THIN-WALLED COMPOSITE PRODUCT REINFORCED BY HYBRID YARNS AND METHOD FOR PRODUCEING SUCH A PRODUCT

Description

Scope of the invention

[0001] The present invention relates to a thin-walled composite product reinforced with fibers and the method for manufacturing such a composite product.

[0002] Such a composite product forms in particular a portion of an article such as, but not limited to, an automotive body part, including doors, roof, hood, fenders, wing, spoiler, front and rear bumpers, aerodynamic kits, or automotive interior parts including door covers, dashboard, center console, pillar trim, trunk lining, headliner, or sporting goods such as a canoe, kayak or light boat hull, a seat post, a bicycle saddle, a bicycle frame, a bicycle handlebar, a baseball bat, a paddle, a ski or walking pole or an item of furniture, or aircraft interior parts, including side panels, ceiling panels, baggage compartments, or light aircraft aerodynamic parts, including the engine cowling, wheel covers, or any aerodynamic fairing of a moving machine.

[0003] Such a composite product can take on a multitude of geometries, including a flat sheet, a non-planar sheet, and in particular a sheet with a convex face and a concave face, or even a corrugated sheet, a three-dimensional hollow shape, and in particular a hollow tube of circular section, polygonal section or other shape, and in particular any three-dimensional thin-walled shell. State of the art

[0004] There are various arrangements of reinforced thin-walled composite products, specifically a composite product with a plastic matrix made of a polymer or resin and a reinforcement that can take the form of a preform with fibers. The product has a thin wall, meaning that it is generally initially in the form of a sheet or panel where one dimension is significantly smaller (at least 10 times smaller) than the other two.

[0005] Composite materials have been used for over 40 years, particularly in aerospace applications, primarily due to their high specific mechanical properties. Since then, the field of composite materials research has evolved, from the initial pursuit of very high specific properties, driven by aerospace applications, to the need to maintain high properties while reducing manufacturing time and production costs, thanks to automotive and other large-scale applications, and more recently to include the need to integrate additional functionalities into the composite part. In recent years, natural fiber-based composites have received increasing attention due to growing environmental awareness.Due to their low cost, low environmental impact and relatively high specific mechanical properties, natural fibers are emerging as a new alternative to glass or carbon fibers as reinforcement in composites.

[0006] US patent 6805939 proposes a thin-walled composite material containing plastic-impregnated fibers arranged in at least two parallel fiber arrays extending in different directions to form a strip, lattice, or grid. The fiber bundles may be bundled or strip-bound. The fibers in one array are impregnated with significantly more plastic than the fibers in a second array. The composite material is rigid in the direction of the fibers in the first array and flexible transversely to that direction. Advantageously, openings exist between the fiber bundles.

[0007] If we seek to strengthen the thin wall product in bending, but also in compression, it is known to propose protruding reinforcements in the form of a ribbed network or grid as in WO2017099585 in which these ribs are formed by molding above and / or below the base plate.

[0008] We know of certain types of thin wall composite products from document EP2648890, in particular with first thickness wires and second thickness wires greater than the first thickness which serve as reinforcement, these second thickness wires being composed of twisted vegetable fibers, this twisting providing in particular better resistance to compression of these second thickness wires.

[0009] There are situations in which this type of composite product exhibits a ratio between mechanical properties per unit weight and / or cost per unit weight for equal mechanical properties that is not satisfactory for the intended application.

[0010] FR3073167A1 describes the production of a composite product comprising a prepreg resulting from the asymmetric impregnation of a mesh made of plant-fiber-based yarns by sprinkling polymer particles onto one face of the mesh. This results in a yarn mesh with a polymer coating that is thicker on the upper face of the mesh, the yarns themselves being impregnated with this polymer in their central portion made of plant fibers.

[0011] GB1331431A also features a composite product that can use yarns with a fiber core covered with a polymer matrix. Brief summary of the invention

[0012] One aim of the present invention is to provide a thin-walled composite product reinforced by fibers forming an improved thin-walled composite product compared to the prior art.

[0013] Another goal is to provide a thin-walled, wire-reinforced composite product that exhibits an improved mechanical properties-to-unit-weight ratio.

[0014] Another goal is to provide a thin-walled, fiber-reinforced composite product that has an improved cost per unit weight for otherwise at least equal mechanical properties.

[0015] The composite product according to the invention makes it possible to achieve these objectives.The composite product according to the invention is, according to claim 1, an organic matrix composite product, thin-walled forming a three-dimensional sheet or shell, whose reinforcing yarns comprise hybrid yarns having a core in a first material having a density less than 1500 Kg / m 3< and a cover over the core, the cover being made of a second material, said second material being different from the first material and having a longitudinal Young's modulus in tension, along the axis of the hybrid yarn, corresponding to the tensile modulus of elasticity Et determined by the slope of the stress / strain curve σ(ε) in the interval between the two strains ε1 = 0.05 % and ε2 = 0.25 %, greater than 25 GPa, and said composite product having at least one ribbed face, said ribs being created at least in part by the hybrid yarns.

[0016] It is understood that, according to the invention, by using hybrid yarns, it is possible to have a core for these hybrid yarns that is lighter and / or less expensive than the outer layer of the hybrid yarn, with an outer layer exhibiting sufficient mechanical properties to allow the hybrid yarn to provide satisfactory mechanical reinforcement to the composite product containing it at the location of all or some of the ribs formed on at least one of its faces. The use of these hybrid yarns also makes it possible to optimize both the radial compressive strength required to withstand pressure during processing and to create ribs, this strength being provided primarily by the yarn core, and the longitudinal rigidity and bending strength of the yarn, this being provided primarily by the outer layer. This results in a composite product with an organic matrix stiffened by yarns containing hybrid yarns.

