Geodesic draping method

Abstract

The invention relates to a method for draping fibrous structures on a draping shape (F) comprising at least one developable portion, the fibrous structures comprising fibres extending in a determined direction (t1, t2, t3, t4, t11, t21), the method being characterised in that the fibrous structures are deposited on the draping shape so that the fibres of the fibrous structures overlap at straight lines of the developed surface of the developable portion of the draping shape.

Description

[0001] Description

[0002] Title of the invention: Geodesic draping method

[0003] Technical Field

[0004] The invention relates to the general field of methods for draping a shape using fibrous structures, and in particular to methods for draping by automatic placement of fibers.

[0005] Prior art

[0006] It is known to produce composite material parts by draping them over a form of strata or layers of dry or pre-impregnated fibrous structures. In some current techniques, draping is carried out manually by an operator. These techniques can lead to relatively high part production costs and risks of positioning errors in the layers or fibrous structures. This leads to a certain variability in the mechanical performance of the parts obtained, or even to parts with insufficient mechanical properties.

[0007] Mechanized solutions have been developed to reduce the production cost of these composite material parts, such as the automatic fiber placement technique, also known as AFP for "Automated Fiber Placement". Such a technique is described in particular in document FR 3 066 719. The fibers are then automatically deposited in the form of fibrous strips called "wicks".

[0008] In the prior art, when it is desired to drape a developable conical or truncated conical draping shape F o including generators g O i, go2 and extending between a smaller contour p Oi and a larger outline p 02 , the deposited wicks are oriented according to the Cartesian reference of the draping shape F o , as illustrated in Figure 1. Thus, the trajectories of the deposited fibers or fiber strands intersect the generatrices g O i, go2 of the developable form F owith the same angle. Figure 2 shows the developed surface F Od of the developable form F o open at generator level g O i. Several fibrous layers can thus be deposited, each fibrous layer having a different fiber orientation. It is thus possible to achieve quasi-isotropic draping.

[0009] However, it has been found that strands deposited using this method can exhibit significant deformation and undulation. The strength and mechanical characteristics of the draped piece obtained using this method may therefore be insufficient.

[0010] It is also known to lay the rovings with a "spiral" winding, as described in document US8677622. However, this draping method generates large variations in thickness, with some areas of the draping shape being covered by a lot of fibers and other areas by very few fibers. In addition, the piece thus draped has a large heterogeneity in the fiber orientations, with not all areas having the same proportion of fibers for each orientation. It is therefore extremely difficult to achieve quasi-isotropic draping with this method.

[0011] Statement of the invention

[0012] The present invention aims to overcome the aforementioned drawbacks. In particular, it has been found that the further the conical or truncated cone-shaped draping form is from the shape of a cylinder, that is to say, the more it has a significant slope relative to its axis, the more difficult it is to apply the strands without undulations or deformations. Indeed, when the strand is deposited on a significant slope with the method(s) of the prior art, the two longitudinal edges of the strand do not travel the same distance on the draping form. Thus, the deposited strand undulates or deforms. This phenomenon is even more marked when the section of the draping form is reduced or when the width of the applied strand is large.

[0013] Thus, the invention proposes a method for draping fibrous structures on a developable draping form, the fibrous structures comprising fibers extending in at least one determined direction, the method being characterized in that the fibrous structures are deposited on the draping form so that the fibers of said fibrous structures are superimposed on straight lines of the developed surface of the draping form.

[0014] Preferably, the developable draping shape comprises at least one portion of conical or frustoconical shape. Indeed, the method as described above is particularly suitable for conical or frustoconical shapes.

[0015] According to a variant, the draping shape is not fully developable, and comprises a developable portion. The method of the invention and its variants then apply only to the developable portion of the draping shape.

[0016] By laying the fibers of the fibrous structures so as to follow trajectories corresponding to straight lines of the developed shape of the draping form, it is ensured that the draping of the fibrous structures is carried out properly, without undulation or deformation.

[0017] According to a particular embodiment of the invention, the fibrous structures are draped so as to form one or more developable fibrous layers on the draping form, the fibrous layer(s) extending around the draping form between a first and a second edge, the fibrous structures of the same fibrous layer being deposited so that the fibers of the fibrous structures of said fibrous layers are superimposed on at least one set of parallel straight lines of the developed surface of said fibrous layer.

[0018] Thus, the invention makes it possible to produce a draping with several layers which are themselves developable. This ensures that a multi-layer draping is produced without any risk of undulation or deformation, despite the superposition of the layers.

[0019] According to another particular embodiment of the invention, a set of fibrous layers is draped over the draping form so that in each fibrous layer of the set of fibrous layers the fibers extend in at least one direction of extension which forms a non-zero crossing angle with the direction(s) of extension of the fibers of the other layers of the set of fibrous layers.

[0020] Thus, the resulting draping will have interesting mechanical characteristics in several directions, and will therefore be more robust. The draping can include several sets of fibrous layers, the sets of fibrous layers being able to be identical or distinct from each other.

[0021] Preferably, the set of fibrous layers comprises at least three fibrous layers, in order to obtain satisfactory mechanical resistance in sufficiently varied directions.

[0022] According to another particular embodiment of the invention, the crossing angle is between 80% and 120% of a multiple of the ratio of 180° by the total number of layers in the set of fibrous layers. Preferably, the crossing angle is between 90% and 110% of a multiple of the ratio of 180° by the total number of layers in the set of fibrous layers.

[0023] This ensures that the most isotropic draping possible is obtained, adapted to the number of layers in the assembly. For example, in the case where the set of fibrous layers is made up of four fibrous layers, it is advantageous for each fibrous layer to have fibers with an extension direction offset by approximately 45°, 90° and 135° relative to the extension directions of the fibers in the other three layers to obtain the most isotropic draping possible.

