FR2937583A1 - Intermediate novel material associated to a thermohardening resin for producing composite parts, comprises unidirectional carbon fibers, associated, on each sides, to veil of thermoplastic fibers - Google Patents

Abstract

The intermediate novel material comprises unidirectional carbon fibers (1) having a weight of 100-280 g/m 2>, associated, on each sides, to veil (2a, 2b) of thermoplastic fibers. The veil has a thickness of 3-35 microns along its same sides, and a weight of 0.2-20 g/m 2>. The intermediate material has a thickness of 90-320 microns. Independent claims are included for: (1) a process for fabricating a composite part; and (2) a composite part.

Description

The present invention relates to the technical field of reinforcing materials, suitable for the constitution of composite parts. More specifically, the invention relates to a new intermediate material for the production of composite parts, by injection or subsequent infusion of thermosetting resin, a method of manufacturing composite parts from a stack of such a material, and parts composites obtained. The manufacture of composite articles or articles, that is to say comprising, on the one hand, one or more reinforcements or fibrous webs and, on the other hand, a matrix mainly of the thermosetting type (resin) and which may include thermoplastics, may, for example, be carried out by a process known as "direct" or "LCM" (Liquid Composite Molding English). A direct process is defined by the fact that one or more fibrous reinforcements are used in the "dry" state (that is to say without the final matrix), the resin or matrix, being implemented separately. for example by injection into the mold containing the fibrous reinforcements ("RTM" process, of the English Resin Transfer Molding), by infusion through the thickness of the fibrous reinforcements ("LRI" process, of the English Liquid Resin Infusion or process "RFI" (English Resin Film Infusion), or even by coating / manual impregnation by roller or brush, on each of the unitary layers of fibrous reinforcement applied successively to the shape. For RTM, LRI or RFI processes, it is generally necessary to first make a fiber preform of the shape of the desired finished article, and then impregnate this preform with a resin. The resin is injected or infused by a differential pressure of temperature, then once all the necessary amount of resin is contained in the preform, the assembly is brought to a higher temperature to carry out the polymerization / crosslinking cycle and thus cause hardening.

Composite parts used in the automotive, aeronautical or naval industry, in particular are subject to very stringent requirements, particularly in terms of mechanical properties. However, the mechanical properties of the parts are mainly related to a parameter which is the fiber volume ratio (FVT). In these sectors, a large number of preforms are made of reinforcing material, mainly carbon fibers, especially of the unidirectional type. It is possible to theoretically calculate the maximum volume content of fibers contained in a unidirectional layer assuming two types of arrangements: hexagonal or square. Assuming respectively a hexagonal type arrangement and a square type arrangement, the maximum TVF obtained is respectively 90.7% and 78.5% (An Introduction to Composite Materials, D.Hull, TW Clyne, Second Edition, Cambridge Solid State Science Series, 1996). In contrast, in reality, it seems difficult to obtain fiber volume fractions greater than 70% for composite parts. In practice, it is generally accepted by those skilled in the art that a fiber content by volume (FVT) of about 60% is a standard for the production of satisfactory composite parts and this, with good reproducibility (ST Peters, Introduction, composite basics and road map, Handbook of Composites, Chapman & Hall, 1998, pp. 1- 20 and in particular page 8). The resin which is subsequently associated, in particular by injection or infusion, with the unidirectional reinforcement layers during the production of the part may be a thermosetting resin, for example of the epoxy type. To allow a correct flow through a preform consisting of a stack of different layers of carbon fibers, this resin is, in most cases, very fluid. The major disadvantage of this type of resin is their fragility, after polymerization / crosslinking, resulting in low impact resistance of the composite parts made. In order to solve this problem, it has been proposed in the documents of the prior art to associate the unidirectional layers of carbon fibers with a web of thermoplastic fibers. Such solutions are especially described in patent applications or patents EP1125728, US 628016, WO 2007/015706, WO 2006/121961 and US 6,503,856. The addition of this veil improves the mechanical properties of the Post-Impact Compression Test (CAI), a test commonly used to characterize the resistance of structures to impact. Some details on these earlier solutions are given below. Patent Application EP1125728 in the name of Toray Industries Inc. discloses a reinforcing material combining a sheet of reinforcing fibers with a nonwoven of short fibers. The nonwoven is laminated on at least one side of the reinforcing sheet, so that the fibers constituting the nonwoven pass through the reinforcing fibers (carbon) of the sheet and are therefore integrated into the reinforcing fibers. . The nonwoven consists of a blend of low melting point fibers and high melting point fibers. It is important to note that all of the examples cited utilize a single nonwoven associated on one side of the reinforcing fiber sheet made of a unidirectional fabric or web, leading to a non-symmetric reinforcing material. Example 4 uses a reinforcing fiber sheet consisting of a unidirectional fabric of 300 g / m 2. The thickness of the nonwoven used is not indicated, but is certainly quite high, given its surface density (8 g / m2) and the vacuum rate of 90% indicated. The stack used is of the type [-45 / 0 / + 45/90] 2si is 7 interplis containing a single nonwoven. If the teaching of this document is applied to a sheet of carbon fibers of lower density, 134 g / m 2 for example, the association to the same type of veil, but on each side to obtain a symmetrical material, would lead to a very low fiber volume ratio, which is not compatible with the production of primary structures for aeronautics.