[0017] According to a first possible arrangement of the invention, the composite product comprises at least one first layer, said first layer comprising both a first type of yarn (A) having a first thickness and a second type of yarn (B) having a second thickness greater than the first thickness, said second type of yarn (B) being made up of said hybrid yarns. Thus, the ribs result from the extra thickness created by the hybrid yarns relative to the first type of yarn (A) in the first layer, said hybrid yarns constituting said second type of yarn (B).

[0018] According to a second possible arrangement of the invention, the composite product comprises at least a first layer having a first thickness, said first layer being covered by a second layer of fibers, said fibers of the second layer comprising said hybrid fibers, the hybrid fibers being spaced to create a ribbed surface. In this second layer, according to one possibility, only hybrid fibers are used: the spacing between the hybrid fibers creates, at the location of the hybrid fibers, an additional thickness, in the form of ribs, on the face of the second layer of fibers facing in the opposite direction to the first layer.

[0019] In this second layer, another possibility is to use both hybrid yarns and another type of yarn, or other types of yarns different from the hybrid yarns. In this case, different configurations can exist for the formation of ribs on the face of the second layer oriented in the opposite direction to the first layer. At least some of the ribs result from the extra thickness of the hybrid yarns relative to all or part of the other yarns in the second layer and / or from the spacing between the hybrid yarns. Alternatively, other ribs may exist and result from the extra thickness of some of the other yarns (and not the hybrid yarns) relative to some of the other yarns in the second layer and / or from the spacing between some of the other yarns.

[0020] According to one possibility of the invention, said hybrid yarns have a second thickness greater than the first thickness of the first layer.

[0021] According to one embodiment, the core of the hybrid yarns is formed from plant fibers from the following plants: flax, hemp, sisal, jute, abaca, kenaf, coconut, cotton, nettle, ramie, kapok, abaca, henequen, pineapple, banana, palm, wood, these fibers being impregnated with an organic matrix in the form of a polymer

[0022] According to one embodiment, the covering of the hybrid yarns is formed of carbon fibers impregnated with an organic matrix in the form of a polymer.

[0023] According to one embodiment of the invention, the organic matrix of the composite product is a plastic material matrix among a polymer or a resin, and in particular among a thermosetting polymer (in particular a resin) and a thermoplastic polymer.

[0024] According to one embodiment of the invention, the weight of the hybrid yarn impregnated with the organic matrix is ​​between 500 and 15,000 tex (g / km), preferably between 1,000 and 10,000 tex, preferably between 2,000 and 8,000 tex.

[0025] According to one embodiment of the invention, the weight of the hybrid yarn (core and cover) not yet impregnated with the organic matrix is ​​between 200 and 10,000 tex (g / km), preferably between 400 and 6,000 tex, preferably between 800 and 5,000 tex.

[0026] According to one embodiment of the invention, the weight of the hybrid yarn's coating represents between 10% and 70% of the weight of the hybrid yarn, preferably between 20% and 60%, and preferably between 25% and 50% of the weight of the hybrid yarn before impregnation with the organic matrix. Consequently, in this case, the weight of the core represents between 30% and 90% of the weight of the hybrid yarn before impregnation with the organic matrix, preferably between 40% and 80%, and preferably between 50% and 75% of the weight of the hybrid yarn before impregnation with the organic matrix.

[0027] According to one embodiment of the invention, in each hybrid yarn, the covering is formed of one or more rovings (one or more strands). In one possibility, this or these rovings form an angle of less than 15° with the longitudinal axis of the hybrid yarn, this angle being able to be zero, or non-zero and in particular between 1° and 15°, including equal to these limit values.

[0028] The present invention also relates, according to claim 23, to the method of manufacturing a thin-walled composite product as described above, in which the following steps are carried out: manufacturing a preform comprising wires, said wires comprising hybrid wires, said hybrid wires comprising a core of a first material and a covering over the core, the covering being made of a second material different from the first material, impregnating said preform with an organic matrix, applying pressure with a membrane or flexible pad on a raised side of the preform against a mold, controlling the temperature of the mold so as to solidify said organic matrix, so as to obtain a solidified product in which at least one external face forms ribs created at least in part by said hybrid wires, in which said first material has (after impregnation by the organic matrix) a density of less than 1500 kg / m³ and in which said second material has (after impregnation by the organic matrix) a longitudinal Young's modulus in tension, along the axis of the hybrid wire,corresponding to the tensile modulus of elasticity and determined by the slope of the stress / strain curve σ(ε) in the interval between the two strains ε1 = 0.05% and ε2 = 0.25%, greater than 25 GPa. Brief description of the figures

[0029] Examples of implementation of the invention are given in the description illustrated by the accompanying figures, in which: There Fig.1 represents a hybrid yarn used in the composite product according to the invention, schematically, in perspective and in semi-transparency, on the fig.1a , and according to different structural modalities for the core and the covering on the fig. 1b to 1d , There Fig. 2 schematically and in perspective, represents a possible arrangement for a non-woven fabric using hybrid yarns to form a composite product according to the invention. Fig.3schematically and in perspective, represents another possible arrangement for a non-woven fabric using hybrid yarns to form a composite product according to the invention. Fig. 4 schematically and in perspective, represents another possible arrangement for a non-woven fabric using hybrid yarns to form a composite product according to the invention. Fig. 5 schematically and in perspective, represents another possible arrangement for a non-woven fabric using hybrid yarns to form a composite product according to the invention. Fig. 6 schematically and in perspective, represents another possible arrangement for a non-woven fabric using hybrid yarns to form a composite product according to the invention. Fig. 7 represents, in perspective, another composite product according to the invention, The Fig. 8schematically represents certain steps of a treatment and consolidation method for manufacturing ribbed sheets according to the invention, The Fig. 9 represents examples of tubes and sheets forming thin-walled composite products according to the invention and obtained by the manufacturing process according to the invention, The Fig. 10 represents other examples of tubes and sheets forming thin-walled composite products according to the invention and obtained by the manufacturing process according to the invention, The Fig. 11 represents an example of a composite product according to the invention, forming a motor vehicle hood.

