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 common bottom precursor and domes intended to form the end bottoms are secured to a body previously cured 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 ("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, according to a first aspect, to a method of manufacturing a compartmentalized composite material tank, comprising: - positioning a common bottom precursor inside a body of the cylindrical tank made of thermoset composite material, said common bottom precursor comprising a thermoset composite reinforcement, defining the common bottom, covered by at least one thermoset pre-impregnated fibrous skin which defines an intermediate cylindrical junction zone which is coated with a first thermoset adhesive and positioned opposite the body, the reinforcement being configured to allow conformation of said at least one skin against the body on this intermediate cylindrical junction zone, - the conformation of the common base precursor thus positioned by maintaining the intermediate cylindrical junction zone and the first adhesive resting on the body and by heating so as to harden the junction zone and the first adhesive and secure the common base to the body, - the positioning, after the common bottom has been secured to the body, 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 second thermosetting adhesive and positioned opposite the body, and - the conformation of the domes thus positioned by maintaining the cylindrical end junction zones and the second adhesive resting on the body and by heating so as to harden the junction zones and the second adhesive and thus secure the end bases to the body.

[0009] The present disclosure relates, according to a second aspect, to a method of manufacturing a compartmentalized composite material tank, comprising: - positioning a common bottom precursor inside a body of the cylindrical tank made of thermoset composite material, said common bottom precursor comprising a thermoset composite reinforcement, defining the common bottom, covered by at least one thermoset pre-impregnated fibrous skin which defines an intermediate cylindrical junction zone which is coated with a first thermoset adhesive and positioned opposite the body, the reinforcement being configured to allow conformation of said at least one skin against the body on this intermediate cylindrical junction zone, - the positioning, after the positioning of the common bottom precursor, 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 precursor 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 second thermosetting adhesive and positioned opposite the body, and - the conformation of the common bottom precursor and the domes thus positioned by keeping the junction zones and the adhesives resting on the body and by heating so as to harden the junction zones and the adhesives and thus secure the end bottoms and the common bottom to the body.

[0010] The first and second aspects of the invention each make it possible to obtain a composite material tank in which the common bottom separates two adjacent compartments inside the tank. In these two aspects, the common bottom precursor and the domes are secured to the body, already thermoset, either sequentially (first aspect) or simultaneously (second aspect). The invention is remarkable in that it makes it possible to dispense with the presence of an internal mandrel which, in the prior art, is delicately dismantled and extracted through small openings at the ends of the tank. It is sufficient, within the framework of the invention, to use positioning tooling for the placement of the common bottom precursor and the domes, which has a much simpler design and is more easily dismantled than the internal mandrel of the prior art.

[0011] 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. 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 guaranteeing good attachment of the common base to the body. As will be described below, the reinforcement may have various structures making it possible to fulfill this function.

[0012] 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.

[0013] In an exemplary embodiment, the common bottom precursor comprises a first skin covering a first face of the frame 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 frame, 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.

[0014] 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.

[0015] In particular, the common bottom precursor may further comprise a filler material between the first and second portions of the intermediate cylindrical junction zone.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Alternatively or in combination, the frame defines a plurality of flexible tabs allowing the conformation of said at least one skin on the body on the intermediate cylindrical junction zone.

[0020] 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.

[0021] In an exemplary embodiment, the frame comprises an insulating material configured to thermally insulate the compartments of the tank.

[0022] 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.

[0023] In particular, the insulating material may be cellular, for example in the form of a honeycomb or in the form of a filling foam.

[0024] Such a characteristic advantageously makes it possible not to penalize the mass of the structure.

[0025] 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.

[0026] Such a characteristic advantageously makes it possible to further improve the material health 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.).

[0027] In an exemplary embodiment, each skin comprises several sectors juxtaposed around the longitudinal axis.

[0028] 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 body without constraint.

[0029] In particular, the neighboring sectors may have a thinning of thickness on their overlap zone in the direction of their longitudinal edges.

