Geodesic draping process

Abstract

Geodesic draping process. The invention relates to a method for draping fibrous structures onto a developable conical or frustoconical draping form, the fibrous structures comprising fibers extending in a determined direction (t1, t2, t3, t4, t11, t21). The method is characterized in that the fibrous structures are deposited on the draping form such that the fibers of said fibrous structures overlap with straight lines on the developed surface of the draping form. Figure for the abstract: Fig. 6

Description

Title of the invention: Geodesic draping process technical field

[0001] The invention relates to the general field of draping processes of a shape by fibrous structures, and in particular to draping processes by automatic placement of fibers. Previous technique

[0002] It is known to produce composite parts by draping layers or strata of dry or pre-impregnated fibrous structures onto a mold. In some current techniques, the draping is performed manually by an operator. These techniques can lead to relatively high production costs and risks of errors in the positioning of the layers or fibrous structures. This results in some variability in the mechanical performance of the resulting parts, or even in parts with insufficient mechanical properties.

[0003] Mechanized solutions have thus been developed to reduce the production cost of these composite parts, such as the automated 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 "strands".

[0004] In the prior art, when it is desired to drape a developable conical or frustoconical draping shape Fo comprising generatrices gOb gO2 and extending between a smaller contour pOi and a larger contour pO2, the deposited fibers me are oriented according to the Cartesian coordinate system of the draping shape Fo, as illustrated in [Fig. 1]. Thus, the trajectories of the deposited fibers or fiber strands intersect the generatrices gOi, go2 of the developable shape Fo at the same angle. [Fig. 2] shows the developed surface FOd of the developable shape Fo open at the generatrice gOi. Several fibrous layers can thus be deposited, each fibrous layer having a different fiber orientation. It is therefore possible to achieve quasi-isotropic draping.

[0005] However, it has been observed that the strands deposited using this method can exhibit significant deformations and undulations. The strength and mechanical properties of the draped part obtained by this method may therefore be insufficient.

[0006] It is also known to lay the wicks with a "spiral" winding, as described in US patent 8677622. However, this draping method This method generates significant variations in thickness, with some areas of the draped shape being covered by a large number of fibers and other areas by very few. Furthermore, the draped part exhibits considerable heterogeneity in fiber orientation, with different proportions of fibers in each orientation. Therefore, achieving near-isotropic draping with this method is extremely difficult. Description of the invention

[0007] The present invention aims to overcome the aforementioned drawbacks. It has been observed, in particular, that the further the conical or frustoconical draping form deviates from a cylindrical shape—that is, the steeper its slope relative to its axis—the more difficult it is to apply the wicks without waviness or deformation. Indeed, when the wick is deposited on a steep slope using the prior art method(s), the two longitudinal edges of the wick do not travel the same distance along the draping form. Thus, the deposited wick ripples or deforms. This phenomenon is even more pronounced when the cross-section of the draping form is small or when the width of the applied wick is large.

[0008] Thus, the invention proposes a method of draping fibrous structures on a developable draping form comprising at least a portion of conical or frustoconical shape, the fibrous structures comprising fibers extending along 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.

[0009] By depositing the fibers of the fibrous structures so as to follow trajectories corresponding to straight lines of the developed shape of the draping shape, it is ensured that the draping of the fibrous structures is carried out properly, without waviness or deformation.

[0010] According to another 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 or layers 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 overlap at least one set of parallel lines of the developed surface of said fibrous layer.

[0011] Thus, the invention makes it possible to create a drape with several layers that are themselves developable. This ensures that a multilayer drape can be achieved without risk of waviness or deformation, despite the superposition of the layers.

[0012] 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 along at least one extension direction which forms a non-zero crossing angle with the extension direction(s) of the fibers of the other layers of the set of fibrous layers.

[0013] Thus, the resulting drape will exhibit interesting mechanical characteristics in several directions, and will therefore be more robust.

[0014] The draping may comprise several sets of fibrous layers, the sets of fibrous layers being either identical or distinct from one another.

[0015] Preferably, the set of fibrous layers comprises at least three fibrous layers, in order to obtain satisfactory mechanical resistance in sufficiently varied directions.

[0016] According to another particular embodiment of the invention, the crossing angle is between 80% and 120% of a multiple of the ratio of 180° to the total number of layers in the fibrous layer assembly. Preferably, the crossing angle is between 90% and 110% of a multiple of the ratio of 180° to the total number of layers in the fibrous layer assembly.

[0017] Thus, we ensure that we obtain the most isotropic drape possible, adapted to the number of layers in the assembly. For example, in the case where the assembly of fibrous layers consists 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° with respect to the extension directions of the fibers of the other three layers in order to obtain the most isotropic drape possible.