[0030] With reference to these drawings, the composite product comprises hybrid fibers schematically represented on the figure 1aThese hybrid yarns 20 have a core 21 housed within a sheath 22. The core 21 is made of a first material different from the second material constituting the sheath 22. The hybrid yarns 20 are made of several materials in order to reinforce the mechanical properties of the composite into which they are inserted and thus also reduce its cost and / or weight. The core 21 of the hybrid yarn 20 is made of a lightweight and inexpensive material with good radial compression resistance, while the outer layer or sheath 22 of the hybrid yarn 20 is made of a very strong material that is more rigid in the longitudinal direction. When this hybrid yarn 20 forms a reinforcement in the form of a raised surface, and more specifically ribs protruding from the surface of the ribbed structure of the composite product, it is the portion of the ribs furthest from the neutral axis of the hybrid yarn that bears the greatest load.Therefore, having a second rigid / resistant material on the outer portion of the yarn (the sheath 22) very effectively increases the overall flexural properties of the composite structure incorporating the hybrid yarn. Thus, using a first, less resistant material for the core 21 does not negatively impact the overall mechanical properties of the composite product reinforced with the hybrid yarns 20.

[0031] The first core material 21, according to the invention, has a density less than 1500 kg / m³, or even a density less than 1350 kg / m³, or even a density less than 1200 kg / m³ (this density is characterized for this first material in association with the organic matrix impregnating it). In all cases, this density is greater than 50 kg / m³, and according to certain embodiments, this density is greater than 150 kg / m³, and in some possible embodiments, this density is greater than 300 kg / m³.Regarding the mechanical strength properties of the first core material 21, high mechanical strength characteristics (particularly tensile and flexural) are not specifically required, although this is conceivable. Therefore, for example, a longitudinal Young's modulus of less than 25 GPa is acceptable (this Young's modulus is characterized for this first material in combination with an organic matrix). However, good radial crush resistance of the first core material (not yet impregnated with the organic matrix) is required to withstand the pressure during the manufacturing process. Typically, the aim is for this first material (considered alone) to have a crushing of less than 50% when pressurized to 6 bar by a plastic film (autoclave manufacturing process).

[0032] The second material of the cover 22 exhibits significant mechanical strength and rigidity characteristics (particularly in tension and bending): thus, according to the invention, the second material has a longitudinal Young's modulus greater than 25 GPa (this second material being characterized when impregnated with an organic matrix, thus forming a composite of fibers and an organic matrix, this Young's modulus therefore corresponding to the modulus of this fiber-organic matrix composite in the direction of the fibers), or even greater than 50 GPa, or even greater than 100 GPa. If we consider the characterization of the fibers reinforcing this second material, and therefore not the organic matrix composite incorporating these fibers as reinforcement as described above, these fibers can have a longitudinal Young's modulus greater than 40 GPa, or even greater than 70 GPa, or even greater than 200 GPa.The measurement of the longitudinal Young's modulus is carried out by a tensile test according to the DIN EN ISO 527 standard for plastics and composite materials. According to this standard, it is the tensile modulus of elasticity Et determined by the slope of the stress / strain curve σ(ε) in the interval between the two strains ε1 = 0.05% and ε2 = 0.25%.

[0033] These hybrid yarns have two distinct and clearly identifiable parts: the core and the cover. The core and cover are clearly separated. The core material differs from the cover material. This means that the core and cover materials do not have the same composition, and in most cases, they do not share any common components. In other words, the component(s) of the core material are different from the component(s) of the cover material. Various embodiments are possible for such hybrid yarns.20

[0034] According to a first embodiment of the hybrid yarns 20, the core 21 of the hybrid yarn 20 comprises or is made of plant fibers such as fibers from the following plants: flax, hemp, sisal, jute, abaca, kenaf, coconut, cotton, nettle, ramie, kapok, henequen, pineapple, banana, palm, and wood fibers. The core 21 of the hybrid yarn 20 may comprise long fibers or short fibers or both long and short fibers from one or more of these plants. The core 21 of the hybrid yarn 20 preferably has a twist, and in particular a high twist, to withstand radial compression well and maintain its round shape during the processing of composite products. Preferably, the plant fibers of the core 21 of the hybrid yarns 20 are twisted as shown in the fig. 1b, so that the angle formed by the outer fibers of the core 21 with the longitudinal axis of the hybrid yarn 20 is between 10 and 45°, preferably between 12 and 40°, preferably between 15° and 35°.

