Reinforcement material comprising twisted carbon threads for producing composite parts and corresponding method and use

Abstract

The present invention relates to a reinforcing material (1) made from the following: a unidirectional reinforcing layer (2) formed by one or more carbon reinforcing threads (3) combined with a polymer fiber layer (4, 5) on each side thereof, wherein the polymer fiber layer is selected from a non-woven web, the polymer part of the reinforcing material accounting for between 0.5% and 10% of the total weight of the reinforcing material (1) and preferably between 2% and 6% of its total weight, the unidirectional reinforcing layer (2) comprising one or more reinforcing threads (3) individually twisted according to a twist of 3 to 15 rpm, preferably 6 to 12 rpm.

Description

Technical Field

[0001] The present invention relates to the technical field of reinforcing materials suitable for forming composite parts. More specifically, the present invention relates to materials suitable for manufacturing composite parts in combination with an injected or infused resin, said material comprising a unidirectional web at least partially made of one or more individually twisted reinforcing yarns, the twist of said reinforcing yarns being suitable for ensuring the diffusion of said injected or infused resin during the production of said composite part. Background Art

[0002] The manufacture of composite parts or articles, i.e. comprising firstly one or more fiber reinforcements, in particular of the unidirectional fiber web type, and secondly a matrix, said matrix being generally mainly of the thermosetting type and possibly comprising one or more thermoplastics, can be produced, for example, by the so-called direct or LCM (Liquid Composite Molding) process. The direct process is defined by the fact that the fiber reinforcement or reinforcements are used in a "dry" state, i.e. without a final matrix, the resin or matrix being implemented separately, for example, by injection into a mold containing the fiber reinforcement (resin transfer molding (RTM) process), by infusion through the thickness of the fiber reinforcement (Liquid Resin Infusion (LRI) process or Resin Film Infusion (RFI) process), or else by manual coating / impregnation on each individual layer of the fiber reinforcement by means of a roller or a brush, applied successively to the form. Within the scope of the manufacture of composite parts, in particular in the aerospace sector, the mass production rates can be very high. For example, for the manufacture of single-aisle aircraft, an aerospace customer would like to be able to produce several dozen aircraft per month. Direct methods such as infusion or injection are particularly relevant methods that can meet this requirement.

[0003] For RTM, LRI or RFI methods, it is usually necessary to first manufacture a fiber preform or stack in the shape of the desired finished product, and then impregnate the preform or stack with resin to form a matrix. The resin is injected or infused with the help of temperature and pressure differentials, and then after all the required amount of resin is contained in the preform, the assembly is brought to a higher temperature to perform a polymerization / crosslinking cycle and thereby harden it.

[0004] Composite parts used in the automotive, aerospace or naval industries are subject to very stringent requirements, especially in terms of mechanical properties. In order to save fuel and facilitate the maintenance of parts, the aerospace industry has replaced many metal materials with lighter composite materials.

[0005] During the production of the part, the resin subsequently combined with the fiber reinforcement (especially by injection or infusion) may be a thermosetting resin, for example an epoxy type thermosetting resin. In order for the resin to flow correctly through the preform made of the stack of multiple fiber reinforcement layers, such resins are usually very fluid, for example having a viscosity of about 50 mPa.s. to 200 mPa.s. or even lower at the infusion / injection temperature. The main disadvantage of this type of resin is its brittleness after polymerization / crosslinking, which leads to low impact resistance of the produced composite parts.

[0006] In order to solve this problem, it has been proposed in the literature of the prior art that a fiber reinforced layer, particularly a unidirectional web of reinforcing yarns is combined with a porous thermoplastic polymer veil and particularly with a thermoplastic fiber nonwoven material (also referred to as a ply). Such solutions are notably described in patent applications or patents EP 1125728, US 6,828,016, WO 00 / 58083, WO 2007 / 015706, WO 2006 / 121961, US 6,503,856, US2008 / 7435693, WO 2010 / 046609, WO 2010 / 061114 and EP 2 547816, US2008 / 0289743, US2007 / 8361262, US2011 / 9371604, WO 2011 / 048340. The addition of such a porous thermoplastic layer (particularly a nonwoven porous thermoplastic layer) makes it possible to improve the mechanical properties of the composite parts obtained in the Compression After Impact (CAI) test, which is generally used to characterize the impact resistance of the structure. The use of nonwoven materials makes it possible in particular to achieve mechanical properties adapted to the aerospace sector.

[0007] In order to achieve satisfactory composite part production rates, the time between applying the dry reinforcements and impregnating or infusing the resin into the resulting dry reinforcement stack or preform should be as short as possible.

[0008] Furthermore, in the aeronautical sector, the stresses associated with the electrical environment of an aircraft both in flight and on the ground, in particular in the event of lightning, make it necessary to provide a material that meets the high level of standards in this sector.

[0009] To this end, solutions have been proposed in the prior art to:

[0010] - Increase the permeability of dry reinforcement materials to injected or infused liquid resin;

[0011] - Provide satisfactory lateral conductivity.

[0012] The Applicant has proposed microperforation of the aforementioned material, which increases the transverse permeability of the material (WO 2010 / 046609), improves its transverse cohesion and thus facilitates its processing by automated applications (WO 2014 / 076433), increases the transverse conductivity of the composite parts produced (WO 2013 / 160604).

[0013] Nevertheless, from an industrial point of view, this technology requires special tools to produce the microperforations and results in complex application operations for microperforated materials, especially for those with high grammages.

[0014] Furthermore, application WO 2008 / 155504 in the name of the present applicant describes a method for manufacturing a composite material, wherein at least one twisted yarn is applied to an application surface and has a trajectory with at least one curved area on the application surface, and wherein a reinforcing yarn is bonded to the application surface by means of a polymer adhesive. The method is used for producing preforms or parts of complex shape requiring application of the yarn on a curved area, and proposes applying a twist to the yarn upstream of the yarn application, the twist being selected to at least compensate for the difference in length presented by the extreme paths of the yarn on either side of the yarn width, measured parallel to the application surface.

[0015] WO 2013 / 133437 describes a very specific material made of carbon yarns, comprising 50,000 to 60,000 twisted filaments, with a twist of 5 turns / m to 50 turns / m and arranged in the same direction so as not to overlap, to provide a carbon sheet with a basis weight greater than 800 g / m and less than or equal to 26,000 g / m, suitable for RTM methods. The proposed material is intended for the design of wind turbine blades, vehicles or boats, but not for the aerospace sector.

[0016] The object of the present invention is therefore to propose an alternative solution to the known prior art suitable for the aeronautical sector, with the aim of providing new reinforcements for composite parts combined with injected or infused resins, which, while retaining a high transverse permeability, also have improved application characteristics, reduced post-application overflow and increased transverse conductivity. Summary of the invention

[0017] In this context, the present invention relates to a reinforcing material consisting of: a unidirectional reinforcing mesh formed by one or more carbon reinforcing yarns, with a polymer fiber layer bonded to each side of the unidirectional reinforcing mesh, the polymer fiber layer being selected from a non-woven material, the polymer portion of the reinforcing material accounting for 0.5% to 10% of its total weight and preferably accounting for 2% to 6% of its total weight, the unidirectional reinforcing mesh containing one or a series of individually twisted carbon reinforcing yarns having a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m.

[0018] According to some embodiments, the unidirectional reinforcement mesh is formed by multiple carbon reinforcement yarns, and at least every fifth reinforcement yarn, preferably at least every second or third reinforcement yarn, and preferably all reinforcement yarns are individually twisted, with a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m.

[0019] In particular, the weight of the unidirectional reinforcement mesh is 126g / m 2 Up to 280g / m 2 In the range of 126 g / m 2 Up to 210g / m 2 or 210g / m 2 Up to 280g / m 2 within the range.

[0020] Within the scope of the present invention, the polymer fiber layer is thermoplastic in nature and consists in particular of a thermoplastic polymer, a partially crosslinked thermoplastic polymer, a mixture of such polymers, or a mixture of a thermoplastic polymer and a thermosetting polymer.

[0021] The polymer fiber layer has thermal adhesiveness. In addition, its combination with the unidirectional reinforcement net is achieved by means of this thermal adhesiveness.

[0022] Advantageously, the layers of polymer fibers are of the same nonwoven material.

[0023] Typically, the nonwoven material has a density of 0.2 g / m 2 Up to 20g / m 2 The invention also provides a basis weight within a range and / or a thickness within a range of 0.5 micrometer to 50 micrometers, preferably 3 micrometer to 35 micrometers.

[0024] The reinforcing material according to the invention advantageously has the feature of being neither perforated, nor sewn, nor knitted, nor woven.

[0025] Within the scope of the invention, the use of carbon reinforcing yarns that have previously been subjected to a twisting operation (thus having a range of reinforcing yarns with twists ranging from 3 t / m to 15 t / m in the reinforcing material according to the invention) makes it possible:

[0026] - Obtain adhesion between the upper and lower sides of the unidirectional web, increasing lateral cohesion;

[0027] - creating, with the help of the twisted reinforcing yarns, diffusion continuity between the two faces of the unidirectional web for the resin that will be injected or infused during the production of the composite part. The continuity of the filaments of the twisted reinforcing yarns connecting the two faces of the unidirectional web contributes to the transverse permeability. In addition, the twisted reinforcing yarns are able to create channels extending along the filaments of the twisted reinforcing yarns connecting the two faces of the unidirectional web. The transverse permeability is thus obtained following the filaments extending from one face of the unidirectional sheet to the other, with the help of a large amount of permeability extending at the level of the twisted reinforcing yarns;

[0028] - With the carbon reinforcement yarn acting as an electrical conductor, continuity of electrical conductivity is created along the filaments of the twisted reinforcement yarn connecting the two faces of the unidirectional sheet.

[0029] The present invention relates to a reinforcing material for producing composite parts by a direct method. That is, in order to produce composite parts, the reinforcing material according to the present invention should be combined with a polymer resin, which will be injected or resin-into the reinforcing material or a stack of such reinforcing materials. In addition, conventionally, the weight of the polymer part of the reinforcing material according to the present invention accounts for at most 10% of the total weight of the reinforcing material according to the present invention. Typically, the polymer part of the reinforcing material accounts for 0.5% to 10% of the total weight of the reinforcing material and preferably accounts for 2% to 6% of its total weight. This polymer part corresponds to the total part of one or more polymers present in the reinforcing material according to the present invention: therefore it contains or even consists of the nonwoven material present in the reinforcing material according to the present invention. The advantages of the present invention are obtained without increasing the polymer part of the material, that is, the amount of polymer material present in the polymer fiber layer formed by the nonwoven material, which is present on both sides of the unidirectional web.

[0030] Apart from the use of twisted reinforcing yarns, the polymer fiber layer of the reinforcing material, before the microperforation step, corresponds to those described in the prior art and in particular in WO 2010 / 046609.

[0031] When the unidirectional reinforcing web is formed by an assembly of carbon reinforcing yarns, the carbon reinforcing yarns are positioned side by side. The twisted reinforcing yarns may be arranged adjacent to each other, wherein one or more non-twisted reinforcing yarns may also be inserted between two consecutive twisted reinforcing yarns. After the unidirectional web is formed, it may be combined with a layer of polymer fibers selected from nonwoven materials, in particular by lamination on each of its faces.

[0032] According to an alternative embodiment using a unidirectional reinforcing web called hybrid S / Z, the reinforcing material is characterized by the fact that all the carbon reinforcing yarns forming the unidirectional reinforcing web are individually twisted, with a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m, the unidirectional reinforcing web comprising at least 3 carbon reinforcing yarns thus twisted, with at least one twisted carbon reinforcing S-twist yarn and at least one twisted carbon reinforcing Z-twist yarn, and:

[0033] - when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing network (referred to as the total number of yarns) is an even number, the number of twisted carbon reinforcing S-twisted yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twisted yarns on the other side of the plane Δ are each independently an integer in the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}, and if its definition formula results in an integer, each endpoint of the range is rounded to the nearest integer, and the other twisted carbon reinforcing yarns are Z-twisted yarns;

[0034] - when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing yarn (referred to as the total number of yarns) is an odd number, the number of twisted carbon reinforcing S-twisted yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twisted yarns on the other side of the plane Δ are two integers or two half-integers and are each independently within the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}; if its definition formula results in an integer or half-integer, each endpoint of the range is rounded to the nearest integer or half-integer, and the remaining twisted carbon reinforcing yarns are Z-twisted yarns;

[0035] The plane Δ is a plane parallel to the general extension direction of the unidirectional web and divides the unidirectional web into two equal parts, perpendicular to its surface.