[0024] The crossing angle between the fibers of two distinct fibrous layers may be different depending on the portions of the layup. Thus, according to a particular embodiment of the invention, the crossing angle is between 80% and 120% of a multiple of the ratio of 180° by the total number of layers in the set of fibrous layers at at least one generatrix of the layup shape. According to another embodiment of the invention, the crossing angle is between 80% and 120% of a multiple of the ratio of 180° by the total number of layers in the set of fibrous layers at any point of the layup.

[0025] According to another particular embodiment of the invention, the first edges of the fibrous layers of the set of fibrous layers are circumferentially offset relative to each other on the draping form and the second edges of the fibrous layers of the set of fibrous layers are circumferentially offset relative to each other on the draping form.

[0026] Indeed, the edges of the fibrous layers constitute weaknesses in the draping. It is therefore preferable that the edges of the fibrous layers do not overlap on the draping form, in order to improve the robustness of the draping and the final part obtained.

[0027] According to another particular embodiment of the invention, at least a first part of the second edge of at least one fibrous layer joins the first edge of said fibrous layer, said first part of the second edge extending from the largest end contour of said fibrous layer connecting the first edge to the second edge.

[0028] By draping the fibrous layer so that its edges meet at least in part from the largest end contour of said fibrous layer, it is possible for at least a part of the fibrous structures emerging from the first or second edge to be able to block the fibrous structures emerging from the other edge. The hold of the draped layer is thus improved. In addition, by producing fibrous layers which make a complete turn of the draping form, it is easier to obtain a generally uniform thickness over the entire circumference of the draping form.

[0029] According to another particular embodiment of the invention, the first and second edges of at least one fibrous layer meet and correspond to a generatrix of said fibrous layer.

[0030] According to another particular embodiment of the invention, the first edge of at least one fibrous layer extends in the same direction as the fibers of the fibrous structures of said layer present on the side of the first edge.

[0031] The first edge will then be defined by a single fibrous structure, or at least by a very limited number of successive fibrous structures. The first edge will therefore be able to easily block the fibrous structures emerging from the second edge, for example by slightly overlapping the ends of the fibrous structures forming the second edge. According to another particular embodiment of the invention, the second edge comprises a second part distinct from the first part extending in the same direction as the fibers of the fibrous structures of said layer present on the side of the second edge.

[0032] Thus, the ends of the fibrous structures emerging at the first and second edges are limited, thus greatly improving the strength of the layup thus obtained. In addition, this particular embodiment makes it possible to limit the number of short draped fibrous structures, which have a greater chance of becoming detached from the rest of the layup while they do not provide any real improvement in the mechanical properties. Short fibrous structures are also more difficult to deposit, in particular with the automatic fiber layup method. Finally, such an overlap makes it possible to obtain a “net shape” fiber preform, i.e. one that does not require additional cutting operations to cut the protruding fibers.

[0033] According to another particular embodiment of the invention, the first edge covers at least the first part of the second edge.

[0034] The first edge can thus better block the fibrous structures emerging from the second edge, by overlapping the ends of the fibrous structures forming the second edge.

[0035] According to another particular embodiment of the invention, the method further comprises draping a plurality of stiffening fibrous structures onto the draping form, the stiffening fibrous structures being draped such that the fibers of said stiffening fibrous structures overlap generatrices of the developed surface of the draping form.

[0036] By carrying out a “classic” draping of the fibers along the generators, the rigidity and the resistance of the draping obtained are improved.

[0037] According to a particular embodiment of the invention, the draping of the fibrous structures is carried out by automatic placement of fibers.

[0038] By using automatic fiber placement draping, the repeatability and quality of the process are improved while limiting manufacturing costs. The invention also relates to a fiber preform comprising at least one developable part, said preform comprising a plurality of fiber layers formed by fiber structures, characterized in that the fibers of the fiber structures of at least one fiber layer correspond to straight lines of the developed surface of the developable part of the fiber preform.

[0039] Preferably, the developable portion of the fiber preform comprises at least one portion of conical or frustoconical shape.

[0040] Brief description of the drawings

[0041] [Fig. 1] Figure 1 is a schematic perspective view of a developable draping form on which fibrous strands according to the prior art are draped.

[0042] [Fig. 2] Figure 2 is a schematic representation of the developed surface of the shape of Figure 1.

[0043] [Fig. 3] Figure 3 is a schematic perspective view of a developable draping form.

[0044] [Fig. 4] Figure 4 is a schematic sectional view of an AFP dispensing head.

[0045] [Fig. 5] Figure 5 is a schematic front perspective view of a first geodesic fibrous layer according to the invention having an orientation of 90°.

[0046] [Fig. 6] Figure 6 is a schematic perspective view from behind of the first geodesic fibrous layer of Figure 5.

[0047] [Fig. 7] Figure 7 is a schematic view of the developed surface of the first geodesic fibrous layer of Figures 5 and 6.

[0048] [Fig. 8] Figure 8 is a schematic front perspective view of a second geodesic fibrous layer according to the invention having an orientation of 0°.

[0049] [Fig. 9] Figure 9 is a schematic perspective view from behind of the second geodesic fibrous layer of Figure 8.

[0050] [Fig. 10] Figure 10 is a schematic view of the developed surface of the second geodesic fibrous layer of Figures 8 and 9. [Fig. 11] Figure 11 is a schematic front perspective view of a third geodesic fibrous layer according to the invention having an orientation of 45°.

[0051] [Fig. 12] Figure 12 is a schematic perspective view from behind of the third geodesic fibrous layer of Figure 11.

[0052] [Fig. 13] Figure 13 is a schematic view of the developed surface of the third geodesic fiber layer of Figures 11 and 12.

[0053] [Fig. 14] Figure 14 is a schematic front perspective view of a fourth geodesic fibrous layer according to the invention having an orientation of 135°.

[0054] [Fig. 15] Figure 15 is a schematic perspective view from behind of the fourth geodesic fibrous layer of Figure 14.

[0055] [Fig. 16] Figure 16 is a schematic view of the developed surface of the fourth geodesic fiber layer of Figures 14 and 15.

[0056] [Fig. 17] Figure 17 is a schematic perspective view of a geodesic fibrous layer according to a first variant of the invention.