[0030] 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.

[0031] In an exemplary embodiment, each dome comprises a thermoset composite dome frame covered by the thermoset pre-impregnated fibrous material defining the end cylindrical junction zone and configured to allow conformation of said material on the body.

[0032] The dome frame makes it possible to dispense with the presence of molding tooling on the domes during the manufacture of the tank, thus making it possible to further simplify the tooling structure. The dome frame may have the characteristics described above for the common bottom precursor frame.

[0033] In an exemplary embodiment, said at least one skin and the domes are positioned in the half-cooked state.

[0034] 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”).

[0035] 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.

[0036] In an exemplary embodiment, said at least one skin and the domes have been formed by automatic fiber placement.

[0037] 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. The automatic placement of fibers also makes it possible to obtain elements of low permeability in comparison with parts obtained by winding, suitable for example for the storage of cryogenic propellants.

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

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

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

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

[0042] In an exemplary embodiment, the precursor domes have a thinning in thickness on their end cylindrical junction zones towards a circumferential edge of the dome.

[0043] Such a characteristic helps to further minimize the misalignments and stress concentrations in the reservoir.

[0044] 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.

[0045] The sectorization of the domes further improves their conformation during cooking by allowing relative sliding between the petals.

[0046] In particular, the neighboring petals may have a thinning of thickness on their overlap zone in the direction of their longitudinal edges.

[0047] Such a characteristic helps to further minimize the misalignments and stress concentrations in the reservoir. 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 body taken in cross section relative to its longitudinal axis. [Fig.lA] [Fig.lA] represents, in a schematic and partial manner, the angle of bevel of the panel of [Fig.l]. [Fig.2] [Fig.2] represents, schematically and partially, a variant of cylinder intended to form the body. [Fig.3] [Fig.3] represents, schematically and partially, another variant of cylinder intended to form the body. [Fig.4] [Fig.4] represents, schematically and partially, another variant of cylinder intended to form the body. [Fig.5] [Fig.5] represents, schematically and partially, another variant of cylinder intended to form the body. [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.l 1] [Fig.l 1] 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.l 1] 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] represents, schematically and partially, the implementation of a first step of a method according to the first aspect of the invention. [Fig. 19] [Fig. 19] represents, schematically and partially, the implementation of a second step of a method according to the first aspect of the invention. [Fig.20] [Fig.20] represents, schematically and partially, the implementation of a method according to the second aspect of the invention. Description of the embodiments

[0048] 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.

[0049] The description below addresses, in a first step, the structure and the obtaining of the body, the precursor domes of bottoms and the common bottom precursor. The joining of the different elements together, as well as the cooking phases will be detailed in a second step.

[0050] Tank body to be obtained

[0051] The body is obtained by baking a cylinder 100 made of thermosetting pre-impregnated fibrous material. Vacuum baking 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. The temperature imposed during baking of the cylinder 100 depends on the resin used and may, 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. The cylinder may be impregnated with an epoxy resin.

[0052] 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, for example after draping on a mandrel. 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, designated by "axis X" in the following.

[0053] Generally speaking, the cylinder may comprise at least two fibrous panels, or even at least three fibrous panels. The example described here concerns the case of a cylinder with four panels.

[0054] 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 reinforcement 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. Advantageously, the same resin is used in the different panels, or, failing that, compatible resins.

[0055] 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.

[0056] [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 el0 of at least 50%, for example at least 90%. This reduction in the thickness el0 is for example between 50% and 95%, or even between 90% and 95%. [Fig.1A] 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.

[0057] Figures 2 to 5 describe the juxtaposition of these panels 10 to form the cylinder 100, precursor of the body of the tank.

[0058] [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.

[0059] 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.

[0060] 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.

[0061] The variants of Figures 4 and 5 show cases where there is no tiling which are also covered by the present invention.

[0062] 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.

