Patent Application
20240131807
The invention relates to high-performance composite parts. The invention relates more particularly to a semi-finished composite product based on long fiber segments embedded in a resin matrix.
Composite materials are increasingly present in sectors where there are moving parts. The sectors that are most concerned are for example the aeronautics, space, medical and motor vehicle sectors and mobility in general because these materials make it possible to produce parts with performance levels that are equivalent to the usual metal parts but with lesser weights. For example, the density of titanium is 4.40 kg/dm3, that of aluminum is 2.70 kg/dm3 and that of epoxy carbon is 1.60 kg/dm3.
This optimization of the weight makes it possible for example for the aeronautics constructors to lighten the structures of the aircraft and therefore reduce the power of the engines embedded by said aircraft. This provision allows the airlines to lower the fuel consumptions, reduce their carbon footprint and increase the number of passengers as well as the action radii of the airplanes. All of these advantages make it possible to lower the per-passenger flight costs.
The new airplanes incorporate composite materials over more than 50% of their weight. These composite materials are composed firstly of a network of fibers that are generally woven or unidirectional and secondly of a resin that is usually thermosetting or thermoplastic.
However, one great issue with the composite materials remains how to optimize the costs associated with the implementation of said materials. Effectively, the standard composite materials used in aeronautics are primarily based on carbon fabrics or resin-pre-impregnated carbon sheets, which give parts that have significant mechanical performance levels to the detriment of their costs. Indeed, they require significant implementation times, and since the parts are all overall of complex and different forms, the production thereof is difficult to industrialize.
The reinforcing fibers, typically carbon or glass fibers, but also aramid or natural fibers (for example plant fibers), have high orthotropic properties in the lengthwise direction. By embedding the fibers in a resin that gives its form to a composite part, a strain applied to the part is transmitted by the resin to the fibers through the interface between the fibers and the resins. The longer the fibers are, the longer and more effective is the interface through which the transmission of a strain can occur between the resin and a fiber. Thus, a distinction is made between the composites with high-performance long fibers and the composites with lower performance short fibers. In some cases, the term long fibers is used for fibers with a length of at least 2 mm, because beyond these lengths it becomes very difficult, even impossible, to mold such a composite by injection molding. However, in the context of the present invention, long fibers are defined as fibers that have a length of at least 10 mm, preferably of at least 50 mm or even of at least 100 mm. Continuous fibers are of course considered as long fibers. This criterion is chosen not with respect to the possibility or impossibility of injection molding, but rather on the basis of a matrix-fiber interface length that is sufficient to obtain a sufficient transfer of loads from the matrix to the fibers when a composite part is subjected to external strains.
The short fiber composites therefore have mechanical properties that are lower than the long fiber composites, but make it possible to manufacture parts with complex geometries, for example by injection molding. By contrast, while the composites with long fibers oriented in a targeted manner in order to benefit from the orthotropic properties of the fibers offer very high performance levels, they do not generally make it possible to manufacture parts with complex geometries. It has been a long-time objective in the field of composite materials to be able to increase the complexity of the geometry of the parts while maintaining the mechanical properties specific to the long fiber composites at a high level. The present invention proposes a solution to this historical, and still current, problem.
Despite the progress in robotization during the method for manufacturing composite parts of large size, many applications generate significant pre-impregnated composite material scraps, which are too small to be reused in the manufacturing of these same parts and that are difficult to reuse in composite parts of smaller sizes with complex geometries. In fact, most of the small composite parts of complex forms intended for the aeronautic sector are still meticulously draped by hand by the operators. This step demands great dexterity and therefore involves significant production costs.
Several methods have been considered to industrially produce lightweight structural composite parts with optimized costs.
As is known, the document US 2010/0233423 A1 describes the production of a molding material which has cuts made transversely to a direction of extension defined by the direction of the warp of the fibrous reinforcement on the fabric reinforcement. This document describes partial cuts and therefore cuts which do not make it possible to fully separate the fibrous bundles from one another. Nor does this document describe the cutting of the resin system, and in the case where these partial cuts allow the deformation of the fabric in the warp direction, they do not make it possible to conserve all of the segments in the relative movement thereof.
For the final part to exhibit the best possible mechanical characteristics, it is important, during the molding, in the step of heating up and pressurizing the part, for all of the bundles to be independent of one another. The independence of the bundles is important in order to retain full mobility, that is to say that, under the effects of a pressure produced on the part, the unitary segment can be displaced without provoking tearing or crimping of the fibrous reinforcements and this can be done without involving separation between the fibers and the resin. The solutions to the technical problems cited previously are not discussed. Furthermore, the cuts in the warp direction are geometrically aligned, which provokes a weakness path on the final part. Said weakness path is prejudicial to the final mechanical characteristics of the part.