Patent Application WO 2007/015706 in the name of The Boeing Company describes a method for the manufacture of preforms combining a stitched assembly alternating layers of carbon fibers and nonwoven layers to increase the impact resistance of the structures composites. The nonwovens are arranged at each interpli and not on each side of the carbon fiber layers. This patent application does not mention a surface density range for the carbon layers nor a range of thicknesses for the nonwovens. The examples mention the use of three different nonwovens, of which only the surface weights of 4.25 g / m2 (0.125 oz / yd2 with US units of measurement), 8.5 g / m2 (0.25 oz / yd2), 12.7 g / m2 (0.375 oz / yd2) are specified. No indication is given on the thickness of these products.

One of the copolyester-based webs even has a negative effect on the impact resistance properties. The examples indicate the thickness of the panels made, the surface density of the carbon layers (190 g / m 2) and the type of carbon fiber (T700 having a density of 1780 kg / m 3). Thicknesses range from 0.177 to 0.187 inches (4.5 to 4.75 mm) for panels with the best results in post-impact stress (CAI). From these thicknesses and information on the type of fibers and the surface density of the carbon folds, it is possible to evaluate the TVF of the panels which vary between 54 and 57%, a rate lower than that generally taken into account by the skilled in the art for producing primary parts. The best result of CAI (39.6 ksi or 273 MPa) is obtained for a TVF of 54%. In the patent application WO 2006/121961, a nonwoven made of soluble fibers (in epoxy type resins for example) is interposed at each interpli layer of carbon fibers during the production of the preform. The nonwoven is not directly associated with the carbon layer. The example presented uses a carbon fiber fabric with a surface mass of 370 g / m 2 with a nonwoven of 60 g / m 2. The realized plate makes it possible to obtain a TVF only of 55%. Moreover, the lack of precision on the impact-compression test (CAI) (lack of precision of the energy to which the impact has been realized) does not make it possible to deduce the mechanical performances from the indicated measured value. US Pat. No. 6,503,856 mentions the use of a carbon layer on which two adhesive layers in the form of a web are superimposed on at least one side of the carbon layer. This patent does not indicate the thicknesses of the adhesive layers (only the fiber diameters of the two layers) and the preferred carbon weight per unit area. is between 200 and 1000 g / m2. Electrical generators (batteries, fuel cells) are the intended application for this type of product and the interest of such a product is not highlighted. Therefore, it appears that, in the techniques of the prior art, the addition of a veil is done, usually at the expense of other mechanical properties. Indeed, as mentioned above, the mechanical properties are mainly driven by the fiber volume ratio (NF) and the techniques described in the prior art do not allow in particular to obtain composite parts which have a NF of the order of 60%. Also, one of the objectives of the present invention is to propose a new intermediate product, adapted to the production of composite parts based on thermosetting resin, and in particular by injection or infusion of resin, which makes it possible to produce composite parts with a volume ratio of fibers of the order of 60% and satisfactory mechanical properties, to meet some very strict specifications, imposed for example in the field of aeronautics. Another object of the invention is to fulfill this specification, while proposing a symmetrical intermediate product that is easier to implement and more suitable for automated processes. In this context, the invention relates to a new intermediate material for the production of composite parts, by injection or subsequent infusion of thermosetting resin, consisting of a unidirectional sheet of carbon fibers having a basis weight of 100 to 280 g / m2 associated on each of its faces with a web of thermoplastic fibers having a thickness of 0.5 to 50 microns. The subject of the present invention is also a process for manufacturing a composite part comprising the following steps: a) making a stack of intermediate materials according to the invention, b) optionally securing the stack obtained in the form of a preform c) adding, by infusion or injection, a thermosetting resin, d) consolidating the desired part by a heat treatment step under pressure, followed by cooling. The intermediate material and the process according to the invention make it possible to produce composite parts having a fiber volume ratio (FFT) of the order of 600%, which corresponds to the standard rate for the primary structures in aeronautics (that is, that is to say the vital parts for the device) and, also, to greatly improve the low-speed impact resistance of the composite parts obtained: for example, the falling of a tool in a workshop during the manufacture of a composite structure, a shock with a foreign body during its use in operation. The pressure applied during an injection process is greater than that used in an infusion process. As a result, it is easier to make parts with a correct TVF with an injection method than infusion. The materials according to the invention make it possible to achieve the desired volume content of fibers, in particular of the order of 60%, even when the composite part is produced with a step c) which implements an infusion and not an injection of resin. Such an embodiment is also an advantageous variant. The composite parts that can be obtained according to the process of the invention are also integral parts of the invention, in particular, parts that have a fiber volume content of 57 to 63% and especially 59 to 61%. The description which follows, with reference to the appended figures, makes it possible to better understand the invention.

Figure 1 schematically shows a sectional view of an intermediate material according to the invention. Figure 2 gives a block diagram of a machine for manufacturing an intermediate material according to the invention. Figures 3a and 3b show a device for measuring the thickness of a vacuum preform.

Figures 4 to 7 are microscopic sections of intermediate products consisting of a unidirectional web associated on each of their large faces with a web (non-woven). Unidirectional sheet of carbon fibers means a sheet consisting exclusively or almost exclusively of carbon fibers deposited parallel to each other. It can be provided the presence of binding son of the thermoplastic type, in particular polyamides, copolyamides, polyesters, copolyesters, copolyamides block ester / ether, polyacetals, polyolefins, thermoplastic polyurethanes, phenoxy, to facilitate the handling, if necessary of the tablecloth , before its association with the veils of thermoplastic fibers. These binding yarns will most often extend transversely to the carbon fibers. The term unidirectional web also includes unidirectional fabrics, in which spaced apart weft yarns interleave the carbon fibers which extend parallel to one another and form the warp yarns of the unidirectional fabric. Even in these different cases, where such binding, sewing or weft yarns are present, the carbon fibers parallel to each other will represent at least 95% by weight of the web, which is therefore described as unidirectional.

