Abstract:
The present invention relates to a dashboard crossmember ( 1 ) for a vehicle, including a crossbar ( 2 ) as well as at least one connection flange ( 3 ) designed to enable said crossbar to be attached to the body of said vehicle, said crossmember being characterized in that said crossbar ( 2 ) includes a bearing web ( 10 ) made of a fiber-reinforced composite material including continuous libers ( 7 ) arranged within a matrix ( 8 ), and preferably results from the assembly of a plurality of preformed basic parts ( 13, 14, 15 ) each produced by bending a composite material lap piece ( 11 ) about a single direction of the space so as to avoid overstretching or dislocating the network of fibers ( 7 ) of each of said laps.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2013/061387, which was filed Jun. 3, 2013 and which claims priority of French application 1255342 filed on Jun. 7, 2012, the content (text, drawings and claims) of which are incorporated here by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to the general domain of crossmembers used in vehicle construction, especially automotive vehicles, and more specifically to crossmembers which are mounted to the vehicle body, transversally to the drive direction, to provide means for mounting the dashboard of the vehicle as well as various accessories such as climate control unit, steering column, glove compartment, etc. 
     It is known that crossmembers generally comprise a crossbar made of steel tubing which extends between two mounting flanges securing the crossbar to the body of the vehicle, and which is usually also supported by a central strut attached to the floor of the vehicle. 
     Although known crossmembers generally perform satisfactorily, in particular because of their rigidity, they may nevertheless have some drawbacks. 
     In particular, their fabrication may require heavy, cumbersome and costly equipment, including, for instance, shear presses and welding machines, as well as stamping presses specially equipped with the necessary punches and dies. 
     In addition, the relatively heavy weight of known crossmembers complicates their manipulation during assembly and contributes to make the vehicle heavy, to the detriment of the vehicle&#39;s fuel consumption. 
     SUMMARY 
     Consequently, the goal of the invention is to propose a new crossmember for a vehicle dashboard with a structure which is both light in weight and high in mechanical strength as required for the application. 
     Another goal of the invention is to propose a new fabrication method for dashboard crossmembers which is simple, reproducible, fast and inexpensive. 
     The goals of the invention are achieved by means of a dashboard crossmember for a vehicle, the crossmember comprising a crossbar and at least one connecting flange designed for mounting the crossbar to the body of the vehicle, the crossmember being characterized in that the crossbar includes a carrier core made of a first fiber-reinforced composite material which extends over most of the length, and by preference over the whole length of, the crossbar, the first composite material comprising continuous fibers, arranged in a matrix, and running without interruption over the whole length of the carrier core. 
     The goals of the invention are also achieved by means of a fabrication method for a vehicle dashboard crossmember which must include a crossbar and at least one connecting flange for mounting the crossbar to the body of the vehicle, the method being characterized in that it comprises a step a) in which the crossbar is created at least partially by curving or bending a piece of sheet of composite material around one direction of space in order to avoid overstretching or dislocating the fiber network of the sheet. 
     Advantageously, the invention provides means for producing a crossmember with the main part, the crossbar, made of an especially light composite material, at least over part of its length, and more in particular in the transverse direction of the vehicle on which it is used, which is lighter than steel, but nevertheless very strong because of the presence of appropriately arranged reinforcement fibers. 
     Advantageously, the method according to the invention is specifically based on employing the composite material and preserving the homogeneity of its structure, and consequently its mechanical properties, without creating specific weak zones in which the matrix is depleted of its fibers by heavy stamping or deep drawing operations. 
     Furthermore, the invention provides means for producing the crossbar, and, more generally, the crossmember, with simpler tooling, potentially consuming less energy, while using relatively little raw material, and by means of relatively simple and fast operations (shearing, bending and assembly), due in particular to the ease of transforming composite materials, which renders the method especially compatible with the mass production throughput required in the automotive industry, and more specifically with the automation used in the industry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objectives, characteristics and advantages of the invention will be presented in more detail in the following description, with reference to the attached drawings, provided strictly for illustrative and non-limiting purposes, among which: 
         FIG. 1  is an exploded perspective view illustrating an example of a dashboard crossmember. 
         FIG. 2  is a perspective view illustrating the assembled crossmember of  FIG. 1 . 
         FIGS. 3A, 3B and 3C  illustrate the problem of overstretching the composite sheet observed during stamping of a complex form, a problem which is resolved with the method according to the invention. 