[0063] End bottom precursor domes

[0064] [Fig. 6] represents a petal 20, which has the shape of a dome sector, draped in shape. According to this example, each base precursor dome is obtained by juxtaposition of thermosetting pre-impregnated fibrous petals 20. Generally 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.

[0065] 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. advantageously for the petals 20 a resin identical to that of the panels 10, or failing that compatible therewith. In a similar manner to the panels 10, the petals 20 can be draped over male or female tooling.

[0066] 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.

[0067] 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.

[0068] The petals 20 define a sector 203d of a cylindrical end junction zone which is intended to come opposite 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.

[0069] 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.

[0070] 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 meeting 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 latitude 25, and substantially constant over the zone 210.

[0071] A possible structure for the body 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.

[0072] Common background precursor

[0073] [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.

[0074] 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 body 1000 in the assembly.

[0075] 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 part 312 of the intermediate cylindrical junction zone 310.

[0076] A draping possibility to obtain the precursor 300 is now detailed.

[0077] 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 frame 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.

[0078] 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.

[0079] 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.

[0080] 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 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.

[0081] The sectors 304 are juxtaposed at their edges 304al, 304bl with overlap between neighboring sectors, in a manner similar to what was described above for the petals 20. Thus, [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.

[0082] 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. Part 312 is also intended to come opposite the body.

[0083] 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.

[0084] 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 precisely, 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.

[0085] The extension of the skins beyond the reinforcement ensures that they can conform against the body during the vacuum cooking step. Thus, the possibility of 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 conceivable to allow the desired conformation of the skins as will be described below.

[0086] Other common background precursor variants can be used within the scope of the invention.

[0087] [Fig. 13] shows a common base precursor 300a of similar structure to that of [Fig. 10], comprising a frame 302a interposed between first 304a and second 306a skin sectors. The first 304a and second 306a sectors extend beyond the frame 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.

[0088] [Fig. 14] shows a common bottom 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.

[0089] [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 single-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.

[0090] [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.

[0091] [Fig. 17] illustrates a variant of a common base precursor in which the armature is extended compared to the examples just described.

[0092] [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 body despite an increased length of the frame. The tabs 3027e are not in direct contact with the body during cooking, the skin 306e coming to the interface between the frame and the body. 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.

[0093] The various elements used in the manufacture of the tank have just been described. Figures 18 to 20, which will now be described, illustrate possible steps for obtaining the tank from these elements.

[0094] [Fig. 18] illustrates a first step of a method according to the first aspect of the invention. The body 1000 made of thermoset composite material has been obtained beforehand by curing the precursor cylinder as described above. The common base precursor 300a, for example of the type illustrated in [Fig. 13], is positioned inside the body 1000. The precursor 300a defines an intermediate cylindrical junction zone 310a which here comprises a first portion 311a which extends towards a first longitudinal end 1000a of the body 1000, and a second portion 312a which extends towards a second longitudinal end 1000b of the body 1000 opposite the first end 1000a. The first 1000a and second 1000b ends are open in the illustrated example. The precursor 300a extends circumferentially around the X-axis. The precursor 300a may have a general shape of revolution around the X-axis.The precursor 300a may comprise a zone 305a which is intended to form a common bottom separating the compartments 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 3051a 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 body 1000. In the example considered, the end 3051a is housed in a circumferential support tool 362 attached around a shaft 36. The shaft 36 extends inside the body 1000 from one end 1000a to another 1000b. The tool 362 is for example in the form of a ring. A vacuum cover 345 is positioned on each of the faces of the precursor 300a and seals 347 are made on each axial end of the tooling 362 and on the body 1000 as illustrated. The . The tarpaulin may be made of elastomeric material, reinforced or not, and constitutes an element known per se. The person skilled in the art will recognize that other solutions are possible for positioning the precursor, the illustrated embodiment being only one example among others. 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 body 1000. This securing is achieved by means of a first thermosetting adhesive 322, distinct from the resin impregnating each skin of the precursor 300a, which covers the zone 310a.As an example of adhesive 322, we can cite: the FM® adhesive films marketed by the company SOLVAY, for example: FM300, FM309-1, FM377, FM209-1, the 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 AF 191 or AF3109-2.