[0035] In this first embodiment, the cover 22 is made of carbon fibers, the fibers being oriented along the length (principal direction) of the hybrid yarn 20 (see the fig.1c) or forming an angle with the principal direction of the hybrid yarn 20 that is less than 15°. This composition of the hybrid yarn 20 has the advantage of presenting a coating (cover 22) with a high-performance material (second material), with fibers aligned in the direction of the load, and a core (stem 21) with a relatively lightweight, inexpensive material (first material) that exhibits good radial compressive strength. Furthermore, since plant fibers such as flax have a coefficient of thermal expansion similar to that of carbon, this allows the hybrid yarn 20, according to the first embodiment, to be used over a wide temperature range without thermal stress or residual deformation.

[0036] Since hybrid yarns are made of fibers impregnated with a polymer matrix during the manufacturing of the composite product, it is necessary to bond the core to the cover in the unimpregnated state of the hybrid yarn. Several methods exist for manufacturing such hybrid yarns 20, and in particular for bonding the core 21 to the cover 22. The cover layer 22 can be created by applying one or more rovings (or strands of fibers) to the core 21 of the hybrid yarn 20. In this case, in each hybrid yarn 20, the cover 22 is formed from one or more rovings. The strands of the cover 22 can be bonded to the core 21 of the hybrid yarn, or they can be held onto the core 21 of the hybrid yarn with a small bonding yarn 23 wound helically around the hybrid yarn 20 (see the fig.1c). This bonding wire 23, wound helically around the assembly formed by the core 21 and the cover 22, also allows the circular section of the hybrid wire 20 to be maintained during the manufacture and then the use of the composite product.

[0037] Alternatively, the strands of the cover 22 can be braided around the core 21 at a very shallow angle (between 5 and 30°). Finally, if the hybrid yarn 20 is pre-impregnated, the assembly of the two layers (cover 22 and core 21) of the hybrid yarn 20 can be carried out during the impregnation step. For example, for impregnation with a thermosetting matrix, particularly with a resin such as epoxy, the core 21 and the cover material 22 are each dipped in an epoxy bath and then assembled during the resin pre-polymerization step. This is because the resin remains sticky and soft and is fully polymerized later by baking during the manufacturing of the composite part, which allows the matrix to harden.If the composite product or part is manufactured using the thermoplastic impregnation technique, the core 21 and the cover 22 can be assembled in the tool (in particular the forming tool) with the molten polymer and held together in shape while the polymer cools. Thus, the resin or polymer acts as an adhesive between the core 21 and the cover 22.

[0038] Generally, and this applies to all embodiments of the hybrid yarn 20, in each hybrid yarn 20, the core 21 of the hybrid yarn 20 is connected to the sheath 22 of the hybrid yarn 20. Furthermore, once the fibers constituting the hybrid yarn are impregnated with the organic matrix and after polymerization of the matrix, the matrix establishes a bond between the sheath and the core. This creates cohesion between the core and the sheath of the hybrid yarn 20.

[0039] To further improve resistance to radial compression during processing, the plant fibers of the core 21 can also be coated with starch or another natural cement before being assembled with the cover 22.

[0040] According to a second embodiment of the hybrid yarns 20, the core material 21 consists of or comprises plant fibers (as in the first embodiment), but the sheath 22 is formed of one or more ribbons of high-quality plant fibers. This ribbon or these ribbons are in the form of roving(s), roving(s), or lamination(s) consisting essentially of long fibers. Thus, the sheath of the hybrid yarns is formed of plant fibers in the form of rovings, said rovings being made up of plant fibers aligned at an angle of less than 5° (between 0° and 5°) with the longitudinal or principal direction of the roving, such that the Young's modulus of the roving impregnated with an organic matrix, in the longitudinal direction of the rovings, is greater than 30 GPa, and preferably greater than 32.5 GPa, and preferably greater than 35 GPa.Note that the rovings / ribbons, forming the cover 22, can have an angle of 0 to 15° between their main direction and the main direction of the hybrid yarn 20.

[0041] This solution has the advantage of being entirely plant-based, and uses high-quality fibers on the outer layer (cover) only of the hybrid yarn, and a core of cheap plant fibers, thus offering the best performance / price ratio.

[0042] According to a third embodiment, the hybrid yarns 20 comprise a polymer core 21, said polymer belonging to the group comprising polyurethane (PU), polyethylene terephthalate (PET), polylactic acid (PLA), polyvinyl chloride (PVC), polystyrene (PS), polymethacrylamide (PMI), and styrene-acrylonitrile copolymer (SAN). This polymer can be in various forms, including a solid yarn, a yarn, a polymer foam, or polymer fibers. This polymer core 21 is, for example, obtained by extrusion, which allows, for example, its cross-section to be given a predefined shape, such as a circular, elliptical, square, or polygonal shape.The cover 22 can be made of carbon fibers, glass fibers, or plant fibers (for these plant fibers, one of the following is preferred: flax, hemp, sisal, jute, abaca, kenaf, nettle, ramie, kapok, henequen, pineapple, banana, palm, and wood fibers). This third embodiment has the advantage of providing a hybrid yarn 20 that has a low density and thus offers a very high performance-to-weight ratio.

[0043] According to a fourth embodiment, represented in the fig.1d, the core 21 of the hybrid yarns 20 is a hollow, tubular polymer yarn, the wall of which has holes 21a. By way of example, the core polymer belongs to the following list: PLA polylactic polymer, PE polyester, PA polyamide, PVC polyvinyl chloride, PS polystyrene, CP (cellulose propionate) or CAP (cellulose acetopropionate), or CAB (cellulose acetobutyrate). This hybrid yarn 20 has the advantage of acting as a flow medium for vacuum resin infusion molding processes, the resin being able to flow rapidly through the central passage of the polymer tube forming the core 21 and then to flow through the holes 21a of the wall of the polymer tube forming the core 21 during infusion, thus impregnating the cover 22 of the hybrid yarn 20 and the adjacent fibers (cover 22 of the adjacent hybrid yarns 20 as well as any adjacent yarns (A) and / or the possible lower layer(s)).Also, the internal passage of the polymer tube forming the core 21 and the holes 21a in the walls of the polymer tube being filled with resin, this allows for the formation of a mechanical anchorage of the layers present around the polymer tube forming the core 21 during the manufacture of the composite product 30.