[0018] The crossover angle between the fibers of two distinct fibrous layers can vary depending on the portion of the drape. Thus, according to a particular embodiment of the invention, the crossover angle is between 80% and 120% of a multiple of the ratio of 180° to the total number of layers in the set of fibrous layers at at least one generatrix of the drape shape. According to another embodiment of the invention, the crossover angle is between 80% and 120% of a multiple of the ratio of 180° to the total number of layers in the set of fibrous layers at any point of the drape.

[0019] According to another particular embodiment of the invention, the first edges of the fibrous layers of the set of fibrous layers are circumferentially offset from one another on the draping form and the second edges of the fibrous layers of the set of fibrous layers are circumferentially offset from one another on the draping form.

[0020] Indeed, the edges of the fibrous layers constitute weaknesses in the draping. It is therefore preferable that the edges of the fibrous layers not overlap. not on the draping shape, in order to improve the robustness of the draping and the final piece obtained.

[0021] 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.

[0022] By draping the fibrous layer so that its edges meet at least partially from the largest end contour of said fibrous layer, at least some of the fibrous structures emerging from the first or second edge can block the fibrous structures emerging from the other edge. The stability of the draped layer is thus improved. Furthermore, by creating fibrous layers that make a complete circumference of the draping form, it is easier to obtain a generally uniform thickness around the entire circumference of the draping form.

[0023] 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.

[0024] 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.

[0025] 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 can therefore easily block fibrous structures emerging from the second edge, for example by slightly overlapping the ends of the fibrous structures forming the second edge.

[0026] 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.

[0027] Thus, the ends of the fibrous structures protruding at the first and second edges are limited, thereby significantly improving the strength of the resulting drape. Furthermore, this particular embodiment limits the number of short draped fibrous structures, which are more likely to detach from the rest of the drape without providing any real improvement in mechanical properties. Short fibrous structures are also more difficult to deposit, especially with the automated fiber draping method. Finally, such an overlap makes it possible to obtain a "net shape" fibrous preform, that is, one that is not requiring no additional cutting operations to trim protruding fibers.

[0028] According to another particular embodiment of the invention, the first edge covers at least the first part of the second edge.

[0029] 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.

[0030] According to another particular embodiment of the invention, the method further comprises draping a plurality of stiffness fibrous structures over the draping form, the stiffness fibrous structures being draped so that the fibers of said stiffness fibrous structures overlap with generatrices of the developed surface of the draping form.

[0031] By carrying out a "classic" draping of the fibers along the generatrices, the rigidity and strength of the draping obtained are improved.

[0032] According to a particular embodiment of the invention, the draping of the fibrous structures is carried out by automatic placement of fibers.

[0033] By using draping by automatic fiber placement, the repeatability and quality of the process are improved while limiting manufacturing costs.

[0034] The invention also relates to a fibrous preform comprising at least one developable part comprising at least one portion of conical or frustoconical shape, 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 part of the fibrous preform. Brief description of the drawings

[0035] [Fig.1] Fig.1 is a schematic perspective view of a developable draping form onto which fibrous strands are draped according to the prior art.

[0036] [Fig.2] The [Fig.2] is a schematic representation of the developed surface of the shape of the [Fig.1].

[0037] [Fig.3] The [Fig.3] is a schematic perspective view of a developable drape shape.

[0038] [Fig.4] The [Fig.4] is a schematic cross-sectional view of an AFP dispensing head.

[0039] [Fig. 5] Fig. 5 is a schematic front perspective view of a first geodesic fibrous layer according to the invention having a 90° orientation.

[0040] [Fig.6] The [Fig.6] is a schematic rear perspective view of the first geodesic fibrous layer of the [Fig.5].

[0041] [Fig.7] Fig.7 is a schematic view of the developed surface of the first geodesic fibrous layer of figures 5 and 6.

[0042] [Fig-8] The [Fig.8] is a schematic front perspective view of a second geodesic fibrous layer according to the invention having an orientation of 0°.

[0043] [Fig.9] The [Fig.9] is a schematic rear perspective view of the second geodesic fibrous layer of the [Fig.8].

[0044] [Fig. 10] The [Fig. 10] is a schematic view of the developed surface of the second geodesic fibrous layer of figures 8 and 9.

[0045] [Fig. 11] The [Fig. 11] is a schematic front perspective view of a third geodesic fibrous layer according to the invention having an orientation of 45°.

[0046] [Fig. 12] The [Fig. 12] is a schematic rear perspective view of the third geodesic fibrous layer of the [Fig. 11].

[0047] [Fig. 13] The [Fig. 13] is a schematic view of the developed surface of the third geodesic fibrous layer of Figures 11 and 12.

