Abstract:
A structure, made from composite materials for a vehicle chassis, being configured to receive an undercarriage at its ends and includes at least one central beam that includes a median box having a central part and two ends with a reinforced structure, and the central part includes a reinforced part increasing the strength of the beam with respect to the bending stresses imposed by the transported load. The median box is reinforced by two lateral boxes extending over the entire length of the median box), assembled to the median box, the upper faces of which, together with the upper face of the median box, form the upper face of the beam. The structure includes a floor that covers the upper faces of the median box and the lateral boxes. The elements making up the structure have shapes that are simple, easy to make from composite materials and easy to assemble.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the National Stage of International Application No. PCT/EP2014/066236, having an international Filing Date of 29 Jul. 2014, which designates the United States of America, and which International Application was published under PCT Article 21(2) as WO Publication No. 2015/014819 A1, and which claims priority from and the benefit of French Application No. 13576.88, filed 2 Aug. 2013, the disclosures of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The disclosed embodiment relates to the general field of rolling stock structures. The disclosed embodiment relates more particularly to a composite beam design intended, by using composite materials, to reduce the weight of the structure of a rail transport vehicle (railroad car), notably for transportation of freight by rail. 
         [0004]    2. Brief Description of Related Developments 
         [0005]    As is the case in all transport fields, the railroad car construction sector seeks to reduce the mass of the structures forming the vehicle in order to increase the payload and/or to reduce transportation costs through controlling both the production costs of the vehicles and their energy consumption. 
         [0006]    At present railroad cars are formed exclusively of metal structures, generally of steel and sometimes aluminum. 
         [0007]    Where transport is concerned, however, it is only natural. to envisage lighter aspects, in particular using composite materials. However, it is also known that it is not possible, through simple substitution of materials, to replace a metal structure with a composite material structure of identical shape. It is generally necessary to redesign the structures completely to exploit all the technical characteristics and properties specific to composite materials. 
         [0008]    The necessity to redesign these structures in the context of the use of composite materials notably concerns the particular features described hereinafter. 
         [0009]    A first particular feature to be considered is the anisotropic character of composite materials, as a result of which their properties, in particular their mechanical properties, are not identical in all directions, because of the presence of the reinforcing fibers of which the material is composed. Such a particular feature imposes the definition of a material architecture suited to each application. 
         [0010]    Another particular feature to be considered is the variety of manufacturing processes employed (molding, vacuum infusion, RTM (Resin Transfer Molding), draping, etc.) and that the assembly techniques used to assemble composite material. elements are generally specific to those materials. In contrast to what is the case with metals, it is in fact hardly feasible to weld heat-setting composite materials, for example, but it is entirely appropriate to assemble such materials by gluing, which is exactly the opposite of what it is possible to achieve with metals. 
         [0011]    A further particular feature resides in the specifics of the various variants of composite materials that are available, in particular where the nature of the fibers used is concerned, whether mineral fibers (glass fibers, carbon fibers, etc.) or organic fibers, the nature of which confers on the corresponding composites different properties, behaviors and costs. Thus composite materials based on glass fibers are the least costly whereas carbon fiber composites appear the most costly. 
         [0012]    Because of these particular features, the use of composite material structures to produce rolling stock capable of transporting heavy loads has at present not been developed much or at all, in particular where the manufacture of railroad cars, notably freight cars, is concerned. 
         [0013]    It is pointed out here that the composite materials concerned are so-called “structural” composite materials which are based on long and continuous fibers that represent approximately 50% of the material, the other approximately 50% consisting of a matrix, generally a heat-setting resin, of epoxy (EP), diallyiphtalate (DAP), polyester OT vinylester type, for example, and, more rarely, a thermoplastic resin, of polyamide, PEEK or PEI type, for example. 
       SUMMARY 
       [0014]    One object of the disclosed embodiment is to propose a particular composite material structure that can be used to manufacture vehicles such as those referred to above. In particular, one object of the disclosed embodiment is to define a railroad car platform structure the shape characteristics of which are optimized to enable its manufacture from composite materials. 
         [0015]    Here the final objective is to reduce significantly the mass of the structure of a railroad car, at the same time as optimizing the manufacturing costs for performance in terms of robustness equal to or better than the performance of current structures. 
