Method for manufacturing an aeronautical frame made of composite material for an aircraft fuselage

Abstract

A method for manufacturing an aeronautical frame comprising steps consisting in forming a preform (1P) extending rectilinearly along a neutral axis (Xn), the preform (1P) comprising a plurality of plies superimposed along a stacking axis (Ze), each ply comprising a plurality of rectilinear reinforcing fibers impregnated with a resin, the preform (1P) comprising 0° plies (Pa) oriented at 0° with respect to the neutral axis (Xn), at least one 0° ply (Pa) comprising discontinuous longitudinal fibers, inclined plies (Pc) oriented at between [a1, a2] with respect to the neutral axis (Xn), a1 being between [-70°; -50°], a2 being between [50°; 70°], bending the preform (1P) to a bend radius and then consolidating the bent preform (1P) in order to obtain the aeronautical frame.

Description

Method of manufacturing an aeronautical frame made of composite material for an aircraft fuselage

[0001] The present invention relates to the field of manufacturing aeronautical frames to form a fuselage of an aircraft.

[0002] In a known manner, with reference to the, an aircraft comprises a fuselage 200 on which the wings are mounted in particular. The fuselage 200 extends longitudinally along a fuselage axis Xf and comprises an outer skin 300 which is stiffened by a plurality of aeronautical frames 101 extending orthogonally to the fuselage axis Xf and by a plurality of stringers 102 extending parallel to the fuselage axis Xf. In a known manner, a fuselage 200 has a circular or ovoid section. Also, with reference to the, an aeronautical frame 101 has a curved overall shape. An aeronautical frame 101 comprises a core 110, also called a “web”, and a sole 120, which is bent relative to the core 110, also called an “outer flange”, and configured to be fixed to an inner surface of the outer skin 300 of the fuselage 200.In this example, the aeronautical frame 101 also comprises a heel 121, which is angled relative to the core 10, also called an “inner flange”. Preferably, the sole 120 and the heel 121 extend in opposite directions relative to the core 110 as illustrated in. An aeronautical frame 101 thus has a complex shape.

[0003] In practice, as illustrated in the, an aeronautical frame 101 has a radius of curvature R, an angular opening α, a height H of the core 110 and a height S of the sole 120. An aeronautical frame 101 is traditionally made of metallic material. In order to reduce the mass of the fuselage 200, it has been proposed to make an aeronautical frame 101 of composite material.

[0004] To form an aeronautical part from a composite material, it is known to use plies comprising rectilinear reinforcing fibers impregnated with thermosetting resin. In order for the aeronautical part to have optimal mechanical characteristics, it is important that the number of reinforcing fibers is substantially constant in the aeronautical part.

[0005] A difficulty exists for an aeronautical frame 101 due to its overall curved shape. An ideal solution would be to position curved plies, that is to say with reinforcing fibers arranged in a curved manner, to form the core 110 but also the sole 120. Such a manufacturing method has a very low yield and does not guarantee the manufacture of aeronautical frames 101 with homogeneous characteristics.

[0006] To eliminate this drawback, with reference to the, it has been proposed in the prior art to implement a manufacturing method comprising steps consisting of forming a rough part 101P extending rectilinearly along a neutral axis Xn.

[0007] It is known that the blank part 101P comprises a core 110P and a sole 120P bent relative to the core 110P, the blank part 101P comprising a plurality of plies, each ply comprising a plurality of rectilinear reinforcing fibers impregnated with a thermosetting or thermoplastic resin. In order to obtain significant mechanical strength, the blank part 101P comprises: plies at 0° P A which are oriented at 0° relative to the neutral axis Xn, also called neutral folds, 90° folds P B which are oriented at 90° to the neutral axis Xn, also called perpendicular folds, inclined folds P Cwhich are oriented between [-45°; +45°] relative to the neutral axis Xn.

[0008] The P folds A , P B , P C are stacked along a stacking axis Ze. The manufacturing method comprises a step of bending the blank part 101P according to a bending radius R (corresponding to the desired radius of curvature R of the aeronautical frame 101) and then consolidating the bent blank part 101P to obtain the aeronautical frame 101.

[0009] In practice, the bending step changes the orientation of the reinforcing fibers, which affects its mechanical strength. This is particularly the case for 0° P bends A which are heavily stressed during bending. To eliminate this drawback, it has been proposed in the prior art to remove them.