[0048] [Fig. 14] The [Fig. 14] is a schematic front perspective view of a fourth geodesic fibrous layer according to the invention having an orientation of 135°.

[0049] [Fig. 15] The [Fig. 15] is a schematic rear perspective view of the fourth geodesic fibrous layer of the [Fig. 14].

[0050] [Fig. 16] The [Fig. 16] is a schematic view of the developed surface of the fourth geodesic fibrous layer of Figures 14 and 15.

[0051] [Fig. 17] The [Fig. 17] is a schematic perspective view of a geodesic fibrous layer according to a first embodiment of the invention.

[0052] [Fig. 18] The [Fig. 18] is a schematic view of the developed surface of the geodesic fibrous layer of the [Fig. 17].

[0053] [Fig. 19] The [Fig. 19] is a schematic perspective view of a geodesic fibrous layer according to a second embodiment of the invention.

[0054] [Fig.20] The [Fig.20] is a schematic view of the developed surface of the geodesic fibrous layer of the [Fig. 19].

[0055] [Fig.21] Fig.21 is a schematic front perspective view of a first draping comprising the first, second, third and fourth geodesic layers of figures 5 to 16.

[0056] [Fig.22] The [Fig.22] is a schematic rear perspective view of the first drape of the [Fig.21].

[0057] [Fig.23] The [Fig.23] is a schematic view of the developed surface of the first draping of figures 21 and 22.

[0058] [Fig.24] Fig.24 is a schematic front perspective view of a second draping comprising two of the third layer of figures 11 to 13.

[0059] [Fig.25] The [Fig.25] is a schematic rear perspective view of the second drapery of the [Fig.24].

[0060] [Fig.26] The [Fig.26] is a schematic view of the developed surface of the second draping of figures 24 and 25.

[0061] [Fig.27] The [Fig.27] is a schematic view of a developed surface of a third drape. Description of the implementation methods

[0062] The invention makes it possible to produce a fibrous preform having the shape of the part to be obtained by draping a plurality of fibrous structures onto a draping form. The fibrous preform is intended to form the fibrous reinforcement of the part to be obtained.

[0063] 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.

[0064] The draping surface is developable. By extension, a "developable draping shape" is defined as a draping shape whose draping surface is developable. The draping surface has at least one conical or frustoconical portion. The draping shape may be conical or frustoconical. The draping shape may also have a complex developable shape, comprising portions that are at least partially conical or frustoconical. For example, the draping shape may have a developable crown formed by a plurality of lobes distributed around a circumference, said lobes having, for example, a partially frustoconical shape. Such a draping shape may, for example, allow the draping of a fibrous preform intended to form the fibrous reinforcement of a turbojet flow mixer, the draping shape itself having, overall, the shape of a turbojet flow mixer.An example of a turbojet flow mixer is described in document FR 3 061 749.

[0065] 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 cross-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 cross-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 elliptical cross-sections.

[0066] The draping shape F, or 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 draping surface, of the smallest dimension. The largest contour p2 corresponds to the end contour of the draping shape F, or draping surface, of the largest dimension.

[0067] The draping surface of the draping shape F comprises an infinite number of generatrices g, as illustrated in [Fig.3].

[0068] The fibrous structures are preferably in the form of fibrous strands or layers of fabric. A "strand" is defined as a collection of long, substantially parallel fibers or filaments bound together in a nonwoven strip. The fibrous structures may include continuous, long fibers. When the fibrous structures are in the form of layers of fabric, they are generally formed by the woven interlacing of fibers along two directions, which are usually perpendicular to each other.

[0069] The fibers of the fibrous structures may be ceramic, glass, or carbon fibers. Ceramic fibers may be made of a non-oxide material, such as silicon carbide (SiC), or of an oxide material, such as alumina, or of a material consisting mainly of alumina. Glass fibers may comprise a mixture consisting mainly of silica.

[0070] The fibrous structures may be dry, i.e., not impregnated with a resin, pre-impregnated, or loaded with particles. The fibers of the dry fibrous structures may, however, be coated with a temporary binder, for example, an organic one, which may or may not be removed before the densification of said fibrous structures.

[0071] The fibrous structures may be impregnated with a thermoplastic or thermosetting material, which may contain solid fillers. The fibrous structures may also be impregnated with a thermoplastic or thermosetting material that does not contain solid fillers. The fibrous structures may be impregnated solely with an organic phase consisting of a thermoplastic material.

[0072] Thermoplastic materials suitable for impregnating fibrous structures may be selected from: polyaryletherketones (PAEKs) such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimides (PEIs), polyphenylene sulfide (PPS), polyvinyl alcohol (PVA), aliphatic polyethers, and polysulfone (PSU). Thermosetting materials suitable for impregnating fibrous structures may be selected from: epoxides, phenolics, and polybismaleimides (BMIs).