         [0016]    To this end, the disclosed embodiment consists in a composite material structure, for chassis of vehicles for transporting freight or passengers, said structure. being configured to accept running gear or a bogie at each of its ends, said structure including at least one central beam forming a platform on which the load of the vehicle rests. In accordance with the disclosed embodiment, said beam includes: 
         [0017]    a middle box having a central portion and two ends, said ends having reinforcements to withstand the stresses transmitted to the chassis by the articulation elements of the running gear and by the shock absorber elements disposed at the ends of the vehicle, the central portion of the middle box being configured so as to have a reinforced portion increasing the resistance of the beam to bending forces imposed by the transported load; 
         [0018]    two lateral boxes extending over all the length of the middle box, assembled to said middle box, the upper faces of Which form with the upper face of the middle box the upper face of the beam, said lateral boxes being configured so as to reinforce the resistance of the beam to longitudinal and transverse bending forces imposed on it; 
         [0019]    a covering floor forming a skin, configured so as to cover the upper faces of the middle box and the lateral boxes. 
         [0020]    In accordance with the disclosed embodiment, the various elements constituting the beam are made of composite materials reinforced with glass fibers or carbon fibers or a mixture of glass fibers and carbon fibers. 
         [0021]    In accordance with various features that may be considered separately or in combination, the structure in accordance with the disclosed embodiment has various complementary features. Accordingly: 
         [0022]    In accordance with one particular feature, the middle box consists of an upper half-box extending over all the length of the beam and a lower half-box disposed in the central portion, the two half-boxes each including a bottom and two lateral walls. The upper half-box and the lower half-box are arranged relative to each other so that the bottom of the upper half-box forms the upper face of the middle box and the bottom of the lower half-box forms the lower face of said box. The bottom of the lower half-box moreover extends externally thereof toward the ends of the beam. 
         [0023]    In accordance with another particular feature, a composite material intermediate partition is placed between the upper half-box and the lower half-box so as to reinforce the stiffness of the middle box and the resistance to buckling of the lateral walls of the upper half-box and of the lateral walls of the lower half-box. 
         [0024]    In accordance with another particular feature, the covering floor consists of a principal element ( 61 ) in the form of a monolithic composite material plate reinforced with glass fibers including in its middle portion a composite material reinforcing element ( 52 ) sized so as to cover the upper face of the middle box ( 314 ). 
         [0025]    In accordance with another particular feature, the bottom of the upper half-box, the bottom of the lower half-box and a middle reinforcing element of the principal element of the skin disposed on the upper face of the structure are made of monolithic composite material reinforced primarily with unidirectional fibers, said fibers preferably being carbon fibers. 
         [0026]    In accordance with another particular feature, the structure in accordance with the disclosed embodiment further includes composite material lateral reinforcements disposed on either side of the beam and adapted to absorb forces applied to the lateral portions of the structure by the transported load. Each reinforcement is fastened to a lateral box by one of its ends and to the middle box by its other end. 
         [0027]    In accordance with another particular feature, the elements forming the beam consist of composite material plane faces. 
         [0028]    In accordance with another particular feature, the upper half-box includes a bottom consisting of a monolithic composite material plate and lateral walls with a sandwich structure consisting of two composite material thin skins reinforced with glass fibers and a core consisting of an element formed of polymer material foam or a honeycomb structure material or a balsa type wood. 
         [0029]    In accordance with another particular feature, the lower half-box includes a bottom consisting of a monolithic composite material plate and lateral walls with a sandwich structure consisting of two composite material thin skins reinforced with glass fibers and a core consisting of an element made of polymer material foam or a honeycomb structure material or a balsa type wood. 
         [0030]    In accordance with another particular feature, the lateral reinforcing elements have a sandwich structure consisting of two composite material thin skins reinforced with glass fibers and a core consisting of an element made of polymer material foam or a honeycomb structure material or a balsa type wood. 