         FIGS. 4A to 4D  are perspective views illustrating a first variant of the crossmember, starting from an assembly of individual pieces made of composite material preformed through bending. 
         FIGS. 5A to 5E  are perspective views of a second variant of the crossmember, starting from an assembly of individual pieces made of composite material preformed through bending. 
         FIGS. 6A to 6C  are perspective views illustrating a variant of the fabrication method of the crossmember. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to a dashboard crossmember  1  for a vehicle, the crossmember comprising a crossbar  2  as well as connecting flanges  3 ,  4  designed for mounting the crossbar to the body of the vehicle (not shown). 
     The invention relates also to a vehicle (not shown), and in particular an automotive vehicle, equipped with a dashboard crossmember according to the invention. 
     By preference, as illustrated in  FIGS. 1 and 2 , crossmember  1  comprises at least two connecting flanges,  3 ,  4  arranged lengthwise on both sides of the crossbar  2 , at the extremities of the the crossbar, so that the flanges can be attached to both sides (left and right) of the vehicle body. Once mounted, the crossmember extends transversally to the drive direction of the vehicle, and approximately over the whole width of the vehicle. 
     By preference, the crossmember includes a strut  5  anchored to the floor of the vehicle and supporting the crossbar  2  in an intermediate position, at a distance from the two connecting flanges  3 ,  4  as well as, by preference, a mounting fork  6 , which is by preference deformable in case of impacts, and for instance made of steel, connecting the crossmember, and, more particularly, crossbar  2  to a forward portion of the vehicle body, approximately facing the steering column. 
     By convention, and for ease of description, the horizontal forward/reverse driving direction of the vehicle is designated by “X”, the transverse direction of the vehicle, which corresponds in general with the lengthwise extension of the crossmember  1  and more in particular of the crossbar  2 , is designated by “Y,” and the vertical direction, which forms with the preceding directions a direct trihedral, by “Z”. 
     The crossbar  2  is made partially or completely, and more particularly over at least a portion of its length, and therefore over at least a portion of the width of the vehicle in which it is mounted, of at least fiber-reinforced composite material containing fibers  7 , by preference continuous fibers, arranged in a matrix  8 . 
     Fibers  7  can be glass, carbon or aramid fibers, etc. 
     The matrix is made by preference of polymer material, such as polypropylene or polyamide, and more preferentially of resin type thermoplastic polymer. 
     The advantage of the composite material is that the crossbar  2 , and therefore the crossmember  1  is lighter than a metallic construction, while maintaining, thanks to reinforcement fibers  7 , a high elasticity module, great rigidity, and high resistance against traction, bending and buckling under lateral compression stresses or shearing forces. 
     By preference, the crossbar  2  has a hollow or tubular structure, covered by a relatively thin composite skin, with low density compared to metal, but with good rigidity and toughness. 
     By preference, the form and dimensions of the crossmember  1 , and more in particular of crossbar  2 , will be studied in order to limit vibrations, and in particular the occurrence of resonance in the spectrum of the vibrations generated by the engine or the movement of the vehicle. 
     By preference, the crossbar  2  comprises a carrier core  10  made of a first fiber-reinforced composite material which extends over most of its length, and by preference over the whole length L2, of the crossbar, and more particularly over at least 50%, 75% or 90% of the length L2. 
     Advantageously, the carrier core  10  can form a beam type support structure, capable of supporting the crossbar over its length, and in particular of absorbing the compression, traction, torsion or flexion stresses that the latter is subjected to inside the vehicle. 
     In a particularly preferential manner, the crossbar can be made entirely of one or more fiber-reinforced composite materials, without having a metallic reinforcement structure such as a rod, a beam, a tube or a shell. 
     In a particularly preferential manner, the composite material of the carrier core  10  contains continuous fibers  7 , each extending uninterrupted over the whole length occupied by the fiber-reinforced composite material, and more particularly over the whole length L10 of the carrier core, and therefore, for instance, by preference over the whole length of the crossbar  2 . 
     Advantageously, the use of continuous fibers, advantageously arranged parallel to each other and by preference straight and parallel to the generating line of the carrier core  10 , forming in this way a regular network of warp yarn inside the first composite material, as partially illustrated in  FIGS. 4A-5E , results in a particularly effective lengthwise reinforcement of crossbar  2 , which is free of weak zones, because each fiber is made of a single wire from one end to the other of core  10 , and in general if necessary of crossbar  2 , covering in the manner of a tension rod the whole portion that is effectively subjected to stresses. 