[0010] Furthermore, not all aeronautical frames 101 have the same radius of curvature depending on their position in the fuselage, in particular, if they are located in a wide or narrow section. When the radius of curvature R is small, in particular when the ratio of the radius of curvature R to the height of the web H is less than 17 (R / H<17), it has been observed that the 90° folds P B have unwanted undulations. To eliminate this drawback, one solution would be to remove them, but it is then complex to manufacture an aeronautical frame 101 with sufficient mechanical resistance.

[0011] The invention thus aims to eliminate at least some of these drawbacks by proposing a new method for manufacturing aeronautical frames in composite material which is particularly suitable when the radius of curvature R over the height of the core H is less than 17 (R / H<17). PRESENTATION OF THE INVENTION

[0012] The invention relates to a method for manufacturing an aeronautical frame made of composite material for an aircraft fuselage, the frame comprising a core and a sole configured to be fixed to an outer skin of the aircraft fuselage, the manufacturing method comprising steps consisting of:Forming a blank part extending rectilinearly along a neutral axis, the blank part comprising a plurality of plies superimposed along a stacking axis, each ply comprising a plurality of rectilinear reinforcing fibers impregnated with a resin, the blank part comprising:0° plies oriented at 0° relative to the neutral axis, at least one 0° ply comprising discontinuous longitudinal fibers,inclined plies oriented between [a1, a2] relative to the neutral axis, a1 being between [-70°; -50°], a2 being between [50°; 70°], Bend the rough part according to a bending radius then Consolidate the bent rough part to obtain the aeronautical frame.

[0013] Thanks to the invention, discontinuous longitudinal fibers at 0° are advantageously provided in a rough part to absorb mechanical stress. This prevents the degradation of said fibers during bending. The presence of inclined folds makes it possible to strengthen the aeronautical frame while making it possible to omit 90° folds which would be liable to damage depending on the desired radius of curvature.

[0014] According to one aspect, the plies of the blank part are made up, for the part forming the core: plies at 0° oriented at 0° relative to the neutral axis, at least one ply at 0° comprising discontinuous longitudinal fibers, and inclined plies oriented between [a1, a2] relative to the neutral axis, a1 being between [-70°; -50°], a2 being between [50°; 70°].

[0015] In one aspect, the plies of the blank part are carbon.

[0016] In a particular aspect, the blank part is covered at its ends with glass folds. This improves galvanic insulation.

[0017] According to one aspect, the plies of the blank part are made up of: 0° plies oriented at 0° relative to the neutral axis, at least one 0° ply comprising discontinuous longitudinal fibers, and inclined plies oriented between [a1, a2] relative to the neutral axis, a1 being between [-70°; -50°], a2 being between [50°; 70°].

[0018] According to one aspect, the rough part comprises:At least one first 0° ply comprising discontinuous longitudinal fibers defining cuts spaced apart according to a first pattern,At least one second 0° ply comprising discontinuous longitudinal fibers defining cuts spaced apart according to a second pattern, the second 0° ply being superimposed on the first 0° ply in the rough part, the first pattern and the second pattern being offset in projection according to the stacking axis.

[0019] The offset of the patterns, that is to say the offset of the cuts, makes it possible to avoid creating weak zones in the thickness of the rough part.

[0020] According to one aspect, the blank part further comprises at least a third 0° ply comprising discontinuous longitudinal fibers defining cutouts spaced apart according to a third pattern, the first pattern, the second pattern and the third pattern being offset in projection according to the stacking axis.

[0021] According to one aspect, the blank part further comprises at least a fourth 0° ply comprising discontinuous longitudinal fibers defining cutouts spaced apart according to a fourth pattern, the first pattern, the second pattern, the third pattern and the fourth pattern being offset in projection according to the stacking axis.

[0022] In one aspect, all of the 0° plies forming the core of the frame comprise discontinuous longitudinal fibers.

[0023] In one aspect, all 0° plies of the frame comprise discontinuous longitudinal fibers. In other words, the core, sole, and optionally a heel comprise only 0° plies comprising discontinuous longitudinal fibers.

[0024] According to one aspect, the aeronautical frame having a radius of curvature and a web height H, the ratio of the radius of curvature to the web height is less than 17.

