CAR FACE WALL ARCHITECTURE FOR A CAR SUCH AS A TRAIN CAR MADE FROM SANDWICH COMPOSITE MATERIAL

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No. PCT/EP2015/073863, having an International Filing Date of 15 Oct. 2015, which designates the United States of America, and which International Application was published under PCT Article 21(2) as WO Publication No. 2016/059147 A1, and which claims priority from and the benefit of French Application No. 1460011, filed 17 Oct. 2014, the disclosures of which are incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The presently disclosed embodiment concerns a car face wall architecture such as a train car made from sandwich composite material equipped with openings.

The disclosed embodiment relates to a design solution for a structural panel made of composite material equipped with openings, i.e. bays, hatches, windows which are designed to lighten globally the weight of the structure, and are applicable in particular for the walls of a railway transport body, whether this involves urban rolling stock or stock for a subway, tramway, regional train or cars for high-speed lines.

2. Brief Description of Related Developments

The designers of train structures must obtain compromises between various requirements which are sometimes contradictory, i.e.:

They attempt to decrease the weight of the structures in order to increase the useful load and/or to reduce the energy consumption, but they must control the production costs, and therefore find simple solutions, whilst ensuring the comfort and safety of the passengers, and in particular, in a non-limiting manner:

• • By limiting the structural deformations of the train cars, which involves sufficient flexural rigidity of these cars. This rigidity is also important in order to avoid coupling with the suspension modes of the trains;
  • By limiting the noise inside the cars;
  • By ensuring that the passengers are protected against fire and fumes;
  • By withstanding the pressure waves;
  • By withstanding the traction and compression associated with the traction.

More specifically, a train body structure acts mechanically like a caisson subjected to flexion, the top (the roof) and the chassis (the floor) of which constitute the bearing surfaces, and the faces of which constitute the vertical shells.

As represented in FIG. 1, the faces for their part are mostly subjected to shearing stresses 201.

In addition, the panels are also subjected to flexion stresses induced by the pressure waves of approximately 8000 Pa sustained when a high-speed train crosses another and/or passes into a tunnel, as well as to the effect of the vertical loads 201, the weight of the equipment and passengers on the chassis, and local forces or the like.

Hitherto, the bodies have been substantially constituted by metal structures, for example mechanically welded aluminum profiles or steel plates, as described for example in document EP0392828A1 or JP2000264200A.

In general, it is found that these structures are, as in document JP4427273B2, in the form of sandwich walls, i.e. two metal skins which are connected to one another by elements, or of panels which are reinforced by strengtheners as described in document JP2000264200A, or by a combination of two types of solutions.

However, it is natural in the field of transport to envisage lighter solutions, using high-performance composite materials, as may have been the case in the past in the pioneering fields of aeronautics and space. This has been proposed for example in documents EP0544473A1 and EP0544498A1 in the form of sandwich panels with a honeycomb core and strengtheners inserted.

The need for longitudinal flexural rigidity of the lateral panels is derived from the fact that a train structure is a beam which is supported on its axles. This rigidity must be controlled firstly in order to limit the flexion, but also to control the vibration and resonance associated with the speed of travel of the trains.

In addition to the problem of the rigidity, it should be noted that there are two patents which show the difficulties of controlling this rigidity because of the presence of windows, i.e. document JP2000264200A which proposes strengtheners which are not simply vertical, but the angle of which relative to the vertical is also optimized. This patent even proposes a continuous window, which is simply concealed locally by inclined floor-to-ceiling connection pillars.

Document U.S. Pat. No. 8,656,841B1 proposes windows which are oblong and not rectangular as usual, and in both cases the form of the window is modified in order to be compatible with control of the rigidity of the panels.

The composite structural materials which make it possible to ensure the saving of weight sought, together with the required level of performance, are based on continuous long carbon or glass fibers. In this type of material, the fiber represents approximately 50% to 60% of the volume, the remainder being constituted by an organic matrix (in general a resin of the epoxy type, but also sometimes polyester, vinyl ester, etc., and optionally thermoplastic resins such as polyamides, peeks, etc.).

For the production of structures, there are two main families of composite materials:

• • So-called monolithic materials, constituted by a stack of fibers;
  • Sandwich materials, constituted by two skins with a nature identical to the monolithic materials, separated by a core. This core is often constituted by a very low-density material of the honeycomb or foam type or the like (sometimes balsa). This makes it possible to obtain the required off-plan flexural inertia properties. This type of structure is advantageous in terms of performance and cost.