[0044] The cover 22 can be, as in the case of the third embodiment, made of carbon fibers, glass fibers or plant fibers.

[0045] According to a fifth embodiment, the hybrid yarns 20 comprise a core 21 made of aramid fibers, or of stretched ultra-high-molecular-weight polyethylene (UHMWPE) fibers, or of stretched thermoplastic fibers. For example, these fibers are Kevlar (registered trademark), Twaron (registered trademark), and Dyneema (registered trademark). The hybrid yarns 20 of this fifth embodiment include a carbon fiber covering 22, which provides strength and stiffness to the hybrid yarn 20. Preferably, the fibers of the core 21 are twisted or braided together to provide good radial compression resistance to the hybrid yarn 20. This fifth embodiment provides very high flexural stiffness to composite products and parts using this hybrid yarn 20 as reinforcement, while also offering very advantageous crash performance.If a reinforcement grid is formed with these hybrid 20 yarns which have a high tenacity core, the formation of fragments is indeed avoided in the event of a crash, the high tenacity fibers keeping all parts of the structure, even heavily damaged, in one piece.

[0046] The possible assembly methods between the cover 22 and the core 21 of the hybrid wires of the second embodiment, the third embodiment, the fourth embodiment and the fifth embodiment are analogous to those described previously in relation to the first embodiment.

[0047] According to an example of an embodiment, the core 21 of the hybrid yarn 20 is made of linen and the cover 22 of the hybrid yarn 20 is made of carbon fibers.

[0048] THE figures 2 to 6show the diagrams of the sheet prepregs which serve as the basis for the manufacture of composite products according to the invention, incorporating two different wire diameters (A) and (B).

[0049] We refer to figures 2 and 3 which represent two variants of a first possible arrangement for the composite product 30. In this first arrangement, the composite product 30 comprises at least one first layer 31, said first layer 31 comprising both a first type of yarn (A) having a first thickness and a second type of yarn (B) having a second thickness greater than the first thickness, said second type of yarn (B) being made up of hybrid yarns 20 as described above. In the case shown in the figures 2 and 3, the composite product 30 comprises a single layer of yarn formed from the first layer 31 but in cases not shown, the composite product 30 may comprise this first layer 31 and one or more other layers stacked with this first layer 31.

[0050] In the variants of figures 2 and 3 , the thicker B threads are sewn into the same first layer 31 of threads as the thinner A threads, all A and B threads being parallel to each other, while the order in which the thicker B threads are placed may or may not repeat regularly.

[0051] In the variant of the figure 2 , this first layer 31 has two faces F1 and F2 which are not planar because the hybrid wires B being thicker than the wires A, they form ribs 33 on the two faces.

[0052] In the variant of the figure 3The composite product 30 comprises a single layer 31 with fibers A of a first diameter and second fibers B of a larger diameter formed from hybrid fibers 20; however, one of the two faces (face F1, which is the lower face in this example) comprises fibers A and B that are flush with each other, resulting in a flat surface for face F1. This flat face F1 can be obtained, for example, by pressing the sheet prepreg against the flat face of a mold. The other face F2 of this layer 31 (the upper face in this example) comprises ribs 33 resulting from the fibers B or hybrid fibers.

[0053] We refer to figures 4 to 7which represent three variants of a second type of arrangement possible for the composite product 30. In this second type of arrangement, the composite product 30 comprises at least a first layer 31 of yarns having a first thickness, and a second layer 32 of yarns covering the first layer 31, said yarns of the second layer 32 comprising hybrid yarns 20 as described previously, the hybrid yarns 20 being spaced apart to create a ribbed surface for the composite product 30, by the fact that the ribs 33 result from the extra thickness generated by the hybrid yarns 20 (B yarns) on the face F2 of the composite product 30 opposite to that (face F1) bearing the first layer 31.

[0054] In the first variant of the figure 4The composite product 30 comprises a first layer 31 of parallel, pairwise contiguous fine fibers A. This first layer 31 is superimposed on or under a non-planar face of a second layer 32 configured as the single layer of the composite product 30. figure 2 This results in a composite product 30 with at least one non-flat side forming ribs 33 (face F2). In the specific case of the figure 4 The composite product 30 comprises two faces (F1 and F2) with ribs 33 at the location of the B or hybrid yarns. The first layer 31 is preferably made of yarns A all having the same diameter; it can be stitched onto the second layer 32, or bonded with resin or with the polymer of the composite product 30.

[0055] In the second variant of the figure 5The composite product 30 comprises spaced thick yarns B formed from hybrid yarns 20 and constituting a second layer 32, which are sewn (or held in place by other techniques, e.g., gluing, obtained directly by weaving, knitting, braiding, or any other known textile manufacturing process) onto a first layer 31 of finer, densely aligned yarns A (all yarns A are parallel to each other and in contact with the two adjacent yarns A). The second layer 32 (top layer on the figure 5 ) can be made of B wires which are of equal or greater thickness than the A wires of the first layer 31 (base layer formed from a lower layer on the figure 5, and which defines a flat face F1), the second layer 32 defining a face F2 of the composite product 30 with ribs 33. In addition to the wire diameter, the fibers used in each of the wires A and B may differ, for example by using one type of fiber in the thin wires A and a second type of fiber in the thicker wires B, namely in the core 21 and / or the sheath 22 of these wires B. The angle between the wires B of the second layer 32 may also vary (angle of 0° for parallel wires B on the figure 5 ).