[0036] In other words, the number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web (for simplicity, referred to as the "total number of yarns" in the definition of the scope of the unidirectional so-called hybrid S / Z web) is equal on both sides of the plane Δ, at the level of the neutral fibers of the unidirectional reinforcing web. Therefore, if the unidirectional reinforcing web consists of n (in the case of unidirectional reinforcing webs (called hybrid S / Z), n is an integer greater than 3) twisted carbon reinforcing yarns, there are n / 2 twisted carbon reinforcing yarns on either side of the plane Δ.

[0037] Furthermore, the hybrid S / Z unidirectional reinforcement web comprises an integer number m of twisted carbon reinforced S-twist yarns, the sum of the number m1 of twisted carbon reinforced S-twist yarns located on one side of the plane Δ and the number m2 of twisted carbon reinforced S-twist yarns located on the other side of the plane Δ being an integer. Similarly, the unidirectional reinforcement web comprises an integer number p of twisted carbon reinforced Z-twist yarns, the sum of the number p1 of twisted carbon reinforced Z-twist yarns located on one side of the plane Δ and the number p2 of twisted carbon reinforced Z-twist yarns located on the other side of the plane Δ being an integer. Thus, for example, in the case of a unidirectional reinforcement web formed by a sequence of twisted carbon reinforced SZSZSZS yarns (yarn twists laid side by side) satisfying definition I1, the number n / 2 of yarns on either side of the plane Δ is 3.5, m1=m2=2 and p1=p2=1.5.

[0038] In particular, such materials according to the invention comprising unidirectional reinforcing webs (called hybrid S / Z webs) have the advantage that they can be produced in long lengths and at high speeds. In such embodiments with unidirectional so-called hybrid S / Z reinforcing webs, the material according to the invention advantageously has a width greater than 7 mm, preferably greater than 12 mm and preferably in the range of 12 mm to 51 mm and preferably has a length of 2 m to 5000 m, preferably 100 m to 2000 m.

[0039] According to another aspect, the present invention relates to a method for preparing a reinforcement material, said method comprising the following consecutive steps:

[0040] a1) providing a unidirectional reinforcement mesh formed of one or more reinforcing yarns individually twisted to a twist of 3 turns / m to 15 turns / m,

[0041] a2) providing at least two polymer fiber layers, said polymer fiber layers being selected from nonwoven materials,

[0042] a3) bonding each polymer fiber layer to each face of the unidirectional reinforcing web.

[0043] For example, the preparation method comprises, upstream of step a1), a step of making a unidirectional reinforcing mesh comprising applying to a reinforcing yarn or a series of yarns a twist ranging from 3 to 15 turns / m, the twist being applied to each yarn individually.

[0044] According to one embodiment, the unidirectional reinforcing mesh is formed from a plurality of reinforcing yarns and the preparation method comprises, upstream of step a1):

[0045] i) applying to a series of reinforcing yarns a twist of 3 turns / m to 15 turns / m, said twist being applied to each yarn individually,

[0046] ii) Aligning the twisted yarns thus obtained, potentially with other reinforcing yarns, and placing said yarns side by side, so as to form a unidirectional reinforcing web.

[0047] In such a method, the polymer fiber layers have thermobond properties and the bonding of step a3) is advantageously obtained by applying each polymer fiber layer to each face of the unidirectional reinforcing web, said application being accompanied or followed by heating the polymer fibers, causing them to soften or melt, and then cooling.

[0048] The invention also has as its object a preform which consists at least partially of one or more reinforcing materials according to the invention.

[0049] Another object of the invention relates to a method for manufacturing a composite part from at least one reinforcing material according to the invention. According to this manufacturing method, a thermosetting resin, a thermoplastic resin, or a mixture of a thermosetting resin and a thermoplastic resin is injected or poured into the reinforcing material, a stack of several reinforcing materials according to the invention, or a preform according to the invention.

[0050] In particular, such a method comprises, before the infusion or injection of the resin, the steps of forming a ply or stack comprising several reinforcing materials according to the invention, during which said reinforcing materials are continuously conveyed in guide members and circulated so as to ensure their positioning during their application, resulting in the desired ply or stack. Conventionally, the material according to the invention is cut to the desired size, in particular to the desired length, to form the folds or stacks to be produced.

[0051] Advantageously, such a method for manufacturing a composite material part comprises an application or shaping prior to infusion or injection of resin, said application or shaping preferably taking advantage of the thermo-bonding properties of the polymer fiber layers present in said one or more reinforcement materials.

[0052] Another object of the invention relates to the use of one or more reinforcing materials according to the invention for producing preforms or composite parts combined with a thermosetting resin or a thermoplastic resin or a mixture of a thermosetting resin and a thermoplastic resin.

[0053] Advantageously, a thermosetting resin, and in particular an epoxy resin, is injected or infused to achieve the method of manufacturing or the use of the reinforcing material according to the invention.

[0054] The present invention will be better understood from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A is a partial schematic cross-sectional view of a reinforcing material according to the present invention.

[0056] Figure 1 B is a schematic perspective view, partially cut away, showing a reinforcing material according to the present invention having a unidirectional web formed of a series of twisted yarns.

[0057] Figure 1 C is a schematic, partially cut-away perspective view showing a reinforcing material according to the present invention having a unidirectional web formed by a series of twisted reinforcing yarns 3 in a SZSZSZ configuration, with the figure being read from right to left, i.e., S-twisted yarns are laid adjacent to Z-twisted yarns, which in turn are laid adjacent to S-twisted yarns, and so on.

[0058] Figure 2 is a schematic diagram depicting the twist on a twist-reinforced yarn according to the present invention.

[0059] Figure 3 is a schematic view illustrating the principle of a twisting machine for applying twist to a reinforcing yarn.

[0060] Figure 4 is a schematic view of a station suitable for measuring the width of a reinforcement yarn, in particular a twisted yarn.

[0061] Figure 5 is a graph showing the average width of the reinforcement yarn (mm) as a function of twist (tpm) for various reinforcement yarns.

[0062] Figure 6 is a graph showing the standard deviation of the average width (mm) of the reinforcement yarn as a function of twist for various reinforcement yarns.

[0063] Figure 7 is a graph showing the percentage of values ​​above the target value for the reinforcement yarn width as a function of various reinforcement yarn twists for a weight of 140 g / m2.

[0064] Figure 8 is a graph showing the percentage of values ​​above the target value for the reinforcement yarn width as a function of various reinforcement yarn twists for a grammage of 210 g / m2.

[0065] Fig. 9 The figure shows the value for 280 g / m 2 Graph of the percentage of grammage above the target value of the reinforcement yarn width as a function of various reinforcement yarn twists.

[0066] FIG. 10 shows a graph for 252 g / m 2 Graph of the percentage of grammage above the target value of the reinforcement yarn width as a function of various reinforcement yarn twists.

[0067] FIG. 11 shows a graph for 350 g / m 2Graph of the percentage of grammage above the target value of the reinforcement yarn width as a function of various reinforcement yarn twists.

[0068] FIG. 12 is a diagram illustrating the locations of measurement points on a preform.

[0069] FIG. 13 is a schematic illustration showing the principle of thickness measurement of a reinforcement yarn preform.

[0070] FIG. 14 is a graph showing the variation of overrun with the number of plies applied for material 8 according to the invention and comparative material 3.

[0071] FIG. 15 is a graph showing the variation of overrun with the number of plies applied for material 4 according to the invention and comparative material 3 .

[0072] FIG. 16 is a graph showing the lateral permeability (m) of the comparative material and the material of the present invention. 2 ) and fiber volume ratio (FVR).

[0073] Figure 17 shows that the width of the 6.35mm and the weight of 280g / m 2 Differences observed during the formation of plies made of a unidirectional web of carbon yarns made with 4 yarns twisted at 10 turns / m but with 3 configurations: SSSS, SZZS and SZSZ. On the right are presented partial schematic views of the top of the unidirectional layers present in each case in the reinforcement used, wherein above each partial schematic view a section along the yarn is presented, the S or Z twist direction of the reinforcing yarns of each unidirectional layer.

[0074] FIG. 18 shows the results of producing a 210 g / m2 yarn made with a SSSSSSSZZZZZZZSSSS configuration (7 S twist yarns, then 5 Z twist yarns, then 6 S twist yarns). 2 The gap obtained at the junction between the twist of 7 S-twisted reinforcing yarns and 5 Z-twisted reinforcing yarns when producing a unidirectional carbon yarn web with a width of 38.1 mm. In fact, during the production of the unidirectional web, the S-twisted yarn group is driven to the left, while the Z-twisted yarn group is driven to the right, which creates a gap at the junction of 7 S-twisted yarns / 5 Z-twisted yarns.

[0075] FIG. 19 is a schematic illustration of a production line used in the examples. DETAILED DESCRIPTION

[0076] like Figure 1A shows, one object of the present invention relates to a reinforcing material 1, said reinforcing material consisting of: a unidirectional reinforcing web 2 formed by one or more carbon reinforcing yarns 3, on each face of which is incorporated a veil corresponding to the polymer fiber layers 4, 5 forming the nonwoven material. More precisely, as will be described in detail in the rest of the description, at least some of the carbon reinforcing yarns 3 are individually twisted.

[0077] "Unidirectional reinforcement web" means a web consisting exclusively or almost exclusively of carbon reinforcement yarns arranged parallel to one another.

[0078] Figure 1 B shows a unidirectional web 2 consisting of several individually twisted carbon reinforcement yarns 3, with face yarns 4, 5 combined on each face. Each twisted reinforcement yarn 3 has a general extension direction D which is straight in the extension plane of the unidirectional sheet. G (It corresponds to the central axis of the yarn). Each twisted reinforcing yarn 3 has a general extension direction D extending in a straight line. G , parallel to the extension surfaces S4 and S5 of the veils 4 and 5, which are Figure 1 B is a plane. In a unidirectional web, the overall extension direction of the reinforcing yarn is D G Parallel or substantially parallel to each other. It is generally accepted by those skilled in the art that some general extension directions D of the two reinforcing yarns G A deflection between the two directions of the mesh of less than or equal to 3°, preferably less than or equal to 2° and preferably less than or equal to 1° does not change the unidirectional character of the mesh. If the reinforcing yarns are all parallel to each other, the general extension direction of the unidirectional mesh corresponds to the general extension direction D of the reinforcing yarns. G , or for all extension directions D of the reinforcing yarns 3 forming the unidirectional web 2 G The rare cases where there is no strict parallelism correspond to the average of these general extension directions.

[0079] In a unidirectional web, the reinforcing yarns are arranged side by side to ensure optimal surface coverage. In particular, it is desirable to avoid local gaps greater than 1 mm perpendicular to the direction of extension of the unidirectional web over a length of more than 10 cm (ie parallel to the direction of extension of the unidirectional web).

[0080] Thermoplastic bonding yarns, in particular polyamide, copolyamide, polyester, copolyester, ester / ether block copolyamide, polyacetal, polyolefin, thermoplastic polyurethane or phenoxy type thermoplastic bonding yarns can be provided to facilitate the processing of the mesh before it is combined with the polymer fiber veil when necessary. These bonding yarns usually extend transversely to the carbon yarns. The term "unidirectional mesh" also includes unidirectional fabrics, in which the spaced weft yarns are interwoven with the carbon yarns extending parallel to each other and form the warp yarns of the unidirectional fabric. Even in these different cases where there are such bonding, sewing or weft yarns, the carbon yarns parallel to each other account for at least 95% of the weight of the mesh and are therefore classified as "unidirectional". Nevertheless, according to a specific embodiment of the present invention, the unidirectional mesh does not include any weft yarns interwoven with the carbon yarns to avoid any corrugation. In particular, the reinforcing material according to the present invention does not include any perforations, weaving, sewing or knitting. In the unidirectional web, the carbon reinforcement yarns are preferably not combined with a polymer binder and are therefore classified as dry, i.e. they are not impregnated, coated or combined with any polymer binder prior to combining with the polymer fiber face veils 4, 5. However, the carbon reinforcement yarns are typically characterized by a standard sizing rate of up to 2% of their weight.