[0073] The pre-impregnation of the fibrous structures can be carried out by any conventional technique, for example by dipping, by roller application or by spraying.

[0074] The fibrous structures can be applied to the F-shape by manual draping. Preferably, in order to improve the repeatability and quality of the application of the fibrous structures to the F-shape while reducing operating time, the fibrous structures are applied to the F-shape by automatic fiber placement.

[0075] Figure 4 schematically illustrates the structure of a dispensing head 1 of a device implementation of an automated fiber placement technique. The structure of the placement head 1 is well known. The placement head 1 is fed by the fibrous structures 3, preferably in the form of a strip or a strand.

[0076] 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 in the form of a pair of counter-rotating rollers 5a and 5b between which the strip or wick 3 is positioned. The conveying element 5 advances the strip or wick 3 to the pressure application element 7. The pressure application element 7 applies pressure to the strip or wick 3 to deposit it onto the draping form F. The pressure application element 7 is in the form of a roller.

[0077] The dispensing head 1 may, in addition, include a heating element 9 located in the vicinity of the pressure application element 7. This heating element 9 allows, in the case of a strip or wick 3 impregnated with a thermoplastic polymer, the said impregnated strip or wick 3 to be heated during its dispensing in order to fluidize the thermoplastic polymer and thus to give the desired adhesion power to the dispensed strip or wick 3.

[0078] During deposition, the deposition head 1 is mobile 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, a first fibrous structure is thus deposited, formed by a first section of the strip or wick 3, along a first trajectory on the draping form F.

[0079] The draping operation is then continued by advancing the strip or wick 3 in the dispensing head 1 to the pressure application element 7 by actuating the conveying element 5. The dispensing head 1 can be moved to deposit the wick or strip 3 along a second trajectory onto 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.

[0080] The draping form F can obviously be rotated around its central axis A during draping to facilitate the deposition of fibrous structures.

[0081] The draping is then continued by depositing several other fibrous structures of in the same way as described previously.

[0082] Regardless of the draping method used, the fibrous structures can be deposited to form fibrous layers on the draping shape F. Thus, each fibrous layer is itself developable, extends around the central axis A, and has an infinite number of generatrices. The fibrous layers extend around the draping shape F between a first edge and a second edge.

[0083] 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 opposite ends of the fibrous layer along the central axis A. The smaller contour and the larger contour connect the first and second edges.

[0084] 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 can thus be considered as one.

[0085] In the present application, it is considered that two edges or parts of edges coinciding with a fibrous layer are superimposed, immediately adjacent or separated by a very small gap in front of the perimeter of the section of said fibrous layer.

[0086] According to the invention, the trajectories of the fibrous structures deposited on the draping form F are determined; that is, 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.

[0087] According to the invention, the fibrous structures of at least one fibrous layer are deposited such that the fibers of said fibrous structures overlap with straight lines on the developed surface of the drape shape F. Thus, said fibrous layer is itself developable, and the fibers present in said fibrous layer extend along trajectories that correspond to straight lines on the developed surface of said layer. Said fibrous layer is therefore geodesic.

[0088] The term "geodesic" herein refers to a developable fibrous layer in which the fibers of the fibrous structures extend along trajectories that correspond to straight lines on the developed surface of said layer. These trajectories are also referred to as "geodesic." By contrast, the term "Cartesian" herein 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 at a constant angle, or that coincide with the generatrices of said layer. fibrous. These trajectories are also referred to as "Cartesian". Figures 1 and 2 illustrate an example of a Cartesian fibrous layer, in which the fibers extend along Cartesian trajectories.

[0089] Preferably, within a geodesic fibrous layer, the fibers of the fibrous structures extend along trajectories that correspond to a set of parallel lines on the developed surface of said layer. Hereinafter, a "uniform geodesic" is defined as a developable fibrous layer in which the fibers of the fibrous structures extend along trajectories that correspond to a set of parallel lines on the developed surface of said layer.

[0090] When at least the first part of the second edge of a uniform geodesic fibrous layer joins the first edge of said fibrous layer, the fibrous layer is defined by a reference generatrix and by an orientation.

[0091] The reference generatrix of such a uniform geodesic fibrous layer is the generatrix of the fibrous layer furthest from the generatrix of said fibrous layer extending from the intersection between the smallest contour of the fibrous layer and the extension of the first part of the second edge. The orientation of such a uniform geodesic fibrous layer is the angle of intersection between the fiber trajectories of the fibrous structures of the fibrous layer and the reference generatrix. The orientation of a uniform geodesic fibrous layer corresponds to the orientation of the geodesic trajectories within said layer. If the reference generatrix coincides with a geodesic trajectory of said layer, that is, coincides with a fibrous structure trajectory of said layer, the orientation of the layer is considered to be 0°.

