EP3271233A1

EP3271233A1 - Assembly with flexible link and flexible link for such an assembly

Info

Publication number: EP3271233A1
Application number: EP16714784.2A
Authority: EP
Inventors: Sylvain Claudel
Original assignee: Airbus Defence and Space SAS
Current assignee: ArianeGroup SAS
Priority date: 2015-03-19
Filing date: 2016-03-18
Publication date: 2018-01-24
Anticipated expiration: 2036-03-18
Also published as: WO2016146800A1; FR3033846B1; EP3271233B1; FR3033846A1

Abstract

The invention relates to an end-to-end link between two panels (1, 2, 200, 300, 300') each including two plates or skins (10, 11, 23, 26), defining outer surfaces of said panels, connected by a solid or cellular core or by boxes (12, 27), and including an end edge, for which one of the plates or skins of each panel is extended by a tab (17, 24), the tab of a first one of said panels engaging, during the linking between the panels, with the outer surface of the skin or plate (10, 26) that is not provided with a tab of a second one of said panels and for which the edge of a first one of said panels, referred to as bevelled edge (13), is bevelled relative to said surfaces of the panel (10, 11) that include same, while the edge of the second one of said panels, referred to as straight edge (22), is an edge substantially perpendicular to said surfaces of the panel that include same, so that the tab of the straight-edge panel, referred to as compensation tab (24), includes in the width thereof a bearing end portion (b, c) and a free intermediate portion (a) capable of bending to compensate for the differences in thickness between the panels while the tab of the panel including said bevelled edge, referred to as bearing tab (17), engages over substantially the entire width thereof with the bearing portion (21) of the surface of the panel receiving same. The invention can be used for assembling long panels.

Description

ASSEMBLY WITH SOFT BONDING AND

FLEXIBLE CONNECTION FOR SUCH ASSEMBLY

Field of the invention

The present invention relates to a flexible link assembly and a flexible link for such an assembly. It applies in particular to the fixing between composite panels and large metal structures.

Technological background

During the manufacture of large structures such as aircraft or train crates, it is necessary to assemble structures of several tens of meters. This is the case for example of the connection between the front panel and the lower part (stretcher) of a train body.

These panels initially made of metallic materials, are expected to be replaced at least partially by panels made of composite materials that allow to design and realize even lighter structures, which is particularly important for the transport industry.

Whether metal or composite materials, large panels that have a structural function are often sandwich panels, that is to say they consist of two skins interconnected by various well-known techniques. This is usually the technology that gives the panels stiffness and inertia for an optimized mass as low as possible.

Like all manufactured parts, these panels have manufacturing tolerances, which are in fact of two kinds:

General tolerances related to the stacking of the elementary layers of each panel to be assembled

Tolerances of shape of parts However, because of the large dimensions, the parts to be assembled have shape tolerances that can induce games that can reach several millimeters between the parts to be assembled. These games are not acceptable for many reasons, mechanics, weatherproofness, and thus the definers use different methods to fill these games.

We can first use panels whose tolerances of shape are very low, much lower than those of standard products, either by better controlling the manufacturing process, or by performing machining after this manufacture: it is conceivable that this type of solution is particularly expensive.

Or we can fill the games:

For example, in aeronautics, one often practices a "rigid filling", that is to say that one introduces metal shims in the intervals, which requires to measure very precisely the games on a case by case basis.

When the game is weak - a few tenths of a millimeter, we can just fill it with a putty.

In other industries, one can seek to catch up with the games, and use the flexibility of the panels and deform them until the games are eliminated for example using screws or rivets.

All of these methods have disadvantages, and generally:

The aeronautical technologies are very powerful but also very expensive (measurements and realization of specific and precise fillings, reworking of large parts, ..)

Deformation technologies are less expensive, but they require that the materials have large plastic deformations, and introduce residual stresses in the materials that make the assemblies mechanically less efficient, in static but also in fatigue.

To fix ideas include the NF EN 755-9 standard in the version in force on ¹ March 2015, which defines acceptable form tolerances during manufacturing of Aluminum profiles, evaluates the games can usually expect an overall straightness tolerance of 1.5 mm / m, or 15 mm for a 10m long piece plus a tolerance of local straightness of 0.6 mm / 300 mm, ie a 30 mm clearance for an assembly of two metal pieces 10 m long.