[0025] In one aspect, the blank part does not have folds oriented between [80°;100°], preferably 90° folds.

[0026] In one aspect, a1 is between [-65°; -55°] and a2 is between [55°; 65°].

[0027] According to one aspect, the blank part comprises at least one pair of adjacent inclined plies having opposite orientations, in particular, a first ply inclined at +a1° and a second ply inclined at -a1°.

[0028] In one aspect, the blank part includes at least three pairs of adjacent inclined plies having opposite orientations.

[0029] In one aspect, the 0° ply comprising discontinuous longitudinal fibers, each discontinuous longitudinal fiber comprising continuous segments having a maximum length of 175mm, preferably 150mm. In one aspect, each discontinuous longitudinal fiber comprising continuous segments having a minimum length of 100mm.

[0030] According to one aspect, the cutouts are distributed substantially uniformly in their 0° fold in order to avoid overlapping or juxtaposition of cutouts. Preferably, the cutouts are spaced substantially the same distance apart, here, in a plane. The cutouts are spaced evenly apart.

[0031] According to one aspect, the cutouts are distributed substantially uniformly in the thickness of the rough part. Preferably, it is understood that the cutouts are spaced substantially the same distance apart, here, in a three-dimensional manner. PRESENTATION OF FIGURES

[0032] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0033] This is a schematic representation of an aircraft fuselage comprising an outer skin, stringers and aeronautical frames according to the prior art.

[0034] This is a schematic representation of an aeronautical frame according to the prior art after its manufacture.

[0035] This is a schematic representation of a manufacturing process according to the prior art.

[0036] This is a schematic representation of an aircraft fuselage comprising an outer skin, stringers and aeronautical frames according to the invention.

[0037] This is a schematic representation of an aeronautical frame according to the invention after its manufacture.

[0038] This is a schematic representation of the steps of a method of manufacturing an aeronautical frame according to the invention.

[0039] This is a schematic representation of a step in the formation of a rough part.

[0040] This is a schematic representation of a superposition of plies to form the core of the rough part.

[0041] This is a schematic representation from above of a first fold at 0° with cuts distributed according to a first pattern.

[0042] This is a schematic representation from above of a second 0° fold with cuts distributed according to a second pattern.

[0043] This is a schematic representation of the superimposed cuts of the first fold and the second fold.

[0044] This is a schematic representation of the rough part after bending, in particular, of the first bend at 0°.

[0045] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention if necessary. DETAILED DESCRIPTION OF THE INVENTION

[0046] The invention will be presented for the production of an aeronautical frame to form the fuselage of an aircraft.

[0047] In a known manner, with reference to the, an aircraft comprises a fuselage 200 on which the wings are mounted in particular. The fuselage 200 extends longitudinally along a fuselage axis Xf and comprises an outer skin 300 which is stiffened by a plurality of aeronautical frames 1 extending orthogonally to the fuselage axis and by a plurality of stringers 102 extending parallel to the fuselage axis Xf.

[0048] In a known manner, a fuselage 200 has a circular or ovoid section. Also, with reference to the, an aeronautical frame 1 has a curved overall shape. An aeronautical frame 1 comprises a core 10, also called a "web", and a sole 20, which is bent relative to the core 10, also called an "outer flange", and configured to be fixed to an inner surface of the outer skin 300 of the fuselage 200. In this example, the aeronautical frame 1 also comprises a heel 21, which is bent relative to the core 10, also called an "inner flange". Preferably, the sole 20 and the heel 21 extend in opposite directions relative to the core 10 as illustrated in the. An aeronautical frame 1 thus has a complex shape.

[0049] The invention is presented for an aeronautical frame having an L-shaped section but it applies to any type of section, in particular, having a Z-shaped or C-shaped section.

[0050] In practice, as illustrated in , an aeronautical frame 1 has a radius of curvature R, an angular opening α, a height H of the web 10 and a height S of the sole 20. According to a preferred aspect, the radius of curvature R is between 1000 and 2500. According to a preferred aspect, the height H of the web 10 is between 60mm and 150mm. According to a preferred aspect, the height S of the sole 20 is between 15mm and 40mm.