[0057] [Fig. 18] Figure 18 is a schematic view of the developed surface of the geodesic fibrous layer of Figure 17.

[0058] [Fig. 19] Figure 19 is a schematic perspective view of a geodesic fibrous layer according to a second variant of the invention.

[0059] [Fig. 20] Figure 20 is a schematic view of the developed surface of the geodesic fibrous layer of Figure 19.

[0060] [Fig. 21] Figure 21 is a schematic front perspective view of a first drape comprising the first, second, third and fourth geodesic layers of Figures 5 to 16.

[0061] [Fig. 22] Figure 22 is a schematic perspective view from behind of the first layup of Figure 21.

[0062] [Fig. 23] Figure 23 is a schematic view of the developed surface of the first layup of Figures 21 and 22. [Fig. 24] Figure 24 is a schematic front perspective view of a second layup comprising twice the third layer of Figures 11 to 13.

[0063] [Fig. 25] Figure 25 is a schematic perspective view from behind of the second drape of Figure 24.

[0064] [Fig. 26] Figure 26 is a schematic view of the developed surface of the second layup of Figures 24 and 25.

[0065] [Fig. 27] Figure 27 is a schematic view of a developed surface of a third layup.

[0066] Description of the embodiments

[0067] The invention makes it possible to produce a fiber preform having the shape of the part to be obtained by draping a plurality of fiber structures on a draping form. The fiber preform is intended to form the fiber reinforcement of the part to be obtained.

[0068] The draping form comprises an internal or external draping surface intended to be draped by the fibrous structures. The draping of the draping form is carried out by applying fibrous structures to the draping surface of said draping form. Preferably, the draping is carried out on the external surface of the draping form, which is more accessible. However, it does not depart from the scope of the invention if the draping is carried out on the internal surface of the draping form.

[0069] The draping surface comprises at least one developable portion. The draping surface may be entirely developable. By extension, the term “developable draping shape” refers to a draping shape whose draping surface is developable. The draping surface may have at least one portion of a conical or frustoconical shape. The draping shape may be a conical or frustoconical shape. The draping shape may also have a complex developable shape, comprising portions at least partially of a conical or frustoconical shape. For example, the draping shape may have a developable crown formed by a plurality of lobes distributed over a circumference, said lobes having, for example, a partially frustoconical shape.Such a draping form may, for example, allow the draping of a fiber preform intended to form the fiber reinforcement of a turbojet flow mixer, the draping form itself having the overall shape of a turbojet flow mixer. An example of a turbojet flow mixer is described in document FR 3 061 749.

[0070] Figure 3 illustrates an example of a draping shape F. The draping shape F extends around a central axis A. Thus, the draping surface of the draping shape F extends around the central axis A. In the example illustrated in Figure 3, the draping shape F and the draping surface have a circular section. The central axis A then corresponds to the axis of revolution of the draping surface. However, it does not depart from the scope of the invention if the section of the draping surface is an ellipse, provided that said draping surface remains developable. The central axis then corresponds to the axis passing through the center of all the elliptical sections.

[0071] The draping shape F, or the draping surface, extends along the central axis A between a smaller contour pi and a larger contour p2. The smaller contour pi corresponds to the end contour of the draping shape F, or the draping surface, of smaller dimension. The larger contour p2corresponds to the end contour of the draping shape F, or the draping surface, of larger dimension.

[0072] The draping surface of the draping shape F includes infinitely many generators g, as illustrated in Figure 3.

[0073] The fibrous structures are preferably in the form of fibrous rovings or fabric plies. A "roving" is understood to mean a collection of long fibers or filaments substantially parallel to each other and joined together in a non-woven web. The fibrous structures may comprise continuous and long fibers. In the case where the fibrous structures are in the form of fabric plies, they are generally formed by the woven interlacing of fibers in two directions, which are usually perpendicular to each other.

[0074] The fibers in the fibrous structures may be ceramic, glass, or carbon fibers. The ceramic fibers may be fibers made of a non-oxide material, such as silicon carbide (SiC), or of an oxide material, such as alumina, or of a material comprising predominantly alumina. The glass fibers may comprise a mixture predominantly based on silica.

[0075] The fibrous structures may be dry, i.e. not impregnated with a resin, pre-impregnated or filled with particles. The fibers of the dry fibrous structures may, however, be coated with a temporary binder, for example organic, which may or may not be removed before the densification of said fibrous structures.

[0076] The fibrous structures may be impregnated with a thermoplastic or thermosetting material, which may include solid fillers. The fibrous structures may also be impregnated with a thermoplastic or thermosetting material that does not include solid fillers. The fibrous structures may be impregnated solely with an organic phase consisting of a thermoplastic material.

[0077] Thermoplastic materials that can impregnate the fibrous structures can be chosen from: polyaryletherketones (PAEK) such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimides (PEI), polyphenylene sulfide (PPS), polyvinyl alcohol (PVA), aliphatic polyethers and polysulfone (PSU). Thermosetting materials that can impregnate the fibrous structures can be chosen from: epoxies, phenolics and polybismaleimides (BMI).

[0078] Pre-impregnation of fibrous structures can be carried out by any conventional technique, for example by dipping, by roller application or by spraying.

[0079] The fibrous structures can be applied to the F-form by manual draping. Preferably, in order to improve the repeatability and quality of the application of the fibrous structures to the F-form while reducing the operating time, the fibrous structures are applied to the F-form by automatic fiber placement.

[0080] Figure 4 schematically illustrates the structure of a deposition head 1 of a device for implementing an automatic fiber placement technique. The structure of the deposition head 1 is well known. The deposition head 1 is fed by the fiber structures 3, preferably in the form of a strip or a wick.

[0081] The strip or wick 3 can be conveyed by a conveying element 5 to a pressure application element 7 located on the side of the draping form F. The conveying element 5 is here in the form of a pair of counter-rotating rollers 5a and 5b between which the strip or wick 3 is present. The conveying element 5 makes it possible to advance the strip or wick 3 to the pressure application element 7. The pressure application element 7 applies pressure to the strip or wick 3 in order to carry out the deposition on the draping form F. The pressure application element 7 is here in the form of a roller.