The major point of the maturation of the resin is not broached. Now, it is known to the person skilled in the art that, in a pre-impregnated material, the resin is liable to change and that its state is not set, effectively, when the resin has been recently impregnated, it is still fluid, it will therefore be able to be separated from the fibers easily upon implementation. On the other hand, if it is too viscous, it will prevent the good separation between the networks of fibers that are not trimmed in the longitudinal direction. Now, it is scientifically recognized that the misalignment of fibers by an angle of five degrees with respect to their longitudinal axis provokes a loss of tensile modulus which can range up to 30%. This loss of tensile modulus is clearly a problem associated with the partial cutting of the segments.
Nor is the issue associated with the movement of the fibrous networks when the latter have to be displaced broached. Indeed, in the case of the production of a part with complex geometry, the movements of the networks of fibers will either move apart, or tighten up in the plane according to the zones of the part. In the case of the material presented in the document US 2010/0233423 A1, because of the juxtaposition of the cutting zones, the ends of the fibers on the cutting line will press against one another and be creased in the case of a necking movement within the part. This phenomenon will be amplified by the absence of lateral mobility induced by the resin bond.
High-performance SMC (sheet molding compound) or BMC (bulk molding compound) technologies have been developed to reduce the implementation times. Many molding products of BMC or SMC type make it possible to optimize the costs because they make it possible to reduce the production times, but, because of their uncontrolled and non-repetitive fibrous organization, these types of moldings are difficult to apply to parts that are subject to great mechanical strains. Indeed, the SMC type allows greater industrialization, but without achieving the performance levels or the reproducibility of the manual methods applicable to pre-impregnated composite materials. The technical problem with the SMC type lies in the fact that the reinforcing fibers are cut while they are still dry and not impregnated, then distributed by gravity on a film of resin. Since this distribution is random, the final fraction by volume of fibers of the composite varies significantly. The random distribution also gives uncontrolled and non-reproducible fiber directions, so these materials are therefore difficult to use for applications in which the mechanical strains are significant.
The document U.S. Pat. No. 6,838,148 B1 describes an enhanced SMC material composed of a stack of pre-impregnated unidirectional fibers and of cut fibers distributed randomly. The fibers are superposed in successive layers each having a different direction. While this product can represent an advance over a traditional SMC, it does not settle two major technical issues, the first being the capacity of the material to be deformed to be able to meet the different form constraints of widely diverse parts and the second being that of having relatively low mechanical properties because of the random distribution of the fibers.
The document EP 0916477 A1 describes a technology of fully cutting segments of pre-impregnated fiber sheets which are then mixed three-dimensionally. It is therefore clearly established from this phase that the segments will be mixed randomly in space (3 dimensions), which will confer on the final product very low mechanical characteristics because of a very significant crossing between the sheet segments, and, in addition, this disposition will not make it possible to control and therefore reproduce accurately the mechanical characteristics of a part. Now, it is important, when producing a series of parts, for all of the parts to have the same mechanical characteristics.
The document EP 1134314 A1 describes a composite intermediate product which takes the form of layers of pre-impregnated fiber segments. These segments are disposed randomly in the plane (2 dimensions), but, even though their median distribution is almost isotropic, their precise distribution in the plane is random and there is a significant crimping between the bundles, and thus, their mechanical characteristics are low and cannot be finely controlled or result in a production of parts with reproducible characteristics.
The document EP 3140104 A1 describes the production of preforms using strips of small widths with the aid of an automatic carbon strip deposition machine. One significant issue with the use of such a machine is the cost linked to the purchase thereof which remains difficult to amortize. This document does not deal with the possibility of using this machine to produce a standard base material of SMC type.
However, these solutions are not entirely satisfactory.
In order to resolve all or part of the abovementioned drawbacks, the patent application FR 3078010 A1 proposes producing a composite part by stacking several continuous pre-impregnated layers comprising multifiber flat segments, the segments of one and the same layer being oriented in a single direction, and said segments being linked by adhesion in line with their zones of crossing-superpositioning with the segments of layers of adjacent segments, so as to form a mat of constant weight and thickness, of low inherent cohesion exhibiting relative flexibility.
The manufacturing of such a composite product necessitates previously forming segmented continuous pre-impregnated sheets which are then stacked one on top of the other in an operation of formation of a continuous multilayer strip. This operation is optimal in the case of a unidirectional continuous multilayer strip, in which all the fibers are aligned at 0°. If, however, the orientation of the fibers in the segmented continuous pre-impregnated sheets of the continuous multilayer strip have to vary from one layer to the other, an automatic fiber placement (AFP) machine must be used to orient the fibers of at least one segmented continuous pre-impregnated sheet with a reinforcing angle other than 0°, for example, ±45° or 90°. The step of automatic fiber placement to form such a segmented continuous pre-impregnated sheet with a reinforcement angle other than 0° is lengthy and does not make it possible to directly use, as starting material, pre-impregnated multilayer sheets that are available on the market or that originate from scraps from another large-size composite part method. A reinforcement angle (β) is here defined in the present document with a tolerance of ±5°.
The invention therefore aims to propose a method for manufacturing composite parts with high performance levels and complex geometries, using an innovative discrete segmented multilayer mat obtained from segmented discrete plies that can use as starting material, directly and without prior manipulation, pre-impregnated single-layer sheets that are available on the market or that originate from scraps from another large-size composite part method. The present invention relates also to methods for manufacturing discrete pre-impregnated plies and discrete segmented multilayer mats. These advantages and others are described in more detail in the following detailed description of the invention.