         [0031]    In accordance with another particular feature, the various elements of the structure in accordance with the disclosed embodiment include rims adapted to enable the assembly of said elements by gluing and/or bolting and/or riveting, two elements assembled to each other having rims adapted to be placed face-to-face at the time of assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The features and advantages of the disclosed embodiment will be better appreciated thanks to the following description with reference to the appended figures, which show: 
           [0033]      FIGS. 1 and 2  are diagrammatical illustrations showing the theoretical structure of the chassis in accordance with the disclosed embodiment in lateral view and in frontal section at the level of the middle portion of the chassis; 
           [0034]      FIG. 3  is a diagrammatic lateral view, in section, of one chassis embodiment in accordance with the disclosed embodiment; 
           [0035]      FIG. 4  is a diagrammatic view in cross section of the chassis from  FIG. 3 , in a plane passing through the central area of the structure; 
           [0036]      FIG. 5  is a diagrammatic view in cross section of the chassis from  FIG. 3 , in a plane passing through one end of the structure; 
           [0037]      FIG. 6  is a diagrammatic view in cross section of the platform surmounting the structure of the chassis in accordance with the disclosed embodiment, in the  FIG. 3  aspect; 
           [0038]      FIG. 7  is a diagrammatic view in cross section of the upper half-box constituting the beam of the chassis in accordance with the disclosed embodiment, in the same aspect; 
           [0039]      FIG. 8  is a diagrammatic view in cross section of the lower half-box constituting the beam of the chassis in accordance with the disclosed embodiment, in the same aspect; 
           [0040]      FIG. 9  is a diagrammatic view in cross section of a lateral box constituting the beam of the chassis in accordance with the disclosed embodiment, in the same aspect; 
           [0041]      FIG. 10  is a diagrammatic view in cross section of a lateral reinforcement panel that can be integrated into the beam of the structure of the chassis in accordance with the disclosed embodiment; 
           [0042]      FIG. 11  is a diagrammatic illustration of various steps of assembling the structure in accordance with the disclosed embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    The purpose of the diagrammatic  FIGS. 1 and 2  is to show the theoretical structure of the chassis in accordance with the disclosed. embodiment. In accordance with this principle, the chassis in accordance with the disclosed embodiment primarily includes an upper platform  11  intended to support the transported load  13 , having reinforcements  111  and  112  at the ends, and a lower box  12 , or reinforcement, situated under the central portion of the platform  11  and intended to confer an increased stiffness in the central portion of the assembly, in particular in terms of longitudinal and transverse bending. 
         [0044]    For their part, the reinforcements at the ends have the principal function of absorbing forces imposed on the structure at the level of the axes  113  and  114  about which the chassis is articulated to the running gear (bogies) of the vehicle as well as absorbing forces to which the vehicle, the railroad car, is subjected at the level of the couplings, the shock absorbers or buffers at the ends, etc. 
         [0045]    In accordance with the disclosed embodiment, the various structural elements of the chassis are made of composite materials. The structure of each of the elements is moreover defined so that the portions having to be subjected to in-plane stresses are constituted by single composite material webs of monolithic structure, preferably including a reinforcement by fibers oriented longitudinally, whereas the portions of an element having to be subjected to out-of-plane stresses, for example torsion stresses, have a sandwich structure formed of two composite material skins separated by an interleaved element, a core, consisting of a filler material, preferably as light as possible, for example a PS, PVC, PU, PET type polymer material foam, or a honeycomb structure material or a wood of low density, for example of balsa type. 
         [0046]    Depending on the stresses that the structural element concerned has to withstand, the fibers constituting the reinforcement of the composite material used are either glass fibers or carbon fibers, either unidirectional (UD) fibers or woven fibers (mat) that are stacked as required. The structure of each panel, i.e. the choice of the plies, their orientation in the material, their stacking is carried out using simulation tools well known to the person skilled in the art, knowing that what is still looked for is optimization of the part that is being designed in terms of mass and production cost. 
         [0047]    The following description features one aspect of a railroad car chassis constructed on this typical structure. The purpose of this example is to show clearly the particular technical features of the disclosed embodiment. The scope of the disclosed embodiment is not limited to the framework of this example alone, of course. 
         [0048]    As  FIGS. 3 to 5  show, in this aspect the railroad car chassis in accordance with the disclosed embodiment consist primarily of a beam  31  that combines the functions of the upper platform  11  and the bottom box  12  of the theoretical structure described above, the beam  31  being covered by a coating  32 . 
         [0049]    The coating  32 , or skin, is a relatively thin plane composite material element the dimensions of which are defined so that it covers all of the surface of the structure (of the chassis). In a preferred aspect, the skin  32  consists of a composite material plane first element  321  reinforced with glass fibers having a middle portion reinforced on its lower face, by a composite material plane, second element  322  also reinforced with glass fibers. In particular aspects, however, the second element  322  may equally well be made from a composite material reinforced with carbon fibers, where, appropriate UD fibers, so as notably to have greater mechanical strength (in particular in traction/compression and in bending) and a higher strength-to-weight ratio. 