In the unidirectional layer, the carbon threads are preferably non-associated with a polymeric binder and thus described as dry, that is to say they are not impregnated, coated or associated with any binder polymeric before their association with thermoplastic sails. Carbon fibers are most often characterized by a mass content of standard size that can represent at most 2% of their mass. In the context of the invention, the sheet of carbon fibers constituting the core of the intermediate material has a basis weight of between 100 and 280 g / m 2. This grammage range makes it easy for design engineers to correctly size composite structures by adapting the stacking sequences of different layers, depending on the different mechanical stress modes of the composite structures. A carbon weight of a weaker elementary layer will offer all the more versatility in the choice of different stacks possible constant thickness. The grammage of the unidirectional web within the intermediate material corresponds to that of the unidirectional web before its association with the webs, but it is not possible to measure the grammage of the unidirectional web before it is associated with the webs because the webs have no cohesion between them. The grammage of the carbon fiber web can be determined from the grammage of the intermediate material (unidirectional web + 2 webs). If we know the surface mass of the sails, it is then possible to deduce the surface mass of the unidirectional layer. Advantageously, the basis weight is determined from the intermediate product by chemical etching (possibly also by pyrolysis) of the web. This type of method is conventionally used by those skilled in the art to determine the carbon fiber content of a fabric or a composite structure. A method of measuring the grammage of the intermediate material is described below. The grammage of the intermediate material is measured by weighing cut samples of 100 cm 2 (i.e. 113 mm in diameter). To facilitate the cutting of the samples of intermediate material which is flexible, the intermediate material is placed between two glossy cardboard Cartonnage Roset (Saint Julien en Genevois, France) of 447 g / m2 and 0.450 mm thick to ensure some rigidity of the whole. A circular pneumatic punch of the company Novi Profibre (Eybens, France) is used to cut the whole; 10 samples are taken by type of intermediate product manufactured. In the unidirectional web, the carbon fibers are most often in the form of yarns of at least 1000 filaments, and in particular from 3000 to 50,000 filaments, for example 3K, 6K, 12K or 24K. The carbon threads have a title of between 60 and 3800 Tex, and preferably between 400 and 900 tex. The thicknesses of the unidirectional carbon sheet vary between 90 and 270 μm.

The unidirectional sheet is associated, on each of its faces, with a web of thermoplastic fibers, to lead to an intermediate product as shown schematically in Figure 1. The use of a symmetrical intermediate product makes it possible to avoid any error of stacking, during its manual or automatic removal for the constitution of composite parts, and thus to limit the generation of fragile areas, including a interpli without sail. Sailing means a nonwoven of continuous or short fibers. In particular, the constituent fibers of the nonwoven will have average diameters in the range of 0.5 and 70 dam. In the case of a nonwoven of short fibers, the fibers will have, for example, a length of between 1 and 100 mm. In the context of the invention, the fibers constituting the web are advantageously made of a thermoplastic material, especially chosen from: Polyamides (PA: PA6, PAl2, PA11, PA6.6, PA 6.10, PA 6 , 12, ...), Copolyamides (CoPA), Polyamides - block ether or ester (PEBAX, PEBA), Polyphthalamide (PPA), Polyesters (Polyethylene terephthalate -PET-, Polybutylene terephthalate - PBT -...) Copolyesters (CoPE), thermoplastic polyurethanes (TPU), polyacetals (POM, etc.), polyolefins (PP, HDPE, LDPE, LLDPE, etc.), polyethersulfones (PES), polysulfones (PSU), .), polyphenylenesulfones (PPSU ...), Polyetheretherketones (PEEK), PolyetherKetoneKetone (PEKK), Poly (Phenylsulfide) (PPS), or Polyetherimides (PEI), thermoplastic polyimides, liquid crystal polymers (LCP) ), phenoxys, block copolymers such as Styrene-Butadiene-Methyl methacrylate (SBM) copolymers, Methylmethane copolymers Butyl-Methylmethacrylate Acrylate (MMA) or a mixture of fibers consisting of these thermoplastic materials. The material is of course adapted to the different types of thermosetting systems used for the constitution of the matrix, during the subsequent production of the composite parts. The thickness of the webs before their association with the unidirectional web will be chosen, depending on how they are associated with the carbon fiber web. Most often, their thickness will be very close to the desired thickness on the intermediate product. It may also be possible to choose to use a thicker web that will be laminated under temperature during the association step, so as to reach the desired thickness. Preferably, the carbon sheet is associated on each of its large faces with two substantially identical webs, so as to obtain a perfectly symmetrical intermediate product. The thickness of the web before association on the unidirectional sheet of carbon is between 0.5 and 200 μm, preferably between 10 and 170 μm. On the intermediate product according to the invention, the thickness of each veil is in the range of 0.5 to 50 microns, preferably in the range of 3 to 35 microns. The thickness of the different sails before association is determined by the NF EN ISO 9073-2 standard by using method A with a test area of 2827 mm 2 (disc of 60 mm diameter) and an applied pressure of 0.5 kPa . Advantageously, the intermediate product according to the invention has a thickness in the range of 80 to 380 microns, preferably in the range of 90 to 320 microns.

The NF EN ISO 9073-2 standard does not make it possible to measure one of the constituents of a combined material of several elements. Two methods have therefore been put in place: one to measure the thickness of the web once laminated on the unidirectional web and the other to measure the thickness of the intermediate product.