The present invention is defined in the independent claims. Preferred variants are defined in the dependent claims. In particular, the present invention relates to a segmented discrete ply comprising
The segmented discrete ply is formed by a transverse cutting of a segmented continuous sheet. The segmented continuous sheet comprises
The segmented continuous sheet is formed by supplying a continuous single-layer sheet comprising
A continuous sheet is defined as being a sheet having a geometry inscribed within a rectangle of length (L) and of width (I) with a length-to-width ratio (L/I) greater than 20 (i.e. L/I>20). A discrete ply is defined as being a ply having a geometry inscribed within a rectangle of length (L) and of width (I) with a length-to-width ratio (L/I) less than or equal to 20 (i.e. L/I≤20).
The segmented discrete ply of the present invention is formed by cutting the segmented continuous sheet over all of its width and its thickness, including the antiadhesive lining along two cutting lines parallel to cutting directions that are oriented obliquely with respect to the longitudinal direction (D). The cutting lines form a cutting angle (α) with the longitudinal direction (D). The cutting angle (α) can for example be equal to 90°, +45°, −45°, +60°, −60°, +30°, or −30°, to within ±5°.
In one and the same segmented discrete ply, the segments preferably have a geometry comprising two opposite sides parallel to the longitudinal direction (D) having dimensions that are identical within the segmented discrete pre-impregnated ply. The geometry of the segments is preferably inscribed in a rectangle with a length measured along the longitudinal direction (D) preferably lying between 10 mm and 200 mm, preferably between 50 and 150 mm, more preferably between 70 and 130 mm or substantially equal to 100 mm, and a width preferably lying between 5 mm and 50 mm, preferably substantially equal to 8 mm.
The present invention relates also to a discrete segmented multilayer mat composed of a stack of discrete pre-impregnated layers comprising, on the one hand,
The fibers of a given discrete pre-impregnated layer form a reinforcement angle (β) lying between 0 and 180° (i.e. β=0 to 180°) with the fibers of the discrete pre-impregnated layers of the same discrete stack which are adjacent to and in contact with the given discrete pre-impregnated layer. In a variant of the invention, all the discrete pre-impregnated layers of a discrete stack are discrete segmented pre-impregnated layers whose cutting angles are 90° or ±45° and whose reinforcement angles (β) are equal to the cutting angle (α) plus a multiple (n) of 45° with n=0 to 4 (i.e. β=α+n×45°, with n=0 to 4).
The discrete segmented multilayer mat can be produced in two ways. In a first variant, a series of stacks of discrete pre-impregnated layers laid on a continuous strip is formed. The continuous strip can then be cut between two stacks to obtain a discrete segmented multilayer mat. In a second variant, discrete pre-impregnated plies can be stacked one on top of the other by removing, when necessary, the discrete antiadhesive lining, to directly form the discrete segmented multilayer mat.
In the first variant, a continuous strip must be supplied that is composed of a continuous single-layer sheet, a segmented continuous sheet, or a continuous antiadhesive lining, as defined above, to form a first layer of the discrete segmented multilayer mat.
In the second variant, the first layer is formed by a discrete pre-impregnated ply comprising, on the one hand,
On a face of the first layer not comprising the continuous antiadhesive lining or on the continuous antiadhesive lining if the continuous strip is formed by a continuous antiadhesive lining, N discrete pre-impregnated plies are laid sequentially by removing the discrete antiadhesive lining from each discrete pre-impregnated ply, before laying a new discrete pre-impregnated ply thereon and optionally compacting the duly stacked discrete pre-impregnated plies, such that,
In the first variant in which the first layer is formed by a continuous strip, a series of stacks as described above is deposited, side-by-side. A continuous strip is thus obtained comprising a series of stacks of N layers, that can be separated by cutting the continuous strip between two adjacent stacks.
The two variant methods for manufacturing a discrete segmented mat are each distinguished from the prior art in that at least one discrete pre-impregnated ply, preferably all the discrete pre-impregnated plies, are segmented discrete plies as described above, in which the discrete pre-impregnated layer is formed by the discrete segmented pre-impregnated layer.
The invention relates also to a method for producing a composite part comprising
At least a part of the duly formed composite part can be either
The fibers can be carbon, glass, aramid, ceramic or natural fibers and are embedded either
The invention will be better understood using the detailed description which is set out hereinbelow in light of the attached drawings in which:
The present invention relates to
Referring to
The continuous single-layer sheet 1 comprises
The continuous antiadhesive lining 2 will advantageously be composed of a paper support covered with a silicone-based layer. The continuous antiadhesive lining 2 will notably have the capacity to be easily separated from the layer of fibers 3, without leading to a migration of the fibers on the continuous antiadhesive lining 2.
The fibers of the layer of fibers 3 will be able to be composed either of carbon fibers, or of glass fibers, or of aramid fibers, or even ceramic or natural fibers.