In a sandwich material, the flexural inertia of the panels in the direction of their thickness is provided naturally by the spacing of the skins. This is one of the major advantages of this type of architecture.

Other core materials can be used, for example denser materials which are designed to provide the sandwich structure with sound-absorption capacities, see for example document JP2001278039A.

The composite materials thus make it possible to implement the same technical solutions as the metal materials, i.e. strengthened monolithic structures or sandwich structures, but with a wide variety of possible solutions, since many combinations are possible between the various fibers (carbon, glass, SiC, vegetable fibers, etc.), resins (epoxy, polyester, vinyl ester, peek, polyamides, thermosetting or thermoplastic), and the cores (metal honeycombs, foams or the like).

In addition, since the optimum mechanical properties of the composite materials are ensured by the fibers, these materials are by nature anisotropic, and consequently their optimization of the structures needs the orientations of the fibers in the thickness of the material to be defined according to the mechanical stresses to which the structure is subjected.

Thus, for the roof and the chassis, the rigidity requirements lead to orientation of the fibers preferably in the direction of the length. On the other hand, as far as the face panels are concerned the shearing stress which is applied must be absorbed by fibers which are oriented rather at + and −45°. It is in fact in these conditions that the mechanical functioning of the structure is optimized, and thus consequently its weight and cost.

Like any vehicle which is destined for passenger transport (motor cars, motor coaches, trains, aircraft, and even space vehicles), train cars must comprise windows. Since these windows are made from materials which are different from the remainder of the structure of the vehicle, they must form the basis of a specific design.

A device for securing the windows to the remainder of the wall or the structure must be put into place, as for example in patent FR 2911112A1 relating to aircraft. In addition, the structure in the vicinity of the windows must be reinforced as described in US Publication No. 2012/0223187A1.

In the case of cars consisting of structures made of composite materials as previously described, the shearing stress which is applied to the face must be absorbed by fibers oriented at +45° and −45° relative to the horizontal.

However, as represented in FIG. 3, at the panels of the faces, the presence of the angles of conventional bays with a rectangular form leads to cutting of the fibers between the top and the bottom of the face panel, which may make it necessary to increase the distance between two windows, or the local thickness of materials between two windows, which complicates the production of the panel and makes it more costly.

Thus, it has been proposed to modify the form of the windows in the case of a structure made of composite materials, and document US Publication No. 2012/0223187A1 thus proposes in this case hatches in the form of a “diamond” for an aircraft fuselage, as well as the manner of establishing their dimensions. This form of hatch with a small size is obviously unsuitable for a passenger train.

SUMMARY

It is thus known to produce train bodies made of composite materials, in particular in the form of sandwich panels.

This being the case, numerous technologies can be envisaged, both in terms of materials (fibers, resins, cores) and of methods of implementation (draping of pre-impregnated products, infiltration and its variants, etc.). It is also then known to adapt the form of the windows in order to improve the longitudinal rigidity of the body, and for aircraft a form of the diamond type has been proposed for the hatches, such as to adapt them even better to the preferred orientations of the fibers, which involves the optimization of composite materials. The same also applies to the modification of the skins of the sandwich composite materials, in order to improve their capacity to withstand more forces locally.

On the other hand, it is not known to optimize the windows of cars made of composite material, and the same applies to the manner of production.

However, train windows are distinguished from those of aircraft by their unit surface, which is significantly larger than that of aircraft, by their geometry, which is characterized by elongation (ratio of the high length relative to the square on the surface, i.e. more than 2 for most windows of a body), and by the total glazed surface compared with the wall surface of the lateral structure, which is also very much greater than that of aircraft. These aspects are justified by the need to provide the passengers with maximum comfort during the journey, with visibility and light being important aspects of this comfort.

Apart from these distinctions, the dimensions of the main part of a section of train body are also distinguished from those of an aircraft fuselage by the following specific features:

• • lack of stress caused by the need for static pressurization of the structure, but on the other hand pressure stresses in the form of excess pressure waves followed by low pressure affecting the structure and the bays with rapid dynamics when passing into tunnels and/or crossing other trains. The levels of these pressures (peak values) are approximately ±5000 to ±, 6000 Pa, up to 8000 Pa for high-speed;
  • the need to control the structure's own frequency, in order to prevent it starting to resonate when the car is travelling, typically at >11 Hz;
  • the need to withstand the forces (traction/compression) of the traction between cars.