Thus, the thickness of the nonwoven or web attached to the unidirectional carbon web was determined from microscopic sections that allow an accuracy of +/- 1 μm. The method is as follows: An intermediate material combining a unidirectional sheet consisting of carbon threads and two webs laminated on each side of the sheet is impregnated with a brush of a resin that polymerizes at room temperature (Araldite and Araldur 5052 from Huntsman). The assembly is fixed between two plates to apply a pressure of the order of 2-5 kPa during the polymerization. The measurement of the thickness of the web present in the intermediate product is independent of the pressure exerted during this step. One slice of the assembly is coated with Struers Epofix Kit cold setting resin, then polished (using 320 micron silicon carbide grit sandpaper and various felts). at a grain size of 0.3 μm) to be observed with an Olympus BX 60 optical microscope coupled to an Olympus ColorView IIIu camera. The use of this resin which polymerizes at ambient temperature has no influence on the thickness of the web but only makes it possible to carry out the measurements. The analySlS auto 5.0 software from Olympus Soft Imaging Solution GmbH can take pictures and make thickness measurements. For each intermediate material (unidirectional web combined with webs on each side), 5 images are taken with a magnification of 20. On each image, 15 thickness measurements of the web are made and the mean and standard deviation of these measures are determined. The thickness of the intermediate product was determined from the following method, the device of which is shown diagrammatically in FIGS. 3a and 3b, which determines a mean on a stack of intermediate products. In these figures, A designates the preform; B the support plate; C the silicone paper; D the vacuum film; E the vacuum seal; F the drainage felt and G the vacuum plug. This method is conventionally used by those skilled in the art and allows a global measurement by minimizing the variability that may exist locally within the same intermediate product. A preform consisting of a stack of different oriented layers of the intermediate product is placed between two layers of silicone paper 130 g / m2 and a thickness of 0.15 mm sold by the company SOPAL in a vacuum film CAPRAN 518 by Aerovac (Aerovac Systems France, Umeco Composites, 1 rue de la Sausse 31240 Saint-Jean, France) and in contact with an Airbleed 10HA drainage felt marketed by Aerovac. The tightness of the assembly is ensured by means of a SM5130 vacuum seal marketed by Aerovac. A vacuum between 0.1 and 0.2 kPa is drawn using a Leybold SV40 B vacuum pump (Leybold Vacuum, Bourg les Valence, France). Then, the thickness of the preform is measured between two digital TESA Digico 10 comparators after subtraction of the thickness of the vacuum cover and the silicone papers. 25 measurements are made by preform and the mean and standard deviation of these measurements are determined. The resulting thickness of the intermediate product is then determined by dividing the thickness of the total preform by the number of superposed intermediate product layers.

Advantageously, the thickness of the intermediate product has a low variability, in particular with thickness variations of not more than 20 μm in standard deviation, preferably not exceeding 10 μm in standard deviation, as is particularly the case illustrated in the examples below.

Advantageously, the basis weight of the web is in the range of 0.2 to 20 g / m 2. The association of the unidirectional web with the two webs can be done via an adhesive layer, for example chosen from epoxy adhesives, polyurethane adhesives, thermosetting adhesives, polymerizable monomer-based adhesives, structural acrylic adhesives. or modified acrylics, hot-melt adhesives. But most often the association will be achieved thanks to the sticky nature that the sails hot, during a step of thermocompression. This step causes the softening of the thermoplastic fibers of the web, allowing to unite the unidirectional web to the web after cooling. The conditions of heating and pressure, will be adapted to the material constituting the sails and their thickness. Most often a thermocompression step at a temperature in the range of Tf sail at 15 ° C and Tf sail + 60 ° C (with Tf sail which designates the melting temperature of the veil) and at a pressure of 0.1 at 0.6 MPa will be achieved. It is thus possible to achieve compression rates of the web before and after association ranging from 1 to 10. The step of bonding the web on the unidirectional carbon is also critical to properly control the final thickness of the product. intermediate. Indeed, depending on the temperature and pressure conditions, especially during lamination, it is possible to modify, and therefore adjust, the thickness of the web present on each side in the intermediate product. The unidirectional web can be created directly upstream of its association with the thermoplastic webs. It may also be used a commercial unidirectional web whose cohesion and manipulability is, for example, provided by binding son, according to a mechanical bond by weaving, or by a chemical bond due to the polymeric nature of the binding son. Such plies are, for example, marketed by SIGMATEX UK Limited, Runcom Cheshire WA7 1TE, United Kingdom under the references PW-BUD (ex: product no. PC2780600 200GSM / PW-BUD / T700SC 12K 50C / 0600mm), or by the company OXEON AB, Sweden, under TEXERO references. Advantageously, a machine as shown in Figure 2 may be implemented. In this case, the webs are associated with the unidirectional sheet of carbon fibers, just after the production of the latter at the desired density per surface by a step of fixing or continuous hot pressing under pressure (thermocompression). The intermediate product according to the invention has good handling, due to the presence of thermoplastic webs laminated on each side of the unidirectional web. This architecture also allows easy cutting, without fraying in particular, in non-parallel directions, particularly transverse or oblique, the fibers of the unidirectional web. For the production of composite parts, a stack or draping of intermediate materials according to the invention (also called folds) is produced. In the stack obtained, the folds are generally arranged so as to orient the unidirectional plies of the folds in different directions. The preferred orientations are most often oriented in the directions at an angle of 0 °, + 45 ° or - 45 °, and 90 ° with the main axis of the part to be made. The main axis of the part is generally the largest axis of the part and the 0 ° merges with this axis. Before adding the resin necessary for producing the part, it is possible to secure the folds together in the stack, in particular by an intermediate step of preforming temperature and vacuum or welding in a few points with each addition fold, and thus achieve a preform. Next, a resin or matrix, of thermosetting type, is then added, for example by injection into the mold containing the plies ("RTM" process, of the English Resin Transfer Molding), by infusion (through the thickness of the folds: process "LRI", of English Liquid Resin Infusion or process "RFI", of English Resin Film Infusion). According to a non-preferred variant, it is also possible to carry out, before the completion of the stack, manual coating or impregnation with a roller or a brush on each of the plies, applied successively to the shape of the mold used. The matrix used is of the thermosetting type. The injected resin will be, for example, chosen from the following thermosetting polymers: epoxides, unsaturated polyesters, vinyl esters, phenolics, polyimides and bismaleimides. The composite part is then obtained after a heat treatment step. In particular, the composite part is generally obtained by a conventional consolidation cycle of the polymers in question, by performing a heat treatment, recommended by the suppliers of these polymers, and known to those skilled in the art. This consolidation step of the desired part is carried out by polymerization / crosslinking according to a cycle defined in temperature and under pressure, followed by cooling. The pressure applied during the treatment cycle is low in the case of vacuum infusion and stronger in the case of injection into a RTM mold. According to an advantageous characteristic of the invention, the composite parts obtained have a fiber volume content of 57 to 63%, preferably 59 to 61%. These volume levels of fibers are compatible with the use of structures for primary parts, that is to say, critical parts in aeronautics that take up the mechanical forces (fuselage, wing ...).