The fibers of the continuous pre-impregnated layer 3 will be able to be embedded in a thermosetting resin, such as an epoxy, polyester, vinyl ester, bismaleimide, polymide or phenolic resin, or in a thermoplastic resin, such as a polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK) and polyamide (PA) resin.
The advantage of the present invention is that any continuous single-layer sheet 1 as described which is available in the market or originates from scraps from a method for manufacturing another composite part of large dimensions can be used in the method of the present invention. This is a considerable advantage, because the continuous single-layer sheets 1 already qualified in other methods can be used in applications in, notably, the aeronautical, medical or motor vehicle fields, thus facilitating the procedures for qualifying a new product, which can be very lengthy and costly in these fields. The re-use of material scrap originating from other methods for high-performance composite parts of large dimensions, notably in the aeronautical field, in a method for manufacturing high-performance composite parts with complex geometries, represents a considerable saving in the production of composite parts used in manufacturing an airplane.
The cutting station 12 will be able to be a cutting head, as illustrated in
The segments 4 are advantageously oriented in a single direction. Within the meaning of the present invention, “in a single direction” means “in a single direction to within 5°”. Such unidirectional segments in fact provide good mechanical characteristics, such as high tensile and flexing strengths for example. Preferably, the segments 4 comprise two opposite sides parallel to the longitudinal direction D, thus limiting the number of unnecessary cuts of the reinforcement fibers, thus maximizing their length in the segmented continuous sheet 5.
The segmented continuous sheet 5 obtained by the step b) comprises
Only the continuous segmented layer 3s, not the continuous lining 2, comprises segments 4 that are cut over its entire thickness and disposed in staggered fashion.
Moreover, the segments 4 will be able to have an identical form, notably a rectangular form. In a preferential embodiment of the invention, they will have a length preferably parallel to the longitudinal direction D, which lies between 10 mm and 100 mm, preferably substantially equal to 50 mm, and a width lying between 5 mm and 50 mm, preferably substantially equal to 8 mm.
Furthermore, the segments 4 are advantageously positioned in staggered fashion. This staggered positioning of the segments 4 in fact produces enhanced mechanical characteristics in the part to be formed.
The segmented continuous sheet 5 thus produced can then be packaged in the form of a reel 13 that has to be transferred to a rework machine where an operation of transverse cutting of the segmented continuous sheet 5 is performed so as to form one or more series of segmented discrete plies 8 as illustrated in
A structure, such as a ply or a laminate, is considered to be discrete if it has a geometry inscribed within a rectangle of length (L) and of width (I) with a length-to-width ratio (L/I) less than or equal to 20 (i.e. L/I≤20). A structure, such as a sheet or a strip, is considered to be continuous if it has a geometry inscribed in a rectangle of length (L) and of width (I) with a length-to-width ratio (L/I) greater than 20 (i.e. L/I>20).
Referring to
In this cutting step, the segmented continuous sheet 5 is paid out from a reel 13 to a cutting station 14 in which it is notably cut over its entire width and thickness, including the continuous antiadhesive lining 2, along two cutting lines 6, 7 that are parallel and oriented obliquely with respect to the longitudinal direction D. The cutting lines 6, 7 thus form a segmented discrete ply 8 in parallelogram form and, preferably, in rhomboid form. This segmented discrete ply 8 is notably defined by a main direction d1 which, in
The cutting station 14 making it possible to cut the segmented continuous sheet 5 into a series of segmented discrete plies 8 can notably comprise a table on the plane (X, Y) of which a cutting head moves, said head being able to be a rotary blade, a laser, a water jet or any other cutting head available on the market that makes it possible to accurately and cleanly cut the segmented continuous sheet 5 into segmented discrete plies 8.
Referring to
In this cutting step, the segmented continuous sheet 5 is cut over its entire width and thickness, including the continuous antiadhesive lining 2, along two cutting lines 6, 7 that are parallel and oriented obliquely with respect to the longitudinal direction D. The cutting lines 6′, 7 thus form a segmented discrete ply in parallelogram form. This segmented discrete ply 8 is notably defined by a cutting direction d2, which is parallel to the cutting lines 6, 7. This main direction d2 forms an angle of +45° with the longitudinal direction D of the segmented continuous sheet 5. Thus, in this segmented discrete ply 8, the fibers are oriented according to an angle α equal to +135° with the cutting direction d2.
Referring to
In this cutting step, the segmented continuous sheet 5 is cut over its entire width and thickness, including the continuous antiadhesive lining 2, along two cutting lines 6′, 7′ that are parallel and oriented in a cutting direction d3 at right angles to the longitudinal direction D. The cutting lines 6″, 7″ thus form a segmented discrete ply 8 in the form of a rectangle. This segmented discrete ply 8 is notably defined by a cutting direction d3, which is parallel to the cutting lines 6, 7. This cutting direction d3 forms an angle of 90° with the longitudinal direction D of the segmented continuous sheet 5. Thus, in this segmented discrete ply 8, the fibers are oriented according to an angle α equal to 90° with the main direction d3.