[0082] The deposition head 1 may, in addition, comprise a heating element 9 located in the vicinity of the pressure application element 7. This heating element 9 makes it possible, in the case of a strip or wick 3 impregnated with a thermoplastic polymer, to heat said impregnated strip or wick 3 during its deposition in order to fluidify the thermoplastic polymer and thus to confer the desired adhesive power to the strip or wick 3 deposited.

[0083] During deposition, the deposition head 1 is movable in order to apply the strip or wick 3 along a first determined trajectory on the draping form F. Once the application has been carried out along this first trajectory, a cutting element 8 of the deposition head 1 cuts the strip or wick 3. After this cutting, the deposition of a first fibrous structure is thus obtained, formed by a first section of the strip or wick 3, along a first trajectory on the draping form F.

[0084] The draping operation is then continued by advancing the strip or wick 3 in the deposition head 1 to the pressure application element 7 by actuating the conveying element 5. The deposition head 1 can be moved in order to deposit the wick or strip 3 along a second trajectory on the draping form F. The deposition of a second fibrous structure, formed by a second section of the strip or wick 3 along a second trajectory, is then obtained in a manner similar to that described previously.

[0085] The draping form F can obviously be rotated around its central axis A during draping to facilitate the deposition of the fibrous structures.

[0086] The draping is then continued by depositing several other fibrous structures in the same manner as described previously.

[0087] Regardless of the draping method used, the fibrous structures can be deposited so as to form fibrous layers on the draping shape F. Thus, each fibrous layer is itself developable, itself extends around the central axis A and itself has an infinite number of generators. The fibrous layers extend around the draping shape F between a first edge and a second edge.

[0088] The fibrous layers extend along the central axis A between a smaller contour and a larger contour. The smaller contour corresponds to the end contour of the smaller fibrous layer. The larger contour corresponds to the end contour of the larger fibrous layer. The end contours of a fibrous layer correspond to the ends of the fibrous layer opposite each other along the central axis A. The smaller contour and the larger contour connect the first edge and the second edge.

[0089] Preferably, at least a first portion of the second edge of the fibrous layers joins the first edge, said first portion of the second edge extending from the largest end contour of the fibrous layer. At least the first portion of the second edge of the fibrous layers and the first edge may thus be merged.

[0090] In the present application, it is considered that two edges or parts of edges of a fibrous layer are superimposed, immediately adjacent or spaced by a very small gap in front of the perimeter of the section of said fibrous layer.

[0091] According to the invention, the trajectories of the fibrous structures deposited on the draping form F are determined, i.e. the trajectories of the fibers of the draped fibrous structures are determined. The trajectories of the fibrous structures deposited on the draping form F preferably correspond to the trajectories of the fibers deposited on the draping form F.

[0092] According to the invention, the fibrous structures of at least one fibrous layer are deposited so that the fibers of said fibrous structures are superimposed on straight lines of the developed surface of the draping shape F. Thus, said fibrous layer is itself developable, and the fibers present in said fibrous layer extend along trajectories which correspond to straight lines on the developed surface of said layer. Said fibrous layer is therefore geodesic.

[0093] Here, the term "geodesic" refers to a developable fibrous layer in which the fibers of the fibrous structures extend along trajectories that correspond to straight lines of the developed surface of said layer. Said trajectories are also referred to as "geodesic". In contrast, here, the term "Cartesian" refers to a developable fibrous layer in which the fibers of the fibrous structures extend along trajectories that intersect the generatrices of said fibrous layer with a constant angle, or that coincide with the generatrices of said fibrous layer. These trajectories are also referred to as "Cartesian". Figures 1 and 2 illustrate an example of a Cartesian fibrous layer, in which the strands m0 extend along Cartesian trajectories.

[0094] Preferably, within a geodesic fibrous layer, the fibers of the fibrous structures extend along trajectories which correspond to a set of parallel straight lines of the developed surface of said layer. Here, the term "uniform geodesic" denotes a developable fibrous layer in which the fibers of the fibrous structures extend along trajectories which correspond to a set of parallel straight lines of the developed surface of said layer.

[0095] When at least the first part of the second edge of a uniform geodesic fiber layer joins the first edge of said fiber layer, the fiber layer is defined by a reference generatrix and by an orientation. The reference generatrix of such a uniform geodesic fiber layer is the generatrix of the fiber layer furthest from the generatrix of said fiber layer extending from the intersection between the smallest contour of the fiber layer and the extension of the first part of the second edge. The orientation of such a uniform geodesic fiber layer is the angle of intersection between the trajectories of the fibers of the fiber structures of the fiber layer and the reference generatrix. The orientation of a uniform geodesic fiber layer corresponds to the orientation of the geodesic trajectories within said layer.If the reference generator is confused with a geodesic trajectory of said layer, that is to say is confused with a trajectory of fibrous structure of said layer, the orientation of the layer is considered to be 0°.

[0096] Figures 5 to 16 illustrate four examples of uniform geodesic fibrous layers Ci, C2, C3, C4 within which the fibers of the fibrous structures are deposited along geodesic trajectories ti, t2, t3, t4, the first edge and the second edge of each layer Ci, C2, C3, C4 joining and corresponding to a singular generatrix gi, g2, g3, g4 of said fibrous layer Ci, C2, C3, C4.

[0097] Figures 5 to 7 schematically illustrate a first uniform geodesic layer Ci within which the fibers of the fibrous structures extend according to first geodesic trajectories ti which correspond to straight lines on the developed surface Cid of said layer Ci. In particular, the first geodesic trajectories ti correspond to a set of parallel straight lines of the developed surface Cid of said layer Ci as illustrated in Figure 7.

[0098] The first layer Ci extends around the central axis A between a first edge and a second edge which meet and correspond to a first singular generator gi. The first layer Ci extends along the central axis A between a smaller end contour pu and a larger end contour pi2.