[0092] Figures 5 to 16 illustrate four examples of uniform geodesic fibrous layers Ch C2, C3, C4 in which the fibers of the fibrous structures are deposited along geodesic trajectories tb t2, t3, t4, the first edge and second edge of each layer Cb C2, C3, C4 joining and corresponding to a singular generatrix gb g2, g3, g4 of said fibrous layer Cb C2, C3, C4.

[0093] Figures 5 to 7 schematically illustrate a first uniform geodesic layer Ci within which the fibers of the fibrous structures extend along first geodesic trajectories b which correspond to straight lines on the developed surface Cid of said layer Cb In particular, the first geodesic trajectories 0 correspond to a set of parallel straight lines on the developed surface Cw of said layer Ci as illustrated in [Fig.7].

[0094] 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 gb The first layer Ci extends along the central axis A between a smaller end contour pu and a larger end contour p[2.

[0095] The fibrous layer Ci also includes a first reference generatrix gk which corresponds to the generatrix diametrically opposite the first and second edges, that is, to the generatrix diametrically opposite the first singular generatrix gk

[0096] The orientation 0i of the geodetic trajectories 0 within the uniform geodetic fibrous layer Ci is defined by the angle formed between the first geodetic trajectories ti and the first reference generatrix gk. In the example of the first fibrous layer Ch, the first geodetic trajectories ti intersect the first reference generatrix gk at an angle of 90°. The first uniform geodetic layer Ci therefore has an orientation 0i of 90°.

[0097] 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 C2d of said layer C2. In particular, the second geodesic trajectories t2 correspond to a set of parallel straight lines on the developed surface C2d of said layer C2, as illustrated in [Fig. 10].

[0098] 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 p2[ and a larger end contour p22.

[0099] The fibrous layer C2 also includes a second reference generatrix g 2r which corresponds to the generatrix diametrically opposite to the first and second edge, that is to say to the generatrix diametrically opposite to the second singular generatrix g2.

[0100] The orientation 02 of the geodetic trajectories t2 within the uniform geodetic fibrous layer C2 is defined by the angle formed between the geodetic trajectories t2 and the second reference generatrix g2r. In the example of the second fibrous layer C2, the second geodetic trajectories t2 do not intersect the second reference generatrix g2r, except for one second geodetic trajectory t2 which coincides with the second reference generatrix g2r. The second uniform geodetic layer C2 therefore has an orientation 02 of 0°.

[0101] Figures 11 to 13 schematically illustrate a uniform third geodesic layer C3 within which the fibers of the fibrous structures extend along third geodesic trajectories t3 which correspond to straight lines on the developed surface C3d of said layer C3. In particular, the third geodesic trajectories t3 correspond to a set of parallel straight lines on the developed surface C3d of said layer C3, as illustrated in [Fig. 13].

[0102] The third layer C3 extends around the central axis A between a first edge and a second edge which join together and correspond to a third singular generator g3. The third layer C3 extends along the central axis A between a smaller end contour pM and a larger end contour p32.

[0103] The fibrous layer C3 also includes a third reference generatrix g3r which corresponds to the generatrix diametrically opposite to the first and second edges, that is to say, to the generatrix diametrically opposite to the third singular generatrix g3.

[0104] The orientation 03 of the geodetic trajectories t3 within the uniform geodetic fibrous layer C3 is defined by the angle formed between the geodetic trajectories t3 and the reference generatrix g3r. In the example of the third fibrous layer C3, the third geodetic trajectories t3 intersect the third reference generatrix g3r at an angle of 45°. The third uniform geodetic layer C3 therefore has an orientation 03 of 45°.

[0105] 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 C4d of said layer C4. In particular, the fourth geodesic trajectories t4 correspond to a set of parallel straight lines on the developed surface C4d of said layer C4, as illustrated in [Fig. 16].

[0106] 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 p4[ and a larger end contour p42.

[0107] The fibrous layer C4 also includes a fourth reference generatrix g 4r which corresponds to the generatrix diametrically opposite to the first and second edge, i.e. to the generatrix diametrically opposite to the fourth singular generatrix g4.

[0108] The orientation 04 of the geodetic trajectories t4 within the uniform geodetic fibrous layer C4 is defined by the angle formed between the geodetic trajectories t4 and the reference generatrix g4r. In the example of the fourth fibrous layer C4, the fourth geodetic trajectories t4 intersect the fourth reference generatrix g4r at an angle of 135°. The fourth uniform geodetic layer C4 therefore has an orientation 04 of 135°.