Other cutting angles could be envisaged without departing from the framework of the invention. Furthermore, the cutting lines 6, 7 are not necessarily parallel to one another, thus also being able to form segmented discrete plies 8 in triangular or trapezoid form. In particular, in other embodiments of the invention, the transverse cutting lines will be able to be oriented with respect to the longitudinal direction D such that, in each of the pre-impregnated unitary plies, the fibers will be oriented at +60°, or at −60°, at +30°, or at −30°, or even at 90° with respect to a main direction defined by the cut sides of the segmented discrete ply 8.
Hereinafter in this application, the segmented discrete plies 8 formed by transverse cutting of the segmented continuous sheet 5 will be able to be called “processed plies”, the two expressions being considered synonymous.
A segmented discrete ply 8 (or processed ply) obtained by the method described above has a discrete geometry inscribed within a rectangle of length (L) and of width (I) with a length-to-width ratio (L/I) less than or equal to 20 (i.e. L/I≤20). As illustrated in
The discrete segmented pre-impregnated layer 3ds—and not the discrete antiadhesive lining 2d—comprises segments 4 cut over its entire thickness and disposed in staggered fashion. The segments thus cut give the segmented discrete ply 8 a flexibility and drapability greater than most of the long-fiber unidirectional pre-impregnated plies available on the market. In a preferred variant, the segments have a geometry comprising two opposite sides parallel to the longitudinal direction (D) having identical dimensions within the segmented discrete ply. The geometry of the segments is inscribed in a rectangle with a length measured along the longitudinal direction (D) and a width measured in a direction at right angles to the longitudinal direction.
The length measured along the longitudinal direction (D) of the rectangle in which each segment 4 is inscribed can lie between 10 mm and 200 mm, preferably between 50 and 150 mm, more preferably between 70 and 130 mm or be substantially equal to 100 mm. The width of the rectangle in which each segment is inscribed can be less than or equal to the length and can lie between 5 mm and 100 mm, preferably between 8 and 50 mm or substantially equal to 10 mm. The lesser the width becomes, the more flexible the processed ply becomes in the direction normal to the longitudinal direction (D).
Cutting the segments in a direction transversal to the longitudinal direction (D) also reduces the length of the fibers and therefore, on the one hand, considerably increases the flexibility of the segmented discrete ply in a direction parallel to the ply and at right angles to the longitudinal direction (D), which can be used to produce composites with complex forms but, on the other hand, below a certain fiber length, that reduces the mechanical properties of the composite formed from such plies. It is therefore essential to correctly determine, according to the application and the fiber/matrix system used, the optimal length of the segments 4.
By contrast, cutting the segments parallel to the longitudinal direction (D) and to the direction of the fibers has only very little effect on the mechanical properties of the composite produced from such a processed ply, since the fibers are only very little damaged. The longitudinal cuts confer flexibility on the processed ply in the longitudinal direction (D) (that is to say a ply can be folded more easily around an axis parallel to the longitudinal axis (D)).
The greater the segment length becomes, the more effective becomes the transfer of strains between the resin (or matrix) and the fibers and the higher the mechanical properties become. This is done however to the detriment of the drapability of the processed plies in the direction normal to the longitudinal direction (D).
For example, the segments (4) can have a rectangular or trapezoidal form. In a preferred variant, the segments have a rectangular form, with the ‘small sides’ defining the width of the rectangle curved, preferably semicircular, forming a small concave side at one end of the segment and a small convex side at the other end, the small convex side matching the geometry of the small concave side. This geometry gives the segmented discrete ply greater flexibility in the plane of the ply, making it possible to bend the segments like a chain whose links formed by the segments are linked to one another by hinges formed by the small concave sides matching the small convex sides.
The discrete antiadhesive lining (2d) adheres sufficiently to the discrete segmented pre-impregnated layer (3ds) to ensure that the segments of the discrete segmented pre-impregnated layer 3ds do not move or drop when handling the processed ply. The discrete antiadhesive lining (2d) must however be easily removed when stacking the processed plies 8 to form a discrete segmented multilayer mat 80 composed of a stack of discrete pre-impregnated layers 3d comprising at least one discrete segmented pre-impregnated layer 3ds.
The segmented discrete ply 8 can have a rectangular (or square), parallelogram (or rhomboid), triangular or trapezoid geometry depending on the cutting angles (a). By controlling the cutting angle (α), it is possible to control the angle formed by the fibers with the sides cut according to the cutting angle of the segmented discrete ply 8. There are thus two clear reference frames for orienting the fibers according to a reinforcement angle (β) when producing discrete segmented multilayer mats 80 by stacking the segmented discrete plies 8:
By aligning the sides of the continuous strip or the cut sides, it is possible to control the sequence of reinforcement angles (β) in the stack forming a discrete segmented multilayer mat 80.