     Obviously, it can also be envisaged that the first composite material constituting core  10  comprises also “weft” fibers  7  arranged across the lengthwise “warp” fibers  7 , and by preference perpendicular to the latter. 
     If necessary, the fibers  7  can also form a woven or non-woven textile type crossed network. 
     Although numerous fiber arrangements can be envisaged, by varying the relative disposition and orientation of the fibers  7 , a fiber network can be implemented comprising approximately 90% lengthwise fibers at 0° (according to X, considering a flat development), and 10% transverse fibers at 90° degrees (according to Z, considering a flat development). 
     By preference, the distribution of the continuous lengthwise fibers, considered within the width of the crossbar  2  at the orientation of the fibers, will be regular and homogenous over the whole width of the crossbar  2 , if necessary both in sheet  11  used to make the part prior to its forming as well as on the finished part obtained by setting the volume of the sheet  11 , and this in order to ensure high strength and homogeneous behavior in all points of the crossbar  2 . 
     By preference, the carrier core  10  is made over most of its length L10, and by preference over the whole length L10, of one continuous composite sheet  11  of the same thickness E11. 
     The sheet  11  will have by preference continuous fibers  7 , which extend at least lengthwise or transversally of the sheet. 
     Advantageously, a homogenous and particularly thin structure of core  10  can be obtained due to the fact that a single enveloping layer of composite, preferentially with continuous fibers, is in practice sufficient to give core  10 , and by extension crossbar  2 , specifically in the central portion of the latter, the necessary strength and self-supporting characteristics. 
     Although it is not excluded that sheet  11  can be superimposed locally, in particular to connect the individual pieces  13 ,  14 ,  15 ,  16 ,  17  to each other such as illustrated in  FIGS. 4D and 5E , the overlap of sheets  11  will cover by preference only a small part of the surface of each sheet  11  placed in contact in this manner, since the unitary thickness E11 and the composition of each sheet are chosen so as to intrinsically confer to it the required mechanical properties. 
     In a particularly preferential mode, crossbar  2  will in general not comprise more than three, and by preference never more than two, layers of sheet  11  overlapping each other in thickness when in contact with each other. 
     This simplified structure which eliminates the need for a multilayer arrangement containing a multitude of distinct superimposed sheets, not only preserves the light weight of the crossmember  1 , but reduces also the consumption of raw material needed for its fabrication, and reduces the cycle time required to create each piece, and more particularly the carrier core  10 , because it is sufficient to form each time, directly and in a single pass, one existing single layer of sheet  11 , by preference containing continuous fibers, and simply precut to the desired dimensions. 
     By preference, as illustrated in  FIGS. 1 and 2 , the carrier core  10 , and more generally the crossbar  2 , is coated, over its whole length or part thereof, on at least one of its faces, with a non-metallic reinforcement layer  12 , made by preference by over-molding, in a second material, different from the first composite material constituting the carrier core  10 . 
     The over-molded reinforcement layer  12  can be made, for instance, of a polymer material, such as polypropylene or polyamide, if necessary reinforced with short non-continuous fibers, with a length of 10 mm to 25 mm, or even ultra-short fibers measuring between 2 mm and 4 mm. 
     Advantageously, such material is in fact suitable for injection over-molding on the carrier core  10 , which forms the true functional armature of the crossbar  2 . 
     Such a coating layer can be used to add to crossmember  1 , and more particularly to crossbar  2 , elements providing additional functions which do not contribute, or only marginally contribute, to the structural strength of crossbar  2 , such as for instance leg or eyelet mounting interfaces, used to mount crossmember accessories such as climate control group, radio, glove compartment, etc. 
     Advantageously, all or some of the interface surfaces, until now made of metal, can be replaced by elements made of (the second) composite material, in order to make the crossmember even lighter. 
     The crossmember  1  can therefore have a dual layered structure, differentiated in its composition and function, comprising a first layer of carrier armature formed by core  10 , by preference by means of at least one sheet  11  with continuous long fibers, and a second reinforcement layer  12  providing for instance additional mounting interfaces, by preference created by over-molding with a short fiber composite. 
     By preference, where the connecting flanges  3 ,  4  are made of a fiber containing composite material, the material can be identical or different from the material of core  10 . 
     Advantageously, even the connection points at the extremities of crossbar  2  can be made of composite material, rather than massive metal alloy, so that the structure of crossmember  1  is comprised over its whole length of a solidly connected sub-assembly made mostly if not totally of composite material. 