The fiber volume ratio (FVT) of a composite part is calculated from the measurement of the thickness of a composite part by knowing the surface density of the unidirectional carbon layer and the properties of the carbon fiber, from the following equation: TVF (%) = n plies x UD carbon mass x Io., (1) Carbon fiber x ply Where plate is the thickness of the plate in mm, carbon fiber is the density of the carbon fiber in g / cm3, the surface weight UD carbon is in g / m2. The composite parts obtained also have optimal mechanical properties, and in particular the impact resistance (CAI, Compression After Impact), the mechanical properties showing the sensitivity to the holes such as perforated compression (OHC, Open Hole Compression in English), the perforated traction (OHT, Open Hole Traction in English), the matage (Bearing in English), the shear in the plane (IPS, In-Plane Shear in English). In particular, it is possible to obtain composite parts having a compressive impact rupture stress (CAI), measured according to the preliminary European standard prEN 6038 published by ASD-STAN (AeroSpace and Defense Standard, Avenue de Tervueren 270, 1150 Woluwe-Saint-Pierre, Belgium), greater than 200 MPa under an impact of 3. It has also been found, particularly when the resin matrix is of epoxy type, a small drop in the Tg of the epoxy after aging. of the same order of magnitude as that obtained for standard prepregs, known to those skilled in the art. The examples below illustrate the invention but are not limiting in nature. 1. Materials used The intermediate products tested are unidirectional webs consisting of carbon fibers associated with a web on each side. 3 types of carbon fibers were used: 12K intermediate modulus (IM) fibers marketed by Hexcel, 12 K high strength (HR) fibers marketed by Hexcel, 12K high strength (HR) fibers marketed by Toray; their mechanical and physical properties are summarized in Table 1.

Several surface carbon masses of the unidirectional layers were tested. These sheets are made in line and their weight in carbon fibers is estimated at 134 g / m 3% from Hexcel IM carbon fibers, 194 g / m 3% from Hexcel IM fibers, 134 g / m 2 3% from Hexcel HR fibers, 268 g / m2 3% from Hexcel HR fibers and 150 g / m2 3% from Toray HR fibers. Table 1: Characteristic Properties of Carbon Fibers Hexcel IM Hexcel HR Toray HR Failure Stress (MPa) 5610 4830 4900 Traction Module (GPa) 297 241 240 Elongation (%) 1.9 1.8 2 Mass / Unit Length 0.443 0.785 0.800 (9 / m) Density (g / cm 3) 1.80 1.79 1.80 Diameter of the filaments (μm) 5 7 7 Three types of sails were used, referred to as Sail 1, Sail 2 (1R8D03 sold by Protechnic, 66, rue des Fabriques, 68702 - CERNAY Cedex - France), sail 3. These sails are based on a mixture of polyamides and copolyamides (sail 1 and 2) or polyamides (sail 3). This type of sail is also marketed by companies such as Spunfab Ltd. / Keuchel Associates, Inc. (175 Muffin Lane Cuyahoga Falls, OH 44223, USA).

The web 1 consists of continuous filaments. The sails 2 and 3 are made from short fibers. The characteristics of the sails used are shown in Table 2. The seals melting point indicated in Table 2 is determined by differential scanning calorimetry (DSC) according to ISO 11357-3. The basis weight is measured according to the ISO standard. 3801. The porosity ratio shown in Table 2 is calculated from the following formula: Pore velocity (%) = 1 'Surface mass of the veil x 100 (2) Veiling mass X evoile Where - the basis weight of the veil is expressed in kg / m 2, the weight of the veil is expressed in kg / m 3, veil is expressed in m.