         [0050]    For its part, the beam  31  forming the platform has a central. portion  311  and two areas  312  and  313  at the ends to which the running gear of the vehicle is articulated, in other words the bogies of the railroad car in the present example. From a structural point of view, the central portion  311  and the two ends  312  and  313  of the beam  31  consist of one and the same composite material element integrating reinforcing elements  35 ,  36  at its ends, as shown by  FIGS. 3 and 5 . These reinforcing taking the form of composite material webs or beams, are notably intended to reinforce the area of connection and articulation to the bogies and the transmission of forces applied to the buffers. 
         [0051]    In this aspect, the beam  31  in accordance with the disclosed embodiment consists of a middle box  314  and two lateral boxes  315 ,  316  situated at respective, opposite longitudinal ends of the middle box  314  and assembled to the middle box  314 . 
         [0052]    In accordance with the variant aspect considered here, the middle box  314  may be made in one piece. Nevertheless, for reasons of ease of manufacture in particular, it is preferably produced in two parts, an upper half-box  317  extending over all the length of the railroad car and a lower half-box  318  that reinforces the upper half-box  317  in the central area  311  of the beam  31 . The upper half-box forms both the central portion  311  and the reinforced ends  312  and  313  of the beam  31 . 
         [0053]    The lower half-box  318 , situated only in the central portion of the railroad car, has a lower wall  319  the function of which is to reinforce the bending inertia of the assembly. 
         [0054]    To this end, as  FIG. 3  shows, this wall  319  is extended beyond the limits of the lower half-box  313  as far as the areas  312  and  313  at the ends of the upper half-box  317  so as to close said upper half-box and thereby participate in the absorption of forces notably imposed by the pivots of the bogies. 
         [0055]    The height of each half-box, in particular that of the lower half-box  313 , is defined as a function of the manufacturing choices adopted to respond to the mechanical stresses that the structure must withstand, in particular the weight of the load. 
         [0056]    For their part, the lateral boxes  315  and  316  are elements continuous over all the length of the car. Situated on respective opposite sides of the upper half-box  317 , they constitute with it the upper face of the beam  31  on which the skin  32  rests. They further contribute to the resistance to longitudinal and transverse bending of the chassis formed in this way and participate in the absorption of forces in line with the buffers. 
         [0057]    In one particular aspect, shown by  FIG. 4 , the central portion of the beam  31  is moreover reinforced laterally by composite material lateral elements  33  and  34  disposed obliquely which, in accordance with the variant aspect considered here, clothe this central portion continuously over all its length and form two lateral reinforcing walls, or, alternatively, constitute localized reinforcements, forming oblique reinforcing bars spaced from one another along the central portion of the beam  31 . These, reinforcing elements  33  and  34  serve to absorb transverse, bending forces and thus limit any twisting of the structure. 
         [0058]    It should be noted that, depending on the respective, heights of the upper and lower half-boxes, it is possible in one particular aspect to add an intermediate plate to stabilize the middle box  314  produced from these two half-boxes  317  and  318 , the function of this intermediate plate or partition being to prevent buckling of the lateral partitions of the upper and lower half-boxes. 
         [0059]      FIGS. 6 to 10  show the morphological and structural characteristics of the various elements described above. 
         [0060]    As shown by  FIG. 6 , the panel constituting the skin  32  disposed on the upper face, of the structure consists of a plane, principal element  61  covering by virtue of its dimensions the whole of the surface formed by the upper faces of the middle box  314  and the lateral boxes  315  and  316  and a middle reinforcing element  62 , also plane, disposed facing the upper face of the middle box  314 . 
         [0061]    In accordance with the aspect envisaged here, the principal element  61  may be made of a composite material reinforced with glass fibers, for example, like the reinforcing element  62 . However, in particular aspects, the second element  62  may equally well be made from a composite material reinforced with carbon fibers, where appropriate UD fibers, so as to have greater mechanical strength (in particular in traction/compression and in bending) and a higher strength-to-weight ratio. 
         [0062]    The illustrations in  FIGS. 7 and 8  show in detail the morphology and the structure of the upper half-box  317  and the lower half-box  318  that constitute the middle box  314 . 
         [0063]    The upper half-box  317  is primarily formed of a bottom  71  consisting of a composite material monolithic wall and two lateral walls  72  and  73 , these walls extending over all the length of the middle box. The monolithic bottom  71  may in accordance with the aspects envisaged here consist of two composite material skins ( 76 ,  77 ) reinforced with glass fibers, the reinforcement primarily consisting of UD layers of glass fibers, or alternatively, notably for reasons of mechanical strength and higher strength-to-weight ratio, composite material reinforced with carbon fibers. For their part, the two lateral walls  72  and  73  have a sandwich structure formed of the two composite material skins  76 , separated by an interleaved element  78 , a core, consisting of a filler material, a PS, PVC, PU, PET type polymer material foam, for example, or a honeycomb structure material or a wood of balsa type, for example. Their sandwich structure enables the lateral walls to have better stability in terms of buckling. 