According to FIG. 1, in order to connect such parts, it is possible to provide each piece with an end wing and to assemble the head-to-tail parts so that the end flanges attach to opposite sides of the parts, in particular by riveting: sets of assemblies will be at the junction between the terminal wings and opposite sides, areas where it will be necessary to provide solutions to fill these games

We are interested here in solutions that allow an optimal compromise between the technical performance of the assembly and its economic cost: it is a question of using a method of assembly as simple as possible, which is the least demanding possible vis- with respect to the manufacturing tolerances of the parts and which induces only a minimum of residual stresses in the assembled parts, so as to preserve the structural strength in the duration of the assembled parts.

The solution envisaged here is intended to obtain a contact between the two parts of the connection which will give a proper mechanical strength of the connection.

Brief description of the invention

To this end, the present invention provides an end connection between two panels each comprising two plates or skins, defining external faces of said panels, connected by a solid or cellular core or by a box, and comprising a termination edge, for which a plates or skins of each panel is extended by a tongue, the tongue of a first of said panels coming, during the connection between the panels, to be applied on the outer face of the skin or plate without tongue of a second said panels and for which the edge of a first of said panels, said bevel edge, is beveled with respect to said faces of the panel comprising it while the edge of the second of said panels, said right edge, is an edge substantially perpendicular to said face of the panel comprising it, so that the tongue of the panel with a straight edge, called catch tab, has in its width an end portion in the ui and a free intermediate portion capable of flexing to make up for differences in thickness between the panels while the tongue of the panel comprising said edge in bevel, said tongue support, bears substantially all of its width on the bearing portion of the face of the panel receiving it.

Preferably, said support tongue defines a substantially rigid reference surface for the connection.

According to a particular embodiment, said right edge is at a 90 ° angle

± 15 ° with respect to said faces of the skins or plates of the panel comprising it.

According to an alternative or complementary embodiment, said beveled edge makes an angle of 45 ° ± 15 ° with respect to the normal to said faces of the panel having it.

Said bevel edge is advantageously made by folding a first skin at a first inclination at the beginning of the bevel and then at a second inclination at the end of the bevel where the first skin joins the second skin of the panel to form a first tongue called a tongue. support at the end of said beveled edge.

Said straight edge is advantageously a wall connecting the two plates of the right-sided panel and disposed at the end of a first of these plates, said catch-up tab of the panel comprising said right edge being constituted by an extension of a second of its plates cantilevered with respect to said right edge.

According to a particular embodiment, the panel comprising said right edge is a panel or a metal structure.

Said catch tab is made so as to have a flexibility adapted to make up the differences in thickness of the panels by flexing its free intermediate portion.

In particular, by producing a retraction tongue and a sufficiently long bevel, the free intermediate portion can be sufficiently deformable to come into contact with the face of the panel receiving it and allow riveting while minimizing the stresses induced by the assembly.

According to a preferred aspect of the invention, the link comprises a substantially rectangular triangular section day for which said beveled edge constitutes the hypotenuse of said section, the right edge and said free intermediate portion constituting the other two sides of said section. The invention further proposes an assembly of two panels which comprises between the two panels a riveted connection comprising at least a first line of fastening rivets of the support tongue of the panel comprising said beveled edge on a bearing face of the panel comprising said right edge and at least a second line of fastening rivets of said end portion of said catch tab on a bearing face of the panel having said beveled edge.

The support wall of the panel comprising said right edge is advantageously a recessed edge of the tongue-free face of said panel so as to compensate for the thickness of the support tongue to have the flat faces outside the two panels in continuity.

The support wall of the panel comprising said right edge is advantageously a recessed edge of the tongue-free face of said panel and connected to said face by a heel forming a stop for the support tongue.

The catch tab is preferably adapted to bend under the action of the assembly of the first panel and the second panel is towards the first panel or in the opposite direction.

According to a particular embodiment, the flexibility of said catch tab is calculated to allow it to flex by a distance at least equal to the sum of the tolerances of the layers that constitute each panel. According to an alternative embodiment, the flexibility of said catch-up tab is calculated to allow it to flex by a distance at least equal to the quadratic sum of the tolerances of the layers constituting each panel.

For the quadratic sum we take the square root of the sum of the squares of the uncertainties of each layer.

