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

Abstract

A car belonging to a rolling vehicle, characterized in that it includes sidewalls in the form of a single piece made from composite material including a sandwich structure provided with a first skin on the outside of the car, a second skin on the inside of the car and a closed-cell foam or honeycomb core between the skins, the walls being provided with window openings formed by interruptions in the drapes of longitudinal fibres, transverse fibres and intersecting diagonal fibres, the openings having a polygonal shape that reduces the surface area of interrupted diagonal fibres in the corners of the openings.

Claims

1. A rolling vehicle car comprising lateral walls each in a single piece formed by a sandwich composite panel made of a single part 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 forming said skins, said openings having a polygonal form which reduces the surface of diagonal fibers interrupted in the corners of the openings, said walls forming the faces of the car.

2. The car as claimed in claim 1, wherein the openings have a generally hexagonal or octagonal form comprising two large horizontal sides connected by convex lateral borders.

3. The car as claimed in claim 1, wherein the openings are equipped with a reinforcement border provided with a tubular frame.

4. The car as claimed in claim 3, wherein 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.

5. The car as claimed in claim 4, wherein the tubular frame has a rectangular cross-section, with the inner wing extending a face of the tubular frame on the interior of the wall.

6. The car as claimed in claim 5, wherein the inner wing is secured on the interior of the wall by means of screws, rivets or other securing means.

7. The car as claimed in claim 3, wherein a face of the tubular frame which faces towards 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.

8. The car as claimed in claim 3, wherein the reinforcement border comprises an inner collar which receives a fastening of a window.

9. The car as claimed in claim 1, wherein 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°.

10. The car as claimed in claim 9, wherein the plies are plies impregnated with unit gsm substance of between 125 g/m.sup.2 and 500 g/m.sup.2.

11. The car as claimed in claim 1, wherein 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 of the wall.

12. The car as claimed in claim 9, wherein the threads at 45° are in the form of at least two ±45° plies made of carbon fiber.

13. The car as claimed in claim 1, wherein the core of the sandwich is made of material selected from amongst polyethylene terephthalate, polymethacrylimide polyetherimide, an aluminum honeycomb or a poly(m-phenyleneisophthalamide) honeycomb (structure impregnated with phenolic resin).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] 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:

[0061] FIG. 1 is a skeleton diagram of the shearing stresses according to the longitudinal direction of a lateral panel of a train car;

[0062] FIG. 2 is a detail of a panel according to the disclosed embodiment;

[0063] FIG. 3 is a representation of a panel according to the prior art;

[0064] FIG. 4 is a view in perspective of part of a panel and openings according to the disclosed embodiment;

[0065] FIGS. 5A, 5B are a detail in cross-section of a reinforcement frame at a window opening in the wall according to two embodiments;

[0066] FIG. 6 is a front view of an aspect of a panel according to the disclosed embodiment for a double-decker car;

[0067] FIG. 7 is a schematic representation of the structure of the wall according to the disclosed embodiment between window openings;

[0068] FIG. 8 is a view in perspective of a car body with walls according to an aspect of the disclosed embodiment;

[0069] FIG. 9A is a schematic view of passages of fibers inclined between openings;

[0070] 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

[0071] The disclosed embodiment is described mainly in FIGS. 2 and 4 to 8.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In comparison with a monolithic structure equipped with a strengthener, sandwich structures provide the following advantages in particular: [0076] Reduced production costs and weight, thermal insulation function provided by the core.

[0077] Compared with a sandwich structure solution of this type, monolithic panels have the following disadvantages: [0078] Higher production cost (assembly of the frames and strengtheners on the skins), high assembly cost (local assembly in the frame areas); [0079] In addition, the frames are thicker than the sandwich, which reduces locally the inner volume of the structures constructed.

[0080] 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.

[0081] The main constraints to be taken into account are described below, firstly in relation to the mechanical constraints.

[0082] For the skins: [0083] 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; [0084] 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.

[0085] 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.

[0086] 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:

TABLE-US-00001 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)

[0087] 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:

TABLE-US-00002 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)

[0088] For the core of the panel: [0089] 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.

[0090] 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.

[0091] 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/m.sup.3).

[0092] The material must also comply with railway standards for fire resistance, and in particular the 2013 version of standard EN45545.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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:

[0097] 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.

[0098] According to these examples, the reinforcement border 21 is provided with a tubular frame 30.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] The reinforcement border 21 also comprises an inner collar 34 for securing of the window.

[0104] 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.

[0105] 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.

[0106] The reinforcement border 21 additionally comprises an inner collar 34 for securing of the window.

[0107] 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.

[0108] A seal 37c is interposed between the plate on one side and the border and the panel on the other side.

[0109] 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).

[0110] 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.

[0111] For the core a PET foam is selected with a density of 100 kg/m.sup.3 or more, a PMI foam with a density of 50 kg/m.sup.3 or more, or a honeycomb with a density of kg/m.sup.3 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.

[0112] The method selected is polymerization under vacuum pocket (outside an autoclave) with a temperature which does not exceed 120° C.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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%.

[0120] The table below describes the fibrous architecture which can result according to the areas of application of the composite material.

TABLE-US-00003 Gram 500 500 500 weight of dry fiber (g/m.sup.2) 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)

[0121] In general, it is found that the optimization of the structure requires the presence of fibers at 0°, 90° and ±45°.

[0122] The fibers at 45° are particularly suitable for absorbing the shearing forces within the context of the panel concerned.

[0123] 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.

[0124] 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.

[0125] It is in fact in these conditions that the mechanical functioning of the structure is optimized, and thus consequently its weight and cost.

[0126] However at the panels of the faces, the presence of bay angles leads to cutting of the fibers.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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”.

[0133] 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°.

[0134] 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).

[0135] The results of the analysis are given in FIGS. 9B and 9C.

[0136] 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.

[0137] 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.

[0138] The analysis also shows that the angle of the bays could be opened up to approximately 55° without requiring reinforcements.

[0139] 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.

[0140] The self-rigidified body can be assembled directly to a support chassis of the bogies of the car.

[0141] The presently disclosed embodiment can be used for all types of railway transport vehicles which are designed for passenger transport.