[0051] Preferably, the ratio of the radius of curvature R to the height H of the core 10 is between 14 and 17. The invention thus applies when the ratio of the radius of curvature R to the height of the core H is less than 17 (R / H<17).

[0052] An example of the implementation of a manufacturing process for an aeronautical frame made of composite material for an aircraft fuselage will now be presented with reference to the.

[0053] In general, the manufacturing method comprising steps consisting of: Forming S1 a rough part 1P extending rectilinearly along a neutral axis Xn, then Bending S2 the rough part 1P along a bending radius R then Consolidating S3 the curved rough part 1P to obtain the aeronautical frame 1.

[0054] Form (S1) a 1P rough part

[0055] With reference to the, the method comprises a step S1 consisting of forming a rough part 1P extending rectilinearly along a neutral axis Xn. The rough part 1P is flat and will be bent subsequently so as to form the core 10 and the sole 20 and, in general, the heel 21. The formation of the part of the rough part 1P intended to form the core 10 will be presented subsequently.

[0056] With reference to the, the rough part 1P comprises a plurality of plies superimposed along a stacking axis Ze (perpendicular to the neutral axis Xn). Preferably, the number of superimposed plies is between 10 and 20. In this example, a superposition of 14 plies is shown.

[0057] Each ply comprising a plurality of rectilinear reinforcing fibers impregnated with a resin. The reinforcing fibers may be of different types, in particular, glass or carbon. Similarly, the resin may be of different types, in particular, a thermoplastic or thermosetting resin.

[0058] The 1P rough part has 0° bends P A oriented at 0° relative to the neutral axis Xn.

[0059] The rough part 1P also has inclined folds P Cwhich are oriented between [a1, a2] relative to the neutral axis Xn. Preferably, a1 is between [-70°; -50°], preferably between [-65°; -55°]. According to a preferred aspect, a1 is equal to -60°. a2 is between [50°; 70°], preferably between [55°; 65°]. According to a preferred aspect, a2 is equal to 60°. Such a high inclination is particularly advantageous when the blank part 1P does not have 90° folds. Indeed, as presented previously, such 90° folds have unwanted undulations when the ratio of the radius of curvature R to the height of the core H is less than 17 (R / H<17).

[0060] The part of the rough piece 1P intended to form the heel or the sole has folds at 0° P A and inclined folds P C.De manière préférée, tous les plis à 0° PAcomportent des fibres longitudinales discontinues. Il va être présenté en détails la formation de la partie de la pièce d’ébauche 1P destinée à former l’âme 10 ne comportant que des plis à 0° PAetdes plis inclinés PC. Autrement dit, la pièce d’ébauche 1P ne comporte pas de plis à 90°.

[0061] Preferably, with reference to the, the rough part 1P comprises at least one pair PR1, PR2, PR3, PR4 of adjacent inclined folds P Chaving opposite orientations, in particular, a first fold inclined at +a1° and a second fold inclined at -a1°. Preferably, the rough part 1P comprises at least three pairs PR1, PR2, PR3 of adjacent inclined folds P C having opposite orientations, 0° folds PA are interposed between the first pair PR1 and the second pair but also between the second pair PR2 and the third pair PR3 as illustrated in. In this example, the rough part 1P has four pairs PR1, PR2, PR3, PR4 of adjacent inclined folds P C having opposite orientations.

[0062] According to the invention, at least one fold at 0° P Acomprises discontinuous longitudinal fibers. Thus, a discontinuous longitudinal fiber comprises alternating continuous segments S as illustrated in. Preferably, a discontinuous longitudinal fiber is obtained by cutting a continuous longitudinal fiber into continuous segments S. Preferably, a 0° fold P A preferably comprises continuous segments S having a maximum length of 175mm, preferably 150mm. Preferably, the continuous segments S have a minimum length of 20mm, preferably 25mm.

[0063] Preferably, the rough part 1P comprises at least 4 folds at 0° P A comprising discontinuous longitudinal fibers, preferably at least 6 as shown in.

[0064] Subsequently, we define a pattern for each fold at 0° P A comprising discontinuous longitudinal fibers. A pattern corresponds to the distribution of the cuts in said ply at 0° P Acomme illustré à la.