The deflection of said catch tab is measured at the point of docking between said tongue and the face of the panel on which it is applied.

The invention is also applicable to a composite panel / metal structure composite assembly for which a first of said panels is a composite panel and a second of said panels is a metal structure.

The composite panel is advantageously the panel comprising said beveled edge and the composite panel comprising a core between a first skin and a second skin, the soul has a beveled edge extending from the first skin to extend towards the second skin, the first skin marrying the slope of the beveled edge to join the second and realize the support tongue.

The metal structure is advantageously the panel comprising said right edge.

Brief description of the drawings

Other characteristics and advantages of the invention will become apparent on reading the following description of a nonlimiting exemplary embodiment of the invention with reference to the drawings which represent:

in FIG. 1: a metal structure termination and a composite panel termination of the invention in cross-sectional and opposite view;

in Figures 2A and 2B: views of the termination of Figure 1 respectively for a negative game and a positive game;

in Figure 3: a detail of the structure of Figure 1;

in FIG. 4: the modeling of a catch-up tab of the metal structure of FIG. 1;

in FIGS. 5A and 5B: modelizations of the stresses in the structure for the games of FIGS. 2A and 2B;

in Figure 6: an example of structure receiving a panel according to the invention;

in FIGS. 7A and 7B: schematic representations of the assembly of FIG. 1 at the level of the catch tab in front view;

FIGS. 8A to 8C: an example of a rivet that can be used for the invention.

in Figure 9: a perspective view of a rail car comprising composite panels fixed with a lower metal structure by means of a connection according to the invention;

in Figure 10: a perspective view of the assembly of a panel and structural portion of Figure 9;

in Figure 1 1: a side sectional view of the assembly of Figure 10.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention is part of the assembly of large length panels and especially in the context of the study of replacement aluminum or steel panels including rail car bodies by composite side panels. In this context, as shown in FIG. 9, composite panels 300 attach to metal frame members 200 constituting the base of the cars in order to save weight on the structure, and roof panels 301 attach to said side panels. . This makes it possible to increase the payload of the body, whether in number of passengers or on-board equipment.

One of the constraints of such an embodiment is to minimize the assembly costs of large parts such as those that make up the train body, including the side walls, the metal frame and the roof. For this we must find the ideal compromise between the cost of manufacturing primary parts and the cost of pure assembly. The latter is directed by the time required for handling and the complexity of operation.

The riveting process is well suited to making connections between large parts and is suitable for assembling the aforementioned parts.

In the aeronautics sector, many case-by-case solutions are used during assembly (metrology, re-machining of parts, use of machined physical calles, etc.). In the railway field concerned, the accepted price per unit of mass earned on a train crate is significantly lower than the accepted price for the same unit of mass gained on an aircraft for example. In addition the cost of manufacturing parts such as panels must remain reduced which does not reduce as much as in the aeronautical acceptable dimensional tolerances of parts.

Too stringent manufacturing tolerances would impose excessive manufacturing costs. It is known that highly hyperstatic structures consisting of large relatively flexible parts and subject to geometric defects can not be assembled without undergoing deformation. This results in a geometrical state and partially controlled residual stresses.

The present invention proposes a new approach that uses the flexibility of a part during the assembly of panels which will allow to allow greater tolerance on the dimensions of the parts, particularly the thickness composite panels that will be assembled on metal structures. The present invention also makes it possible to obtain wider form defect tolerances for the manufacture of the parts, thus a lower cost possible, while ensuring the performance of the assembly by using the flexibility of part of the assembly.

Composite panels are solid products comprising skins or plates made of a bonding material called a matrix and a reinforcing material in general in the form of fibers which sandwich a lightweight filler material, foam, foam material, material or the like. bee or other called soul.

The matrix retains the geometrical arrangement of the fibers and transmits them the stresses to which the piece is subjected. The material obtained is thus light, has good fatigue strength and has good mechanical properties in the direction of the fibers.

In the case of long pieces, a lack of thickness or flatness of a panel such as a composite panel will result for example by undulations of the panel along the length of the panel.

The preferred assembly method for joining two large thin pieces is riveting. This process frequently uses so-called blind rivets because they require access to only one side of the assembly. With the help of a pressure gun, the rivet rod is pulled, which makes it possible to crush the head on the other side. The rod is sized to break at its base from a certain pressure.