The segmented discrete plies 8 described above are used to manufacture a discrete segmented multilayer mat 80. As illustrated in
The discrete segmented multilayer mat 80 of the present invention is distinguished from the discrete multilayer mats of the prior art in that at least one of the (N+1) discrete pre-impregnated layers 3d, preferably all the (N+1) discrete pre-impregnated layers 3d, are discrete segmented pre-impregnated layers 3ds as defined above with reference to the pre-impregnated segmented discrete plies 8. They are also distinguished in that at least one discrete segmented pre-impregnated layer 3ds has a triangular, trapezoid or parallelogram geometry, preferably rhomboid geometry. A rectangle is a parallelogram with four right angles and a square is a rhomboid with four right angles. The geometry of the discrete segmented pre-impregnated layer 3ds can be a trapezium or parallelogram having at least two angles different from 90°.
Such geometries of plies are obtained in the manufacturing of segmented discrete plies 8 by cutting the segmented continuous sheet 5 along two cutting lines 6, 7 that are parallel to cutting directions (d1, d2, d3), each of the cutting directions forming a cutting angle (α) with the longitudinal direction (D). This is advantageous, because the side of the segmented discrete ply cut along the cutting direction (d1) forming an angle (α) defines a reference that then makes it possible to stack a segmented discrete ply 8 on a discrete pre-impregnated layer 3d, to precisely define a desired reinforcement angle (β) with respect to the direction of the fibers in the adjacent layers, by aligning the corresponding sides of the segmented discrete ply 8 and of the discrete pre-impregnated layer 3d. The reinforcement angle (β) is not necessarily equal to the cutting angle (α) because, as illustrated in
An automatic fiber placement (AFP) machine is optimized to manufacture parts of large dimensions and ill-suited to placing fibers or tapes on strips of small dimensions, as must often be used for parts with complex geometry. Since it is difficult to automize on an industrial scale the formation of sub-preforms and final preforms for parts with complex geometry and of a size that is generally too small for an AFP machine to be effective, the present invention has shifted the automation step further upstream of the formation of the sub-preform or final preform. Thus the step of cutting of the segments 4 on a continuous single-layer sheet (1) fed continuously along the longitudinal direction (D) regardless of the desired reinforcement angle (β).
Thus, for example, if the cutting angle (α) is 90°, it is easy to stack the segmented discrete ply 8 with a reinforcement angle (β) of 0° or 90°, simply by aligning a cut side or a non-cut side with the longitudinal direction (D), for example by aligning it with the discrete pre-impregnated layer on which the segmented discrete ply 8 is laid, by turning it or not by 90°. In another example, by cutting a rhomboid with a cutting angle α=45°, it is easy to stack the segmented discrete ply 8 so as to obtain a reinforcement angle β=0° or 45°.
In a first variant of the present invention, a discrete segmented multilayer mat 80 can be produced from a continuous strip of discrete stacks as illustrated in
A continuous strip (15) is supplied, composed of a continuous single-layer sheet 1 or of a segmented continuous sheet 5, or even a continuous antiadhesive lining (2) as defined above in relation to the method for manufacturing a segmented discrete ply 8. A series of stacks each composed of N discrete pre-impregnated layers 3d stacked one on top of the other, in which N∈N and N≥1, is deposited on a face of the continuous strip 15 not comprising the continuous antiadhesive lining 2 or on the continuous antiadhesive lining (2) if the continuous strip (15) is formed by a continuous antiadhesive lining (2), to form the continuous strip of discrete stacks. Each stack is deposited on the continuous strip by the following steps.
N discrete pre-impregnated plies are supplied, each comprising, on the one hand,
Next, the N discrete pre-impregnated plies are deposited sequentially on the continuous strip 15 by removing the discrete antiadhesive lining 2d from each discrete pre-impregnated ply, before laying a new discrete pre-impregnated ply thereon and optionally compacting duly stacked discrete pre-impregnated plies, such that
According to the present invention, at least one discrete pre-impregnated ply, preferably all the discrete pre-impregnated plies, are segmented discrete plies 8 obtained by the method described above, in which the discrete pre-impregnated layer 3d is formed by the discrete segmented pre-impregnated layer 3ds.
A series of discrete segmented multilayer mats 80 each comprising (N+1) discrete pre-impregnated layers 3d can be obtained simply by cutting the continuous strip 15 of the continuous strip of discrete stacks between two adjacent discrete stacks, as illustrated in
Referring to
In a first step, illustrated in
The idea of this method of the present invention is to deposit, on a face of the continuous strip 15 not comprising the continuous antiadhesive lining 2, a series of stacks of N discrete pre-impregnated plies laid side-by-side on the continuous strip 15 to form a continuous strip 15 of discrete stacks which will be able to be wound to form a reel that is easy to store and transport.
When necessary, the continuous strip 15 can be cut between two adjacent discrete stacks to obtain discrete segmented multilayer mats 80. Each discrete stack is formed by N discrete pre-impregnated layers stacked one on top of the other, of which at least one, preferably all, the N discrete pre-impregnated layers 3d of each stack is a discrete segmented pre-impregnated layer 3ds. The number N of discrete pre-impregnated layers can vary from one stack to the other, but, generally, it is preferable for all the discrete stacks of one and the same continuous strip 15 of discrete stacks to be formed by a same number N of discrete pre-impregnated layers 3d, 3ds.