Finally, and although costs must be taken into account in all industrial activities, the demands in the field of railways in terms of cost reductions are even more stringent than in aeronautics (the cost per kg accepted is more than 10 times less), which makes this an even more important criterion for the selection of solutions.

The objective of the disclosed embodiment is thus to propose a solution to reduce the weight of the structures of a train body by use of composite materials, whilst maximizing the glazed surface available for the passengers.

The disclosed embodiment makes it possible to design a face (wall) of a car made of composite material in the form of a sandwich in a single piece, reinforced locally only for the interfaces, based substantially on high-strength carbon fibers, sampled in order to optimize the mechanical stresses as well as possible, but also taking into account requirements of finishing and integration, and comprising openings with a form suitable for better use of this sampling.

More particularly, the disclosed embodiment proposes a rolling vehicle car comprising lateral walls in a single piece made of composite material comprising a sandwich structure provided with a first skin on the outer side of the car, a second skin on the inner side of the car, and a closed-cell foam or honeycomb core between said skins, said walls being provided with window openings formed by interruptions of draping of longitudinal fibers, transverse fibers and crossed diagonal fibers, said openings having a polygonal form which reduces the surface of diagonal fibers interrupted in the corners of the openings.

In particular, the disclosed embodiment makes it possible to dispense with strengtheners or metal lattice elements in order to reinforce the structure.

For increased rigidity of the body, the openings preferably have a generally hexagonal or octagonal form comprising two large horizontal sides connected by convex lateral borders comprising two segments, three segments, or one segment with an oval form.

Advantageously, the openings are equipped with a reinforcement border provided with a tubular frame.

According to a particular aspect of the disclosed embodiment, the reinforcement border comprises an inner wing for securing of the border on the edge of the opening on the inner side of the wall.

The tubular frame advantageously has a rectangular cross-section, with the inner wing extending a face of the tubular frame on the interior of the wall.

The inner wing is preferably secured on the interior of the wall by means of screws, rivets or other securing means which render the wing and the inner skin of the composite panel integral.

Advantageously, a face of the tubular frame which faces toward the interior of the car is secured by means of screws, rivets or other securing means on a rim of the opening formed by the second skin projecting from the core of the wall.

According to a particular aspect of the disclosed embodiment, the reinforcement border comprises an inner collar which receives a fastening of a window.

According to a particular aspect of the disclosed embodiment, at least one of the two skins of the sandwich structure is produced by means of plies oriented in four preferred directions, i.e. 0° (longitudinal axis of the body), 90°, +45° and −45°.

According to an advantageous aspect of the disclosed embodiment, the plies are plies impregnated with unit gsm substance of between 125 g/m² and 500 g/m².

According to an advantageous aspect of the disclosed embodiment which limits the number of interrupted plies, the angle segments of said openings are inclined between 45° and 60° relative to a longitudinal direction of the wall, and are preferably inclined between 45° and 50° relative to a longitudinal direction L of the wall.

The threads at 45° are advantageously in the form of at least two ±45° plies made of carbon fiber.

According to a preferred aspect of the disclosed embodiment, the core of the sandwich is made of a material selected from amongst polyethylene terephthalate (PET), polymethacrylimide (PMI), polyetherimide (PEI), an aluminum honeycomb or a poly(m-phenyleneisophthalamide) (MPD-I) honeycomb (structure impregnated with phenolic resin).

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the presently disclosed embodiment will become apparent from reading the following description of a non-limiting aspect of the disclosed embodiment, provided with reference to the drawings which represent the following:

FIG. 1 is a skeleton diagram of the shearing stresses according to the longitudinal direction of a lateral panel of a train car;

FIG. 2 is a detail of a panel according to the disclosed embodiment;

FIG. 3 is a representation of a panel according to the prior art;

FIG. 4 is a view in perspective of part of a panel and openings according to the disclosed embodiment;

FIGS. 5A, 5B are a detail in cross-section of a reinforcement frame at a window opening in the wall according to two embodiments;

FIG. 6 is a front view of an aspect of a panel according to the disclosed embodiment for a double-decker car;

FIG. 7 is a schematic representation of the structure of the wall according to the disclosed embodiment between window openings;

FIG. 8 is a view in perspective of a car body with walls according to an aspect of the disclosed embodiment;

FIG. 9A is a schematic view of passages of fibers inclined between openings;

FIGS. 9B and 9C are curves representative of the stresses and shearing at the cut-out of the openings within the context of the disclosed embodiment.