Table 2 Characteristics of the sails used (the values mentioned after represent the standard deviation) Reference 1 2 3 Melting point of the veil (° C) 178 160 178 Weight per surface area (glm2) 6.7 0.5 2.8 0.1 3.7t 0.1 Diameter of 44 12 9 2 13 3 filaments (pm) * Thinness of the veil (pm) 161 18 59 12 69 12 Porosity rate (%) 96 98 97 calculated from formula (2) * Measured by image analysis

2. Manufacture of Tested Intermediate Products The web is laminated directly to each side of the unidirectional carbon fiber webs by means of a machine (Figure 2) specifically dedicated for this purpose just after formation of the web at the desired basis weight. The carbon yarns 1 are unwound from carbon coils 3 fixed on a creel 4, pass through a comb 5, are conducted in the axis of the machine with the aid of a guide roller 6 and a comb 7, a guide bar 8a. The carbon threads are preheated by means of a heating bar 9 and are then spread by means of the spreading bar 8b and the heating bar 10 to the desired carbon mass per unit area of the unidirectional web 17. The rolls of sails 13a and 13b are unrolled without tension and transported using continuous mats 15a and 15b fixed between the free rotating rollers 14a, 14b, 14c, 14d and the heated bars 12a, 12b. The webs 2a and 2b are preheated in the zones IIa and iib before being in contact with the carbon wires 1 and laminated on either side of two heated bars 12a and 12b whose air gap is controlled. A calender 16, which can be cooled, then applies a pressure on the unidirectional sheet with a web on each side 17. A return roller 18 allows to redirect the product 17 to the traction system comprising a trio 19 call and d motor-driven winding 20 to form a roll consisting of the claimed intermediate 17.

The test conditions for making unidirectional carbon webs combined with a web on each side are shown in Table 3 below.

Table 3: Process parameters for the implementation of unidirectional webs associated with a web on each side Example Type Mass Type Speed T bar TTT line surface bars (° C) preheat bar (° C) fibers measured from the web (mlmin ) (9) (° C) veil (12a & product (10) (° C) 12b) intermediate (11a & (g / m2) 11 b) Comparative Hexcel 134 No - - - - - 1 IM veil 2 Hexcel 149 Veil 1 1,3 200 200 120 270 IM Comparative Hexcel 149 Veil 1 1,3 200 200 120 170 2b IM 25 Example Type Mass Type Speed T bar TTT line surface bars (° C) preheating bar (° C) fibers measured veil (mlmin) (9) (° C) (° C) (12a & product (10) (11a & 12b) intermediate II b) (glm2) 3 Hexcel 141 Veil 2 1.6 200 200 120 255 IM 3b Hexcel 141 Veil 2 1,3 200 200 120 143 IM 4 Hexcel 142 Veil 3 1,8 200 200 120 265 IM 4b Hexcel 142 Veil 3 1,3 200 200 120 187 IM Comparative Hexcel 199 No - - - - - IM Veil 6 Hexcel 213 Sail 1 1,6 200 200 120 270 IM 6b Hexc el 213 Veil 1 1,3 200 200 120 170 IM 7 Hexcel 197 Veil 2 1,8 200 200 120 255 IM 7b Hexcel 197 Veil 2 1,3 200 200 120 145 IM 8 Hexcel 207 Veil 3 1,3 200 200 120 265 IM 8b Hexcel 207 Sail 3 1,3 200 200 120 193 IM Comparative Toray 150 No - - - - - 9 HR Sail Toray 168 Sail 1 1,3 200 200 120 255 HR 11 Toray 159 Sail 2 1,6 200 200 120 250 HR Comparison Hexcel 136 No - - - - - 12 HR Sail 13 Hexcel 156 Sail 1 1,3 200 200 120 270 HR 13b Hexcel 157 Sail 1 1,3 200 200 120 170 HR 14 Hexcel 147 Sail 2 1,8 200 200 120 255 HR 14b Hexcel 146 Veil 2 1,3 200 200 120 145 HR Hexcel 147 Veil 3 1,5 200 200 120 265 HR 15b Hexcel 150 Veil 3 1,3 200 200 120 190 HR Comparison Hexcel 268 No - - - - - 16 HR sail 17 Hexcel 274 Sail 2 1.6 200 200 120 255 HR In the case of unidirectional webs without sail (comparative example 1), the carbon threads are held using a 280-dtex hot-melt thread distributed every 50 mm perpendicular to the orientation of the fibers of carbon. In the case of representative examples of the invention where the unidirectional sheets are associated with two webs, the webs are formed directly on the machine, upstream of the lamination with the sails. 3. Determination of the thicknesses after laminating of the web and the intermediate product The thicknesses of the webs after laminating on the unidirectional sheets are measured by image analysis. Table 4 summarizes the average thicknesses and standard deviations of the sails (out of 75 values) obtained by this method for each studied configuration. In this same Table 4, the thicknesses of the various intermediate products comprising the carbon sheets associated with a web on each side are indicated. These measurements are deduced from the measurement of the thicknesses of preforms at atmospheric pressure according to the methods described in the description.

Table 4: Thickness of the intermediate products (UD plies associated with a veil on each side) used and veils on these plies Example Thickness Standard deviation Ply thickness Standard deviation on ply veil thickness (UD + veils) (μm) thickness ( pm) (pm) Tablecloth (pm) Comparative 1 - - 120 4 2 20 8 153 3 Comparative 2b 62 15 183 4 3 12 6 120 4 3b 14 5 123 5 4 13 4 145 4 4b 23 7 157 4 Comparative 5 - - 6 21 9 198 2 6b 32 8 224 3 7 9 3 184 5 7b 11 3 197 3 8 11 3 185 3 8b 20 7 _ 195 3 Comparative 9 - - 10 19 6 11 13 6 Example Thickness Standard deviation Foil thickness Deviation - sail type over sail thickness web (UD + sails) (pm) thickness (Pm) (Pm) tablecloth (Pm) Comparative 12 - - 13 20 7 162 4 13b 46 12 192 3 14 12 4 155 3 14b 15 6 157 7 15 FIG. 4 is a micrographic section of the intermediate product of Example 2b (134 g / m 2 of Hexcel IM carbon fibers associated with web 1 of each side).