     More generally, according to a preferential characteristic which can constitute an invention by itself, as illustrated in  FIGS. 4A-5E , crossmember  1  comprises an assembly of preformed individual composite parts  13 ,  14 ,  15 ,  16 ,  17  of different form and made separately from a specific patch of fiber-reinforced composite material. 
     The individual parts  13 ,  14 ,  15 ,  16 ,  17  can have different fiber densities and/or orientations. 
     By preference, the individual parts are formed each from a single sheet  11 , style patch, comprising by preference continuous fibers  7  which run uninterrupted from one cut edge of the patch to the opposite cut edge, giving increased strength to the individual parts, as explained above. 
     By preference, the individual parts are assembled so that the direction of the continuous fibers of the patch comprising one of the parts is parallel to the direction of the continuous fibers of the patch constituting the adjacent part. 
     Advantageously, this structure gives to the individual parts, and therefore to the assembly they form once regrouped, the ability to maintain collectively a relatively high strength, notwithstanding the interruptions of the patches. 
     The assembly of individual parts  13 ,  14 ,  15 ,  16 ,  17 , preferably in direct contact with each other, can be created through any suitable process, and specifically by welding, for instance hot welding, ultrasonic welding or laser welding, by gluing, for instance with epoxy or by means of a structural glue such as polyurethane, even by interlace stitching of fibers of one patch  11  with the fibers of the adjacent patch, in case of need through the intermediary of added suturing fibers stitched for this purpose through the patches. 
     By preference, at least some individual parts will have flat mounting surfaces  20 , in the style of peripheral flaps, which provide a good mounting surface on the adjacent individual part. 
     Assembly can of course be facilitated by the fact that the preformed and rigid individual parts  13 ,  14 ,  15 ,  16 ,  17 , which are easy to handle, can have two by two conjugated forms, produced by cutting or bending, simplifying their juxtaposition, superimposition, or encasement. 
     Advantageously, the breakdown of some parts of the crossmember  1 , and specifically of the extremities forming the mounting flanges  3 ,  4 , in several individual pieces  13 ,  14 ,  15 ,  16 ,  17  of relatively simple form makes it possible to create particularly complex general forms, if necessary non-developable forms, which may be necessary because of the arrangement of the vehicle and therefore of the environment in which the crossmember  1  is to be integrated, or by the vibrational properties required of the crossmember. 
     The working volume of crossmember  1  can indeed be created according to a first direction in space (for instance X) by a first individual part (for instance part  14 ), and according to a second direction (for instance Z) by a second part (for instance part  16 ) which comes in contact with the first, advantageously reinforcing the assembly. 
     Advantageously, the breakdown in individual parts makes it possible to accommodate deviations ΔX, ΔZ of the generating line of crossmember  1 , and more in particular of the crossbar  2 , according to one or more, and if necessary conjugated, directions of space, and more particularly of the directions perpendicular to the main direction (Y) of lengthwise extension of the crossbar  2 , forming in this way a non-straight crossmember (or crossbar) having one or more elbows  21 , without making the structure of the composite material fragile by overstretching the matrix or by a risky modification of the fiber distribution, such as illustrated in  FIGS. 3A, 3B, and 3C  to facilitate the comprehension of these phenomena. 
     In addition, individual parts  13 ,  14 ,  15 ,  16 ,  17  can be created by simple bending or folding of the initially flat sheets  11 , corresponding with developed parts of relatively simple contours, in this way simplifying the fabrication of the parts, and limiting the clippings, saving raw material, but also fabricating the raw material without degrading its properties, and in particular preserving the regular distribution and length of fibers  7 , especially of long fibers. 
     Bending and folding can occur for instance by placing the sheet on an appropriate complementary form, or by “soft” forming the sheet, without overstretching, according to a developable surface, between a male and a female mold. 
     More generally, considered individually, each individual part  13 ,  14 ,  15 ,  16 ,  17 , corresponds by preference with a developable surface, even if their assembly creates by preference a general part of non-developable form, and in particular having one or more elbow  21  type transversal deviations. 
     According to a first variant of implementation mode corresponding with the example illustrated in  FIGS. 4A-4D , a dome  13  ( FIG. 4C ), for instance made by bending a rectangular patch, if necessary completed by folding in order to obtain a U or Ω shaped half cylinder, can be assembled ( FIG. 4D ) on a sole  14  ( FIG. 4A ), here having two folding lines  22  forming a ramp in the “Z” direction with three successive secant planes  23 ,  24 ,  25 , whereby the dome  13  is preferably glued by means of its flaps  20  on the first plane  23 , so that the assembly of the dome  13  and the sole  14  extends in the Y-direction in the form of a tunnel forming the central portion of the crossbar  2 , and more particularly of the carrier core  10 , which connects with the second opposite mounting flange  4 . 