DETAILED DESCRIPTION

The disclosed embodiment is described mainly in FIGS. 2 and 4 to 8.

Its principle is to provide a train car 1, an example of which is given in FIG. 8, comprising lateral walls 2 in a single piece made of composite material.

The material selected has a sandwich structure 10 shown in FIG. 2, provided with a first skin 11 on the outer side of the car, a second skin 12 on the inner side of the car, and a core made of closed cells 13a or honeycomb 13b between said skins.

According to the disclosed embodiment, the walls are provided with window openings 20 formed by interruptions of drapes of longitudinal fibers, transverse fibers and crossed diagonal fibers 100 of the sandwich structure, said openings 20 as represented in FIG. 4 having a hexagonal form comprising two large horizontal sides and lateral walls 29 with a profile in the form of a convex “V” or an oval profile which reduce the surface of diagonal fibers 100 interrupted in the corners of the opening, and represented in FIG. 7 having an octagonal form for which the lateral sides comprise three segments.

In comparison with a monolithic structure equipped with a strengthener, sandwich structures provide the following advantages in particular:

• • Reduced production costs and weight, thermal insulation function provided by the core.

Compared with a sandwich structure solution of this type, monolithic panels have the following disadvantages:

• • Higher production cost (assembly of the frames and strengtheners on the skins), high assembly cost (local assembly in the frame areas);
  • In addition, the frames are thicker than the sandwich, which reduces locally the inner volume of the structures constructed.

The materials, i.e. the composite material and core, of the panel, must be selected to comply with many constraints, which leads to elimination of numerous potential solutions and ultimately to selection of solutions which are once again compromises from amongst the multiple solutions envisaged.

The main constraints to be taken into account are described below, firstly in relation to the mechanical constraints.

For the skins:

• • The traction/compression modules of the elementary plies, an elementary ply being the basic element of the stacks of fibers, either a single-layer one-way sheet UD or a fabric, must provide the required rigidity in the stack. In this case, the choice of fiber is of primary importance. For reasons of cost, the choice has been for industrial strength “HR” (high resistance) fibers, in particular T700 made by the company Hexcel, TR50S made by Mitsubishi, or Pannex 35 made by Zoltec;
  • The mechanical strength of the elementary ply under the service loads must be verified. The properties of the resin are just as important as the properties of the fiber.

Taking into account the structural application concerned and the stringent constraints with which the material must comply (service life of 30 years in a humid environment, temperature resistance >60° C., cycle fatigue up to 10 million cycles, etc.), resistance to impacts etc., an epoxy resin was selected.

The minimum mechanical properties of the carbon/resin one-way fiber ply concerned at the end of the service life and at the maximum operating temperature are as follows:

Data (max T°

end of life)

resistance composite material-

>726

traction 0° (Mpa)

composite material modulus-

>114

traction 0° (Gpa)

resistance composite material

>508

in compression 0° (Mpa)

composite material modulus in

>103

compression 0° (Gpa)

composite material modulus in

>3.0

traction at 90° (Gpa)

plane shearing resistance-

>33

Tau_12 (Mpa)

plane shearing modulus-G_12

>2.0

(Gpa)

ILSS (inter-laminar shearing

>29

stress) (Mpa)

The minimum mechanical properties of the one-way glass fiber/resin ply concerned at the end of the service life and at the maximum functioning temperature are as follows:

Data (max T°

end of life)

resistance composite material-

>472

traction 0° (Mpa)

composite material modulus-traction

>35

0° (Gpa)

resistance composite material in

>331

compression 0° (Mpa)

composite material modulus in

>30

compression 0° (Gpa)

composite material modulus in traction

>3.0

at 90° (Gpa)

plane shearing resistance-Tau_12

>29

(Mpa)

plane shearing modulus-G_12 (Gpa)

>2.0

ILSS (inter-laminar shearing stress)

>21

(Mpa)

For the core of the panel:

• • The shearing modulus intervenes in the flexural rigidity of the panel. The resistance in traction/compression and shearing of the material must be designed in particular to ensure sufficient mechanical resistance under the service loads. The density of the material is an important factor for the purpose of minimizing the weight of the structure.