[0099] The fibrous layer Ci also comprises a first reference generatrix gir which corresponds to the generatrix diametrically opposite the first and second edges, i.e. to the generatrix diametrically opposite the first singular generatrix g The orientation 0i of the geodesic trajectories ti within the uniform geodesic fibrous layer Ci is defined by the angle formed between the first geodesic trajectories ti and the first reference generatrix gi r . In the example of the first fiber layer Ci, the first geodesic trajectories ti intersect the first reference generator gi r with an angle of 90°. The first uniform geodesic layer Ci therefore has an orientation 0i of 90°.

[0100] Figures 8 to 10 schematically illustrate a second uniform geodesic layer C2 within which the fibers of the fibrous structures extend along second geodesic trajectories t2 which correspond to straight lines on the developed surface C 2d of said layer C2. In particular, the second geodesic trajectories t2 correspond to a set of parallel lines of the developed surface C 2d of said layer C2, as illustrated in Figure 10.

[0101] The second layer C2 extends around the central axis A between a first edge and a second edge which meet and correspond to a second singular generator g2. The second layer C2 extends along the central axis A between a smaller end contour p 2i and a larger end contour p 22 .

[0102] The fibrous layer C2 also includes a second reference generator g 2rwhich corresponds to the generator diametrically opposite the first and second edges, that is to say to the generator diametrically opposite the second singular generator g2.

[0103] The orientation 02 of the geodesic trajectories t2 within the uniform geodesic fiber layer C2 is defined by the angle formed between the geodesic trajectories t2 and the second reference generator g 2r . In the example of the second fiber layer C2, the second geodesic trajectories t2 do not intersect the second reference generator g 2r , except a second geodesic trajectory t2 which is confused with the second reference generator g 2r . The second uniform geodesic layer C2 therefore has an orientation 02 of 0°.

[0104] Figures 11 to 13 schematically illustrate a third uniform geodesic layer C3 within which the fibers of the fibrous structures extend along third geodesic trajectories ta which correspond to straight lines on the developed surface C 3d of said layer C3. In particular, the third geodesic trajectories t3 correspond to a set of parallel lines of the developed surface C 3d of said layer C3, as illustrated in Figure 13.

[0105] The third layer C3 extends around the central axis A between a first edge and a second edge which meet and correspond to a third singular generator g3. The third layer C3 extends along the central axis A between a smaller end contour p 3i and a larger end contour p 32 .

[0106] The fibrous layer C3 also includes a third reference generator g 3rwhich corresponds to the generator diametrically opposite the first and second edges, that is to say to the generator diametrically opposite the third singular generator g3.

[0107] The orientation 03 of the geodesic trajectories t3 within the uniform geodesic fiber layer C3 is defined by the angle formed between the geodesic trajectories t3 and the reference generator g 3r . In the example of the third fiber layer C3, the third geodesic trajectories t3 intersect the third reference generator g 3r with an angle of 45°. The third uniform geodesic layer C3 therefore has an orientation 03 of 45°.

[0108] Figures 14 to 16 schematically illustrate a fourth uniform geodesic layer C4 within which the fibers of the fibrous structures extend along fourth geodesic trajectories t4 which correspond to straight lines on the developed surface C 4dof said layer C4. In particular, the fourth geodesic trajectories t4 correspond to a set of parallel lines of the developed surface C 4d of said C4 layer, as illustrated in Figure 16.

[0109] The fourth layer C4 extends around the central axis A between a first edge and a second edge which meet and correspond to a fourth singular generator g4. The fourth layer C4 extends along the central axis A between a smaller end contour p 4i and a larger end contour p 42 .

[0110] The fibrous layer C4 also includes a fourth reference generator g 4r which corresponds to the generator diametrically opposite the first and second edges, that is to say to the generator diametrically opposite the fourth singular generator g4.

[0111] The orientation 04 of the geodesic trajectories t4 within the uniform geodesic fiber layer C4 is defined by the angle formed between the geodesic trajectories t4 and the reference generator g 4r . In the example of the fourth fiber layer C4, the fourth geodesic trajectories t4 intersect the fourth reference generator g 4r with an angle of 135°. The fourth uniform geodesic layer C4 therefore has an orientation 04 of 135°.

[0112] According to a first variant, one or more geodesic uniform layers may have a first edge and a second edge joining together, the first edge extending in the same direction as the geodesic trajectories present on the side of said first edge. This variant is particularly advantageous in the case where none of the fibers of the fibrous structures of said layer extends along a generatrix of said layer. Indeed, if in such a case it is chosen to produce edges extending along a generatrix as is the case in Figures 6 to 10, there is a risk that the ends of the fibrous structures are not sufficiently blocked at the first and second edges, because the first and second edges are each formed by a plurality of ends of fibrous structures.By choosing a first edge extending along the trajectory of the fibrous structures present on the side of said first edge, said first edge is then formed by the edge of a single fibrous structure, or at least by the edge of a very limited number of fibrous structures. Thus, the first edge can more easily block the ends of the fibrous structures opening at the second edge, for example by covering over a small distance the ends of the fibrous structures opening at the second edge.

[0113] "First edge side" means the side of the fibrous layer extending from the first edge and away from the second edge. Thus, the first edge side does not include the second edge. Similarly, "second edge side" means the side of the fibrous layer extending from the second edge and away from the first edge. Thus, the second edge side does not include the first edge.

[0114] Figures 17 and 18 illustrate an example of the first variant of uniform geodesic fibrous layer Cu within which the fibers of the fibrous structures are deposited along geodesic trajectories tu, the first edge bu and the second edge bu of the Cu layer joining and the first edge bu extending along the same direction as the geodesic trajectories tu present on the side of the first edge bu-

[0115] The geodesic trajectories tu correspond to straight lines on the developed surface Cud of said Cu layer. In particular, the geodesic trajectories tu correspond to a set of parallel straight lines of the developed surface Cud of said Cu layer as illustrated in figure 18.