In the case of train crates the assembly is composed of two lines of rivets. The first is on the outside of the train, the second is on the inside of the train.

Riveting lines are for example shown under the marks 1 10, 120 in Figure 10 between the panel 300 and the structure or metal frame 200 rail car sill used to receive a fixed panel according to the invention.

In an application to the realization of train crates in particular, depending on the heat and hydrometry, the temperature of a train box can rise to temperatures exceeding 80 ° C which solicits important assemblies and in particular assemblies composite / metal which imposes particular design constraints.

In the context of the invention and according to FIG. 1, the edge of a composite panel 1 to be fastened comprises a return to the skin forming a fastening tab 17 bearing on one face of the metal panel 2 and here called a tab of FIG. in the sense that it constitutes a substantially rigid reference bearing surface for the assembly.

The metal panel 2 has on its side a metal tongue 24 provided with an end portion bearing on one face of the composite panel but also provided with an intermediate free support part over a length which allows to provide flexibility for the assembly, this tongue being called catch tab. The rivets are positioned at the portion of the tongues resting on the faces of the panels and inserted into holes, a series of holes P1 crossing the catching tab and a first skin 10 of the panel and a series of holes P2 crossing the part. in support of the catch tab and a bearing wall 21 of the frame.

By substantially or substantially rigid reference bearing surface is meant that the support tongue is sufficiently rigid so that its eventual deflection remains negligible compared to the flexion of the catch-up tongue in case of difference in thickness of the panels at of the connection, which corresponds for example to an angular deflection of the support tongue 10 to 100 times less than that of the catch tab at their junction with the edge of the panel carrying them for a thickness difference.

Similarly, the support tongue is in abutment on substantially its entire length, which means that even if a small portion of the support tongue is cantilevered, this small part remains of negligible length, for example up to 10% of the length of the tongue and is of insufficient length to bring a significant angular deflection of the support tongue.

The defects of shape of the composite parts are induced in particular by the imperfect shape of the mold. The defects of the mold cause a first family of defects on the piece produced.

A second source of defects comes from deformation efforts after polymerization. The process of manufacturing composite materials entails internal tensions that relax after polymerization, which leads to an overall deformation of the piece spring effect called "spring back".

These two sources of defects induce defects of form D _f on the composite parts.

A third source of defects originates, on the face opposite the mold, variations in thicknesses related to manufacturing dispersions (cumulative tolerances of successive layers of materials assembled on the mold): this gives rise to stacking defects.

The composite panel 1 comprises a first skin 10 and a second skin 1 1 disposed on either side of a core 12 made of foam, honeycomb or other light material. It comprises, at the level of at least one edge of the composite panel, an assembly termination comprising the border 17 of return to the skin made by solidifying together the two skins 10, 1 1 and forming the support tongue.

To improve the junction between the skins and the rigidity of the edge of the panel at the termination, the edge 13 of the core is cut into a bevel to achieve a progressive transition zone from the first face 14 to the second face 15 of the panel , the first skin 10 covering the transition zone from the first face to the second face of the panel to be applied to the second skin 1 1 which extends the second face and make the support tongue 17 by return to the skin of the composite panel.

Due to its constitution by joining the two skins the support tongue is relatively rigid and non-flexible.

The metal structure 2 comprises an end 20 of junction with the composite panel provided with a bearing wall 21 opposite the support tongue 17.

This structure further comprises a connecting wall 22 between said support wall and a second face 23 of the structure, this connecting wall forming a substantially straight edge.

By substantially or essentially straight edge is meant a perpendicular edge or as perpendicular as possible to the skins or plates 23, 24, 21, 26 taking into account cutting, machining or molding tolerances. In the context of the present invention, it is considered that substantially or substantially straight an edge at 90 ° ± 15 ° of the surface of the skins or plates.

The tongue 24 extends beyond the right edge on the face 23 of the structure opposite to that carrying the support wall 17. The tongue 24 is cantilevered and is applied on the first face 14 of the composite panel .

The tongue 24 has a free portion of length "a" and a bearing portion of length "b" + "c".

The free portion is above the beveled edge 13 of the panel 1 and allows the tongue 24 to bend which gives it a catch-up function and defects as will be seen later.