[0065] With reference to the, it is represented along the stacking axis Ze a first fold at 0° P A (M1) comprising a plurality of longitudinal fibers which each comprise at least a first cut D1. The first cuts D1 together define a first pattern M1. Similarly, with reference to the, there is shown along the stacking axis Ze a second fold at 0° P A (M2) comprising a plurality of longitudinal fibers which each comprise at least one second cut D2. The second cuts D2 together define a second pattern M2.

[0066] Preferably, the cuts D1, D2 are distributed substantially uniformly in their fold at 0° P A (M1), P A (M2). Preferably, it is understood that the cuts are spaced substantially the same distance apart in a three-dimensional manner. This makes it possible to avoid concentrating areas of weakness in a 0° fold.

[0067] Preferably, the rough part 1P comprises several folds at 0° P A comprising discontinuous longitudinal fibers, preferably at least 6 plies at 0° P A as shown in. Preferably, all folds at 0° P Acomportent des fibres longitudinales discontinues. La pièce d’ébauche 1P ne comporte aucun pli à 0° PAcomportant des fibres longitudinales continues.

[0068] In the example of the, the rough part 1P comprises: a first pair PR1 of adjacent inclined folds P C ,a first fold at 0° P A (M1) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a first pattern M1, a second fold at 0° P A (M2) comprising discontinuous longitudinal fibers defining spaced cuts according to a second pattern M2, a second pair PR2 of adjacent inclined plies P C ,a third fold at 0° P A (M3) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a third pattern M3, a fourth fold at 0° P A(M4) comprising discontinuous longitudinal fibers defining spaced cuts according to a fourth pattern M4, a third pair PR3 of adjacent inclined plies P C ,a fifth fold at 0° P A (M5) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a fifth pattern M5, a sixth fold at 0° P A (M6) comprising discontinuous longitudinal fibers defining spaced cuts according to a sixth pattern M6 and a fourth pair PR4 of adjacent inclined plies P C .

[0069] The folds at 0° P A (M1), P A (M2), P A (M3), P A (M4), P A (M5), P A (M6) are superimposed in the rough part 1P along the stacking axis Ze. The patterns M1, M2, M3, M4, M5, M6 are offset in projection along the stacking axis Ze. The cutouts are advantageously offset in the thickness so as to avoid the appearance of weak zones.

[0070] As an example, with reference to the, the projection of the first pattern M1 of the first fold at 0° P is shown. A (M1) and the second pattern M2 of the second fold at 0° P A (M2). Cuts D1, D2 are offset from each other. Thus, there is no weak zone in the thickness that is linked to the alignment of cuts.

[0071] Preferably, the cuts fold at 0° P A (M1), P A (M2), P A (M3), P A (M4), P A (M5), P A (M6) are distributed in a substantially uniform manner in the rough part 1P, i.e., in a three-dimensional manner. This avoids concentrating areas of weakness.

[0072] Bend (S2) the rough part

[0073] With reference to the, the blank part 1P is positioned in a bending machine so that the blank part 1P has the desired radius of curvature R. The bending step S2 () does not damage the blank part 1P since it remains flexible due to the presence of unconsolidated resin between the reinforcing fibers.

[0074] The presence of cuts D1, D2 in the folds at 0° P A advantageously avoids the formation of mechanical tensions on the reinforcing fibers of the 0° folds. With reference to, following bending, the segments S of the first 0° fold P Asont écartés d’un premier espacement E1 sans fragiliser les fibres de renfort. En pratique, au cours de l’étape de cintrage, plus les segments sont situés extérieurement à l’axe de cintrage, plus ceux-ci sont écartés du fait des efforts de cintrage. En pratique, l’écartement après cintrage entre deux segments S adjacents est inférieur à 1mm.

[0075] As the patterns M1, M2, M3, M4, M5, M6 are offset in projection along the stacking axis Ze, the cutouts remain spaced apart after bending and there is no weak point in the bent 1P blank part due to a very low density of reinforcing fibers.

[0076] Preferably, following the step S1 of forming the rough part 1P, the method comprises a step of bending the rough part 1P to form the heel 21. After the bending step S2, the method comprises a step of bending the rough part 1P to form the sole 20.

[0077] Consolidate (S3) the rough part

[0078] With reference to the, the bent 1P blank part is then consolidated S3 by a method adapted to the nature of the resin. Thus, for a thermosetting resin, it is preferably heated and put under pressure, for example, with or without an autoclave. A step of consolidating a 1P blank part is known to those skilled in the art and will not be presented in more detail. For a thermoplastic resin, consolidation is carried out simply by cooling.