         [0064]    As may be noted on considering  FIGS. 3, 4 and 5 , the general shape of the upper half-box  317  is that of a parallelepiped with an open face opposite the face forming the bottom  71 . 
         [0065]    In accordance with a preferred aspect, the lateral walls  72  and  73  for their part each have a rim  74  or  75  extending laterally toward the exterior of the half-box over all the length of the latter, this rim being used to carry out the assembly of the complete chassis. 
         [0066]    Like the upper half-box, the lower half-box  318  consists primarily of a bottom  81  and two lateral walls  82  and  83  that border the central portion of the middle box  314 . Like the walls  72  and  73  of the upper half-box, the two lateral walls  82  and  83  here have a sandwich structure. 
         [0067]    The bottom  81 , which, as stated above, extends over all the length of the structure and which has the function of reinforcing the bending inertia of the whole of the structure (of the chassis) also has a monolithic structure consisting, in accordance with the aspects envisaged here, of the two composite material skins reinforced with glass fibers, the reinforcement consisting primarily of UD layers of glass fibers, or alternatively, notably for reasons of mechanical strength and higher strength-to-weight composite material reinforced with carbon fibers. 
         [0068]    From a morphological point of view, the lower half-box  318  has a prism shape with trapezoidal bases which represent the lateral walls  82  and  83  of the half-box. For their part the front and rear faces of the half-box consist of the bottom  81  that is extended obliquely toward the front and toward the rear, beyond the lower half-box  318 , so that its rims  74  and  75  come progressively into contact with the upper half-box  317 , as shown by  FIG. 3 , for example. 
         [0069]    In one preferred aspect, illustrated by  FIGS. 7 and 8 , the lateral walls  72  and  73  each have for their part a rim or  85  extending laterally toward the exterior of the half-box concerned over all the length of the latter, this rim being used to carry out the assembly of the complete chassis. Similarly, the lateral walls  82  and  83  each have a rim  84  or  85  extending laterally toward the exterior of the half-box over all the length of the latter. 
         [0070]    For its part, the bottom  81  has on its portion extending out of the lower half-box flat rims  86  and  87  used to carry out the assembly of the complete chassis. The rims  86  and  87  are configured and arranged so that they are positioned, at the level of the ends of the structure, facing the rims  74  and  75  of the lateral walls of the upper half-box  317 . Similarly, for their part the rims  84  and  85  are configured and arranged so that they are positioned, at the level of the central portion of the structure, facing the rims  74  and  75  of the lateral walls of the upper half-box  317 . The presence of such rims advantageously facilitates the assembly of the lower half-box  318  and the upper half-box  317  to form a single middle box  314 . This assembly may be effected by gluing the rims, for example, or by riveting or by bolting, or by gluing-plus-riveting these same rims. 
         [0071]    From a morphological point of view, the lateral boxes  315  and  316  have, identical shapes. As  FIG. 9  shows, each box includes a vertical internal lateral wall  91  intended to come into contact with one of the lateral walls of the upper half-box  317  and an oblique external lateral wall  92  forming an external upper edge of the chassis. The oblique orientation of the external lateral wall advantageously makes it possible to produce a bearing engagement without adjustment to assemble the lateral elements  33  and  34 . The lateral walls of a lateral box are joined to one another by a flat bottom  93  parallel to the plane of the bottom  71  of the upper half-box. 
         [0072]    From a structural point of view, the lateral box walls consist, like the lateral walls of the upper half-box  317  and the lower half-box  318 , of two composite material skins reinforced with glass fibers separated by a core made from a filler material, polymer material foam or honeycomb structure material, or wood, for example of balsa type. 
         [0073]    In accordance with one particular aspect, filler material may moreover be integrated into the boxes  315  and  316 , a material consisting of polymer material foam or a honeycomb structure material or wood of balsa type for example. This material makes it possible to loin the internal skins  91 - 92 - 93  of the lateral boxes  315 - 316  to one another and to the skin placed on the upper face of the platform  32 . 