In a second step of this method of the present invention, a specific variant of which is illustrated in
This depositing will be able to be done according to a procedure represented in
In a third step, illustrated in
By turning each of the one to N discrete segmented pre-impregnated plies 8 before depositing it on one and the same discrete stack, the sequence of reinforcement angles (β) of the fibers of each ply can be varied. By selecting the cutting angle (α), it is easy to obtain a reinforcement angle (β) with the fibers of an adjacent discrete (segmented) pre-impregnated layer 3d, 3ds by aligning one side of the segmented discrete ply 8 cut according to the cutting direction (d1, d2, d3) with a side of the adjacent discrete (segmented) pre-impregnated layer (3d, 3ds).
In
Segmented discrete plies 8 can be stacked in parallelogram form or preferably in rhomboid form, comprising cutting angles 6, 7, forming a cutting angle α=45°, with reinforcement angles β=0° or 45° as illustrated in
It is thus possible, for example, to form a unidirectional stack, with the fibers of all the discrete pre-impregnated plies oriented at 0° suited to the production of a part with complex geometry which will above all be stressed in the longitudinal direction (D). It is also possible, for example, to form a quasi-isotropic stack with sequences of reinforcement angles of (+45°/0°/−45°/90°) and the mirror thereof for each discrete stack unit each composed of 4 discrete pre-impregnated layers. Any other sequence of reinforcement angles (β) is possible according to the geometry and the specifications of the part to be produced.
In a fourth step, illustrated in
By cutting the continuous strip 15 of the continuous strip of discrete stacks between two adjacent discrete stacks, a series of discrete segmented multilayer mats 80 is obtained. Each discrete segmented multilayer mat thus obtained is therefore formed by (N+1) discrete pre-impregnated layers, of which N discrete pre-impregnated layers are formed by the N discrete pre-impregnated plies of each discrete stack+a discrete pre-impregnated layer is formed by the continuous strip 15 which has been cut (see
Referring to
Manufacturing a continuous strip 15 of the continuous strip of discrete stacks as illustrated in
An alternative method for manufacturing discrete segmented multilayer mats 90 comprises the supply of (N+1) discrete pre-impregnated plies each comprising, on the one hand,
A first discrete pre-impregnated ply 3d is laid on a support on the antiadhesive lining, thus exposing the discrete pre-impregnated layer 3d. Next, N discrete pre-impregnated plies are deposited sequentially on the first discrete pre-impregnated ply 3d by removing the discrete antiadhesive lining 2d from each discrete pre-impregnated ply, before laying a new discrete pre-impregnated ply thereon. It is optionally possible to compact the duly stacked discrete pre-impregnated plies each time one or more is or are added. Thus, a stack is obtained such that
The method for manufacturing a discrete segmented multilayer mat 90 of the present invention is distinguished from the methods of the prior art in that at least one discrete pre-impregnated ply, preferably all the discrete pre-impregnated plies, are segmented discrete plies 8 as described above, the discrete pre-impregnated layer 3d of which is formed by the discrete segmented pre-impregnated layer 3ds.
In a preferred variant of the two methods described above, the fibers of a given discrete pre-impregnated layer 3d form a reinforcement angle (β) lying between 0 and 180° (i.e. β=0 to 180°) with the fibers of a discrete pre-impregnated layer 3d of the same discrete stack which is adjacent to and in contact with the given discrete pre-impregnated layer 3d. If all the discrete pre-impregnated layers 3d of a discrete segmented multilayer mat are the discrete segmented pre-impregnated layers 3d for which the cutting angles are 90° or ±45°, then it is preferable for the reinforcement angles (β) to be equal to the cutting angle (α) plus a multiple (n) of 45° with n=0 to 4 (i.e., β=α+n 45°, with n=0 to 4). Thus, it is possible to control the reinforcement angle (β) of each discrete segmented pre-impregnated layer 3ds when it is being stacked, by aligning the corresponding sides of the segmented discrete ply 8 and of the discrete segmented pre-impregnated layer 3ds on which the segmented discrete ply 8 is laid.
The discrete segmented multilayer mat 80 of the present invention makes it possible to produce high-performance composite parts that have complex geometries. By virtue of the segments 4 cut in the discrete segmented pre-impregnated layers 3ds, the discrete segmented multilayer mat 80 can be adapted to and match complex mold forms, while keeping a good alignment of the reinforcement fibers along their respective reinforcement angles (β).
With this method, high-performance composite parts of complex geometry with long fibers oriented according to any desired scheme can be easily produced. For example, a quasi-isotropic composite part can be produced with a discrete segmented multilayer mat 80 or a final preform 90p, the reinforcement angles (β) of which vary between the discrete pre-impregnated layers 3d between 0°, ±45°, and 90°. Alternatively, a quasi-orthotropic composite part can be produced with a discrete segmented multilayer mat 80 or final preform 90p of which all the fibers are oriented according to a same reinforcement angle (β) of 0°, thus forming a unidirectional composite (UD). Finally, between these two extreme configurations, any hybrid configuration can be obtained with a discrete segmented multilayer mat 80 or a final preform 90p, the reinforcement angles (β) of which vary between the discrete pre-impregnated layers 3d according to the locally desired mechanical properties.