[0056] In the first variant shown on the figure 4 and in the second variant shown on the figure 5 , the B wires of the second layer 32 are parallel to the A wires of the first layer 31 and in the third variant of the figure 6The B wires of the second layer 32 are not parallel to the A wires of the first layer 31 but intersect with the direction of the A wires of the first layer 31. The angle between the B wires of the second layer 32 and the A wires of the first layer 31 can vary from a few degrees (2 or 3)° (B wires substantially parallel to the A wires of the first layer 31) to 90° (B wires perpendicular to the A wires of the first layer 31). Also, in the case of the figure 6 , the B wires of the second layer 32 cross each other, while also crossing with the direction of the wires of the first layer 31. In addition, it is possible to have a sheet preform comprising wires of more than two different diameters and / or more than two types, and / or more than two angles.

[0057] These fabrics or sheet preforms can be obtained in a single step, using yarns of one or more thicknesses in conjunction with textile manufacturing equipment. The yarns are processed to achieve the final textile architecture, where some of the yarns are positioned to construct the ribs. Once the textile has been processed to form the final composite part or composite product, a specific yarn type or yarn grid (comprising or consisting of hybrid yarns) is placed on a standard weave, a fabric or nonwoven made of the same or a different type of yarn, or a fiber mat, which forms a first support layer obtained in a previous step. Other methods can be used to obtain these fabrics, such as weaving, knitting, braiding, and sewing to manufacture fabrics or nonwovens.Alternatively, the threads can be held together by a polymer, either a thermosetting resin cured in the next process step, or a polymer dissolved or melted before the impregnation of the fabric or more generally of the first support layer.

[0058] In the case of the first layer 31 of the figure 2 or of the second layer 32 of the figure 4This invention, which incorporates both hybrid 20 yarns (B yarns) and other, thinner yarns (A yarns), allows for numerous yarn sequences, such as AAABAAAAABAAA, AABAABAAA, AABAABAA, ABABABABA, AAAABAABAAAA, AABAACAABAAC, where A, B, and C represent different yarn diameters, with B being a hybrid 20 yarn. These sequences can be repeated as often as necessary to meet the specific requirements of the final part, and any conceivable sequence of at least two different diameters is included in this invention. Beyond these examples, other types of combinations, including non-repeating sequences, combinations of the above sequences, or combinations of more than two different yarn types, can be used. In addition to thickness, the fiber type can also vary from one yarn type to another.

[0059] If we refer to the Fig. 7A composite product 30 comprises a first layer 31 superimposed with a second layer 32 forming a grid of hybrid wires 20. More precisely, this second layer 32 comprises hybrid wires 20 distributed between a first series of parallel hybrid wires 20 and a second series of parallel hybrid wires 20, the direction of the first series forming an angle between 30° and 90° with the direction of the second series to form a grid with a quadrilateral shape (90° on the figure 7 or the second layer 32 is a rectangular mesh grid of hybrid yarns 20).

[0060] In the case of the Fig. 7 but also in the case of the layouts of figs. 4 to 6, the first layer 31 belongs for example to the group comprising a fabric (in particular a fabric of linen yarns, or carbon fibers) or a mat of plant fibers, carbon fibers, glass fibers or polymer fibers, a metal sheet, an aluminum sheet, and a polymer sheet.

[0061] It follows from the above that the hybrid wires 20 (wires B) are possibly arranged in the first layer 31 or in the second layer 32 parallel to each other in a single direction or in only two directions, or in only three directions or in only four directions.

[0062] According to one possible arrangement, the hybrid yarn 20 is present in the composite product 30 at a rate of at least 5% by weight of parallel reinforcement or at least 10% by weight of cross reinforcement.

[0063] According to one possible arrangement, corresponding to the layouts of the figures 3 , 5 ,6 And 7 , the composite product 30 has a ribbed face and a flat face.

[0064] There figure 8 shows an illustration of the processing and consolidation steps in the case of a composite product 30 with a flat surface (single layer on the figs. 8a and 8b , and two layers on the figs. 8c and 8d The preform 30 is pressed against a rigid mold 41. When the yarns A and B of the preform 30 form a dry fabric, impregnation with a thermoplastic or thermosetting resin is initiated and carried out before, during, or just after the pressure increase. The pressure can be applied using a flexible membrane 40 or a flexible pad (which does not need to be an inflatable bladder, although this is possible) on one side and by applying a pressure P to this flexible membrane 40 ( figs. 8a and 8cThe flexible membrane 40 adapts to the fabric of varying thickness. The mold temperature 41 is then increased to (i) decrease the viscosity of the polymer and optimize fiber impregnation, and (ii) consolidate the part by cross-linking the thermosetting resin. In the case of a thermoplastic matrix, consolidation occurs after heating when the temperature is reduced below the polymer's glass transition temperature. The method can also be applied to single or double curved surfaces. The resulting composite product ( figs. 8b and 8d ) has ribs 33 at the location of the hybrid wires 20 (wires B).