[0079] After consolidation, an aeronautical frame 1 is obtained in composite material which can be conveniently mounted on an outer skin in order to form an aeronautical fuselage.

[0080] By means of the invention, an aeronautical frame having an overall curved shape which is free from weak zones is advantageously obtained. The invention is particularly advantageous for an aeronautical frame having an R / H ratio <17 since it makes it possible to avoid the use of 90° plies and introduces 0° plies comprising discontinuous fibers.

Claims

A method of manufacturing an aeronautical frame (1) made of composite material for an aircraft fuselage (200), the frame comprising a core (10) and a sole (20) configured to be fixed to an outer skin of the aircraft fuselage (200), the manufacturing method comprising steps consisting of: Forming (S1) a blank part (1P) extending rectilinearly along a neutral axis (Xn), the blank part (1P) comprising a plurality of plies superimposed along a stacking axis (Ze), each ply comprising a plurality of rectilinear reinforcing fibers impregnated with a resin, the blank part (1P) comprising: 0° plies (P A ) oriented at 0° relative to the neutral axis (Xn), and at least one fold at 0° (P A ) comprising discontinuous longitudinal fibers, inclined folds (P c) oriented between [a1, a2] relative to the neutral axis (Xn), a1 being between [-70°; -50°], a2 being between [50°; 70°], Bend (S2) the rough part (1P) according to a bending radius (R) then Consolidate (S3) the rough part (1P) bent to obtain the aeronautical frame (1). Manufacturing method according to claim 1, in which the rough part (1P) comprises: At least one first bend at 0° (P A (M1)) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a first pattern (M1),At least one second fold at 0° (P A (M2)) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a second pattern (M2), the second fold at 0° (P A (M2)) being superimposed on the first fold at 0° (P A (M1)) in the rough part (1P), the first pattern (M1) and the second pattern (M2) being offset in projection along the stacking axis (Ze). Manufacturing method according to claim 2, in which the rough part (1P) further comprises: at least one third 0° bend (P A (M3)) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a third pattern (M3), the first pattern (M1), the second pattern (M2) and the third pattern (M3) being offset in projection according to the stacking axis (Ze). Manufacturing method according to claim 3, in which the rough part (1P) further comprises: at least one fourth 0° bend (P A (M4)) comprising discontinuous longitudinal fibers defining cuts spaced apart according to a fourth pattern (M4), the first pattern (M1), the second pattern (M2), the third pattern (M3) and the fourth pattern (M4) being offset in projection according to the stacking axis (Ze). Manufacturing method according to one of claims 1 to 4, in which all the folds at 0° (P A) have discontinuous longitudinal fibers. Manufacturing method according to one of claims 1 to 5, in which, the aeronautical frame (1) having a radius of curvature (R) and a height H of the core (10), the ratio of the radius of curvature (R) to the height of the core (H) is less than 17. Manufacturing method according to one of claims 1 to 6, in which a1 is between [-65°; -55°] and a2 is between [55°; 65°]. Manufacturing method according to one of claims 1 to 6, in which the rough part (1P) does not have 90° folds. Manufacturing method according to one of claims 1 to 8, in which the rough part (1P) comprises at least one pair (PR1, PR2, PR3, PR4) of adjacent inclined folds (P C ) having opposite orientations, in particular, a first inclined fold (P C ) at +a1° and a second inclined fold (P C ) at -a1°. Manufacturing method according to claim 9, in which the blank part (1P) comprises at least three pairs (PR1, PR2, PR3, PR4) of adjacent inclined folds (P C ) having opposite orientations. Manufacturing method according to one of claims 1 to 10, in which the 0° fold (P A ) comprising discontinuous longitudinal fibers, each discontinuous longitudinal fiber comprises continuous segments (S) having a maximum length of 175mm, preferably 150mm. Manufacturing method according to one of claims 2 to 11, in which the cutouts (D1, D2) are distributed substantially uniformly in their fold at 0° P A (M1), P A (M2). Manufacturing method according to one of claims 2 to 12, in which the cutouts (D1, D2) are distributed substantially uniformly in the thickness of the rough part (1P).

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