[0109] According to a first embodiment, one or more uniform geodetic layers may have a first edge and a second edge that meet, the first edge extending in the same direction as the geodetic trajectories present on the side of said first edge. This embodiment is particularly interesting in the case where none of the fibers of the fibrous structures of said layer extends in a geodetic direction. neratrix of said layer. Indeed, if in such a case one chooses to create edges extending along a generatrix as in Figures 6 to 10, there is a risk that the ends of the fibrous structures will not be sufficiently blocked at the first and second edges, since the first and second edges are each formed by a plurality of fibrous structure ends. 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 emerging at the second edge, for example by overlapping the ends of the fibrous structures emerging at the second edge over a small distance.

[0110] The term "side of the first edge" means the side of the fibrous layer extending from the first edge and opposite the second edge. Thus, the side of the first edge does not include the second edge. Similarly, the term "side of the second edge" means the side of the fibrous layer extending from the second edge and opposite the first edge. Thus, the side of the second edge does not include the first edge.

[0111] Figures 17 and 18 illustrate an example of the first variant of a uniform geodesic fibrous layer Cn in which the fibers of the fibrous structures are deposited along geodesic trajectories tu, the first edge bu and the second edge b[2 of the Cn layer joining and the first edge bu extending in the same direction as the geodesic trajectories tn present on the side of the first edge b h-

[0112] The geodetic trajectories tu correspond to straight lines on the developed surface Cnd of said layer Cn. In particular, the geodetic trajectories tn correspond to a set of parallel straight lines on the developed surface Cnd of said layer Cn as illustrated in [Fig. 18].

[0113] The layer Cn according to this first variant extends around the central axis A between the first edge bu and the second edge bn which meet, and do not correspond to a generatrix of said layer Cn- The first edge bu extends in its entirety in the same direction as the geodetic trajectories tnpresent on the side of the first edge bm The layer Cn extends along the central axis A between a smaller end contour pm and a larger end contour pn2.

[0114] The fibrous layer Cn also includes a reference generatrix grn, which is the generatrix of the fibrous layer Cnla furthest from the generatrix gu of said fibrous layer Cus' extending from the intersection between the smallest contour pnide of the fibrous layer Cnet the extension of the second edge bi2.

[0115] The orientation 0n of the geodetic trajectories tn within the fibrous layer The uniform geodetic Cn is defined by the angle formed between the geodetic trajectories tu and the reference generatrix grll. In the example of the fibrous layer Cn, the geodetic trajectories tu intersect the reference generatrix gm at an angle of 90°. The uniform geodetic layer Cn therefore has an On orientation of 90°. The uniform geodetic layer Cn illustrated in Figures 17 and 18 consequently has the same orientation as the first uniform geodetic layer Ci illustrated in Figures 5 to 7.

[0116] According to a second variant, one or more uniform geodesic 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 greatest 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.

[0117] This variant is particularly advantageous when none of the fibers of the fibrous structures of said layer extend along a generatrix of said layer. Indeed, if in such a case one chooses to create edges extending along a generatrix, as in Figures 6 to 10, there is a risk that the ends of the fibrous structures will not be sufficiently restrained at the first and second edges, since the first and second edges are each formed by a plurality of fibrous structure ends. By choosing a first edge extending along the path 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 emerging at the second edge, for example by overlapping the ends of the fibrous structures emerging at the second edge over a small distance.

[0118] Furthermore, by creating a second part of the second edge extending along the geodesic paths of the fibers of the fibrous structures present on the side of the second edge, the number of fibers or short 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, as it is difficult to drape short fibrous structures. Moreover, in this second embodiment, it is avoided that fibrous structures would emerge at the smallest contour as exposed free ends, which would necessitate additional cutting operations.

[0119] Figures 19 and 20 illustrate an example of the second variant of the fibrous layer A uniform geodesic C2i within which the fibers of the fibrous structures are deposited along geodesic trajectories t2b. The layer C2[ according to this second variant extends around the central axis A between a first edge b2[ and a second edge b22. In this variant, the second edge b22 of the layer C2[ includes a first part b22a coinciding with the first edge b2[ of said layer C2[ and extending in the same direction as the trajectories t2 of the fibers of the fibrous structures of the layer C2[ present on the side of the first edge b2i. The second edge b22 of the layer C2[ further includes a second part b22b extending in the same direction as the trajectories t2 of the fibers of the fibrous structures of the layer C2i present on the side of said second edge b22.

[0120] The geodetic trajectories t21 correspond to straight lines on the developed surface C2id of said layer C2p In particular, the geodetic trajectories t21 correspond to a set of parallel straight lines on the developed surface C2id of said layer C2i as illustrated in [Fig.20].

[0121] The C2i layer extends along the central axis A between a smaller end contour p211 and a larger end contour p212.