In addition to the mechanical performance, the choice of materials of the sandwich panel involves other considerations, such as the compatibility with the production process concerned. The cost constraints associated with the large dimensions of the parts justify the selection of a production process under vacuum (outside an autoclave). The impact of this choice plays a primary part in the selection of the resin.

Consequently, the core material must be able to withstand the constraints (pressure=0.1 Mpa+temperature up to 120° C.) induced when the polymerization cycle is implemented. These constraints lead to elimination of the use of certain products (e.g.: PET foam with density of less than 100 kg/m³).

The material must also comply with railway standards for fire resistance, and in particular the 2013 version of standard EN45545.

For cellular foams, certain families of materials such as polyethylene terephthalate (PET) in certain densities, polymethacrylimide (PMI) and polyetherimide (PEI) comply with all of these requirements. Cores made of aluminum honeycomb or poly(m-phenyleneisophthalamide) (MPD-I) honeycomb (structure impregnated with phenolic resin) (known under the brand name NOMEX for example) also comply with them.

The thermal insulation is also a constraint to be taken into account. Use of a core material constituted by close cells, which intrinsically have excellent thermal insulation properties, provides the advantage of incorporating the function of thermal protection in the production of the panel, and thus saves costs and cycle time for the implementation of this function, which is generally carried out on the body structure.

In order to prevent phenomena of accelerated ageing of the materials by absorption of water, but also risks of deterioration under the effect of frost, in this case also the choice of a closed-cell core material is preferred.

Taking into account the above points, and including constraints of cost, the solutions which are preferably selected are described within the context of an application as follows:

The face of the car is a sandwich panel in a single piece pierced in order to provide the openings such as windows, doors, display devices or the like. The openings comprise reinforcements which are used for securing of elements on these openings (windows, doors, etc.), and make it possible to compensate for the loss of rigidity of the face panel associated with the presence of the hole. This reinforcement at the window openings is provided by a reinforcement border with a bordering frame (metal in the case in question) as represented in FIG. 4, and in cross-section of the composite panel hole bordered by the reinforcement border 21 in FIGS. 5A and 5B.

According to these examples, the reinforcement border 21 is provided with a tubular frame 30.

In the case in FIG. 5A, the border comprises a wing 31 known as the inner wing, which makes it possible to secure the border on the edge 2a of the opening in the inner face of the panel, i.e. the face which is inside the body.

The tube which forms the tubular frame 30 has a rectangular cross-section, with the inner wing 31 extending a lateral face 21a of the tubular frame of the reinforcement border 21.

The inner wing 31 is secured on the wall on the inner side of the car by means of screws, rivets or other securing means 32, which, in the case of rivets, will grip the outer wing and the skin forming the inner face of the wall of the car. A seal 37a is interposed between the wing 31 and the inner face of the wall.

The lateral face 21b of the tubular frame 30 which faces towards the exterior of the car is secured by means of screws, rivets or other securing means 32 onto a rim of the opening provided by the skin 2b of the panel which forms the outer face of the body, and projects relative to the core of the panel. A seal 37b is interposed between the lateral face 21b and the second skin 2b.

The reinforcement border 21 also comprises an inner collar 34 for securing of the window.

The inner core 31 is secured on the wall of the inner side of the car by means of screws, rivets or other securing means 32, which, in the case of rivets, will grip the outer wing and the skin forming the inner face of the wall of the car. A seal 37a is interposed between the wing 31 and the inner face of the wall.

The lateral face 21b of the tubular frame 30 which faces towards the exterior of the car is secured by means of screws, rivets or other securing means 32 onto a rim of the opening provided by the skin 2b of the panel which forms the outer face of the body, and projects relative to the core of the panel.

The reinforcement border 21 additionally comprises an inner collar 34 for securing of the window.

In the case in FIG. 5B, in addition to the elements previously described, a framing plate 36 is secured on the outer lateral face 21b of the border and on the panel 2. In this case, the framing plate 36 and the outer skin end in a bevel in a complementary manner, and the securing elements 33b which render the plate and the panel integral are secured in the core of the panel.

A seal 37c is interposed between the plate on one side and the border and the panel on the other side.