Figure 5 is a micrographic section of the intermediate product of Example 2 (134 g / m2 of Hexcel IM carbon fibers associated with web 1 on each side). Figure 6 is a micrographic section of the intermediate product of Example 3b ( 134 g / m 2 of Hexcel IM carbon fibers associated with web 2 10 on each side). Figure 7 is a micrographic section of the intermediate product of Example 4 (134 g / m2 of Hexcel IM carbon fiber associated with web 3 on each side). 4. Making plates 4.1 Defining the stacking sequence The plates produced are quasi-isotropic, that is to say they consist of a set of elementary plies with the different orientations (00/450 / -450 / 90 °). The stack is also symmetrical. The number of plies constituting the stack is determined from the following formula deduced from formula (1): ## EQU1 ##

p. UD carbon mass density knowing that: the target thickness of the plate is the closest to 4 mm (defined by prEN standard 6038), e plate is expressed in mm, the fiber volume ratio (FVT) targeted to obtain the best mechanical properties, is 60% and p carbon fiber defined in Table 1, expressed in g / cm3, The surface mass of the UD c.artone is expressed in g / m2.

The stack thus consists of 32 plies in the case of a carbon weight of 134 and 150 g / m2 and is written in abbreviated notation: [+ 45/0 / - 10 45/90] 4s. For carbon weights of 194 and 268 g / m2, the number of folds is respectively 24 and 16 folds. The stack is written in abbreviated notation [+ 45/0 / -45 / 90] 3s and [+ 45/0 / -45 / 90] 2s. Each fold corresponds to a sail / UD / sail material.

4.2 Manufacture of the composite plate The different plies are held together by welding slightly with each addition of new fold in a few points using a soldering iron. The set is a preform. The 340 mm x 340 mm preform consisting of the stacking sequence adapted to the carbon weight is placed in an injection mold under a press. A frame of known thickness surrounds the preform to obtain the desired fiber volume ratio (FVT). The epoxy resin marketed under the reference HexFlow RTM6 by Hexcel is injected at 80 ° C. under 2 bars through the preform which is maintained at 120 ° C., the temperature of the platens of the press. The pressure applied to each of the two plates of the press is 5 bars. When the resin appears at the outlet point of the mold, the outlet pipe is closed and the polymerization cycle begins (up to 180 ° C at 3 ° C / min, then 2 hours at 180 ° C, then cooling at 5 ° C / min). 6 test pieces per configuration type of 150 x 100mm (standard prEN 6038) are then cut to perform the post-crash test (CAI). 5. Mechanical tests The test specimens (6 per type of configuration) are attached to a device as specified in EN 6038. The specimens were subjected to a single energy impact equivalent to 25% using equipment. adapted to the preliminary European standard prEN 6038 published by ASD-STAN (AeroSpace and Defense Standard, Avenue de Tervueren 270, 1150 Woluwe-Saint-Pierre, Belgium). Compression tests on an Instron 5582 mechanical testing machine of 100 kN capacity renovated by Zwick (Zwick France Sari, Roissy Charles de Gaule, France).

The results of post-impact compression failure stresses are listed in Tables 5a to 5e. Table 5a: Impact stress results (CAI) at 25] for different types of unidirectional IM 134 g / m2 for different types of veil Example ~ Example Example Example Example Example Comparative example 2 comparative 3 3b 4 4b 2b 1 142 260 275 289 279 305 308 6 15 17 6 18 24 19 CAI (MPa) Standard Deviation (MPa) Table 5b: Post-Impact Compression (CIP) stress results at 25] for the different types of unidirectional IM 194 g / m 2 for various types of haze Example ~ Example Example Example Example Example Example 5 6 6b 7 7b 8 8b comparative GAI (MPa) 126 319 247 285 282 291 294, Standard deviation 14 8 4 5 3 17 5 (MPa) Table 5c: Impact stress results at 25] for the different types of unidirectional HR Toray 150 g / m2 for different types of web Example Example 10 Example 11 9 Comparative CAI (MPa) 151 312 354 _ Standard deviation (MPa) 11 9 9 Table 5d: Results of con post-impact (CAI) burst at 25 J for the different types of unidirectional Hexcel HR 134 g / m2 for different types of sail Example Example Example Example Example Example Comparative example 13 13b 14 14b 15 15b 12 145 308 315 276 272 285 332 7 7 7 4 2 3 7 CAI (MPa) Standard deviation (MPa) Table 5e: 25-day post-impact compression fracture (IAC) stress results for unidirectional HR Hexcel 268 g / m2 without sail and with veil 2 Example Example 17 Comparative 16 CAI (MPa) 165 220 Standard deviation (MPa) 10 30 6. Plate thickness control and deduction of fiber volume ratio (FVT) The plates are positioned between two digital comparators TESA 15 Digico 10 to measure their thicknesses. 24 measurements equidistantly distributed on the surface are made per plate. Tables 6a to 6e show the results of thickness measurements of the plates obtained from the various intermediate materials manufactured. From the plate thicknesses, the different TVFs can be calculated by the formula (2). Comparative Example 2b shows the influence of the thickness of the laminated webs on the unidirectional web. The thickness of the laminated web on the web in the case of Example 2b (Table 4) is 62 μm, a thickness greater than the claimed web thickness. The use of this thicker web results in the manufacture of a workpiece having a fiber volume ratio lower than that required for use of the workpiece for a primary structure.