[0095] The armature 302a is present on the first end 3051a and, more generally, on the zone 305a. Thus, the armature 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 shaping. In the example illustrated, the armature 302a stops upstream of the second end 3053a to give sufficient flexibility to the parts 311a, 312a and thus allow their shaping, and their attachment to the body 1000. In general, the skins (or sectors 304a, 306a) may be in the half-baked state when they are positioned inside the body 1000.They can each be draped, during their manufacture, in the semi-cooked 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-cooked state and then undergo a partial polymerization heat treatment to bring them to the semi-cooked state.

[0096] The shaping of the precursor 300a is then carried out by keeping the zone 310a and the first adhesive 322 pressed against the body 1000 and by heating so as to harden the zone 310a and the first adhesive and secure the common base 3000 to the body 1000. Generally speaking, this shaping step can be carried out by vacuum baking. A vacuum is drawn between the tarpaulins 345 which causes the tarpaulins 345 to be pressed against the precursor 300a and against the body 1000 so as to carry out the shaping while having a common base having good material health. The shaping of the parts 311a, 312a is carried out without deformation of the general shape since the frame 302a is completely polymerized.

[0097] The heating fluidizes the resin and allows it to finish polymerizing. The heating also allows the first adhesive 322 to harden so as to secure the common base 3000 to the body 1000. The polymerization of the common base 3000 and the body 1000 is complete after the vacuum curing step.

[0098] 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. 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.

[0099] 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 always open at its ends 1000a, 1000b which makes it possible to position the domes 200 there, precursors of the end bottom of the reservoir as will be described in connection with [Fig. 19].

[0100] The petals 20 can thus 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. 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 tank 241 and an external vacuum tank 243 are positioned on each side of this assembly. The tanks 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 symmetrical portions 38 but it is, of course, within the scope of the invention if this is not the case. The domes 200 are located inside the interior volume defined between the portions 38. Each dome 200 is held in place by a respective portion 38. 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 second thermosetting adhesive 212 positioned opposite the body 1000. The second adhesive 212 may have the same characteristics as the first adhesive 322 described above. The domes 200 may be in a half-baked state when positioned at the ends 1000a, 1000b of the body 1000.

[0101] 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, of the cylinder 100 and of the body 1000 which has been described previously. The dome 200 may have a general shape of revolution around the X axis.

[0102] 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.

[0103] The domes 200 are then shaped by keeping the zones 210 and the second adhesive 212 pressed against the body 1000 and by heating so as to harden the zones 210 and the second adhesive 212 and thus secure the end bottoms to the bodies. Generally speaking, this shaping step can be carried out by vacuum baking. The zones 210 are shaped on the body 1000 during this vacuum baking. Pressure is also applied to the zones 205 by the covers 241, 243 during the vacuum drawing, which makes it possible to improve the material health of the end bottoms obtained after polymerization. Uniform pressure can advantageously be applied by the covers 241, 243 to the domes 200 during their shaping. The compartmentalized tank is obtained after removal of the tools.

[0104] According to a variant not illustrated, stiffeners can be added after securing the common base and fixed at the same time as the domes during vacuum cooking.

[0105] The example which has just been described concerns the use of domes 200 without thermoset reinforcement when they are positioned inside the body 1000 but it is possible, as a variant, to provide them with such reinforcement, the domes then having a structure similar to that of the common base precursor.

[0106] The example which has just been described concerns the first aspect of the invention, that is to say a sequential joining of the common bottom and the end bottoms to the body. The variant of [Fig.20] illustrates a possible embodiment relating to the second aspect where the common bottom and the end bottoms are joined simultaneously to the body 1000 by vacuum cooking. The same references are used for the same elements. The characteristics described above for the first aspect apply mutatis mutandis to the second aspect.

[0107] 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 non-limiting manner with liquid methane, liquid hydrogen or refined kerosene (such as RP-1) 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.