     More generally, no matter which implementation variant is envisaged, the crossmember and more particularly the crossbar  2  and especially the carrier core  10  and/or the mounting flanges  3 ,  4  can be formed advantageously by at least one individual part  13 , and by preference by assembling several individual parts  13 ,  14 ,  15 ,  16 ,  17  made of fiber-reinforced composite material each having an open developable form compatible with their fabrication by bending and/or folding. 
     For this reason, by defining individual parts, which even when completed, but if necessary before their assembly with other individual parts, have a residual opening, and therefore do not wrap around or fold back on themselves, so that their contour around the generating axis is not totally closed, access is maintained advantageously for inserting and retracting the bending/folding tool, which facilitates the fabrication of the individual parts, eventually in a single pass, resulting therefore in productivity gains. 
     In particular, if the first composite material comprises at least a pattern of continuous fibers  7  parallel to each other, preferably parallel to the Y direction of lengthwise extension of the crossbar  2 , and if necessary constituting the majority if not the total pattern of the sheet  11 , one of the individual parts  13 ,  15 ,  17  can have by preference one or more arcs and/or folds  22  with the bending or folding axis in line with the fibers  7 . 
     Advantageously, such disposition maintains the integrity of the material, and especially preserves the regular disposition of fibers, in particular around the bending/folding axis, while providing a part which is both rigid, because of the created volume, transversally to the fibers, by the folds and/or arcs, and lengthwise resistant to traction, in the direction of the fibers  7 . 
     On the other hand, it can be envisioned bending or folding sheet  11  according to a bending/folding axis perpendicular to the long lengthwise fibers, this can be the case for sole  14  ( FIG. 4A ). 
     An elbow  21  can be formed at the extremity of the crossmember, here with an offset ΔX, due to the inclined plane  24  of the sole  14 , integrating the mounting flange  3 , by inserting between on the one hand, the extremity of dome  13  and on the other hand inclined plane  24  and lower plane  25  of sole  14 , a shoulder  15  ( FIG. 4B ), here in the form of a beveled parallelepiped, in which advantageously mounting holes  26  can be made in the flaps  20 , and advantageously having a conjugated inclined plane to the inclined plane  24  against which it is mounted. 
     Each of these three individual parts  13 ,  14 ,  15  can also constitute one or more faces of a box of complex form, meeting the geometric, dimensional and functional specifications of the mounting flange  3  and of crossbar  2 . 
     According to a second variant embodiment illustrated in  FIGS. 5A-5E , in a similar manner a dome  13  ( FIG. 5D ) can be assembled ( FIG. 5E ) on a sole  14  ( FIG. 5A ), and flange  3  can have the form of a cheek comprising at least one angle plate  16  ( FIG. 5B ) of which the cut line of one of its branches corresponds by preference with the transverse section delimited by dome  13 , as well as a clip  17  ( FIG. 5C ), which is for instance rectangular in shape, and placed by preference in the hollow of angle plate  16  to back up the branches, and comprising mounting holes  26  ( FIG. 5E ). 
     In this way, a double elbow can be made, and a double offset ΔX, ΔZ, respectively by the inclination in depth of plane  24  of sole  14  and by vertically offsetting the cut line of the angle plate  16  covering the dome  13  relative to the vertically median plane of the angle plate and/or relative to the vertical location of the mounting clip  17 . 
     It is understood that both extremities of the crossmember  1  can be constructed in the same manner. 
     Of course, a person skilled in the art will be able to adapt the invention to his needs by isolating or combining all or part of the above mentioned characteristics. 
     The invention also relates to a method for fabricating a dashboard crossmember  1  for a vehicle, which must be provided with a crossbar  2  and at least one mounting flange  3 ,  4  designed for mounting the crossbar to the body of the vehicle. 
     According to the invention, the method comprises a step a) in which the crossbar  2  is formed. In this step the crossbar is made at least partially by curving or folding a piece of a sheet  11  (patch) of composite material around a single direction of space in order to avoid overstretching or dislocating the pattern of fibers  7  in the sheet. 