[0065] In the case of flat or curved shapes, both sides of the mold 41 can be rigid (metallic, for example), one surface of the mold 41 containing grooves machined on the surface, corresponding to the negative of the corresponding wires B (or wires A and B) placed on the surface of the composite preform 30. The grooves of the mold 41 then serve as guides to precisely place the preform in the mold 40, before the mold is closed and the composite hardens as described above.

[0066] Examples of 30 composite products, in the form of tubes and sheets of composite fibers obtained using the technology presented, are shown at figures 9a to 9d The resulting stiffeners from the ribs 33 can be either ( Fig. 9a ) placed locally in certain parts of the tube section, either ( Fig. 9b) uniformly around the circumference of the tube section, depending on the structural needs and stiffness requirements of the final part. Examples of different stiffener densities resulting from the ribs 33 in the flat sheets are given in the Fig. 9c and 9dFactors such as the spacing between the ribs, the regularity of the rib sequence, the type of fibers used in the ribs, their orientation, and their thickness can be applied to all shapes, including closed-section hollow parts, flat sheets, and single or double curved surfaces. Furthermore, the ribs can function at any angle and can also intersect if multiple directions require reinforcement. A concrete example of this is a tube with stiffeners extending at ±45° to the longitudinal axis, to increase the buckling and collapse resistance of the section.All possible variables, namely the regularity of the rib sequence 33, the distribution of the ribs 33, the type(s) of fiber(s) used in the ribs 33, their thickness or even their angle, can be applied to all shapes, including tubes, flat sheets and single or double curved surfaces.

[0067] There Figure 10 shows examples of composite material tubes and sheets obtained from the technology described in this application, which combine at least two different types of fibrous materials. In the figures 10a and 10b The tubes are composed of a stack of layers with a first layer 31 on the outside, and a different material forming a second layer 32 on the inside of the tube, while the ribs 33 of the second layer are on the inner face of the tubes. The same applies to the flat sheets ( Fig. 10c and 10d), or for any other single or double curved surface. This approach can be used for composite parts with high damping requirements. The outer part of the tube can then be made of a material with a storage modulus E' significantly higher than the storage modulus of the second layer 32, which, conversely, has a significantly higher loss modulus E‴ (and therefore damping capacity) compared to the material of the outer layer 31.

[0068] There figure 11 This illustrates an embodiment of a product according to the invention. The composite product 30 in this example is a sports car hood. A sports car hood must primarily withstand the bending loads resulting from aerodynamic pressures at high speeds and must be as lightweight as possible. Therefore, only the outer surface of the hood, when mounted on a vehicle, needs to be smooth.

[0069] Using the disclosed technology, a sports car hood with an optimal weight-to-performance ratio can be designed, made from a composite product 30 using, for example, natural fibers and carbon fibers. In one possibility, the top layer of the sheet consists of a laminate (several layers of laminate) with fiber layers oriented at 0°, ±45°, and 90° to the axis. The ribs 33 located on the concave side of the sheet are oriented at 0° and 90° to resist bending loads due to surface pressure (these ribs 33 are located on the rear face of the sheet in the view of the figure 11 , and are therefore seen through this figure 11 ).

[0070] A diagram of the concept is illustrated at the figure 11The composite is preferably composed of a combination of flax and carbon fibers and either a thermosetting resin (such as epoxy) or a thermoplastic polymer such as poly(lactic acid) (PLA), poly(propylene) (PP), or any type of poly(amide) (PA). The thickness of the outer wall (first layer 31) and the ribs 33 inside varies between 0.5 and 3 mm, respectively.

[0071] The sports car hood designed using the present invention offers an optimal combination for a structural design with a minimum amount of material (and therefore weight).

[0072] Alternatively, the sports car hood can be made using as a hybrid yarn a core 21 and a cover 22 both formed solely from flax fibers in different forms, which constitutes a first material for the core 21 and a second material, different from the first material, for the cover 22: for example the first material is formed from short flax fibers treated to form a yarn with a high twist (the angle between the outer fibers of the yarn and the axis of the yarn is preferably between 10° and 45°, preferably between 12° and 40°, and preferably between 15° and 35°, including these limit values, and in one possibility this angle is greater than or equal to 15°) and the second material is formed from long flax fibers in the form of rovings.In this case, by using hybrid yarns made solely of plant fibers in the core 21 and the cover 22, optimal performance is obtained while using bio-sourced materials. Reference numbers used in the figures

[0073] 20 Hybrid yarn 21 Core 21a Holes 22 Cover 23 Bonding yarn 30 Composite product 31 First layer 32 Second layer 33 Ribs 40 Flexible membrane 41 Mold F1 Face of composite product F2 Face of composite product

Claims

1. A thin-walled composite product (30) with an organic matrix forming a sheet or a three-dimensional shell, reinforced by yarns, the yarns comprising hybrid yarns (20), said hybrid yarns (20) comprising a core (21) of a first material having a density of less than 1500 kg / m3 and a sheath (22) covering the core (21), the sheath (22) being made of a second material, said second material being different from the first material, wherein said second material has a longitudinal tensile Young's modulus , along the axis of the hybrid yarn (20), corresponding to the tensile modulus of elasticity Et determined by the slope of the stress-strain curve σ(ε) in the interval between the two deformations ε1 = 0.05% and ε2 = 0.25%, greater than 25 GPa, and wherein said product has at least one ribbed face, said ribs (33) being formed at least in part by the hybrid yarns (20).

2. The composite product (30) reinforced by hybrid yarns according to claim 1, comprising at least a first layer, said first layer comprising both a first type of yarn (A) having a first thickness and a second type of yarn (B) having a second thickness greater than the first thickness, said second type of yarn (B) being constituted by said hybrid yarns (20).