With respect to the beveled edge, a range of 30 ° to 60 ° is considered to be 45 ° ± 15 ° to the plate normal to provide a suitable tab free length for the invention.

The portion of the tongue 24 bearing on the first face 14 of the panel and the rim 17 on the support wall 21 constitute receiving areas of fixing means such as rivets.

The defects that catch the catch tab 24 are including the stacking defects of the composite panel and the structure.

These stacking defects D _e are constituted by the sum of the tolerances of all the layers which constitute each panel (skin, sandwich webs, etc.). It may be a classical addition, or a quadratic addition. (we take the square root of the sum of the squares of the uncertainties of each layer) more realistic from the point of view risk of occurrence, and therefore preferred by the inventors. Its value is of the order of ± 1 millimeter for a stack such as that of Figure 1, when the panels have a thickness of about 50 mm, the skins of the composite sandwich having a thickness of about 3 mm.

The tongue is adapted to bend under the action of the assembly of the panel and the structure in the direction of the panel as shown in Figure 2A with a displacement -y corresponding to a thickness of the panel relative to the structure or in the opposite direction in Figure 2B with a displacement + y corresponding to a thickness of the panel relative to the structure.

FIG. 3 represents an example of structure 200 comprising a first face 26 terminated at the assembly portion with a composite panel by the support wall 21 and which has a second face 23 which is extended by the tongue 24. The enlargement in Figure 3 allows to distinguish a heel 25 connecting the support wall 21 to the first face 26 of the structure. This heel makes it possible here to obtain a flat outer face between the panel and the structure, the difference in height between the bearing portion 21 and the plate 26 of the structure corresponding to the thickness of the support tongue 17 of the panel composite. The heel may further serve as a stop for the edge 17 of the assembly end of the panel.

As seen above, the tongue 24 is intended by its flexibility to catch the stacking games, but it can not make up alone the games due to the shape tolerances: in fact it is the flexibility of the panel and the structure , flexibility due to their large dimension in the sense of the length that allows to catch this game.

It should be noted that it is well known that this flexibility depends on the shape of the panel and the structure, and for example a flat panel will be very flexible while a curved panel like that of Figure 3 will be much less flexible.

As explained in the previous part, to achieve the assembly without having a game to fill, it is necessary to increase the flexibility of the metal part to reduce the internal stress at the assembly. It is the role of the catch tab 24 to provide this flexibility in the assembly, by a suitable design of this tongue.

For this adapted design, it is necessary to give itself a number of objectives, related to the proper functioning of the assembled structure.

In general, for the design of this connection:

- One gives a maximum criterion of maximum buckling stress in the tongue;

- One gives a criterion of maximum residual stress admissible in the tongue;

- We give ourselves a maximum permissible connection set, likely to fill by mastic;

- The thickness of the latch is defined so that it can withstand the efforts in matting due to the connection;

- On the basis of this thickness and buckling criterion, we deduce the maximum possible length of the pawl; - On the basis of this length, the thickness and the criterion of residual stress, one calculates the maximum force of tightening of the connection, from which one deduces the maximum deformation;

- This deformed is compared to the maximum possible tolerance due to the stacks of components of the panels, ensuring that the maximum difference between the deformed and the maximum tolerance is less than the maximum permissible set of connection;

- It is ensured that with the efforts thus defined, it will be possible to make up the clearance of the form tolerances for the actual link to be made.

Assuming that the stacking or shape tolerances can not be made up, the analysis is repeated by reducing these tolerances, respectively.

In practice, starting the analysis with standard tolerances that allow a minimum cost of the panels, it may be necessary to reduce these tolerances and thus to increase the cost of the panels, but this increase will be the lowest possible.

It is first necessary that the catch tab modeled in Figure 4, also called hereinafter pawl, and the link are able to withstand the efforts of the structure in operation. These supposedly known efforts make it possible to determine the number of connecting elements / rivets, their diameter D, the pitch P between two rivets depending in particular on their characteristics. The operation by matting these rivets allows to determine the thickness of the pawl:

e> Shearing / (D ^* o matage)

with:

e = pawl thickness (mm);

o matage = permissible matting stress on (MPa);

D = diameter of the rivet (mm);

Shear = external shear force applied to a rivet (N).