Discrete segmented multilayer mats 80 were produced from continuous single-layer sheets 1 of epoxy reinforced by unidirectional carbon fibers of aeronautical grade available from Hexcel. Discrete segmented pre-impregnated plies 8 according to the present invention were produced by cutting segments 4 in the continuous pre-impregnated layer 1. The segments are rectangular with dimensions of 50×8 mm disposed in staggered fashion.
Quasi-isotropic discrete segmented multilayer mats 80 were produced with four discrete segmented pre-impregnated plies 8 thus obtained, with a sequence of reinforcement angles (β) of 0°/+45°/90°/−45°. Quasi-isotropic composite plates were produced by compression molding. The samples are referred to in
Unidirectional discrete segmented multilayer mats 80 were produced with four discrete segmented pre-impregnated plies 8 thus obtained, with all the fibers oriented in the same direction with a reinforcement angle (β) of 0°. Unidirectional composite plates (=UD) were produced by compression molding. The samples are referred to in
Composite plates were produced by compression molding with sheets of SMC available from HEXCEL under the name of HexMC Aero, 8552. The samples are referred to in
Finally, unidirectional composite plates (=UD) were produced by compression molding from continuous single-layer sheets 1 used to produce the segmented discrete plies 8, but without cutting segments. The samples are referred to in
Tensile samples (=“dog-bone tensile samples”) were cut in each of the INV-Quasi-iso, CEx-SMC, INV-UD and CEx-UD plates with, except for the CEx-SMC sample, the central part parallel to the fibers oriented at the reinforcement angle (β) of 0°. They were tensile tested according to ASTM D3039 with a tensile strain applied parallel to the reinforcement angle (β) of 0°. The Young's modulus (E) and tensile strength (or) at break results are represented in the graph of
By comparing the tests performed on the unidirectional samples, INV-UD and CEx-UD, it can be seen that the Young's modulus drops by only −3% and the breaking strain (σr) by −4% for the INV-UD composites manufactured from unidirectional discrete segmented multilayer mats 80 formed by discrete segmented layers compared to the CEx-UD unidirectional composites (i.e. not segmented) which are the maximum benchmark in aeronautics. It is therefore possible to conclude therefrom that the segmentation of the continuous pre-impregnated layer 3 has only little effect on the rigidity and the breaking strength of the parts thus formed. By contrast, the segmentation makes it possible to produce unidirectional composite parts of much more complex geometries than is currently possible with stacks of non-segmented continuous single-layer sheets 1 corresponding to the CEx-UD test.
The SMCs are, for the time being, practically the only solution for producing long-fiber composite parts having a complex geometry used in the aeronautical industry. By comparing the tensile mechanical properties of the CEx-SMC samples in which the orientation of the fibers is random, with the INV-Quasi-iso samples (=+45°/0°/−45°/90°), an increase of 24% is observed in the Young's modulus (E) and of 50% in the breaking strength (Cr) for the INV-Quasi-iso plates, which is considerable. It is therefore possible to conclude therefrom that, for a comparable drapability, making it possible to manufacture parts of comparable geometrical complexities, and of quasi-isotropic properties, the composites produced from discrete segmented multilayer mats 80 according to the present invention have mechanical properties considerably greater than those of composites produced from SMC.
In addition, the spread of results of the mechanical properties of composites produced from SMC is much greater than for the composites produced from discrete segmented multilayer mats 80 according to the present invention. This can clearly be seen by comparing the error bars (standard deviation) indicated in
These results show that the discrete segmented multilayer mats 80 of the present invention, obtained from discrete segmented pre-impregnated plies 8 according to the present invention, make it possible to manufacture high-performance and long-fiber composite parts combining both
It is estimated that, in aeronautics, the production of large composite parts with simple geometry from stacks of pre-impregnated single-layer sheets generates approximately 70 kg of scrap per passenger airplane. This scrap is generally badly recycled. With the method of the present invention, it is possible to reuse—and not recycle—the scrap to manufacture other high-performance parts which will fly in the airplane. This represents an enormous step forward in the management of the materials in aeronautics in particular.
A stack of woven plies (W—0/90, W=weave) gives a little more flexibility to the preform, depending on the type of weave (e.g. satin 8), but not significantly.
In the bottom right corner, there are SMCs, which allow the formation of parts with complex geometries, but with disappointing mechanical properties.
Finally, on the right, well above the SMCs, there are final preforms according to the present invention, formed from segmented discrete plies 8 in various sequences of reinforcement angles (INV—0°, INV—0/90, INV—Q.iso). These preforms have mechanical properties close to those obtained from UD prepregs, but with a substantially greater flexibility, which allows them to match complex mold forms and form composite parts with complex geometry.
The graph of
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2101805 | Feb 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/054131 | 2/18/2022 | WO |