[0116] The Cu layer according to this first variant extends around the central axis A between the first edge bu and the second edge bu which meet, and do not correspond to a generatrix of said Cu layer. The first edge bu extends entirely in the same direction as the geodesic trajectories tu present on the side of the first edge bu. The Cu layer extends along the central axis A between a smaller end contour pui and a larger end contour pu2.

[0117] The Cu fibrous layer also includes a reference generator g r u, which is the generator of the fibrous layer Cu furthest from the generator gu of said fibrous layer Cu extending from the intersection between the smallest contour Pui of the fibrous layer Cu and the extension of the second edge bu-

[0118] The orientation 0u of the geodesic trajectories tu within the uniform geodesic fibrous layer Cu is defined by the angle formed between the geodesic trajectories tu and the reference generator g r u- In the example of the fibrous layer Cu, the geodesic trajectories tu intersect the reference generator g ru with an angle of 90°. The uniform geodesic layer Cu therefore has an orientation 0u of 90°. The uniform geodesic layer Cu illustrated in Figures 17 and 18 therefore has the same orientation as the first uniform geodesic layer Ci illustrated in Figures 5 to 7. According to a second variant, one or more geodesic uniform layers may have a first edge and a first part of a second edge joining and extending in the same direction as the trajectories of the fibers of the fibrous structures of the layer present on the side of the first edge, the first part of the second edge extending from the largest contour of the fibrous layer and a second part of the second edge extending in the same direction as the trajectories of the fibrous structures of the layer present on the side of said second edge.

[0119] This variant is particularly interesting in the case where none of the fibers of the fibrous structures of said layer extends along a generatrix of said layer. Indeed, if in such a case it is chosen to produce edges extending along a generatrix as is the case in Figures 6 to 10, there is a risk that the ends of the fibrous structures are not sufficiently blocked at the first and second edges, because the first and second edges are each formed by a plurality of ends of fibrous structures. By choosing a first edge extending along the trajectory of the fibrous structures present on the side of said first edge, said first edge is then formed by the edge of a single fibrous structure, or at least by the edge of a very limited number of fibrous structures.Thus, the first edge can more easily block the ends of the fibrous structures opening at the second edge, for example by covering the ends of the fibrous structures opening at the second edge by a small distance.

[0120] Furthermore, by producing a second part of the second edge extending along the geodesic trajectories of the fibers of the fibrous structures present on the side of the second edge, the number of short fibers or fibrous structures is reduced by creating in return an area not covered by the layer between the second part of the second edge and the first edge. The draping of the fibrous layer is thus improved, since it is difficult to drape short fibrous structures. Furthermore, in this second variant, it is avoided that fibrous structures open onto the smallest contour in the form of visible free ends, which would require additional cutting operations. Figures 19 and 20 illustrate an example of the second variant of uniform geodesic fibrous layer C 2i within which the fibers of the fibrous structures are deposited following geodesic trajectories t2Layer C 2iaccording to this second variant extends around the central axis A between a first edge b 2i and a second edge b 22 . In this variant, the second edge b 22 of layer C 2i includes a first part b 22a confused with the first edge b 2i of said layer C 2i and extending in the same direction as the trajectories t 2i fibers of the fibrous structures of layer C 2i present on the side of the first edge b2i. The second edge b 22 of layer C 2i further includes a second part b 22 b extending in the same direction as the trajectories t 2i fibers of the fibrous structures of layer C 2i present on the side of said second edge b 22 .

[0121] The geodesic trajectories t 2i correspond to straight lines on the developed surface C 2idof said layer C2i. In particular, the geodesic trajectories t 2i correspond to a set of parallel lines of the developed surface C 2id of said layer C 2i as shown in Figure 20.

[0122] Layer C 2i extends along the central axis A between a smaller end contour p2n and a larger end contour p 2i2 .

[0123] The fibrous layer C 2i also includes a reference generator g r2 i, which is the generator of the fibrous layer C 2i the furthest from the generator g 2i of said fibrous layer C 2i extending from the intersection between the smallest contour p2n of the fibrous layer Cn and the extension of the first part b 22a second edge b 22 .

[0124] Orientation 0 2i geodesic trajectories t 2iwithin the uniform geodesic fibrous layer C 2i is defined by the angle formed between the geodesic trajectories t 2i and the reference generator g r2 i. In the example of the fibrous layer C2i, the geodesic trajectories t 2i intersect the reference generator g r2i with an angle of 90°. The uniform geodesic layer C 2i therefore has a 0 orientation 2i of 90°. The uniform geodesic layer C 2iillustrated in Figures 19 and 20 therefore has the same orientation as the first uniform geodesic layer Ci illustrated in Figures 5 to 7 and as the uniform geodesic layer Cn illustrated in Figures 17 and 18. The draping of the form F may comprise the production of several uniform geodesic fibrous layers on the draping form F. The orientation of each uniform geodesic fibrous layer applied is chosen according to the mechanical characteristics desired for the part to be obtained. When it is desired to obtain a quasi-isotropic draping, stacks of uniform geodesic fibrous layers are produced allowing a quasi-isotropic distribution of the fibers at any point of the draped fiber preform.

[0125] According to a first embodiment of the invention, the draping of the shape F comprises the production of several uniform geodesic fibrous layers on the draping shape F, the first and second edges of the fibrous layers being superimposed on the draping shape F. In this first embodiment, the reference generatrices of said fibrous layers are superimposed on the shape F.

[0126] An example of Di draping and Di evolute d according to this first embodiment of the invention is shown in Figures 21 to 23, in which a set of fibrous layers consisting of the first, second, third and fourth uniform geodesic fibrous layers Ci, C2, C3 and C4 illustrated in Figures 5 to 16 has been applied to the draping shape F so that the reference generatrices gi r , g 2r , gsr and g 4rare superimposed on the form F. By superimposing uniform geodesic fibrous layers with orientations 0i, 02, 03 and 04 of 90°, 0°, 45° and 135°, we thus obtain a quasi-isotropic draping at any point of the draped fibrous preform.