         [0074]    Also from a structural point of view, the composite material lateral reinforcing elements  33  and  34  intended to reinforce the resistance to twisting and to bending (longitudinally and transversely) of the structure of the chassis in accordance with the disclosed embodiment also consist, like the lateral walls of the upper half-box  317  and the lower half-box  318 , of two composite material skins reinforced with glass fibers separated by a core made of polymer material foam or a honeycomb structure material or wood of balsa type for example. In a preferred aspect shown in  FIG. 10  the body  101  of the reinforcement is extended by rims  102  and  103  arranged relative to the body  101  so as to facilitate the assembly of the reinforcing element concerned with the external lateral wail of the corresponding lateral box  315  or  316  and with the lateral wall of the lower half-box  318 . This assembly may be effected by gluing the rims, for example, or by riveting or by bolting, or by gluing-plus-riveting these same rims. 
         [0075]    As can be seen in  FIGS. 6 to 10 , the chassis structure in accordance with the disclosed embodiment, as described in the foregoing text, has the important advantage of consisting of elements having both a simple morphology that is easy to assemble (faces and bearing engagements on plane faces) and an internal structure that is easy to manufacture. These features advantageously make it possible to facilitate the assembly of such a structure, despite the sometimes large dimensions of the latter. 
         [0076]    The composite material elements forming the structure in accordance with the disclosed embodiment being elements of simple shape having plane faces, the structure in accordance with the disclosed embodiment may advantageously be constructed in a simple manner and at relatively low cost, the various composite material elements constituting the structure can be manufactured using simple processes, primarily by draping pre-impregnated fibers and/or dry fibers, combined with vacuum polymerization or RTM, or by infusion given the large size of the manufactured elements, such as those employed in the production wind turbine blades, for example. 
         [0077]    Moreover, given the composite structure concept of the disclosed embodiment, the assembly of the various composite elements constituting the chassis in accordance with the disclosed embodiment is advantageously simple to carry out in that all the connections occur along plane and linear bearing surfaces provided for this purpose, assembly being achievable using relatively simple tools, by gluing, or by riveting or by bolting, or by gluing-plus-riveting the various elements to one another, for example. 
         [0078]      FIG. 11  shows diagrammatically the method of assembling a chassis structure in accordance with the disclosed embodiment from constituent elements described above, which method includes:
       a first step (step 1) that consists in assembling the upper half-box  317  and the lower half-box  318  to form the middle box  314 ;   a second step (step 2) which consists in assembling the lateral boxes  315  and  316  to the middle box  314  to constitute the beam  31  forming the platform of the structure, assembly taking place at the level of the upper half-box  317 ; where appropriate having incorporated into the boxes  315 - 316  a filler material consisting of a polymer material foam or a honeycomb structure material or wood o balsa type for example;   a third step (step 3) consisting in fixing the skin  32  to the upper face of the beam  31  so as to cover the upper faces of the upper half-box  317  and the lateral boxes  315  and  316 ;   a fourth step (step 4) consisting, where appropriate, in fixing the lateral reinforcing elements  33  and  34  to the beam  31 .       
 
         [0083]    It should be noted that, when the chassis produced actually includes lateral reinforcing elements, steps 3 and 4 may be interchanged. Moreover, in accordance with the aspects envisaged here, steps 1 to 4 may be carried out in a different order, for example 2, 3, 1, 4 or 3, 2, 1, 4. 
         [0084]    It should also be noted that, during the second step, the upper half-box  317  and the lower half-box  318  may be assembled with an intermediate plate interleaved between the two half-boxes, where the rims  74 - 75  and  84 - 85  loin, as described above, the function of this plate being to reinforce the stiffness of the assembled beam. 
         [0085]    In accordance with the disclosed embodiment, the composite beam  31  produced in this way integrates at its ends, at the level of the reinforcements, metal elements the function of which is notably to provide the interface with the bogies and with the buffers at the ends. The metal elements are fixed to the composite material structure in accordance with the disclosed embodiment by appropriate fixing means (bolts and/or rivets), for example using an appropriate technique of assembly between metal parts and composite material parts, like that described in the applicant&#39;s patent FR 2 948 154. 
         [0086]    Thereafter the complete production of a chassis in accordance with the disclosed embodiment also includes an operation of placing and fixing interface elements on and to the beam  31 , at the level of the ends of the boxes  315 ,  316  and  317 , which operation may, depending on the production method adopted, be carried out on the boxes before assembly or during assembly, for example after step 2. 
         [0087]    As is clear from the foregoing description, this disclosed embodiment may be. used on all types of rail vehicle intended for the transportation of freight (railroad cars) or passengers. It may equally well be used to produce road freight vehicle chassis, in particular heavy goods vehicle trailers.