[0122] The fibrous layer C2i also includes a reference generatrix gr2i, which is the generatrix of the fibrous layer C2i furthest from the generatrix g2i of said fibrous layer C2i extending from the intersection between the smallest contour p2nde of the fibrous layer C and the extension of the first part b22a second edge b22.

[0123] The orientation 021 of the geodetic trajectories t2[ within the uniform geodetic fibrous layer C2i is defined by the angle formed between the geodetic trajectories t2i and the reference generatrix gr2i. In the example of the fibrous layer C2b, the geodetic trajectories t2[ intersect the reference generatrix gr2[ at an angle of 90°. The uniform geodetic layer C2i therefore has an orientation 021 of 90°. The uniform geodetic layer C2i illustrated in Figures 19 and 20 consequently has the same orientation as the first uniform geodetic layer Ci illustrated in Figures 5 to 7 and the uniform geodetic layer Cn illustrated in Figures 17 and 18.

[0124] The draping of the F-shaped form may involve applying several uniform geodesic fibrous layers to the draping form F. The orientation of each applied uniform geodesic fibrous layer is chosen according to the desired mechanical characteristics of the part to be obtained. When quasi-isotropic draping is desired, stacks of uniform geodesic fibrous layers are created, allowing for a quasi-isotropic distribution of the fibers at every point of the draped fibrous preform.

[0125] According to a first embodiment of the invention, the draping of the shape F comprises the creation 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 draping Di and development Did 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 form F so that the reference generatrices glr, g2r, g3r and g4r overlap on the form F. By thus superimposing uniform geodesic fibrous layers having orientations 0b 02, 03 and 04 of 90°, 0°, 45° and 135°, a quasi-isotropic draping is obtained at every point of the draped fibrous preform.

[0127] Thus, in each fibrous layer Cb C2, C3, C4 of the set of fibrous layers presented, the fibers extend along an extension direction tb t2, t3, t4, also called trajectory, which forms a non-zero crossing angle with the extension directions or trajectories tb 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 fibrous layers comprises four layers, and the intersection angle between the different layers of the set is a multiple of 45°, which corresponds to a multiple of the ratio 180° by 4. The illustrated set of fibrous layers thus allows for a quasi-isotropic distribution of the drapery fibers. This intersection angle is identical at every point of the drapery Di shown in Figures 21 to 23, that is to say, identical at all the generatrices of the drapery shape F.

[0129] Clearly, several sets of uniform geodesic fibrous layers are possible to obtain a quasi-isotropic drape at every point of the draped fibrous preform according to this first embodiment of the invention. For example, one can superimpose uniform geodesic fibrous layers having orientations of:

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

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

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

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

[0134] The preceding 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. Of course, we do not depart from the scope of the invention if all or part of the draped fibrous layers are fibrous layers according to the first and / or second variant described above, their ge reference points superimposed on the draping form.

[0136] According to a second embodiment of the invention, the draping of the shape F comprises the creation of several uniform geodesic fibrous layers on the draping shape F, the first and second edges of the draped fibrous layers being offset from 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 from each other on the shape F.

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

[0138] An example of draping D2 and developing D2d according to this second embodiment of the invention is shown in Figures 24 to 26, in which two uniform geodesic fibrous third layers C3 such as the geodesic fibrous third layer illustrated in Figures 11 to 13 have been applied to the draping form F such that the reference generatrices g3r and g3r' of these two third layers are offset from each other on the form F. Consequently, the reference generatrices g3r and g3r' of these two identical fibrous layers C3 are superimposed on distinct generatrices of the draping form F.

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

[0140] Figures 25 and 26 show 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 fibrous layers will be about 30°, while 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 fibrous layers will be about 60°.

[0141] Figure 27 illustrates an example of draping and developing D3d according to this second embodiment of the invention, which comprises a set of fibrous layers including four uniform geodesic fibrous third layers C3 such that the geodesic fibrous third layer illustrated in Figures 11 to 13 and 24 to 26 have been applied to the draping form F such that the reference generatrices g3r, g3r', g3r'' and g3r'' of these four third layers are offset from one another on the form F. Consequently, the reference generatrices g3r, g3r', g3r'' and g3r'' of these four identical fibrous layers C3 are superimposed on distinct generatrices of the draping form F. Thus, various fiber extension directions are obtained throughout the draping, which approaches an isotropic configuration.

[0142] The first and second edges of each fibrous layer C3 coincide with a generatrix g3, g3', g3” or g3'”. The orientations 03 of the four third uniform geodesic fibrous layers C3 are identical.

[0143] It can be seen on [Fig.27] that the angle of crossing between the directions of extension of the fibers of the different layers is different according to the areas of the draping, the said areas being delimited by the generatrices g3, g3', g3” or g3”'.