The skins are made of carbon fibers of grade “HR” and glass E according to the areas and requirements, and an epoxy resin which, when impregnated with the above fibers in a monolithic panel with a thickness of between 2 and 8 mm, has properties of FST>HL1, R1, R7 (according to standard EN45545).

The thickness of a skin is from 2 to 5 mm, and the fibers are in the form of one-way sheets or pre-impregnated fabrics.

For the core a PET foam is selected with a density of 100 kg/m³ or more, a PMI foam with a density of 50 kg/m³ or more, or a honeycomb with a density of kg/m³ or more, depending on the areas and requirements. The thickness of the core is from 10 mm to 200 mm, in this case also depending on the areas and the needs.

The method selected is polymerization under vacuum pocket (outside an autoclave) with a temperature which does not exceed 120° C.

It will be appreciated that the precise thickness of the skins, the core and the orientations of the fibers in the skins depend on the stresses on the body.

As previously indicated, these specifications relate to the vehicle's own frequency, which must be more than 10 Hz or so; it is then necessary to select the values of the face in terms of rigidity, compression/traction forces which are associated with the travel of the car, and are approximately a hundred tonnes, and the flexure forces associated with the pressure waves, of approximately 10,000 Pa.

Globally, for a car which is approximately 15 m between bogeys, thus making it possible to transport around 40 passengers in this area, the conventional calculations by means of finite elements result in a sandwich material approximately 40 mm thick.

According to one aspect of the disclosed embodiment, in particular for a double-decker car with lower windows 20a and upper windows 20b, the wall will comprise different skin thicknesses between the low part of the face and the high part. According to the example given in FIG. 6, the lower part of the panel 301 is produced with a skin thickness of 2.78 mm and a core thickness of 38 mm, whereas the upper part 302 is produced with a skin thickness of 3.33 mm and a core thickness of 38 mm.

It will be noted in particular that each skin has a thickness of approximately 3 mm, which incidentally is significantly more than the thickness of aircraft fuselages, which do not exceed 2 mm.

In the main areas (excluding connections and particular points), at least one and preferably both skins of the sandwich structure are produced for example using high-strength plies made of pre-impregnated carbon, for example of the type T700 made by the company Toray.

In order to produce the skin(s), it is possible to use as basic elements, by way of example: a pre-assembly of plies with fibers oriented at +45°, 0°, −45°, respectively with a dry gsm substance of 125 g, 250 g, 125 g, a one-way ply oriented at 0° with a dry gsm substance of 500 g, and a ply which is a fabric oriented at 0°/90° with a dry gsm substance of 500 g, these values being given with a tolerance of ±10%.

The table below describes the fibrous architecture which can result according to the areas of application of the composite material.

Gram

500

500

500

weight of

dry fiber

(g/m²)

Tvf (%)

50.00%

50.00%

50.00%

Unit

0.556

0.556

0.556

thickness

(mm)

density

1500.00

1500.00

1500.00

parts

Skin thickness

and

Height of

height HT of

n × UD

n × UD

n ×

(excl. galvanic

areas

core (mm)

panel (mm)

stack

0° carb

90′ carb

±45° carb

protection ply)

central

10

16.7

n. plies

3

1

2

area roof

th (mm)

1.67

0.56

1.11

3.33

(one skin)

%

50%

17%

33%

100.00%

Upper

38

44.8

n. plies

2

2

2

vertical

th (mm)

1.11

1.11

1.11

3.33

facade

%

33%

33%

33%

100.00%

(one skin)

Lower

38

43.7

n. plies

2

1

2

vertical

th (mm)

1.11

0.56

1.11

2.78

facade

%

40%

20%

40%

100.00%

(one skin)

In general, it is found that the optimization of the structure requires the presence of fibers at 0°, 90° and ±45°.

The fibers at 45° are particularly suitable for absorbing the shearing forces within the context of the panel concerned.

In this example, the preference is for a 50% distribution of one-way fibers at 0°, 17% fibers at 90°, and 33% fibers at ±45°, in order to produce a roof, 33% one-way fibers at 0°, 33% fibers at 90°, and 33% fibers at ±45° for an upper vertical facade, and 40% one-way fibers at 0°, 20% fibers at 90°, and 40% fibers at ±45° for a lower facade.