[0081] Carbon reinforced yarn (which may be more simply referred to as reinforcing yarn or carbon yarn within the scope of the present invention) is generally composed of an assembly of fibers or filaments and generally contains 1,000 to 320,000 filaments, advantageously 12,000 to 24,000 filaments. The reinforcing yarn used within the scope of the present invention is made of carbon. In a particularly preferred manner, within the scope of the present invention, 1K to 24K carbon yarns are used. The constituent fibers are preferably continuous. The yarns used generally have a substantially circular cross-section (classified as round yarns), or preferably, have a substantially parallelepiped or elliptical cross-section (classified as flat yarns). These yarns have a certain width and thickness. As an example of loose yarns that are not in contact with any physical element, a flat carbon yarn with a denier of 200 tex generally has a width of 1 mm to 3 mm, a 12K flat carbon yarn with a denier of 446 tex has a width of 2 mm to 5 mm, a 12K flat carbon yarn with a denier of 800 tex has a width of 3 mm to 7 mm, a 24K flat carbon yarn with a denier of 1600 tex has a width of 5 mm to 12 mm, and a 24K flat carbon yarn with a denier of 1040 tex has a width of 5 mm to 10 mm. Thus, a flat carbon yarn with 3,000 to 24,000 filaments will generally have a width of 1 mm to 12 mm. Among the carbon yarns there are high resistance (HR) yarns with a tensile modulus between 220 GPa and 241 GPa and a yield strength between 3450 MPa and 4830 MPa, intermediate modulus (IM) yarns with a tensile modulus between 290 GPa and 297 GPa and a yield strength between 3450 MPa and 6200 MPa, high modulus (HM) yarns with a tensile modulus between 345 GPa and 448 GPa and a yield strength between 3450 and 5520 Pa (according to "ASM Handbook", ISBN 0-87170-703-9, ASM International 2001). In particular, within the scope of the present invention, the unidirectional reinforcement mesh 2 can be formed by one or more carbon reinforcement yarns 3 with a fineness of 3K to 24K, preferably 6K to 12K.

[0082] According to the invention, the unidirectional reinforcing web 2 comprises one or a series of individually twisted carbon reinforcing yarns 3, with a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m. According to the invention, a carbon reinforcing yarn 3 is used to which a twist has been applied, i.e. a relative rotation of the outer edges of the yarn around its neutral fibers (corresponding to the central axis of the yarn), so that these describe a spiral trajectory, i.e. the tangent at each point forms a substantially constant angle with a given direction. Figure 2 As shown, the twisted carbon reinforcing yarn 3 has a neutral fiber in its core, whose general direction corresponds to the longitudinal direction X of the reinforcing yarn 3 (also called the general extension direction D G), and the filaments follow a helical path around this general direction. Figure 2 The schematic diagram shows the helical shape of the generatrix h of the twisted reinforcing yarn 3, wherein the twisted reinforcing yarn is twisted in the longitudinal direction X (also referred to as the overall extension direction D). G ) has a twist of one turn on the linear distance d intercepted.

[0083] Each carbon reinforcing yarn 3 is individually twisted. Such a twist can be obtained, for example, by using a twisting machine such as the model UT-1000 machine sold by Kamitsu Seisakusho Ltd. Figure 3 is a diagram showing the twisting process achieved by a twisting machine that makes it possible to obtain a twisted reinforcing yarn 3 according to the invention. The bobbin 7 on which the reinforcing yarn to be twisted is wound is mounted so that it can rotate about its axis A to allow the reinforcing yarn to be unwound via a yarn guide 8 onto a bobbin 9 for winding the twisted reinforcing yarn 3. The bobbin 7 provided with the reinforcing yarn to be twisted is mounted on a support 11 driven by a motor 12 to rotate along an axis B perpendicular to the axis of the bobbin 7. The twisting of the reinforcing yarn 3 depends on the linear speed of the unwinding of the reinforcing yarn and on the speed of rotation of the support 11 of the bobbin 7.

[0084] It will be appreciated that twisting causes the width of the twist-reinforced yarn to change.

[0085] The following description describes the effect of the twisting process on the width of the twist-reinforced yarn.

[0086] Figure 4 Describe the method for measuring the width of the reinforcing yarn before and after the twisting operation as described above. The reinforcing yarn whose width is to be measured is unwound from the spool 13 to ensure that it passes through the first fixed cylindrical rod 14, the second fixed cylindrical rod 15 and the third fixed cylindrical rod 16 in sequence, and then is taken up by the winding spool 17. Typically, the tension of the reinforcing yarn leaving from the spool 13 is between 150g and 300g. Cylindrical rods 14-16 are installed so that the width of the reinforcing yarn can be measured under reproducible and predetermined tension conditions. After it is tightened when passing through the first fixed cylindrical rod 14 and the second fixed cylindrical rod 15, the reinforcing yarn expands at the third cylindrical rod 16, and the matrix camera 18 is located above the third cylindrical rod. For example, the first, second and third cylindrical rods 14-16 have diameters of 40 mm, 20 mm and 30 mm, respectively, while the center distances between the first and second cylindrical rods on the one hand and between the second and third cylindrical rods on the other hand are 50 mm and 20 mm in the horizontal direction and 15 mm and 10 mm in the vertical direction, respectively. During the operation of the reinforcing yarn, the width of the reinforcing yarn is measured by means of the camera 18 approximately every 5 mm within a length of 100 ml (linear meters).

[0087] Carbon fibers from HEXCEL Corporation of Stamford, Connecticut, USA were measured with different linear densities, different filament counts, and different twists, as shown in Table 1 below.

[0088] Table 1

[0089]

[0090] Measurements made on the carbon reinforced yarn from Table 1 show that Figure 5 In, it is given that for various reinforcing yarns, the average width of the reinforcing yarn varies with the twist. Figure 5 It is clearly shown that the average width of the reinforcing yarn decreases with increasing twist, which is expected because twisting causes the filaments of the twisted reinforcing yarn to tighten.

[0091] Figure 6 (which shows the standard deviation of the average width as a function of twist for the various reinforcement yarns in Table 1) reveals that the standard deviation of the width decreases as the twist increases. In other words, the twisted reinforcement yarns tend to tighten more uniformly as the twist increases. Thus, as the twist increases, the reinforcement yarns with a parallelepiped cross-section tend to have a round reinforcement yarn with a low standard deviation. It should be noted that the non-twisted reinforcement yarns have a low standard deviation compared to the twisted reinforcement yarns, and a twist greater than 14 turns / meter (tpm) should be achieved in order to obtain such a low width variation.

[0092] It is important to understand that the width distribution of the carbon reinforcement yarns affects the possibility of using them to make a web having a given basis weight.

[0093] For example, a 210 g / m2 web would require 12 KIMA yarns juxtaposed every 2.12 mm to theoretically fully cover the web. The calculation is as follows:

[0094] Necessary width for a given basis weight [mm] = yarn fineness [Tex] / basis weight [g / m 2 ]. The unit of measurement for yarn is Tex, which is the weight of 1000m of yarn in grams.

[0095] In practice, it is possible to produce a web of satisfactory quality if the average width of the reinforcing yarns is at least 75% of this so-called "target" width value. A person skilled in the art will be able to determine this target width value by trial and error.

[0096] Table 2 below lists the target width values ​​by basis weight and by carbon reinforcement yarn used:

[0097] Table 2

[0098]

[0099] Figure 7 to Figure 1 1 is a graph showing the percentage of values ​​above the target width value as a function of twist for various carbon reinforced yarns for various grammages.

[0100] Figure 7 For 140 g / m 2 The network:

[0101] - For IMA-12K fibers, the web can only be made from non-twisted reinforcement yarns;

[0102] - For IM7-6K fibers, webs may only be made from reinforcing yarns with a twist less than or equal to 8 turns / m.

[0103] Figure 8 For 210 g / m 2 The network:

[0104] - For IMA-12K fibers, the web can only be made with reinforcing yarns with a twist less than or equal to 8 turns / m;

[0105] - For IM7-6K fibers, webs can only be made with reinforcing yarns with twists up to 14 turns / m.

[0106] Fig. 9 For 280 g / m 2 For webs, the basis weight becomes high enough to use reinforcing yarns with all twist values ​​within the range.

[0107] Figure 10 shows the results for 252 g / m2 made of AS7-12K fiber. 2 The net can only be made of reinforcing yarn with a twist less than or equal to 6 twists / m.

[0108] Figure 11 shows that for 350g / m 2 For webs, the grammage becomes high enough to use reinforcing yarns with all twist values ​​within the range.

[0109] Therefore, for a given basis weight, it seems possible to define the twist limit that can be used for each reinforcing yarn type, which also makes it possible to choose not only to use the yarn but also to apply the twist, depending on the desired basis weight of the UD web.

[0110] According to another feature of the subject matter of the present invention, the unidirectional reinforcement mesh 2 is formed by at least one twisted carbon reinforcement yarn 3, and the at least one twisted carbon reinforcement yarn has S twist, Z twist or a mixture of the two. The twist directions of the twisted carbon reinforcement S twist and Z twist yarns 3 are different, as shown on the right side of Figure 17. For the definition of the meaning of S twist or Z twist, refer to the book "Handbook of Weaving", pages 16-17, Professor Sabit Adanur, Department of Textile Engineering, Auburn, USA, ISBN 1-58716-013-7.

[0111] As indicated, the unidirectional reinforcing web 2 can be formed from reinforcing yarns 3 having a twist of 3 to 15 turns / m, preferably 6 to 12 turns / m. In this case, the web is classified as unidirectional because the single reinforcing yarn 3 has a neutral fiber (corresponding to the central axis of the yarn) whose general direction corresponds to the longitudinal direction X of the reinforcing yarn 3, while the filaments follow a helical trajectory around this general direction, such as Figure 2 According to an alternative embodiment, the unidirectional reinforcing mesh 2 is formed by a plurality of reinforcing yarns 3, at least some of which each have a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m. Each yarn has an extension direction D corresponding to the center line of the yarn G . The twisted reinforcing yarns 3 forming the unidirectional reinforcing mesh 2 are arranged side by side, and the extension directions of the twisted reinforcing yarns 3 are parallel to each other, thereby forming a unidirectional mesh. According to the latter embodiment, at least every fifth reinforcing yarn 3, preferably at least every second or third reinforcing yarn 3 and preferably all reinforcing yarns 3 are individually twisted, with a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m. It should be understood that according to an advantageous embodiment, all reinforcing yarns 3 forming the unidirectional reinforcing mesh 2 are individually twisted, with a twist of 3 turns / m to 15 turns / m, preferably 6 turns / m to 12 turns / m. If the unidirectional reinforcing mesh 2 does not exclusively contain twisted reinforcing yarns, the unidirectional reinforcing mesh 2 advantageously contains reinforcing yarns that are the same as the untwisted reinforcing yarns that are subjected to twisting according to the present invention.

[0112] According to an alternative embodiment in which all the reinforcing yarns 3 forming the unidirectional web 2 are twisted, it is also possible to use both one or more twisted reinforcing S-twisted yarns 3 and one or more twisted reinforcing Z-twisted yarns 3 within the same web. That is, the unidirectional web 2 comprises twisted reinforcing yarns 3 with different twist directions: therefore, it is not formed exclusively of reinforcing Z-twisted yarns 3 or reinforcing S-twisted yarns 3, but comprises at least one reinforcing Z-twisted yarn 3 extending adjacent to one or more reinforcing S-twisted yarns 3, or comprises at least one reinforcing S-twisted yarn 3 extending adjacent to one or more reinforcing Z-twisted yarns 3. In contrast, each yarn has the same S-twist or the same Z-twist, and therefore the same twist direction over its entire length, as well as the same twist value.