[0127] Thus, in each fibrous layer Ci, C2, C3, C4 of the set of fibrous layers presented, the fibers extend in a direction of extension ti, t2, t3, t4, also called trajectory, which forms a non-zero crossing angle with the directions of extension or trajectories ti, t2, t3, t4 of the fibers of the other layers Ci, C2, C3, C4.

[0128] In the example shown in Figures 21 to 23, the set of fiber layers comprises four layers, and the crossing angle between the different layers of the set is a multiple of 45°, which corresponds to a multiple of the ratio of 180° by 4. The set of fiber layers illustrated therefore allows a quasi-isotropic distribution of the fibers of the draping. This crossing angle is identical at every point of the draping Di shown in Figures 21 to 23, that is to say identical at all the generatrices of the draping shape F.

[0129] Obviously, several sets of uniform geodesic fibrous layers are possible to obtain quasi-isotropic draping at any point of the draped fibrous preform according to this first embodiment of the invention. For example, uniform geodesic fibrous layers having orientations of:

[0130] - 0°+o, 60°+o, and 120°+o, where a is between 0° and 60°; or

[0131] - 0°+a, 45°+a, 90°+a and 135°+a, where a is between 0° and 45°; or

[0132] - 0°+a, 36°+a, 72°+a, 108°+a and 144°+a, where a is between 0° and 36°; or

[0133] - 0°+a, 30°+a, 60°+a, 90°+a, 120°+a and 150°+a, where a is between 0° and 30°.

[0134] The above combinations can obviously be repeated several times in the thickness of the draped preform, i.e. a set of fibrous layers can be repeated several times.

[0135] In the example illustrated in Figures 21 to 23, the edges of the draped fibrous layers coincide with generatrices. It is of course not outside the scope of the invention if all or part of the draped fibrous layers are fibrous layers according to the first variant and / or the second variant described above, their reference generatrices being superimposed on the draping shape.

[0136] According to a second embodiment of the invention, the draping of the shape F comprises the production of several uniform geodesic fibrous layers on the draping shape F, the first and second edges of the draped fibrous layers being offset relative to each other circumferentially on the draping shape F. Thus, in this second embodiment of the invention, the reference generatrices of all or part of said fibrous layers are offset relative to each other on the shape F.

[0137] In this second embodiment of the invention, the draping of the shape F can thus comprise identical uniform geodesic fiber layers, or at least of the same orientation, but whose first and second edges are offset relative to each other on the shape F. The angular offset between the first and second edges of each of the uniform geodesic fiber layers can be determined so as to obtain a quasi-isotropic draping at any point of the fiber preform. This amounts to determining the angular offset between the reference generatrices of each of the uniform geodesic fiber layers so as to obtain a quasi-isotropic draping at any point of the fiber preform.

[0138] An example of draping D2 and development D2d according to this second embodiment of the invention is shown in Figures 24 to 26, in which two third uniform geodesic fiber layers C3 such as the third geodesic fiber layer illustrated in Figures 11 to 13 have been applied to the draping shape F so that the reference generatrices g 3r and g 3r ' of these two third layers are shifted relative to each other on the form F. Therefore, the reference generators g 3r and g 3r ' of these two identical fibrous layers C3 are superimposed on distinct generators of the draping form F.

[0139] The first and second edges of one of the fiber layers are merged with a generatrix g3 and the first and second edges of the other fiber layer are merged with a generatrix g3'. The orientations 03 of the two third uniform geodesic fiber layers C3 are identical. The trajectories t3 of one of the fiber layers and the trajectories t3' of the other fiber layer are not merged, and intersect.

[0140] It can be seen in Figures 25 and 26 that the crossing angle between the extension directions of the fibers of the two layers C3 is different depending on the areas of the drape D2. In the largest portion of the drape D2 extending between the generatrices g3 and g3' the crossing angle between the extension directions t3 and t3' of the two fiber layers will be approximately 30°, whereas in the smallest portion of the drape D2 extending between the generatrices g3 and g3' the crossing angle between the extension directions t3 and t3' of the two fiber layers will be approximately 60°.

[0141] Figure 27 illustrates an example of draping and evolute D 3daccording to this second embodiment of the invention, which comprises a set of fibrous layers comprising four third uniform geodesic fibrous layers C3 such that the third geodesic fibrous layer illustrated in Figures 11 to 13 and 24 to 26 have been applied to the draping shape F so that the reference generatrices g 3r , g 3r ', g 3r " and g3r"' of these four third layers are shifted relative to each other on the form F. Therefore, the reference generators g 3r , g 3r ', gsr" and g 3r "' of these four identical fiber layers C3 are superimposed on distinct generators of the draping form F. Thus, we obtain varied fiber extension directions throughout the draping, which approaches an isotropic configuration.

[0142] The first and second edges of each fiber layer C3 are coincident with a generator g3, g3', g3" or g3'". The orientations 03 of the four third uniform geodesic fiber layers C3 are identical.

[0143] It can be seen in Figure 1 that the crossing angle between the extension directions of the fibers of the different layers is different depending on the areas of the draping, said areas being delimited by the generatrices g3, g3', g3" or g3'".

[0144] In the example illustrated in Figures 24 to 26 and in Figure 27, the edges of the draped fibrous layers coincide with generatrices. It is of course not outside the scope of the invention if all or part of the draped fibrous layers are fibrous layers according to the first variant and / or the second variant described above, their reference generatrices being offset around the draping shape.

[0145] It is also possible to combine the first embodiment and the second embodiment of the invention. For example, it is possible to achieve quasi-isotropic draping by using a first pair of identical layers and a second pair of identical layers different from the first pair of layers, the reference generatrices of the layers overlapping distinct generatrices of the draping shape.

[0146] In all the embodiments presented above, the fibrous layers draped over the form F may be solely geodesic fibrous layers. The fibrous layers draped over the form F may be solely uniform geodesic fibrous layers. The draping of the form F may also be a combination of geodesic fibrous layers and Cartesian fibrous layers. It is particularly advantageous to combine uniform geodesic fibrous layers having different orientations, as presented above, with one or more Cartesian fibrous layers in which the fibrous structures are deposited so that the fibers of said fibrous structures are superimposed on the generatrices g of the draping form F. This significantly increases the rigidity and strength of the fiber preform obtained by draping.

