cooking phase can be carried out with or without additional pressure.

[0103] The heating applied leads to a fluidification of the resin(s) present. The vacuuming of the tooling causes the cover 341 to be pressed against the mandrel 400 (pressure arrows PR) so as to keep the cylinder 100 resting on the zone 310a and to conform the cylinder 100 and the precursor 300a on the mandrel 400. Pressure is also applied by the cover 345, which makes it possible to improve the material health of the products obtained after polymerization of the sectors 304a, 306a. The conformation of the parts 311a, 312a is done without deformation of the general shape since the frame 302a is completely polymerized.

[0104] Heating allows the resin to finish polymerizing with the creation of bonds at the level of the polymer chains of the resins (creation of a three-dimensional network), freezing the interfaces and the overall shape of the structure. The polymerization of thermosetting materials is complete after the vacuum curing step.

[0105] Vacuum curing can be carried out in a heating chamber, such as an oven or an autoclave. The oven will allow polymerization under vacuum, the autoclave will allow additional pressure to be provided in addition to the vacuum drawing. Alternatively or in combination, it is possible to use a molding tool equipped with heating elements (not shown) to carry out this curing. The temperature imposed during vacuum curing depends on the resin used and can, for example, be greater than or equal to 150°C, and for example be between 175°C and 185°C, for example close to 180°C.

[0106] As illustrated in [Fig.20], a baked structure is obtained which comprises a body 1000 of the reservoir to be obtained and the common bottom 3000 secured to the body 1000. The body 1000 is obtained after baking the cylinder 100, and the common bottom 3000 is obtained after baking the precursor 300a. The body 1000 is open at its two longitudinal ends 1000a, 1000b which makes it possible to extract the molding portions 401, 402 through them. The tarpaulin 341 was removed after vacuum baking.

[0107] The petals 20 can then be positioned by being juxtaposed in the manner described above to form a dome 200, precursor of the end bottom of the tank, on each of the ends 1000a, 1000b ([Fig.20]). The petals 20 can first be draped over molding portions 38, each of these portions 38 having the shape of a dome 200 and being in the shape of the end bottoms of the tank to be obtained. An internal vacuum cover 241 and an external vacuum cover 243 are positioned on each side of this assembly. The covers 241, 243 ensure the sealing of each assembly comprising the portion 38 and the dome 200. The seals 245 are on the body 1000 and on the portions 38 (not on the shaft 36). The tarpaulins 241, 243 may be similar to the tarpaulins described above. The portion 38 and the domes 200 are interposed between a tarpaulin 241 and a tarpaulin 243. The illustrated example shows two portions 38 symmetrical but it is, of course, within the scope of the invention if this is not the case. The domes 200 are located inside the interior volume defined between the portions 38. Each dome 200 is held in place by a respective portion 38. As illustrated, the portions 38 cover the bottom area 205 but do not cover the end cylindrical junction area 210. The domes 200 are located inside the body 1000. The body 1000 extends from one dome 200 to another. The area 210 has been covered with a thermosetting adhesive 212 positioned opposite the body 1000. As an example of adhesive 212, mention may be made of: FM® adhesive films marketed by the company SOLVAY, for example: FM300, FM309-1, FM377, FM209-1, HexBond® adhesive films marketed by the company HEXCEL, for example: HexBond 322, HexBond 319, HexBond 340, HexBond ST 1480, or adhesive films marketed by the company 3M, for example AF191 or AF3109-2.The domes 200 may be in a half-baked state when positioned at the ends 1000a, 1000b of the body 1000.

[0108] The bottom zone 205 of the dome 200 defines an orifice 206, here in the general shape of a disc, through which extends a shaft 36, or an alternative centering means for the molding portions 38. The precise positioning of the portions 38 as well as their maintenance can be ensured by the shaft 36. The shaft 36 extends along a longitudinal axis X. The shaft also passes through an orifice 3060a of the common bottom 3000. The orifice 3060a is concentric with the orifices 206 of the domes 200 along the axis X. The axis X corresponds to the longitudinal axis of the panels 10, the cylinder 100 and the body 1000 which was described previously. The dome 200 can have a general shape of revolution around the axis X.

[0109] In the example illustrated, the common bottom 3000 is located substantially equidistant from the domes 200 but it does not depart from the scope of the invention when this is not the case depending on the relative volume desired for the compartments C1 and C2. The domes 200 delimit with the body 1000 an internal volume V of the reservoir to be obtained. The common bottom 3000 delimits with the first dome 200 a first compartment C1. The common bottom 3000 delimits with the second dome 200 a second compartment C2 distinct from the first compartment. The domes 200 close the body 1000 on the side of each of its ends 1000a, 1000b.

[0110] A vacuum curing similar to that described above is then carried out to shape the domes 200 thus positioned by keeping the zones 210 and the adhesive 212 resting on the body 1000 and by heating so as to harden the zones 210 and the adhesive 212 and thus secure the end bottoms to the body 1000. The zones 210 are shaped on the body 1000 during this vacuum curing. Pressure is also applied to the zones 205 by the tarpaulins 241, 243 during the vacuum drawing, which makes it possible to improve the material health of the end bottoms obtained after poly merization. Uniform pressure can advantageously be applied by the covers 241, 243 to the domes 200 during their shaping. The illustrated example proposes securing the domes 200 to the body 1000 by carrying out vacuum cooking. The person skilled in the art will recognize that cooking could alternatively be carried out with application of pressure by mechanical tooling attached to the domes, and in particular to the end cylindrical junction zone. The compartmentalized tank is obtained after removal of the tools.