     Advantageously, this method maintains the structural integrity of the composite sheet  11  during the controlled form modification of the sheet, while avoiding that this forming process, by bending and or folding, is causing tearing or brittleness by depleting matrix  8  of fibers  7 , or by plastic elongation, or by displacing fibers  7 . 
     The parts obtained are therefore particularly homogenous and robust, since the distribution of fibers  7  inside matrix  8  is preserved and guaranteed in reproducible manner. 
     Advantageously, bending, and if necessary folding, are steps which by preference are carried out hot (taking into account the vitreous transition temperature of matrix  8 ). From a dimensional point of view of the developed sheet, they remain neutral transformations, since fibers  7  spontaneously align themselves according to the path of the neutral fiber running through the sheet  11 . 
     Of course, it can be envisaged forming several arcs by bending, and/or several folds  22  by more pronounced folding, whereby the arcs and/or folds by preference run in parallel directions in the same sheet  11 . 
     As an example, in an initially flat rectangular patch, two folds  22  can be made in the Z direction to form sole  14  ( FIG. 4A ), or an arc with large curvature revolving around the Y direction to form dome  13  ( FIG. 4C ). 
     Furthermore, such bending and/or folding operations (and cutting, before or after) are simple transformations, which can be carried out under low stress and/or temperature conditions, therefore the tooling can be simplified, made less massive, and less expensive than the tooling employed for fabricating, and in particular for stamping metal. 
     As detailed above, the method comprises by preference a step (b) in which the individual parts are formed. In this step several distinct and rigid individual parts  13 ,  14 ,  15 ,  16 ,  17  are made, by preparing several pieces of sheet  11  of composite material, by preference reinforced with continuous fiber, then by giving each part a predetermined form, followed by a construction step (c) in which the preformed individual parts  13 ,  14 ,  15 ,  16 ,  17  are assembled on the crossbar  2  in order to reconstitute one or more mounting flanges  3 ,  4  in one or both extremities of the crossbar  2 . 
     It is understood that if necessary all or a number of individual parts can be employed to form the crossbar  2  and/or to integrate the flange(s) in the bar. 
     Of course, each individual part can be formed preferably by curving or folding its patch ( 11 ) around a single direction of space, if necessary with several parallel folds  22 , so as to avoid overstretching or dislocating the fiber  7  network of the sheet  11 . 
     It is to be noted that because of the simplicity of the method, the cycle time for forming a crossmember  1  starting from parts formed from unique single layer sheets, can be reduced to a few minutes, even between 1 and 2 minutes, which is perfectly compatible with the production rates imposed by the automotive industry. 
     According to a variant method which can constitute an invention by itself, prior to the step of bending or folding, or stamping, a patchwork  30  ( FIG. 6B ) can be created grouping at least two sheets  11 ,  11 ′ cut separately ( FIG. 6C ), which advantageously are superimposed so as to overlap each other in the location of a common portion  31 , with a surface smaller than their respective surfaces, the common portion corresponds with the zone of maximum anticipated deformation, as indicated by the superimposition of the views of  FIG. 6A . 
     Although the bending, folding or stamping operations tend to cause some overstretching of patchwork  30 , this can be compensated, at least in the common portion  31  which undergoes the largest deformation, by advantageous migration and redistribution of the fibers  7  of the first sheet  11  relative to the fibers  7 ′ of the second sheet  11 ′, for instance by compressing/pushing one sheet into the other or by relative sliding of one sheet relative to the other, so that the finished part has a relatively homogeneous distribution of fibers  7 ,  7 ′, and at least there is no depletion over a linear distance of matrix  8 ,  8 ′ predefined as representing an acceptable strength threshold. 
     Because of the redistribution of the initial over-density of fibers  7 ,  7 ′ in the common portion  31 , the final density (specifically the linear density) in this zone is close to the density of the adjacent single layer portions  11 A,  11 ′A of the rest of patchwork  30 . 
     Of course, the sheets  11 ,  11 ′ can have continuous fibers  7 ,  7 ′, and by preference can be superimposed in such manner that their respective continuous fibers are aligned, from one sheet to another, and parallel to each other. On the other hand, the patches can be disposed in such way that their respective continuous fibers cross at a chosen angle (for instance 30 and 45 degrees). 
     If needed, the sheets  11 ,  11 ′ can be made of the same composite, or of composites of matrix  8 ,  8 ′ nature, or of composites of fibers  7 ,  7 ′ nature, or of composites with different orientation or density of fibers  7 ,  7 ′.