[0113] For simplicity, these alternative embodiments of the unidirectional reinforcing web 2 are referred to in this specification as "hybrid S / Z unidirectional web 2". The twisted reinforcing yarn 3 with S twist or the twisted reinforcing yarn 3 with Z twist is obtained by the direction of rotation applied to the bobbin 7 about the B axis, as in Figure 3 In the twisting machine shown. By using various types of twisted reinforcing yarns 3 in the same unidirectional reinforcing web 2, namely at least one with S twist and at least one with Z twist, it is possible to limit the risk of defects in the unidirectional reinforcing web 2 obtained, in particular the risk of gaps or overlaps between yarns laid side by side, and the risk of corrugations. The use of two types of twist (S twist and Z twist) in the same unidirectional web tends to homogenize the local corrugations caused by Z twist and S twist with different directions. By combining these two types of yarns in the same unidirectional web, the manufacture and use of mixed S twist and Z twist yarns becomes simpler and tends to produce a more acceptable quality in terms of gaps and overlaps observed in the resulting web, as will be shown in the following examples.

[0114] Examples of particularly suitable twisted reinforcement yarns 3 laid side by side to form the hybrid S / Z unidirectional web 2 include the following sequence: SZ, SZS, ZSZ, SZZS, SZSZ, SZSZS, SSZZSS, SZSSZS, SZSZSZ SSZZSSZZ.

[0115] like Figure 1 B and Figure 1C shows that the unidirectional web 2 (or 2a) formed by a plurality of carbon reinforcing yarns 3 can be divided into two equal parts, each extending on either side of a plane Δ extending perpendicular to the surface of said unidirectional web 2 (and therefore perpendicular to the surfaces S4 and S5 of the two face yarns 4, 5 when the web is combined with the latter) and parallel to the general extension direction of the unidirectional web 2. According to a particularly advantageous embodiment of the reinforcing material of the invention, the (hybrid S / Z type) unidirectional web 2 comprises more than 3 individually twisted carbon reinforcing yarns 3, whose twist is from 3 turns / m to 15 turns / m, preferably from 6 turns / m to 12 turns / m, wherein:

[0116] - In the case where the total number of twisted carbon reinforcing yarns 3 forming the unidirectional web 2 is an even number:

[0117] The number of twisted carbon-reinforced S-twisted yarns 3 on one side of the plane Δ and the number of twisted carbon-reinforced S-twisted yarns 3 on the other side of the plane Δ are each independently an integer in the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}, and if the definition formula yields an integer, each endpoint of the range is rounded to the nearest integer, and the other twisted carbon-reinforced yarns 3 are Z-twisted yarns (Definition P1);

[0118] =Equivalent to the number of twisted carbon-reinforced Z-twisted yarns 3 on one side of the plane Δ and the number of twisted carbon-reinforced Z-twisted yarns 3 on the other side of the plane Δ being independently integers in the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}, if the definition formula yields an integer, then each endpoint of the range is rounded to the nearest integer, and the other twisted carbon-reinforced yarns 3 are S-twisted yarns (definition P2);

[0119] - In case the total number of twisted carbon reinforcing yarns 3 forming the unidirectional web 2 is an odd number:

[0120] The number of twisted carbon-reinforced S-twisted yarns 3 on one side of the plane Δ and the number of twisted carbon-reinforced S-twisted yarns 3 on the other side of the plane Δ are two integers or two half-integers and are each independently in the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}; if its definition formula results in an integer or a half-integer, each endpoint of the range is rounded to the nearest integer or half-integer, and the remaining twisted carbon-reinforced yarns 3 are Z-twisted yarns (Definition I1);

[0121] ·Equivalent to the number of twisted carbon reinforced Z-twisted yarns 3 on one side of the plane Δ and the number of twisted carbon reinforced Z-twisted yarns 3 on the other side of the plane Δ being two integers or two half-integers and each independently being in the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}; if its definition formula results in an integer or half-integer, each endpoint of the range is rounded to the nearest integer or half-integer, and the remaining twisted carbon reinforced yarns 3 are S-twisted yarns (Definition I2).

[0122] The plane Δ is a plane parallel to the general extension direction of the unidirectional web 2, dividing the unidirectional web into two equal parts, perpendicular to its surface. Figure 1 C shows a material according to the invention comprising a unidirectional web 2a formed from a series of twisted, reinforced SZSZSZ yarns 3, on which a plane Δ is shown.

[0123] "Each independently within the range..." in the definitions P1, P2, I1 and I2 means that the relevant two numbers are within the stated range, but may be the same or different.

[0124] As an example of a possible configuration in the case of an odd total number of twisted reinforcing yarns 3 forming the unidirectional web 2, if the total number of such twisted reinforcing yarns 3 is 17 (so that there are 8.5 yarns on either side of the plane Δ), then:

[0125] - According to definition I1, the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%} is equal to {[(17 / 4)-35%; [(17) / 4]+35%}={4.25-35%(4.25); 4.25+35%(4.25)}, and the end points are rounded to {3; 5.5}. Therefore, there may be 3 to 5.5 S yarns on each side of the plane Δ, or a total of 6 to 11 S-twisted yarns, and the remaining yarns are Z-twisted yarns, or a total of 6 to 11 Z-twisted yarns, and there are 3 to 5.5 Z-twisted yarns on each side of the plane Δ;

[0126] - By definition I2, we get the same number of possible S and Z yarns on each side of the plane Δ.

[0127] In the case of such a configuration, the number of twisted reinforcing S-twisted yarns and Z-twisted yarns 3 in the unidirectional reinforcing mesh 2 is more balanced, resulting in a unidirectional mesh 2 that is easier to manufacture and of higher quality. Indeed, during the formation of the unidirectional reinforcing mesh 2, in this case, alignment between the twisted reinforcing yarns 3 is promoted, and the gaps, waveforms and / or overlaps between the twisted reinforcing yarns 3 laid parallel and side by side are reduced, as explained in the embodiments. In addition, during the automated production of several reinforcing materials 1 in parallel, as described in the application WO 2010 / 061114, the cutting of the nonwoven material at the joint between two reinforcing materials 1 produced in parallel results in sharper edges and more uniform materials in this case.

[0128] In addition, the reinforcing material 1 produced by such a hybrid S / Z web will therefore also have a better quality, and so will the composite parts produced. In addition, such reinforcing materials can be used more accurately by the application of an automatic application device (such as those described in EP 2 376 276). As will be explained in the embodiments, such reinforcing materials 1 are better kept in the center of the guide or guide member (particularly groove or comb-type) present at the level of the head or application finger of the automatic application device, while the reinforcing materials 1 made of the unidirectional reinforcing web 2 containing only reinforcing S-twisted yarns 3 or only reinforcing Z-twisted yarns 3 or more generally not satisfying the definitions P1, P2, I1 and I2 tend to deviate from the center and tend to abut on the edge of the guide or guide member they travel.

[0129] In particular, unidirectional reinforcing webs 2 comprising a sequence of perfectly alternating S-twisted and Z-twisted reinforcing yarns 3 are preferred, i.e. those corresponding to the configuration (sequence of yarns laid side by side) (SZ) i, S (ZS) j, Z (SZ) j, wherein i and j are integers, in particular in the range of 1 to 20, preferably in the range of 1 to 10. In particular, i and j will be in the range of 2 to 20, preferably in the range of 2 to 10.

[0130] Other hybrid S / Z unidirectional web configurations that are particularly desirable are those that have the same number of S twist yarns, and therefore by implication the same number of Z twist yarns, on both sides of the plane Δ. The following configurations are some examples: SZZS, SZSZ, SZSZS, SZSSZS.

[0131] Other hybrid S / Z unidirectional web configurations that are particularly desirable are those that are symmetric about the plane Δ. Some examples of these configurations are SZZS, SZSZS, SZSSZS, SZSSZSSZS.

[0132] Thus, the use of hybrid S / Z unidirectional webs and in particular those described more precisely within the scope of the present invention solves a dual technical problem during the manufacture and application of the obtained reinforcement material 1. These materials offer in particular the possibility of production and application according to industrial methods.

[0133] The use of mixed S / Z unidirectional webs and in particular those described more precisely within the scope of the present invention are particularly suitable for producing unidirectional webs 2 and therefore reinforcing materials 1, whose width is greater than 7 mm, preferably greater than 12 mm and preferably in the range of 12 mm to 51 mm. In addition, the present invention using mixed S / Z unidirectional webs is also particularly suitable for reinforcing materials with a length greater than 2 m, in particular a length of 2 m to 5000 m, preferably 100 m to 2000 m. Therefore, according to such preferred embodiments within the scope of the present invention, the reinforcing material according to the present invention has a width greater than 7 mm and a length greater than 2 m, and advantageously a width in the range of 12 mm to 51 mm and a length in the range of 2 m to 5000 m, preferably 100 m to 2000 m. The width of the material is its average width taken perpendicular to the overall extension direction of the unidirectional sheet: the width can be measured by taking measurements every 10 cm over the entire length of the material using any suitable means (in particular a camera) and by taking the arithmetic mean of the measurements obtained. Preferably, the length of the material will be measured on the plane Δ. In particular, the width of the reinforcing material 1 can be measured by running it at a constant speed of 1.2 m / min under a constant tension between 200 cN and 400 cN and by passing it in front of a camera (e.g., Baumer Optronic Type FWX 20, focal length 20 mm, 1624x1236 pixels (Baumer OptronicGmbh, Germany - calibration of the camera is as follows: 1 pixel is equivalent to 0.05 mm) or another camera suitable for the larger width of the reinforcing material) at a distance of 265 mm and without support at this point. In particular, there are automatic application devices for applying materials with a width of 6.35 mm, 12.7 mm, 38.1 mm and 50.8 mm and can be implemented within the scope of the present invention.

[0134] Furthermore, this embodiment of the invention using a hybrid S / Z unidirectional web is particularly suitable for manufacturing a reinforcement material 1 by continuously combining a nonwoven material with each side of the unidirectional reinforcement web, and this is achieved by passing the reinforcement material through a motorized conveying system or device during the manufacturing process.

[0135] Advantageously, each twisted reinforcing yarn 3 entering into the formation of the unidirectional reinforcing mesh 2 has substantially the same twist value over its entire length. It should be noted that all the twisted reinforcing yarns 3 forming the unidirectional reinforcing mesh 2 may have the same or different twist values. Preferably, all the twisted reinforcing yarns 3 forming the unidirectional reinforcing mesh 2 have the same twist value.

[0136] In the scope of the present invention, the gram weight of the unidirectional reinforcement mesh 2 is 126 g / m 2 Up to 280g / m 2 In the range, especially 126g / m 2 Up to 210g / m 2 , and preferably 210g / m 2 Up to 280g / m 2 .

[0137] The gram weight of the unidirectional net in the reinforcing material corresponds to the gram weight of the unidirectional net before it is combined with the veil, but it is impossible to measure the weight of the unidirectional net before it is combined with the veil 4, 5, because the reinforcing yarns have no cohesive force between them. The gram weight of the carbon fiber reinforced net can be determined by the gram weight of the reinforcing material 1 (unidirectional net 2 and two veils 4, 5). If the basis weight of the veil is known, the basis weight of the unidirectional net can be derived. Advantageously, the basis weight is determined by the chemical attack of the reinforcing material by the veil (potentially also by pyrolysis). Those skilled in the art classically use this type of method to determine the carbon fiber content of a fabric or composite material structure.

[0138] The following describes a method for measuring the grammage of the reinforcing material 1. The grammage of the reinforcing material is measured by weighing 100 cm 2 To facilitate the cutting of the flexible reinforcement samples, the reinforcement was placed between two pieces of 447 g / m 2 A pneumatic circular die from Novi Profiber (Eybens, France) was used to cut the assembly; 10 samples were taken for each type of reinforced product manufactured.

[0139] As is clear from the foregoing description, the reinforcing material 1 advantageously consists of a unidirectional reinforcing web 2 which is combined on each of its faces with a veil or polymer fiber layer 4, 5 selected from a nonwoven material. In general, the method for preparing the reinforcing material 1 according to the invention comprises the following successive steps:

[0140] a1) providing a unidirectional reinforcement mesh formed by one or more individually twisted reinforcement yarns 3 having a twist of 3 turns / m to 15 turns / m,

[0141] a2) providing at least two polymer fiber layers 4, 5, said polymer fiber layers being selected from nonwoven materials,

[0142] a3) bonding each polymer fiber layer to each face of the unidirectional reinforcing web.