3. The composite product (30) reinforced by hybrid yarns according to claim 1, comprising at least a first layer having a first thickness, said first layer being covered by a second layer of yarns, said yarns of the second layer comprising said hybrid yarns (20), the hybrid yarns (20) being spaced apart to create a ribbed surface.

4. The composite product (30) according to the preceding claim, wherein said hybrid yarns (20) are arranged in the second layer parallel to one another in a single direction or in only two, three or four directions.

5. The composite product (30) according to claim 3 or claim 4, wherein said hybrid yarns (20) have a second thickness greater than the first thickness of the first layer.

6. The composite product (30) according to one of claims 1 to 5, characterised in that it comprises a ribbed face and a flat face.

7. The composite product (30) according to one of claims 1 to 6, characterised in that in each hybrid yarn (20), said sheath (22) is formed from one or more rovings.

8. The composite product (30) according to any one of claims 1 to 7, characterised in that in each hybrid yarn (20), said core (21) of the hybrid yarn is connected to said sheath of the hybrid yarn (20).

9. The composite product (30) according to the preceding claim, wherein the core (21) of the hybrid yarns (20) is formed from plant fibres selected from the fibres of the following plants: flax, hemp, sisal, jute, abaca, kenaf, coconut, cotton, nettle, ramie, kapok, abaca, henequen, pineapple, banana, palm, wood.

10. The composite product (30) according to claim 9, wherein the plant fibres of the core (21) of the hybrid yarns (20) are twisted such that the angle formed by the outer fibres of the core with the longitudinal axis of the hybrid yarn (20) is between 10 and 45°, preferably between 12 and 40°, preferably between 15° and 35°.

11. The composite product (30) according to claim 9, wherein the plant fibres of the core (21) of the hybrid yarns (20) are coated with starch or another natural cement.

12. The composite product (30) according to any one of claims 9 to 11, wherein the sheath (22) of the hybrid yarns (20) is formed from carbon fibers.

13. The composite product (30) according to any one of claims 9 to 11, wherein the covering (22) of the hybrid yarns (20) is formed from plant fibers in the form of rovings, said rovings being made up of aligned plant fibers forming an angle of less than 5° with the longitudinal direction of the roving, such that the Young's modulus in the longitudinal direction of the rovings of the roving impregnated with an organic matrix, corresponds to the tensile modulus of elasticity Et determined by the slope of the stress-strain curve σ(ε) in the interval between the two deformations ε1 = 0.05% and ε2 = 0.25%, is greater than 30 GPa.

14. The composite product (30) according to any one of claims 1 to 8, characterised in that the core (21) of the hybrid yarns (20) is made of a polymer, said polymer belonging to the group comprising polyurethane (PU), polyethylene terephthalate (PET), polylactic acid (PLA), polyvinyl chloride (PVC), polystyrene (PS), polymethacrylamide (PMI) and styrene-acrylonitrile copolymer (SAN).

15. The composite product (30) according to any one of claims 1 to 8 and 14, characterised in that the core (21) is a hollow, tubular polymer yarn, the wall of which has holes (21a).

16. Composite product (30) according to any one of claims 14 to 15, characterised in that the sheath (22) of the hybrid yarns (20) is made of carbon fibers, glass fibers or plant fibres.

17. The composite product (30) according to any one of claims 1 to 13, 15 and 16, characterised in that the core (21) is made of aramid fibers or of drawn ultrahigh molecular weight polyethylene (UHMPE) fibers or drawn thermoplastic fibers.

18. The composite product (30) according to the preceding claim, characterised in that the sheath (22) of the hybrid yarns (20) is made of carbon fibers.

19. The composite product (30) according to one of claims 17 to 18, characterised in that the fibres of the core (21) are twisted or braided together.

20. The composite product (30) according to any one of claims 1 to 19 and claim 3, characterised in that said first layer belongs to the group comprising a fabric or mat of plant fibers, carbon fibers, glass fibers or polymer fibers, a metal sheet, an aluminum sheet, and a polymer sheet.

21. The composite product (30) according to any one of claims 1 to 12, 16, and 18 to 20, characterised in that the core (21) is made of flax and the sheath is made of carbon fibers.

22. The composite product (30) according to any one of claims 1 to 21, characterised in that said hybrid yarn (20) is present in an amount of at least 5% by weight of parallel reinforcement or at least 10% by weight of cross-reinforcement.

23. A method for manufacturing a thin-walled organic matrix composite product (30) forming a sheet or a three-dimensional shell, comprising the following steps: - manufacturing a preform comprising yarns, said yarns comprising hybrid yarns (20), said hybrid yarns (20) comprising a core (21) made of a first material and a sheath (22) covering the core (21), the sheath being made of a second material, said second material being different from the first material, - impregnating said preform with an organic matrix, - applying pressure with a membrane or a flexible pad on a raised side of the preform against a mold, - controlling the temperature of the mold so as to solidify said organic matrix, thereby obtaining a solidified product in which at least one outer face forms ribs (33) created at least in part by said hybrid yarns (20), wherein said first material has a density of less than 1500 kg / m3 and wherein said second material has a longitudinal Young's modulus in tension, along the axis of the hybrid yarn (20), corresponding to the tensile modulus of elasticity Et determined by the slope of the stress-strain curve σ(ε) in the interval between the two deformations ε1 = 0.05% and ε2 = 0.25%, greater than 25 GPa.