Table 6a: Measurements of the thicknesses of the different plates made from unidirectional sheets of Hexcel IM carbon fiber in 134 g / m2 with different types of sails; stacking sequence [+ 45/0 / -45 / 90] 4s Example Example Example Example Example Example Comparative example 2 Comparati 3 3b 4 4b 1 f2b Thickness 3.93 3.94 4.25 3.95 3.90 3, 94 3.95 measured (mm) Standard deviation 0.03 0.02 0.2 0.03 0.05 0.02 0.03 TVF 60.7 60.5 56.0 60.3 61.2 60.5 60.3 calculated (%) Table 6b: Measurements of the thicknesses of the different plates made from Hexcel IM unidirectional sheets in 194 g / m2 with different types of sails; stacking sequence [+ 45/0 / -45 / 90] Example Example Example Example Example Example Comparative example 6 6b 7 7b 8 8b 5 Thickness 4,28 4,24 4,32 4,25 4,31 4,32 Measured 4.28 (mm) Standard deviation 0.06 0.03 0.02 0.05 0.05 0.03 0.051 FST 60.4 61.0 59.9 60.9 60.0 59.9 60.5 calculated (%) Table 6c: Measurements of the thicknesses of the different plates made from unidirectional sheets HR Toray in 150 g / m 2 with different types of sails; stacking sequence [+ 45/0 / -45 / 90] Example Example 10 Example 11 comparative 9 Measured thickness 4.44 4.40 4.48 (mm) Standard deviation 0.05 0.03 0.04 FVT calculated (%) 60.8 61.3 60.2 Table 6d: Measurements of the thicknesses of the different plates made from unidirectional sheets of Hexcel HR carbon fiber in 134 g / m2 with different types of sails; stacking sequence [+ 45/0 / -45 / 90] 4s Example Example Example Example Example Example Comparative example 13 13b 14 14b 15 15b 12 Thickness - 4,09 4,11 3,96 3,90 3,98 4, 09 measured (mm) Standard deviation - 0.10 0.10 0.04 0.04 0.03 0.09 FTV calculated - 58.6 58.3 60.4 61.4 60.3 58.6 (%) Table 6e: Measurements of the thicknesses of the different plates made from unidirectional sheets of Hexcel HR carbon fibers in 268 g / m2 with different types of sails; stacking sequence [+ 45/0 / - 45/90] 2s Example Example 17 comparative 16 Measured thickness - 3.9 (mm) Standard deviation - 0.04 calculated FV (%) - 61.5 The equation ( 3) makes it possible to calculate the fiber volume ratio of each composite plate produced by injection. It is important to note that whatever the configurations used, the NF of the plates is in the range 60 to 2% which is an essential criterion for the production of parts of primary structures.

Claims (10)

CLAIMS1 - New intermediate material, intended to be associated with a thermosetting resin for the production of composite parts, consisting of a unidirectional sheet of carbon fibers having a weight per unit area of 100 to 280 g / m2, associated on each of its faces , to a web of thermoplastic fibers, said webs each having a thickness of 0.5 to 50 microns. 2 - New intermediate material according to claim 1, characterized in that the webs of thermoplastic fibers each have a thickness of 3 to 35 microns. 3 - New intermediate material according to claim 1 or 2, characterized in that it has a thickness of 80 to 380 microns, preferably 90 to 320 microns. 4 - New intermediate material according to one of the preceding claims, characterized in that the webs present on each of the two faces are substantially identical. 5 - New intermediate material according to one of the preceding claims, characterized in that the thermoplastic fibers are chosen from polyamide fibers (PA: PA6, PA12, PA11, PA6.6, PA 6.10, PA 20 6, 12, ...), Copolyamides (CoPA), Polyamides - Block ether or ester (PEBAX, PEBA), Polyphthalamide (PPA), Polyesters (Polyethylene terephthalate - PET -, Polybutylene terephthalate - PBT - ...), Copolyesters (CoPE ), thermoplastic polyurethanes (TPU), polyacetals (POM ...), polyolefins (PP, HDPE, LDPE, LLDPE ....), polyethersulfones (PES), polysulfones (PSU ...), polyphenylenesulfones (PPSU) ...), Polyetheretherketones (PEEK), PolyetherKetoneKetone (PEKK), Poly (Phenyl Sulfide) (PPS), or Polyetherimides (PEI), thermoplastic polyimides, liquid crystal polymers (LCP), phenoxys, block copolymers such as Styrene-Butadiene-Methylmethacrylate (SBM) copolymers, copolymers Methylmethacrylate-Butyl-M acrylate thylméthacrylate (MMA) or a mixture of fibers composed of these thermoplastic materials. 6 - New intermediate material according to one of the preceding claims, characterized in that the webs have a basis weight in the range of 0.2 and 20 g / m2. 7 - Process for manufacturing a composite part characterized in that it comprises the following steps: a) making a stack of intermediate materials according to one of the preceding claims, b) optionally securing the stack obtained in the form of a preform, c) adding, by infusion or injection, a thermosetting resin, d) consolidate the desired part by a polymerization / crosslinking step in a defined cycle temperature and pressure, followed by cooling. 8 - composite part obtainable by the method of claim 7. 9 - composite part according to claim 8 characterized in that it has a fiber volume ratio of 57 to 63%, preferably 59 to 61%. 10 - Composite part according to claim 8 or 9 characterized in that it has an impact stress value after compression impact (CAI), measured according to the standard prEN 6038 under an energy impact of 25 J, greater than 200 MPa.