[0143] Typically, the unidirectional reinforcing web 2 of step a1) will have a basis weight equal to the desired basis weight in the final reinforcing material 1 and a width equal to the desired width of the final reinforcing material 1 .

[0144] Advantageously, the preparation method comprises, upstream of step a1), a step of manufacturing a unidirectional reinforcing mesh 2 comprising applying to a reinforcing yarn or a series of reinforcing yarns 3 a twist of 3 to 15 turns / m, the twist being applied to each reinforcing yarn 3 individually.

[0145] According to an alternative embodiment of the preparation method, the unidirectional reinforcing web 2 is formed from a plurality of reinforcing yarns and the method comprises, upstream of step a1):

[0146] i) applying to a series of reinforcing yarns a twist of 3 turns / m to 15 turns / m, said twist being applied to each yarn individually,

[0147] ii) Aligning the twisted yarns thus obtained, potentially with other reinforcing yarns, and placing said yarns side by side, so as to form a unidirectional reinforcing web.

[0148] In the case of a web consisting exclusively of twisted reinforcing yarns 3, the use of yarns not all having the same S or Z twist type facilitates the alignment and arrangement of the yarns during step ii). Thus, in step ii), advantageously, aligned yarns will be selected so as to obtain one of the hybrid S / Z unidirectional webs as described in the present invention.

[0149] Thus, according to one embodiment, the method for preparing a reinforcing material 1 according to the invention comprises the following consecutive steps:

[0150] a1) providing a unidirectional reinforcement web as defined within the scope of the present invention, called a hybrid unidirectional web S / Z,

[0151] a2) providing two polymer layers which are nonwoven materials 4, 5,

[0152] a3) Continue to combine each nonwoven material with one side of the unidirectional reinforcing web.

[0153] Advantageously, the preparation method includes, upstream of step a1), a step for producing a unidirectional reinforcing mesh 2, comprising: first, applying a twist of 3 to 15 turns / m to a yarn or a series of carbon S-twisted yarns 3, the twist being applied individually to each carbon yarn 3, and secondly, applying a twist of 3 to 15 turns / m to a Z-twisted yarn carbon yarn 3 or a series of Z-twisted carbon yarns 3, the twist being applied individually to each carbon yarn 3.

[0154] According to an advantageous feature, the polymer fiber layers 4, 5 as nonwoven materials have thermobond properties and the bonding of step a3) is obtained by applying each polymer fiber layer to each face of the unidirectional reinforcing web, said application being accompanied or followed by heating the polymer fibers, causing them to soften or melt and then cooling.

[0155] The unidirectional web 2 is combined with polymer fiber yarns 4, 5 on each side to produce a unidirectional web such as Figure 1 Reinforcement 1 shown in A. The use of symmetrical reinforcement makes it possible to avoid any stacking errors during its manual or automatic laying to form a composite part and thus limit the generation of defects, in particular intermediate plies without veils. This is why the unidirectional web 2 advantageously incorporates on each of its faces a polymer fiber veil 4, 5, the two veils 4, 5 being identical.

[0156] By "porous polymer layer" is meant a permeable layer which allows liquids (such as resin) to pass through the material during the formation of the preform or composite part, thereby enabling injection or infusion through the material. In particular, the openness factor of such a layer determined according to the method described in application WO2011 / 086266 is in the range of 30% to 99%, preferably in the range of 40% to 70%. Particularly advantageous examples of such a layer are nonwoven materials or webs.

[0157] In the context of the present invention, a "polymer fiber layer" is understood to mean a veil or a nonwoven material.

[0158] "Nonwoven material" or "ply" conventionally means a group of potentially randomly arranged continuous or short fibers. These nonwoven materials or veils can be produced, for example, by dry-laid, wet-laid or spun-laid methods, for example, by extrusion ("spunbond"), melt-blown extrusion ("melt-blown"), fiberizing sprayer or solvent spinning ("electrospinning", "flash spinning (Flashspinning)", "force spinning (Forcespinning)"), which are well known to those skilled in the art. In particular, the average diameter of the constituent fibers of the nonwoven material can be in the range of 0.5 μm to 70 μm and preferably 0.5 μm to 20 μm. The nonwoven material can be made of short fibers or preferably continuous fibers. In the case of a nonwoven material made of short fibers, the fiber can have a length, for example, between 1 mm and 100 mm. Preferably, the nonwoven material used provides a random and preferably isotropic coverage.

[0159] Within the scope of the present invention, since the reinforcing material is classified as dry, the total weight occupied by the nonwoven materials 4 and 5 does not exceed 10% of the total weight of the reinforcing material 1 according to the present invention, and typically accounts for 0.5% to 10% of the total weight of the reinforcing material 1 and preferably accounts for 2% to 6% of its total weight.

[0160] In the context of the present invention, the nonwoven material or veil used is advantageously thermoplastic in nature and consists in particular of a thermoplastic polymer, a partially crosslinked thermoplastic polymer, a mixture of such polymers, or a mixture of a thermoplastic polymer and a thermosetting polymer. The thermoplastic or thermosetting nonwoven material or veil is preferably made of a thermoplastic material selected from the group consisting of polyamides (PA: PA6, PA12, PA11, PA6,6, PA 6,10, PA 6,12...), copolyamides (CoPA), polyamide block ethers or esters (PEBAX, PEBA), polyphthalamides (PPA), polyesters (polyethylene terephthalate -PET-, polybutylene terephthalate -PBT-...), copolyesters (CoPE), thermoplastic polyurethanes (TPU), polyacetals (POM...), polyolefins (PP, HDPE, LDPE, LLDPE)... polyethersulfone (PES), polysulfone (PSU...), polyphenylsulfone (PPSU...), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), poly(phenylene sulfide) (PPS), or polyetherimide (PEI), thermoplastic polyimides, liquid crystal polymers (LCP), phenoxys, block copolymers (such as styrene-butadiene-methyl methacrylate (SBM), methyl methacrylate-butyl methacrylate (MAM) copolymers) or fiber mixtures made of these thermoplastic materials. The materials described are of course suitable for use in all types of thermosetting systems for matrix formation during the subsequent production of composite parts.

[0161] The thickness of the veil before being combined with the unidirectional web is selected, depending on how they will be combined with the unidirectional web. In most cases, their thickness will be very close to the desired thickness of the reinforcing material. It is also possible to select veils of greater thickness, which will be laminated at the temperature in the combining stage to achieve the desired thickness. Preferably, the unidirectional web is combined with two substantially identical veils on each of its large faces to obtain a perfectly symmetrical reinforcing material. The thickness of the veil before combining on the unidirectional carbon web is particularly between 0.5 μm and 200 μm, preferably between 10 μm and 170 μm. On the reinforcing material 1 according to the present invention, the thickness of each veil 4, 5 after combining with the unidirectional web is in the range of 0.5 micron to 50 microns, preferably in the range of 3 microns to 35 microns. The thickness of various nonwoven materials before combining is measured by NF EN ISO 9073-2 using method A with 2827 mm 2 The test area (60 mm diameter disc) and the applied pressure of 0.5 kPa were determined.

[0162] Furthermore, advantageously, the basis weight of the veils 4, 5 is 0.2 g / m 2 Up to 20g / m 2 within the range.

[0163] The bonding between the unidirectional web 2 and the face veils 4, 5 may be performed in a discontinuous manner (eg only at certain points or areas), but is preferably performed by bonding extending over the entire surface of the web, classified as continuous.

[0164] Advantageously carry out the combination of unidirectional net 2 with two face yarns 4,5 according to one of the method of describing in patent application WO 2010 / 046609 or the method of describing in application WO 2010 / 061114.Can use the continuous production machine and production line as described in these documents or in the invention embodiment.Within the scope of the present invention and particularly when using mixed S / Z unidirectional net, might produce reinforcing material by combining the nonwoven material on each face of the unidirectional reinforcing net in a continuous manner, by making the reinforcing material produced by the described combination to be carried out by motorized transmission system or device.Such device is for example a transmission belt driven by one or more driving rollers, and reinforcing material circulates between them after the unidirectional net has been placed between two nonwoven materials, to guarantee that it is applied on the latter.

[0165] In addition, the unidirectional web can be bonded to the two webs by means of an adhesive layer, the adhesive layer being selected, for example, from epoxy adhesives, polyurethane adhesives, thermosetting glues, adhesives based on polymerizable monomers, structural acrylic or modified acrylic adhesives, and hot melt adhesives. However, bonding is usually achieved by means of the hot adhesive properties of the heated veil, for example during a hot compression step that ensures bonding between the unidirectional web and the ply. This step causes the thermoplastic fibers of the ply to soften, thereby allowing the unidirectional web to be bonded to the veil after cooling. The heating and pressure conditions are suitable for the material of the veil and its thickness. The hot compression step is usually carried out over the entire surface of the unidirectional web at a temperature in the range of Tf veil -15°C to Tf veil +60°C (where Tf veil specifies the melting temperature of the web) and at a pressure of 0.1MPa to 0.6MPa. Therefore, it is possible to achieve a veil compression ratio in the range of 1 to 10 before and after bonding. The step of laminating the veil to the unidirectional carbon web 2 is also essential for correctly controlling the final thickness of the reinforcing material 1. Indeed, depending on the temperature and pressure conditions, in particular during the lamination process, it is possible to vary and therefore adjust the thickness of the veil present on each side of the reinforcement.

[0166] The reinforcing material according to the invention is easy to handle because there are thermoplastic veils laminated on each face of the unidirectional web. This structure also facilitates cutting in a direction not parallel to, in particular transversely or obliquely to, the fibers of the unidirectional web without particular abrasion.

[0167] The reinforcing materials 1 according to the invention are flexible and spoolable. They can be produced in long lengths, corresponding to the available carbon yarn lengths. After manufacture, they are usually wound on bobbins in the form of rolls and then used for the subsequent manufacture of preforms and parts.

[0168] To produce a composite material part, a stack or drape (also called ply) of the reinforcement material according to the invention is produced. In a conventional manner, the reinforcement material according to the invention is cut into the desired dimensions for producing the part, ply, stack or preform to be manufactured. In a stack, several plies of reinforcement material are stacked on top of each other.

[0169] When the reinforcing material is wide enough to produce the desired parts and when the parts are slightly complicated, plies can be made of a single reinforcing material according to the present invention. But more commonly, in the case of large parts or complex parts, plies are made of an assembly of reinforcing materials 1 according to the present invention arranged side by side to cover the entire surface required for producing the desired parts. In this case, it is necessary to accurately place the reinforcing material. In the automated method, the device for conveying and applying the reinforcing material comprises one or more guide members or guides, in which the reinforcing material is conveyed and transported. The device comprising an application head equipped with such guide members or guides is particularly described in the files WO 2006 / 092514 and EP 2376 276. Such devices are also available from Coriolis Composites SASU (rue Condorcet 56530 Queven, France), MTorres Disenos Industriales SAU (Torrez de Elorz, Navarra, Spain), ElectroImpact Inc (Mukilteo WA98275, USA), Mikrosam DOO (7500 Prilep MACEDONIA). Within the scope of the present invention, it was found that a central reinforcement material 1 according to the invention comprising a hybrid S / Z unidirectional web and in particular one of those described more precisely within the scope of the present invention leads to a more precise placement and thus reduces the risk of defects such as gaps, overlaps, wrinkles or ripples occurring during application. Therefore, parts made from a reinforcement material 1 according to the invention comprising a hybrid S / Z unidirectional web and in particular one of those described more precisely within the scope of the present invention are particularly satisfactory.