[0147] The draping method may include draping over draping shape F, but may also include draping over an additional draping shape extending draping shape F. This additional draping shape is not necessarily developable. The draping performed over this additional draping shape may be different from that described in the present invention.

[0148] The fibrous layers draped over the draping form form a fibrous preform, which has at least one developable portion comprising at least one portion of conical or frustoconical shape. According to the invention, the fibers of the fibrous structures of at least one fibrous layer of the fibrous preform extend along trajectories which correspond to straight lines of the developed surface of the fibrous preform. Preferably, the fibers of the fibrous structures of at least one other fibrous layer of the fibrous preform extend along trajectories which are superimposed on generatrices of the fibrous preform.

[0149] The fibrous preform thus obtained can be densified in a well-known manner by a matrix to obtain a part made of composite material, for example an engine exhaust cone or a rear inverter body.

Claims

Tl Claims

1. Method for draping fibrous structures on a draping form (F) comprising at least one developable portion, the fibrous structures comprising fibers extending in at least one determined direction (ti, t2, t3, , tu, t2i), the method being characterized in that the fibrous structures are deposited on the draping form (F) so that the fibers of said fibrous structures are superimposed on straight lines of the developed surface of the developable portion of the draping form (F), the fibrous structures being draped so as to form one or more fibrous layers (Ci, C2, C3, C4, Cn, C2i) developable on the developable portion of the draping form (F), the fibrous layer(s) (Ci, C2, C3, C4, Cn, C2i) extending around the developable portion of the draping form (F) between a first and a second edge (bu, bi2; b2i, b 22), the fibrous structures of the same fibrous layer (Ci, C2, C3, C4, Cn, C2i) being deposited so that the fibers of the fibrous structures of said fibrous layers (Ci, C2, C3, C4, Cn, C2i) are superimposed on at least one set of parallel lines of the developed surface (Cid, C2d, C3d, C4d, Cnd, C2id) of said fibrous layer (Ci, C2, C3, C4, Cn, C2i).

2. A draping method according to claim 1, wherein a set of fibrous layers (Ci, C2, C3, C4) is draped onto the draping form (F) such that in each fibrous layer (Ci, C2, C3, C4) of the set of fibrous layers the fibers extend in at least one direction of extension (ti, t2, t3, t4, tn, t2i) which forms a non-zero crossing angle with the direction(s) of extension (ti, t2, t3, t4, tu, t2i) of the fibers of the other layers (Ci, C2, C3, C4) of the set of fibrous layers.

3. A draping method according to claim 2, wherein the crossing angle is between 80% and 120% of a multiple of the ratio of 180° to the total number of layers (Ci, C2, C3, C4) in the set of fibrous layers.

4. A layup method according to claim 2 or 3, wherein the crossing angle is between 80% and 120% of a multiple of the ratio of 180° by the total number of layers (Ci, C2, C3, C4) in the set of fibrous layers at at least one generator of the draping shape.

5. A layup method according to any one of claims 2 to 4, wherein the crossing angle is between 80% and 120% of a multiple of the ratio of 180° by the total number of layers (Ci, C2, C3, C4) in the set of fibrous layers at any point of the layup.

6. A layup method according to any one of claims 2 to 5, wherein the first edges (bu, b2i) of the fibrous layers (Ci, C2, C3, C4) of the set of fibrous layers are circumferentially offset relative to each other on the layup form (F) and wherein the second edges (bi2; b22) of the fibrous layers (Ci, C2, C3, C4) of the set of fibrous layers are circumferentially offset relative to each other on the layup form (F).

7. A draping method according to any one of claims 1 to 6, wherein at least a first portion (b22a) of the second edge (bi2; b22) of at least one fibrous layer (Ci, C2, C3, C4, Cn, C21) joins the first edge (bu, b2i) of said fibrous layer (Ci, C2, C3, C4, Cn, C21), said first portion (b22a) of the second edge (bn; b22) extending from the largest end contour (P12, P22, P32, P42, P112, P212) of said fibrous layer (Ci, C2, C3, C4, Cn, C2i) connecting the first edge (bn, b2i) to the second edge (bn; b22)-

8. A draping method according to claim 7, wherein the first and second edges of at least one fibrous layer (Ci, C2, C3, C4) meet and correspond to a generatrix (g g2, g3, g4) of said fibrous layer (Ci, C2, C3, C4).

9. A draping method according to claim 7, wherein the first edge (bn, b2i) of at least one fibrous layer (Cn, C21) extends in the same direction (tn, t2i) as the fibers of the fibrous structures of said layer (Cn, C21) present on the side of the first edge (bn, b2i).

10. A method of draping according to claim 7 or 9, wherein the second edge (b22) comprises a second portion (b22t>) distinct from the first part (b22a) extending in the same direction (t2i) as the fibers of the fibrous structures of said layer (C2i) present on the side of the second edge (b22)-

11. A draping method according to any one of claims 7 to 10, wherein the first edge (bu, b2i) covers at least the first portion (b22a) of the second edge (bi2; b22)-

12. A method of draping according to any one of claims 1 to 11, the method further comprising draping a plurality of stiffening fibrous structures over the draping form (F), the stiffening fibrous structures being draped such that the fibers of said stiffening fibrous structures overlap generatrices (g) of the developed surface of the draping form (F).

13. A draping method according to any one of claims 1 to 12, wherein the draping of the fibrous structures is carried out by automatic placement of fibers.

14. Fibrous preform comprising at least one developable portion, said preform comprising a plurality of fibrous layers formed by fibrous structures, characterized in that the fibers of the fibrous structures of at least one fibrous layer correspond to straight lines of the developed surface of the developable portion of the fibrous preform, said at least one fibrous layer being developable and said fibers of said at least one fibrous layer superimposing at least one set of parallel straight lines of the developed surface of said fibrous layer.

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