In an optimum manner, the shearing stress Tau (t) which is applied to the face panel must be absorbed by the fibers 100 which are oriented at +45° and −45° on each of the two skins of the structure, as illustrated in FIG. 3.

It is in fact in these conditions that the mechanical functioning of the structure is optimized, and thus consequently its weight and cost.

However at the panels of the faces, the presence of bay angles leads to cutting of the fibers.

In a configuration of this type, the shearing stresses pass via the resin, which results in a need for an excess thickness of the skins of the sandwich panel in the area between bays (pier glass) in order to make the shearing stress drop below the level permissible for the resin. For information, the permissible plane shearing stress for the resin (stack at +45° and −45° with all the fibers cut) is approximately 30 MPa whereas it is 500 MPa in the direction of the fiber when it is subjected to compression stress. Cutting of the fibers also makes the structure far more sensitive to environmental conditions and fatigue. Under fatigue loads, the permissible plane shearing stress for the resin is assessed as approximately 10 MPa, whereas it can be assumed that there is resistance of more than 200 MPa in the direction of the fiber.

This leads once again to a need for excess thicknesses, otherwise there will be a risk of weakening of the structure in the long term.

The solution proposed schematized in FIG. 7, in which the windows with a large height comprise an octagonal profile, for which the lateral sides are provided with a convex profile with three segments, i.e. an upper segment at 45°, an intermediate vertical segment, and a lower segment at 45°, consists of modifying the geometry of the bays such that a certain section of fibers 100 oriented at +45° and −45° can be continuous between the high part and the low part of the face, and thus transfer the shearing stresses. This therefore provides a configuration which is reminiscent of that of the hatches described in U.S Publication No. US2012/0223187A1, but which differs from it in the large surface area of the windows and the fact that their large side is according to the axis of the car. This makes it possible to increase the cross-section of working fibers, without decreasing significantly the surface area of windows.

Since the car is subjected to low pressures, the optimum orientation of the fibers is approximately ±45°, and not approximately 70° as for an aircraft fuselage.

One question concerns the optimization of the angle of cutting of the bays (for a spacing imposed), in order to maximize the glazed surface. In fact, for a given spacing between bays, this cutting angle affects directly the cross-section of working fibers.

Simulation by means of analytical calculation was carried out in order to evaluate the stresses in the direction of the thread in the plies at ±45°, and the plane shearing stresses in the plies at 0/90° according to the cutting angle of the windows 20 in accordance with the configuration in FIG. 9A, in which the small sides of the window have a profile in the form of a convex “V”.

This simulation, the parameters of which show that the angle of cutting at 45° is clearly optimum, makes it possible to determine that this angle could be taken to 50° with at least one carbon ply at ±45°, and that an angle of 60° can also be acceptable with the criteria retained, but with two carbon plies at ±45°.

The stacking of the composite panel (draping at 0°, +45°, −45° and 90°) corresponds to that which has been defined in order to comply with the mechanical requirements in the main area of the body. For a bay configuration corresponding to the body concerned (L_pier glass=384 mm and H_bay=620 mm), the angle α of cutting of the bay is varied. Consequently the length “L_uncut_fiber” decreases from a maximum value when α=45°, down to a zero value for a certain value of α (approximately 70° in the case in question).

The results of the analysis are given in FIGS. 9B and 9C.

This analysis shows that, when the angle of the bay is greater than 70°, all the fibers at ±45° are cut, and the shearing stress in the plies at 0° and 90° is greater than the permissible value, point P in FIG. 9B. Consequently, a reinforcement should be used in the area of the pier glass (increase the thickness by +250% in the case concerned), with an impact on the weight and the cost.

This analysis also shows that the cutting angle at 45° is clearly optimum, since the shearing flow is correctly absorbed by the fibers at +45° and −45° which are not cut, as shown in FIG. 9B, whereas the plane shearing stress is also lower than the permissible value, see FIG. 9C.

The analysis also shows that the angle of the bays could be opened up to approximately 55° without requiring reinforcements.

FIG. 8 represents the complete body of the car with the roof 35, the door openings 23 and its frame 25, service openings 22, 26 such as for air-conditioning, and their frames 24, 27, as well as the end frames 28 on which the walls 2 are secured.

The self-rigidified body can be assembled directly to a support chassis of the bogies of the car.

The presently disclosed embodiment can be used for all types of railway transport vehicles which are designed for passenger transport.