[0170] In addition, in order to produce composite parts, several plies are placed one on top of another to produce ply stacking. Therefore, the defects on the reinforcing material 1 are reproduced in each ply and are therefore aggravated on the stacking. Therefore, again, the reinforcing material 1 according to the present invention comprising a mixed S / Z unidirectional net with more uniform and reproducible characteristics is particularly advantageous. In the resulting stacking, plies are usually arranged so that at least two unidirectional nets of the ply are oriented in different directions. From one ply to another, all unidirectional nets or only some of them may have different directions, and other may have the same direction. Preferred orientation is most often the direction of 0 °, + 45 ° or -45 ° (also corresponding to + 135 °) and + 90 ° angles with the main axis of the part to be produced. The main axis of a part is usually the maximum axis of a part, and 0 ° merges with this axis. For example, it is possible to manufacture a stacking of quasi-isotropic, symmetrical or oriented by selecting the orientation of folding. As examples of quasi-isotropic stacking, the stacking may have angles of 45° / 0° / 135° / 90° or 90° / 135° / 0° / 45°. Examples of symmetrical stacking include 0° / 90° / 0° or 45° / 135° / 45°. Before adding the resin required to produce the part, it is possible to connect the plies within the stack together, in particular by an intermediate step of preforming at temperature and vacuum or welding at several points after adding each ply, and thereby produce a preform. In particular, assemblies of 2 to 300 plies, in particular 16 to 100 plies, are contemplated.

[0171] Advantageously, the stack is not joined together by sewing or knitting, but by welding produced by virtue of the polymeric and in particular thermoplastic characteristics of the veils present in the stack. For this purpose, the heating / cooling operation is carried out over the entire surface of the stack or at least in certain areas of the stack surface. The heating causes the veils to melt or at least soften. This bonding using the thermoplastic characteristics of the veils is advantageous because it avoids all the disadvantages of the presence of sewn or knitted yarns, such as in particular the problems of ripples, microcracks and a subsequent reduction in the mechanical properties of the composite part obtained.

[0172] Stacking can be realized by adding each ply one at a time and bonding after each ply is added.An example is the automatic ply application as described in patent application WO 2014 / 076433 and WO 2014 / 191667.In addition, the applied ply (by preheating the ply, heating one at a time or not heating) can be heated again in a global manner, so as to obtain a preformed part formed, for example, from the ply of flat application.Then, those skilled in the art can use the conventional means for thermoforming, wherein applying temperature and pressure (for example, vacuum or pressure system).In particular, the application of reinforcing material according to the present invention can be carried out continuously according to the known method abbreviated as AFP (automatic fiber placement (Automated Fiber Placement)) or ATL (automatic tape lay-up (Automated Tape Lay-up)) (for example, as described in above-mentioned document WO 2014 / 076433A1 or WO 2014 / 191667) perpendicular to the applied surface applying pressure, so as to apply it thereto.

[0173] To produce the composite part, a thermosetting or thermoplastic resin or a matrix or a mixture of thermosetting and thermosetting resins is then added, for example by injection into the mold containing the plies (resin transfer molding method) or by infusion (through the thickness of the plies: liquid resin infusion method or resin film infusion method). According to a non-preferred embodiment, it is also possible to apply manually / impregnate each ply by means of a roller or a brush before stacking, applying successively to the shape of the mold used.

[0174] The matrix used is of the thermosetting or thermoplastic type, or a mixture of thermoplastic and thermosetting resins. The injected resin is, for example, chosen from the following thermosetting polymers: epoxides, unsaturated polyesters, vinyl esters, phenolic resins, polyimides and bismaleimides.

[0175] The composite part is then obtained after a heat treatment step. In particular, the composite part is usually obtained by a conventional hardening cycle of the polymers under consideration, by carrying out a heat treatment recommended by the suppliers of these polymers and known to the person skilled in the art. This step of hardening the desired part is carried out by polymerizing / crosslinking according to a defined cycle at temperature and pressure, followed by cooling. The pressure applied during the treatment cycle is low in the case of vacuum infusion and high in the case of injection into an RTM mold.

[0176] The stacking and bonding method described above can also be implemented with any type of reinforcement material intended to be combined with thermosetting resins to produce composite parts, said any type of reinforcement material being made of a carbon fiber unidirectional web combined on each of its faces with a thermoplastic fiber veil and in particular with reinforcement materials other than those defined in the claims of the present patent application. Indeed, whatever the use of unidirectional veils and webs, such stacking is advantageous in terms of drape and permeability. Of course, preferably, the reinforcement materials comply with those described within the scope of the invention in terms of thickness and grammage, as long as they enable a high fiber volume rate (FVR) to be achieved by means of vacuum infusion.

[0177] The following examples are provided to illustrate the invention but are not intended to be limiting.

[0178] A first series of tests was performed to obtain the data presented in Table 3 below.

[0179] Part A

[0180] Table 3

[0181]

[0182] In Table 3 above, the tested reinforcement material 1 comprises a unidirectional reinforcement mesh with a facing veil bonded to each side.

[0183] 12K medium modulus (IM) carbon yarns sold by HEXCEL, Inc., Stamford, Connecticut, USA, were used for the unidirectional reinforcement mesh. Materials 1 to 3 used such non-twisted carbon reinforcement yarns. Materials 4 to 12 are reinforcement materials according to the invention, which have individually twisted carbon reinforcement yarns (twisted yarns) as explained above. Materials 13 to 18 are reinforcement materials made of twisted yarns with a twist greater than that envisaged by the invention and cannot be manufactured because the materials separate at the production stage or at the processing or application stage, making them unusable.

[0184] For the polymer fiber layer selected from the nonwoven material, a 4 g / m 2 Copolyamide nonwoven 1R8 D04. The face veil is combined with a unidirectional web of carbon reinforcing yarns according to patent application WO 2010 / 046609. More precisely, the reinforcing material 1 according to the invention is manufactured on a production line using the machine and parameters as described in application WO 2010 / 061114 and described hereinafter with reference to FIG. 19 .

[0185] The carbon yarn 3 of the desired twist is unwound from the corresponding carbon yarn bobbin 30 attached to the creel 40, passed through the comb 50, and fed into the machine axis by means of the guide roller 60, the comb 70 and the guide rod 80a.

[0186] The carbon yarn 3 is preheated by the heating rod 90 and then spread by the spreading rod 80b and the heating rod 100 to the desired carbon basis weight of the unidirectional web 2. The face yarn rolls 13a and 13b are unwound without tension and are transported by means of continuous belts 15a and 15b fixed between free-rotating non-motorized rolls 14a, 14b, 14c, 14d and the heating rods 12a, 12b.

[0187] The veils 4 and 5 are preheated in areas 11a and 11b before contact with the carbon yarns 3, and laminated on either side of two heating rods 12a and 12b with a controlled air gap. The calender 16 can be cooled and then pressure is applied to the unidirectional web with the veils on each side to produce the reinforcement material 1 in the form of a tape. The deflection roller 18 enables the reinforcement material 1 to be redirected to a traction system including a motor-driven winding triad 19, and then to a winding arrangement 20 to form a coil of the reinforcement material 1 thus formed.

[0188] It should be noted that in this line the belt is not motorized but is pulled by the reinforcing yarns themselves.

[0189] Furthermore, as explained in application WO 2010 / 061114 and in Figure 8 As presented in the figure, several reinforcing materials according to the present invention presented in the form of bands are manufactured simultaneously. Each twisted carbon yarn forming the unidirectional net to be formed is extracted from the selected twisted yarn roll previously manufactured. The unidirectional net of desired width is parallel to the yarn of the selected number and is positioned in an interval manner, leaving enough space between each unidirectional net. Therefore, a single nonwoven material (corresponding to the face yarn 4 and 5) covering each unidirectional net 2 and the gap is combined with all the unidirectional nets 2 on each of its faces. After the nonwoven material is laminated to the net, it is then cut by means of a heated cutting element between each unidirectional net formed, thereby obtaining various reinforcing materials according to the present invention produced side by side. The gap between each unidirectional net is in the range of 0.5mm to 2mm, so that it can be cut along its edge between each unidirectional net, thereby obtaining various reinforcing materials produced continuously and in parallel.

[0190] 1) Vacuum thickness:

[0191] During the automated application of complex shapes or thick preforms, it is important to have a material that swells as little as possible and therefore an applied material thickness that is close to the final thickness of the composite part. Indeed, if the material presents a significant overrun and therefore a thickness much higher than the final thickness after making the laminate, significant defects will appear on the part. The defects will be mainly due to excessive lengths and wrinkles will be produced. This is unacceptable for the technician. In order to characterize this property, the thickness of the preform is measured after automated application, before and after placing under vacuum.

[0192] As shown in Figure 12, a 200x200 mm preform P is formed with a symmetrical quasi-isotropic stack, more precisely with a [+45 / 0 / -45 / 90]3s overhang. The preform P is placed on a plate. The thickness is measured using a FANUC robot and a HEIDENHAIN / ST3077 LVDT probe. The probe tip is a round key with a diameter of 50 mm. The probe measures the thickness of the preform at 5 points P1 to P5, which then makes it possible to obtain the average thickness value of the preform. Measurements are made every 50 mm on x and every 50 mm on y.

[0193] The preform is then placed under vacuum (residual pressure below 15 mbar) using a vacuum bag and a pump. The thickness of the assembly is then measured and the thickness of the consumables is subtracted to obtain the thickness of the preform under vacuum.

[0194] The ratio of the thickness without vacuum to the thickness under vacuum is then calculated. The higher this ratio is, the greater the thickness without vacuum compared to the thickness under vacuum, and the greater the risk of defects on the final part. The goal is to minimize this ratio.

[0195] Table 4 below summarizes the ratio of thickness (thickness without vacuum) divided by theoretical thickness (thickness under vacuum) for Materials 2 to 12.

[0196] Table 4

[0197]

[0198] Materials 4 to 12 according to the invention make it possible to minimize the ratio of thickness without vacuum to thickness under vacuum, compared to prior art materials 2 and 3. The subject matter of the invention thus allows overgauging to be reduced.

[0199] 2) The effect of twisting on the quality of automatic distribution.

[0200] It is essential that the automated preform application step does not create defects in the preform. The structure of the reinforcing yarn may affect the quality of the application. Therefore, it is necessary to determine whether the twisting of the reinforcing yarn has an impact on the quality of the preform after application.

[0201] More precisely, the twisting of the reinforcing yarns may have an influence on the so-called "shear" phenomenon. During the superimposed laying of the reinforcing material (unidirectional web 2 and face yarns 4, 5), the reinforcing yarns of the ply located directly below the next ply are subjected to shearing due to the pressure and movement of the robot head during the layup. This shearing is most prevalent in the early stages of layup. When several plies are applied, this intra-ply shearing may intensify, which can lead to a local increase in the thickness of the preform and the appearance of defects (such as wrinkles, wear, ply separation, etc.), resulting in poor preform quality.

[0202] An industrial type of automated ply application test was carried out with twisted reinforcement yarns. The laying was carried out using a Coriolis C1 robot equipped with a Coriolis 16ply 1 / 4" AFP head and a 12kw laser type heating means. In this particular case, only 8 of the 16 webs were applied simultaneously side by side. The heating law followed is described in Table 5 below.

[0203] Table 5

[0204]

[0205] The plies made of twisted reinforcing yarns are successively suspended at 0° on a suction table to form a preform of 500 mm (in the 0° direction) x 150 mm. The start of the laying of the reinforcing yarns according to the laying direction presented by the arrow F is always located at the same position on the preform (rectangular area Z1 on Figure 13). Therefore, the thickness studied is located in this area Z1.

[0206] After the draping of each ply, the thickness measurement in the area where the preform starts to lay up (points P'1, P'2, P'3 in the Z1 zone) is carried out with the aid of a marking gauge, a support made of an aluminium bar and a 1 kg weight (representing a pressure of 0.02 bar applied to the preform during the thickness measurement). During the measurement, the thickness measuring device is always positioned in the same position. After each ply application, it is removed to enable the robot to pass and then repositioned after application. When the quality of the preform is judged to be unsatisfactory, the draping is stopped.

[0207] Materials 4 and 8 according to the invention (Table 3) were compared with comparative materials 2 and 3, respectively.

[0208] 14 and 15 show the variation of the overrun as a function of the number of plies applied for comparative material 3 and material 8 according to the invention ( FIG. 14 ) and for comparative material 2 and material 4 according to the invention ( FIG. 15 ).