Moreover, it is necessary that the link is able to withstand all the efforts to which it will be subjected in operation. The most dimensioning force is the buckling behavior of the pawl during a bending effort of the connection to do this, the buckling stress Of must be greater than the elastic limit o _e of the material used, in fact with a coefficient security of 1, 5. The buckling stress can be calculated in various ways, it is estimated here by assimilation of the pawl to an intermediate between a recessed beam - recessed and a beam-guided:

F_critical buckling = T E If / Ik

With:

E = elastic modulus of the pawl material (MPa);

If = bending inertia latch = b ^* e ^3/12;

Ik = 0.6;

From where :

0_circular buckling = ( ^" Π ^{" 2 *} E ^* e ² ) / (4,32 ^* l_ ² )> 1, 5 O _th

with:

L: Length of the latch to the point of insertion of the clamping (mm);

e = pawl thickness (mm);

o _e = elastic limit of the material used (MPa);

From where :

L <π ^* e ^* E ^{1/2 *} 1 / (4,32 ^* 1, 5 ^* σ _θ ) ^1/2

So that the pawl 24 remains usable in its function, it is also necessary that the bending stress induced by the clamping does not reach a fraction of the elastic limit of the material; the maximum value o _m admissible for this residual stress depends on the assembly and its function, but as a first estimate it may be chosen that this maximum stress does not exceed half of the yield stress potential of the material, ie o _m = 1 / (2 ^* 1, 15) ^* o _e . This constraint makes it possible to calculate the maximum arrow attainable by the pawl, and therefore the maximum game that can be caught.

If y _m is this arrow, it is related to the maximum acceptable stress in the latch by the relation (approximation of the latch by a built-in beam): y _m = o _m ^* (2 ^* L ² ) / (3 ^* E ^* e )

The comparison of this maximum arrow achievable with the stacking defect D _e makes it possible to verify whether the assembly is possible:

Let y _m > D _e - m, where m is the residual clearance that can be filled by a putty; m is at most 0.7 mm in a conventional manner. So, the assembly is feasible. Let y _m <D _e - m then the assembly is not feasible; we must review the coastline, which must be more restrictive; and the parts will be more expensive to manufacture.

It remains to verify that the flow of maximum effort landings F _applied to latch end will be sufficient for this distortion. To perform the assembly operation, pins are usually used, which are temporary docking devices that are placed in the holes provided for the rivets of the final assembly; knowing the maximum effort of docking a pin (T _epi ngie) and considering a pin in each hole, calculates K _a = Tepingie / P and that this value is greater than the effort K required to bend the latch the maximum defect value D _e :

K = 3 ^* D _e ^* E ^* e ³ / (L ^{3 *} 12)

At the end of this first phase of predefinition of the pawl, the analysis continues with a calculation which makes it possible to check the requirements of assemblies by taking into account the defects of shapes of the panels to be assembled in their great lengths.

This requires a finite element calculation, in which the assembly of the two parts to be assembled, including the latch or retrofit tab defined above, is modeled with the following assumptions;

The deformation is ensured by assembly pins using the locations provided by the rivets; assembly pins are standard products whose clamping force is known.

The shape defect is modeled either by tools (such as 3DCS assembly simulation software from HITEX) or by finite element calculation software in the form of a sinusoidal defect of variable wavelength, of which the amplitude is the expected form defect.

The calculation gives the final:

- the residual clearance that must be at the maximum mentioned above (m)

- residual stresses that must not exceed 0 _m

If these objectives are not achieved, it is necessary to specify lower form defects, which complicates the parts manufacturing process and therefore their cost. It will be noted that the aforementioned approach relates to the worst case, which indicates the feasibility of the assembly, and the class of manufacturing tolerances necessary for the success of the assembly. When this feasibility is demonstrated, it is always possible to optimize the design in terms of pawl length, choice of material, residual stresses, residual clearance and cost.

Increasing the length of the pawl therefore greatly reduces the maximum stress internal to the frame or metal structure. However, increasing the length of the latch indefinitely is not possible. There is a risk of buckling of the pawl.

Also, a compromise between the length of the pawl and therefore the termination of the composite panel and its return part to the skin and its flexibility is possible depending on the parts to be connected, their dimensions and the efforts it has to go through.