[0108] 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.

[0109] The expression “between ... and ...” must be understood as including the limits.

Claims

Claims

1. Method of manufacturing a compartmentalized composite material tank, comprising: - positioning a common bottom precursor (300a) inside a body (1000) of the cylindrical tank made of thermoset composite material, said common bottom precursor comprising a thermoset composite reinforcement (302a), defining the common bottom, covered by at least one thermoset pre-impregnated fibrous skin which defines an intermediate cylindrical junction zone (310a) which is coated with a first thermoset adhesive (322) and positioned opposite the body, the reinforcement being configured to allow conformation of said at least one skin against the body on this intermediate cylindrical junction zone, - the conformation of the common base precursor thus positioned by maintaining the intermediate cylindrical junction zone and the first adhesive resting on the body and by heating so as to harden the junction zone and the first adhesive and secure the common base (3000) to the body, - the positioning, after the common bottom has been secured to the body, of a dome (200), precursor of the end bottom of the tank, on each of the longitudinal ends (1000a; 1000b) of the body, each dome defining with the common bottom a compartment (C1; C2) distinct from the tank to be obtained and defining a cylindrical end junction zone (210) made of thermosetting pre-impregnated fibrous material covered with a second thermosetting adhesive (212) and positioned opposite the body, and - the shaping of the domes thus positioned by maintaining the cylindrical end junction zones and the second adhesive resting on the body and by heating so as to harden the junction zones and the second adhesive and thus secure the end bases to the body.

2. Method of manufacturing a compartmentalized composite material tank, comprising: - positioning a common bottom precursor (300a) inside a body (1000) of the cylindrical tank made of thermoset composite material, said common bottom precursor comprising a thermoset composite reinforcement (302a), defining the common bottom, covered by at least one thermoset pre-impregnated fibrous skin scissable which defines an intermediate cylindrical junction zone (310a) which is coated with a first thermosetting adhesive (322) and positioned opposite the body, the frame being configured to allow a conformation of said at least one skin against the body on this intermediate cylindrical junction zone, - the positioning, after the positioning of the common bottom precursor, of a dome (200), precursor of the end bottom of the tank, on each of the longitudinal ends (1000a; 1000b) of the body, each dome defining with the common bottom precursor a compartment (Cl;C2) distinct from the reservoir to be obtained and defining a cylindrical end junction zone (210) made of thermosetting pre-impregnated fibrous material covered with a second thermosetting adhesive (212) and positioned opposite the body, and - the conformation of the common bottom precursor and the domes thus positioned by maintaining the junction zones and the adhesives in contact with the body and by heating so as to harden the junction zones and the adhesives and thus secure the end bottoms and the common bottom to the body.;

3. Method according to claim 1 or 2, in which the common bottom precursor (300a) comprises a first skin (304a) covering a first face of the reinforcement and defining a first part (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 reinforcement, opposite the first face, and defining a second part (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 1 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. A method according to any one of claims 1 to 5, wherein the frame (302e) defines a plurality of flexible tabs (3027e) au- allowing the conformation of said at least one skin (306e) on the body on the intermediate cylindrical junction zone.

7. Method according to any one of claims 1 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) towards 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 overlap zone in the direction of their longitudinal edges (304a 1; 304b 1).

11. A method according to any one of claims 1 to 10, wherein each dome comprises a thermoset composite dome frame covered by the thermoset pre-impregnated fibrous material defining the end cylindrical joining zone and configured to allow conformation of said material on the body.

12. A method according to any one of claims 1 to 11, wherein said at least one skin (304a; 306a) and the domes (200) are positioned in a half-baked state.

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

14. A method according to any one of claims 1 to 13, the body (1000), said at least one skin (304a; 306a) and the domes (200) comprise carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

15. A method according to any one of claims 1 to 14, wherein said at least one skin (304a; 306a) and the domes (200) are pre-impregnated with an epoxy resin.

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