[0209] Note that overrun is defined as the ratio of the total thickness of a preform with X applied plies to the number X of applied plies.

[0210] Overrun (mm) = total thickness of preform (mm) / number of applied plies.

[0211] This gives an indication of the average thickness of the plies and therefore allows the overrun phenomenon to be quantified.In order to maximize the expansion phenomenon, the reinforcement stack is manufactured with a unidirectional web extending at 0°.

[0212] As shown in Figures 14 and 15, for the twisted reinforcing yarn (material 8 or 4 according to the invention, respectively), the variation of the thickness of each ply with the number of plies applied is lower than for the microperforation method (comparative material 3 or 2, respectively). The results with the twisted reinforcing yarn demonstrate reduced overrun and better quality of the preform after application compared to the equivalent material with non-twisted and microperforated reinforcing yarn according to the prior art.

[0213] 3) Effect of twisting on the lateral permeability of reinforcement materials:

[0214] It is important to verify that the invention maintains the transverse permeability of the reinforcement at the same level as that obtained with microperforated reinforcements according to the prior art. This can be defined as the ability of a fluid to pass through a fiber material. It is expressed in m 2 The values ​​given in Table 6 below were measured using the equipment and measurement techniques described in the paper entitled “Problématique de la mesure dela perméabilité transverse de préformes fibreuses pour la fabrication destructures composites” [Measuring the transverse permeability of fibrous preforms for the manufacture of composite structures] defended by Romain Nunez on October 16, 2009 at the Ecole Nationale Supérieure des Mines de Saint Etienne, which can be consulted for further details.

[0215] In particular, the measurements are carried out in the following way: the thickness of the sample is monitored during the test using two co-cylindrical chambers, making it possible to reduce the "race-tracking" effect (the passage of a fluid adjacent to or "on one side" of the material whose permeability is to be measured). The fluid used is water and the pressure is 1 bar + / - 0,01 bar. A preform of 270 mm diameter is manufactured from 8 plies according to a symmetrical quasi-isotropic stack [+45 / 0 / 135 / 90] S.

[0216] Table 6 below lists the transverse permeability values ​​measured for 50%, 55% and 60% fiber volume rates (FVR) on comparative materials 1, 2 and 3 and materials 4 to 12 according to the invention (see Table 3). Figure 16 summarizes the transverse permeability values ​​for three samples with different fiber volume rates for each material in Table 6.

[0217] Table 6

[0218]

[0219] For the three volume ratios studied, the transverse permeability of the materials according to the invention (materials 4 and 5) is comparable to that of the comparative microperforated material (comparative material 2) when all reinforcing yarns are twisted with 8 turns / m or 10 turns / m. The choice of twist depends on the fineness and number of filaments in the yarn. Different twists may lead to similar results for yarns with different fineness and number of filaments.

[0220] For 280g / m 2 The carbon fiber grammage, with a 10 twist / m twisted reinforcing yarn appears to produce a better average lateral permeability than the microperforated material according to the prior art.

[0221] As the number of twists / meter decreases (material 6 compared to materials 4 and 5, and material 9 compared to material 8), the transverse permeability of the material is lower. However, it is still higher than the comparative material without microperforations (comparative material 1).

[0222] As the number of twisted reinforcing yarns decreases, the transverse permeability decreases (compared to Material 4), even at higher twists / meter (Material 7). In order to twist the reinforcing yarns to result in increased transverse permeability, it is more efficient to twist all of the reinforcing yarns rather than trying to increase the twists / meter of a single twisted reinforcing yarn.

[0223] 4) Effect of twisted reinforced yarn on the mechanical properties of composite materials:

[0224] The 430mm x 430mm preform consisting of a stacking sequence suitable for carbon gram weight is placed in an injection mold under pressure. A frame of known thickness around the preform is used to achieve the desired fiber volume ratio (FVR). The epoxy resin sold by HEXCEL Corporation in Stamford, Connecticut, USA with reference to HexFlow RTM6 is injected into the preform at 80°C at 2 bars, and the preform is maintained in a press at 120°C. The pressure applied by the press is 5.5 bars. After the preform is filled and the resin comes out of the mold, the outlet pipe is closed and the curing cycle is started (3°C / min to 180°C, then 2h post-curing at 180°C, and cooling with 5°C / min).

[0225] The samples were then cut to appropriate sizes for open hole (OHC) and solid plate (UNC) compression testing as summarized in Table 7 below.

[0226] Table 7

[0227]

[0228] Tests were conducted with eight reinforcement materials 4 to 11 according to the invention and comparative materials 2 and 3 (Table 3). The results of the open hole compression (OHC) test are shown in Table 8 below.

[0229] Table 8

[0230]

[0231] It is known in the prior art that carbon weight can affect mechanical results. Generally speaking, the higher the carbon weight, the lower the mechanical compression properties tend to be. In this application, the results are compared with carbon weight.

[0232] For 210g / m 2 There is no difference between the comparative material and the material according to the invention in the open hole compression test (OHC). 2 The same conclusion can be drawn for 350g / m 2 With a grammage of 1.5mm, it is not possible to compare with microperforated materials as this is not feasible.

[0233] The results of the compression tests on solid panels (UNC) are shown in Table 9 below.

[0234] Table 9

[0235]

[0236] The results of Table 9 allow the same conclusions to be drawn as for the open hole tests.

[0237] 5) The effect of twisting of reinforcing yarn on transverse conductivity:

[0238] The 335 mm x 335 mm preform is made of reinforcement plies, the number of which depends on the grammage of the carbon reinforcement yarn. The stacking sequence is [0 / 90]ns, where ns is an integer, depending on the grammage of the carbon reinforcement yarn, in order to produce a panel with a final thickness of 3 mm and a fiber volume of 60%. The preform is then placed in an injection mold under pressure. In the same way as for the mechanical compression test (see paragraph 4 above), a panel of composite reinforcement material / RTM6 is formed by means of an injection method (same parameters as for the compression panel).

[0239] Twenty-four 40mm x 40mm coupons are pre-cut using a water jet cutter, evenly distributed across the panel. Both surfaces of the pre-cut panel are then sandblasted to expose the carbon fibers. Next, the front and back sides of the panel are processed to apply a conductive metal layer, typically tin and zinc, with the aid of an arc method. The metal application can be removed from the coupon area by sandblasting or sanding. This conductive metal application allows for a low contact resistance between the sample and the measuring instrument. Individual coupons are then cut from the panel.

[0240] The resistance is determined using a power supply capable of varying current and voltage (TTi EL302P programmable 30V / 2A power supply, ThurlbyThandar Instruments, Cambridge, UK). The sample is in contact with the two electrodes of the power supply; these electrodes are brought into contact with the aid of clamps. Care must be taken to ensure that the electrodes do not touch each other or any other metal. A current of 1A is applied and the resistance is measured through the two other electrodes connected to a voltmeter / ohmmeter. The test is performed on each sample to be measured. The conductivity value is then calculated from the resistance value using the dimensions of the sample and the following formula:

[0241] Resistivity (Ohm.m) = Resistance (Ohm) x Area (m 2 ) / Thickness(m)

[0242] Conductivity (S / m) = 1 / resistivity

[0243] Transverse conductivity tests (Table 3) were carried out with comparative material 2 and materials 4 and 5 according to the invention. The test results are shown in Table 10 below.

[0244] Table 10

[0245] Comparative material 2 Material 4 of the present invention Material 5 of the present invention Transverse conductivity 7.5 23.6 34

[0246] Comparative material 2 and materials 4 and 5 according to the invention have the same fiber basis weight. The average transverse conductivity of material 4 according to the invention is higher than the average transverse conductivity of comparative material 2 microperforated according to the prior art. The twisting of the reinforcing yarns increases the transverse conductivity of the reinforcing material.

[0247] Part B

[0248] The results of the second series of tests carried out are presented below in Table 11. The materials obtained were not microperforated, with the exception of comparative material 27.

[0249] Table 11

[0250]

[0251]

[0252] Production of the reinforcement material according to the invention

[0253] These tests were carried out on a new production line meeting the requirements of industrial scale production, which not only requires higher productivity, with the aim of reducing line stoppages and wear of line components, but also improving safety. This increase in speed also increases the overall inertia of the line, generating a greater number of material friction events at various points / rollers of the line and, therefore, notably on the forces required to drive the belts. Therefore, the production line previously described in connection with FIG. 19 was transformed by introducing the motorization of the continuous belts 15a and 15b. The belts 15a and 15b are motorized independently of each other by means of rollers 14a and 14c, rollers 14b and 14d remaining free to rotate.

[0254] This increase in productivity highlights the difficulties encountered in the production of unidirectional webs, using twisted reinforcing yarns all having the same type of S or Z twist to minimize the presence of defects such as gaps, overlaps or ripples between the yarns. Indeed, despite the use of combs or guide rollers, the trajectory of the reinforcing yarns is not fully controlled, which leads to the appearance of defects. These risks can be minimized or even avoided by using a hybrid S / Z unidirectional web, as proposed within the scope of the present invention.

[0255] In this industrial-scale production line several materials 19 are produced in parallel and thus with a higher production rate.

[0256] As in the first series of tests, several reinforcement materials according to the invention in the form of strips were produced simultaneously.

[0257] Similarly, several materials 20 and several materials 21 are manufactured in parallel. It is found that the materials 20 and 21 obtained are more regular, especially at the edges, compared to material 19. Indeed, in the case of materials 20 and 21, the quality of the alignment of the yarns during the formation of the unidirectional web is better. As a result, the distance between two unidirectional webs manufactured side by side is more regular, thus facilitating the cutting of the two veils laminated on their two surfaces between the two formed unidirectional webs.

[0258] The same observations were made for materials 22 and 23, and 24 and 25. In the case of material 22 having only S-twisted yarns, more defects such as wrinkles, gaps or overlaps between yarns, and irregularities at the edges were observed than in the case of material 23 using the SZSZSZ yarn sequence. Similarly, in the case of material 24 including only Z-twisted yarns, more defects such as wrinkles, gaps or overlaps between yarns, and irregularities at the edges were observed than in the case of material 25 using the SSZZSS yarn sequence.

[0259] Furthermore, in the case of a material 26 comprising 18 yarns (with a sequence of 7 S-twisted yarns, 5 Z-twisted yarns, and then 6 S-twisted yarns), forming a unidirectional web by the aforementioned method produces a unidirectional web as shown in FIG. 18 . As can be seen from this figure, there is a clear gap at the junction of the 7 S-twisted yarns / 5 Z-twisted yarns, which constitutes a quality defect, resulting in a continuous gap of more than 1 mm wide along the entire length of the web. The Z-twisted yarn group is stretched to the right, while the S-twisted yarn group is stretched to the left. This results in an unsatisfactory continuous gap. This sequence does not correspond to the definitions P1, P2, I1 and I2 of a mixed S / Z unidirectional web given in the context of the present invention, which results in a unidirectional web that is more balanced in terms of the number of S-twisted and Z-twisted yarns and has a greater coverage due to the reduced risk of gaps between yarns.

[0260] Thus, within the scope of the present invention, it is observed that, despite the use of guides or combs, there are deflection phenomena of the trajectory of the reinforcing yarns during the formation of unidirectional webs in which the twisted reinforcing yarns have the same twist or have a configuration that does not correspond to the definitions P1, P2, I1 and I2 of the hybrid S / Z unidirectional web given within the scope of the present invention. These phenomena do not occur for unidirectional webs with only 3 yarns or less. The use of the hybrid S / Z unidirectional web proposed within the scope of the present invention solves the problem of unidirectional webs consisting of more than 3 yarns.

[0261] Furthermore, the deflection phenomenon increases with the width of the reinforcement material produced. The problem is even more pronounced for production widths greater than 7 mm or even 12 mm. Regardless of the manufacturing method used, i.e. regardless of whether a plurality of reinforcement materials are manufactured in parallel, there is a risk of deflection of the reinforcement yarns, which is overcome by the hybrid unidirectional S / Z web proposed within the scope of the present invention. Indeed, if deflection phenomena occur, they also cause difficulties during the application of the material according to the invention, resulting in unsatisfactory positioning.