[0111] According to a variant not illustrated, stiffeners can be added after formation of the body and the common base and fixed at the same time as the domes during vacuum cooking, or cooking with application of pressure by added mechanical tooling.

[0112] The example which has just been described concerns the use of a common base precursor with thermoset reinforcement but one could alternatively do without such reinforcement.

[0113] The invention which has just been described is suitable for the manufacture of tanks for the main stage of space launchers (lower stage in English). The invention also applies to tanks for upper stages. In operation, the composite tank can be filled, for example and in a non-limiting manner, with liquid methane, liquid hydrogen or refined kerosene (such as RP-1 for example) or a combination of these compounds in a first compartment, and liquid oxygen in a second compartment. The tank can be used in a cryogenic environment.

[0114] The field of the invention is however not limited to a tank for integration into an aerospace launcher but can find an application in the aeronautical field or, more generally, in any application requiring a compartmentalized tank integrating a common bottom.

[0115] The expression “between ... and ...” must be understood as including the limits.

Claims

Claims

1. Method of manufacturing a compartmentalized composite material tank, comprising: - obtaining a structure including: (i) a cylinder (100), precursor of the body (1000) of the tank, made of thermosetting pre-impregnated fibrous material extending along a longitudinal axis (X), (ii) a molding mandrel (400) comprising two molding portions (401; 402) juxtaposed along the longitudinal axis on which the cylinder is positioned, and (iii) a common base precursor (300a), located inside the cylinder and housed between the molding portions, comprising a common base zone (305a) and at least one thermosetting pre-impregnated fibrous skin (304a; 306a) defining an intermediate cylindrical junction zone (310a) positioned opposite the cylinder, - vacuum curing of the structure during which the cylinder is shaped on the molding mandrel, with the cylinder held in contact with the intermediate cylindrical junction zone and co-curing of the common base precursor with the cylinder to secure the common base to the body, - extraction, after cooking, of the molding portions through the longitudinal ends (1000a; 1000b) of the body, - the positioning, after the extraction of the molding portions, of a dome (200), precursor of the end bottom of the tank, on each of the longitudinal ends of the body, each dome defining with the common bottom a compartment (C1; C2) distinct from the tank to be obtained and defining a zone (210) of cylindrical end junction made of thermosetting pre-impregnated fibrous material covered with a thermosetting adhesive (212) and positioned opposite the body, and - the shaping of the domes thus positioned by keeping the cylindrical end junction zones and the adhesive resting on the body and by heating so as to harden the junction zones and the adhesive and thus secure the end bottoms to the body.

2. Method according to claim 1, in which the common bottom precursor (300a) comprises a frame (302a) of thermoset composite material defining the common bottom zone (305a) which is covered by said at least one skin (304a; 306a) and which is configured to allow conformation of said at least one skin on the molding mandrel (400) on the intermediate cylindrical junction zone (310a).

3. The method of claim 2, wherein the common bottom precursor (300a) comprises a first skin (304a) covering a first face of the armature (302a) and defining a first portion (311a) of the intermediate cylindrical junction zone (310a) which extends towards a first longitudinal end (1000a), and a second skin (306a) covering a second face of the armature (302a), opposite the first face, and defining a second portion (312a) of the intermediate cylindrical junction zone which extends towards a second longitudinal end (1000b) opposite the first longitudinal end.

4. The method of claim 3, wherein the common bottom precursor (300) further comprises a filler material (320) between the first (311) and second (312) portions of the intermediate cylindrical junction area (310).

5. Method according to any one of claims 2 to 4, in which the intermediate cylindrical junction zone (310a) is at least partly formed by an extension of said at least one skin (304a; 306a) beyond the reinforcement (302a).

6. Method according to any one of claims 2 to 5, in which the frame (302e) defines a plurality of flexible tabs (3027e) allowing the conformation of said at least one skin (306e) on the molding mandrel (400) on the intermediate cylindrical junction zone.

7. Method according to any one of claims 2 to 6, wherein the frame (300b) comprises an insulating material (302b) configured to thermally insulate the compartments (Cl; C2) of the tank.

8. Method according to any one of claims 1 to 7, wherein said at least one skin (304a; 306a) has a thinning of thickness on the intermediate cylindrical junction zone (310a) in the direction of a circumferential edge thereof.

9. Method according to any one of claims 1 to 8, in which each skin comprises several sectors (304; 306) juxtaposed around the longitudinal axis (X).

10. Method according to claim 9, in which the neighboring sectors (304; 306) have a thinning of thickness on their re- covering towards their longitudinal edges (304a 1; 304b 1).

11. A method according to any one of claims 1 to 10, wherein the cylinder (100) and said at least one skin (304a; 306a) are assembled in the half-baked state to form said structure, and wherein the domes (200) are in the half-baked state when assembled with the body (1000).

12. A method according to any one of claims 1 to 11, wherein the cylinder (100), said at least one skin (304a; 306a) and the domes (200) have been formed by automatic fiber placement.

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

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

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