[0144] In the example illustrated in Figures 24 to 26 and in [Fig. 27], the edges of the draped fibrous layers coincide with generatrices. Of course, this does not depart from the scope of the invention if all or part of the draped fibrous layers are fibrous layers according to the first and / or second variant described above, their reference generatrices being offset around the drape shape.

[0145] It is also possible to combine the first and second embodiments 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 with distinct generatrices of the draping shape.

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

[0147] The draping process may include draping over draping form F, but may also include draping over an additional draping form extending from draping form F. This additional draping form is not necessarily developable. The draping performed on this additional draping form may differ from that described in the present invention.

[0148] The fibrous layers draped over the draping form create a fibrous preform, which has at least one developable portion comprising at least one conical or frustoconical section. According to the invention, the fibers of the fibrous structures of at least one fibrous layer of the fibrous preform extend along trajectories that correspond to straight lines on 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 that overlap with 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 reverse gear rear body.

Claims

Demands

1. A method for draping fibrous structures onto a developable draping form (F) comprising at least one conical or frustoconical portion, the fibrous structures comprising fibers extending along at least one determined direction (tb t2, t3, t4, tu, t2i), the method being characterized in that the fibrous structures are deposited on the draping form (F) such that the fibers of said fibrous structures are superimposed on straight lines of the developed surface of the draping form (F), the fibrous structures being draped so as to form one or more developable fibrous layers (Ci, C2, C3, C4, Cn, C2i) on the draping form (F), the fibrous layer(s) (Cb C2, C3, C4, Cn, C2i) extending around the draping form (F) between a first and a second edge (bu, b[2;b2[, b22), the fibrous structures of the same fibrous layer (Cb C2, C3, C4, Cn, C2i) being deposited such 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. Draping method according to claim 1, wherein a set of fibrous layers (Ci, C2, C3, C4) is draped over the draping form (F) such that in each fibrous layer (Ci, C2, C3, C4) of the set of fibrous layers the fibers extend along at least one extension direction (tb t2, t3, t4, tu, t2i) which forms a non-zero crossing angle with the extension direction(s) (tb t2, t3, t4, tu, t2i) of the fibers of the other layers (Ci, C2, C3, C4) of the set of fibrous layers.

3. Draping method according to claim 2, wherein the crossover 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 fibrous layer assembly.

4. Draping method according to claim 2 or 3, wherein the first edges (bu, b2i) of the fibrous layers (Cb C2, C3, C4) of the fibrous layer assembly are circumferentially offset from one another on the draping form (F) and wherein the second edges (bi2; b22) of the fibrous layers (Ci, C2, C3, C4) of the fibrous layer assembly are circumferentially offset from one another on the draping form (F).

5. Draping method according to any one of claims 1 to 4, in which at least a first part (b22a) of the second edge (bi2; b22) of at least one fibrous layer (Ci, C2, C3, C4, Cn, C2i) joins the first edge (bu, b21) of said fibrous layer (Ci, C2, C3, C4, Cn, C2i), said first part (b22a) of the second edge (bi2; b22) extending from the greatest end contour (pn, p22, p32, p42, pm, p2[2]) of said fibrous layer (Ci, C2, C3, C4, Cn, C2i) connecting the first edge (bn, b2[) to the second edge (bi2; b22).

6. Draping method according to claim 5, wherein the first and second edges of at least one fibrous layer (Ci, C2, C3, C4) meet and correspond to a generatrix (gb g2, g3, g4) of said fibrous layer (Ci, C2, C3, C4).

7. Draping method according to claim 5, wherein the first edge (bn, b2[) of at least one fibrous layer (Cn, C2i) extends in the same direction (tu, t2i) as the fibers of the fibrous structures of said layer (Cn, C2i) present on the side of the first edge (bn, b2i).

8. Draping method according to claim 5 or 7, wherein the second edge (b22) comprises a second part (b22b) 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).

9. Draping method according to any one of claims 5 to 8, wherein the first edge (bn, b2i) covers at least the first part (b22a) of the second edge (bi2; b22).

10. A draping method according to any one of claims 1 to 9, the method further comprising draping a plurality of stiffness fibrous structures over the draping form (F), the stiffness fibrous structures being draped so that the fibers of said stiffness fibrous structures overlap with generatrices (g) of the developed surface of the draping form (F).

11. Draping method according to any one of claims 1 to 10, wherein the draping of fibrous structures is carried out by automatic placement of fibers.

12. A fibrous preform comprising at least one developable portion comprising at least one conical or frustoconical 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 on 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 superimposed on at least one set of parallel lines of the developed surface of said fibrous layer.

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