[0262] Automatic application of the reinforcing material according to the invention

[0263] The materials 19 to 25 are applied by means of an automatic application device comprising a guide consisting of a guide groove in which the material circulates before being applied to the application surface. This guide makes it possible to ensure that the web is correctly positioned at the outlet of the application head of the device, which will then enable the application head to well control the trajectory of the reinforcing material and its positioning on the application surface, as can be seen in the photograph presented in the left part of Figure 17. As shown in Figure 17, in order to evaluate the materials, the application is carried out by applying one adjacent to the other on a flat surface so as to obtain a joint application of a series of parallel strips of material 19 (SSSS). The same procedure is followed with material 20 (SZZS) and material 21 (SZSZ). With the last two materials, the application can be better controlled, which leads to a reduction in gaps and ripples on the application surface. By observing the behavior of the materials in the guide grooves, it is noted that material 19 (SSSS) is incorrectly centered and therefore abuts one of the edges of the groove, while materials 20 and 21 are well centered in the groove and supported on its two edges.

[0264] The same findings were observed first for materials 22 and 23 and secondly for materials 24 and 25. In the case of material 22, which only contained S-twisted yarns, the application was not as good as in the case of material 23, which used a series of SZSZSZ yarns. Similarly, more gaps were observed in the case of material 24, which only contained Z-twisted yarns, than in the case of material 25, which used a series of SSZZSS yarns. Table 12 shows the average gap widths obtained between the two tapes measured with a ruler in the case of application of materials 24 and 25.

[0265] Table 12

[0266]

[0267] It is evident that the use of a SSZZSS web composed of both S-twisted and Z-twisted yarns results in a significant reduction in the areas without reinforcing yarns in the resulting unidirectional web.

[0268] Number of belts 8 8 Application Average gap (mm) 0.1mm 1.5mm

[0269] Properties of the material according to the invention

[0270] The properties of the materials according to the invention were evaluated according to the method described in Part A.

[0271] Regardless of whether the unidirectional web consists only of S-twisted yarns or Z-twisted yarns or whether the unidirectional web consists of both S-twisted yarns and Z-twisted yarns, the advantages of using the twisted yarns proposed in the context of the present invention in terms of a reduction in the ratio of vacuum thickness to non-vacuum thickness, a reduction in overrun, an increase in the transverse permeability of the material, and an increase in the transverse conductivity of the material are retained.

[0272] Due to the reduced defects in the produced reinforcements, the mechanical properties are very satisfactory.

[0273] The results obtained are presented in Table 13 below:

[0274] Table 13

[0275]

[0276] The overrun performance of the unidirectional web composed of both S-twisted yarns and Z-twisted yarns was improved compared to the comparative microperforated material 27. Thus, whether the material has a unidirectional web composed of a series of yarns twisted in the same direction or a unidirectional web composed of a mixture of S-twisted and Z-twisted yarns, the overrun performance is improved. The results obtained are presented in the following Table 14:

[0277] Table 14

[0278]

[0279] The lateral permeability properties of the material 23 according to the invention were also measured and compared with the comparative material 27 and are presented below in Table 15. The lateral permeabilities obtained for both materials are comparable.

[0280] Table 15

[0281]

[0282] The transverse conductivity properties of the material 23 according to the invention were also measured and are presented in the following Table 16:

[0283] Table 16:

[0284] Material Material 23 Transverse conductivity (S / m) 12.3

[0285] Compared to comparative material 2, material 23 according to the invention provides good electrical properties.

Claims

1. A reinforcing material (1), the reinforcing material comprising: A unidirectional reinforcing web (2) formed by one or more carbon reinforcing yarns (3), to each face of which is bonded a polymer fiber layer (4, 5), the polymer fiber layer being a non-woven material, the polymer portion of the reinforcing material accounting for 0.5% to 10% of its total weight, characterised in that the unidirectional reinforcing web (2) comprises one or a series of individually twisted reinforcing yarns (3) having a twist of 3 turns / m to 15 turns / m, All the carbon reinforcing yarns (3) forming the unidirectional reinforcing web (2) are individually twisted, with a twist of 3 turns / m to 15 turns / m, and the unidirectional reinforcing web (2) comprises at least 3 carbon reinforcing yarns (3) twisted in this way, with at least one S-twisted reinforcing yarn and at least one Z-twisted reinforcing yarn: - when the total number of twisted carbon reinforcing yarns (3) forming the unidirectional reinforcing mesh (2) is an even number, the number of twisted carbon reinforcing S-twisted yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twisted yarns on the other side of the plane Δ are each independently an integer in the range {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}, and if the definition formula yields an integer, each endpoint of the range is rounded to the nearest integer, and the other twisted carbon reinforcing yarns (3) are Z-twisted yarns; - when the total number of twisted carbon reinforcing yarns (3) forming the unidirectional reinforcing mesh (2) is an odd number, the number of twisted carbon reinforcing S-twisted yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twisted yarns on the other side of the plane Δ are two integers or two half-integers and are each independently in the range of {[(total number of yarns) / 4]-35%; [(total number of yarns) / 4]+35%}; if its definition formula results in an integer or a half-integer, each endpoint of the range is rounded to the nearest integer or half-integer, and the other twisted carbon reinforcing yarns (3) are Z-twisted yarns; The plane Δ is a plane parallel to the general extension direction of the unidirectional web (2) and divides the unidirectional web (2) into two equal parts, perpendicular to its surface.

2. The reinforcement material (1) according to claim 1, wherein the polymer fraction of the reinforcement material accounts for 2% to 6% of its total weight.

3. The reinforcing material (1) according to claim 1, wherein the unidirectional reinforcing mesh (2) comprises one or a series of individually twisted reinforcing yarns (3) having a twist of 6 to 12 turns / m; and wherein all carbon reinforcing yarns (3) forming the unidirectional reinforcing mesh (2) are individually twisted having a twist of 6 to 12 turns / m.

4. The reinforcing material (1) according to claim 1, characterized in that The unidirectional reinforcing net (2) is formed by a plurality of reinforcing yarns (3), and at least every fifth reinforcing yarn is individually twisted, with a twist of 3 turns / m to 15 turns / m.

5. The reinforcing material (1) according to claim 1, characterized in that The unidirectional reinforcing net (2) is formed by a plurality of reinforcing yarns (3), and at least every second or third reinforcing yarn is individually twisted, with a twist of 3 turns / m to 15 turns / m.

6. The reinforcing material (1) according to claim 1, characterized in that The unidirectional reinforcing net (2) is formed by a plurality of reinforcing yarns (3), and all the reinforcing yarns are twisted individually, with a twist degree of 3 turns / m to 15 turns / m.

7. The reinforcement material (1) according to any one of claims 4 to 6, wherein the reinforcement yarns are individually twisted with a twist of 6 to 12 turns / m.

8. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The unidirectional reinforcement net (2) has a gram weight of 126 g / m 2 Up to 280g / m 2 .

9. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The unidirectional reinforcement net (2) has a gram weight of 126 to 210 g / m 2 within the range.

10. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The unidirectional reinforcement net (2) is formed by one or more carbon reinforcement yarns (3) with a fineness of 3 to 24K.

11. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The unidirectional reinforcement net (2) is formed by one or more carbon reinforcement yarns (3) with a fineness of 6 to 12K.

12. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The reinforcement material has a width greater than 7 mm.

13. The reinforcement material (1) according to claim 12, characterized in that The reinforcement material has a width greater than 12 mm.

14. The reinforcement material (1) according to claim 12, characterized in that The reinforcement material has a width in the range of 12 mm to 51 mm.

15. The reinforcement material (1) according to claim 12, characterized in that The reinforcing material has a length of 2 m to 5000 m.

16. The reinforcement material (1) according to claim 12, characterized in that The reinforcing material has a length of 100 m to 2000 m.

17. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The polymer fiber layers (4, 5) have thermoplastic characteristics and consist of thermoplastic polymers, partially cross-linked thermoplastic polymers, mixtures of such polymers, or mixtures of thermoplastic polymers and thermosetting polymers.

18. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The polymer fiber layers (4, 5) have thermo-bonding properties and their bonding to the unidirectional reinforcing web is achieved due to these thermo-bonding properties.

19. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The polymer fiber layers (4, 5) are the same nonwoven material.

20. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The nonwoven material has a thickness of 0.2 g / m 2 Up to 20g / m 2 The basis weight and / or thickness ranges from 0.5 microns to 50 microns.

21. The reinforcement material (1) according to claim 20, wherein the thickness is 3 to 35 microns.

22. The reinforcing material (1) according to any one of claims 1 to 6, characterized in that The reinforcement material is neither perforated, nor sewn, nor knitted, nor woven.

23. A method for preparing a reinforcing material (1) according to any one of claims 1 to 6, characterized in that: The method comprises the following consecutive steps: a1) providing a unidirectional reinforcing web (2) formed of one or more reinforcing yarns (3) twisted individually with a twist of 3 turns / m to 15 turns / m, a2) providing at least two polymer fiber layers (4, 5), said polymer fiber layers being nonwoven materials, a3) bonding each polymer fiber layer to each face of the unidirectional reinforcing web.

24. The method according to claim 23, characterized in that Said method comprises, upstream of step a1), a step of producing said unidirectional reinforcing mesh (2) comprising applying to a reinforcing yarn or a series of yarns a twist of between 3 turns / m and 15 turns / m, said twist being applied to each yarn individually.

25. The method according to claim 23, characterized in that The unidirectional reinforcing mesh (2) is formed by a plurality of reinforcing yarns (3), and the method comprises, upstream of step a1), i) applying to a series of reinforcing yarns a twist of 3 to 15 turns / m, the twist being applied to each yarn individually, ii) aligning the twisted yarns thus obtained, potentially with other reinforcing yarns, and arranging the yarns side by side, thereby forming a unidirectional reinforcing mesh as defined in claim 1.

26. The method according to claim 24, characterized in that The unidirectional reinforcing mesh (2) is formed by a plurality of reinforcing yarns (3), and the method comprises, upstream of step a1), i) applying to a series of reinforcing yarns a twist of 3 to 15 turns / m, the twist being applied to each yarn individually, ii) aligning the twisted yarns thus obtained, potentially with other reinforcing yarns, and arranging the yarns side by side, thereby forming a unidirectional reinforcing mesh as defined in claim 1.

27. The method according to any one of claims 23 to 26, characterized in that The polymer fiber layers (4, 5) as nonwoven materials have thermobond properties and the bonding of step a3) is obtained by applying each polymer fiber layer to each face of the unidirectional reinforcing web, the application being accompanied or followed by heating the polymer fibers to soften or melt them and then cooling them.

28. A preform consisting at least in part of one or more materials according to any one of claims 1 to 22.

29. A method for producing a composite material part from at least one reinforcing material (1) according to any one of claims 1 to 22, characterized in that A thermosetting resin, a thermoplastic resin, or a mixture of a thermosetting resin and a thermoplastic resin is injected or poured into the reinforcing material, a stack of a plurality of reinforcing materials according to any one of claims 1 to 22, or a preform according to claim 28.

30. A method for manufacturing a composite material part according to claim 29, characterized in that The method comprises, before infusing or injecting the resin, the following steps: forming a ply or stack comprising a plurality of reinforcing materials (1) according to any one of claims 1 to 22, during which the reinforcing materials (1) are continuously conveyed and circulated in a guide member so as to ensure their positioning when laid to produce the desired ply or stack.

31. The manufacturing method according to claim 29 or claim 30, characterized in that: The method comprises application or shaping prior to infusing or injecting the resin, the application or shaping taking advantage of the thermo-bonding properties of the nonwoven material present in the one or more reinforcing materials (1).

32. Use of one or more reinforcement materials (1) according to any one of claims 1 to 22 for producing preforms or composite parts in combination with thermosetting resins, thermoplastic resins or mixtures of thermosetting resins and thermoplastic resins.

33. The method of production according to any one of claims 29 to 31 or the use according to claim 32, characterized in that Injection or infusion of thermosetting resins.

34. The method of production according to any one of claims 29 to 31 or the use according to claim 32, characterized in that Inject or pour epoxy resin.

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