FIGS. 5A and 5B show the location of the stresses σ maximum, σ MI in the case of a negative clearance - y for FIG. 5A, where the maximum stress σ _Μ ι is situated at the junction between the catches or catch tab and the connecting wall 22 and σ _M 2 in the case of positive play + y in the case of Figure 5B where the maximum stress OM ₂ is in the docking area of the pawl on the first side 14 of the panel.

To better describe the implementation of the invention, we will consider the case presented in FIG. This figure shows the aluminum structure 200 of Figure 3 in perspective, this structure to be assembled with a composite sandwich panel. The length of the two pieces and the link is 10 m and the rivets are aligned along two lines 110 and 120 on both sides of the structure.

FIG. 7A shows a defect in shape to catch up with D _f between the composite panel and the metal structure. FIG. 7B shows, in the left-hand part, the gap Ay, and in the right-hand part the result after tightening by means of adapted tools (pins for example). or rivets 30.

By way of example, consider a panel such that the thickness of the foam core of the sandwich panel is 38 mm, the thickness of the skins is 3 mm, the return to the skin of the composite panel is carried out with a angle of 45 ° and a clearance of 10 mm is provided between the latch or catch tab 24 and the first face 14 of the panel when the edge 17 is placed on the support wall 21 was chosen to avoid double contact.

The structure of the example is aluminum 6005 T6 of 3 to 5 mm thick, its modulus of elasticity is E = 70GPa, and its elastic limit is o _> 220 MPa

In addition, the stresses in use made it possible to define the connection which will be carried out using blind rivets to shoot passivated stainless steel of 6,58mm of diameter, distributed in a step of P = 60mm, to make it possible to ensure the holding under a shear stress flow of 70 N / mm

The pins used to make the assembly allow to spend an effort of 2000N.

Concerning the stacking defect (dimension string), it is considered equal to ± 0.74 mm (quadratic approach retained).

We thus obtain for the latch the following result:

Thickness> 2.1 mm or 3mm retained;

Maximum length L <69 mm with this thickness of 3mm;

Maximum allowable deflection by the pawl in bending = 1, 5mm, therefore greater than the defect to catch up

Approach force flow required to deform the pawl of the defect value = 1, 1 N / mm, therefore less than the maximum docking effort flow provided by the 33N / mm pins

It is therefore found that the criteria that have been set to define the pawl are therefore verified. The analysis will continue by taking into account the defects of shapes of parts to be assembled, neglected at this stage.

The defects of form of the pieces in the great length of the panel of 10m of the example, as initialization starting from the analysis, will be represented by:

- For the metal structure: a sinusoid of amplitude 15mm peak-to-peak, and a wavelength of 2.5m, this defect corresponding to an overall shape tolerance of 15mm associated with a local shape tolerance of 0.6mm on 300mm, consistent with defects that may be encountered on a spun aluminum profile; - For the composite panel: a sinusoid of amplitude 15 mm peak-to-peak, and a wavelength of the fault identical to that of the metal panel, ie 2.5 m, but in phase opposition with respect to the latter.

The boundary conditions used to perform the assembly simulations and the conditions of validity of the link are specified below and by way of example, the docking forces are set at 2000N every 240mm (1 pin every 5 holes), ie a pinning force flux of 8333N / mm.

In terms of maximum permissible clearance between parts after docking:

In B: m <0.7mm;

In A: m <0.1 mm (lower than in A because we do not want to make liquid filling in this area);

In terms of maximum permissible stresses in the parts after docking: Metal part: Von Mises criterion o _m <220 ^* (1 / (2 ^* 1, 15) = 95MPa; Composite part: Hashin criterion <0.15 = (1 / (2 ^* 1, 3)) ²

The coefficient 1, 3 corresponds to the breaking coefficient of safety specified in the dimensioning standard of cases EN 12663-1.

The flexibility of the parts depending on the curvatures of the panel, two cases of assemblies corresponding to two geometries of composite panels were studied: the case of a composite panel plane (such as a face), and the case of a composite panel curve (such as a roof panel).

Fig. 11 shows the view of a curved panel case 300 'assembled with the body structure 200 or another panel.

In the analyzes that follow, the length of the latch or catch tab 24 'is geometrically fixed at 62mm.

The results of the two finite element analysis are presented below:

For the connection between a planar composite panel as in figure 10 and a metal structure or panel, the validity requirements of the connection are ensured for the following tolerances on the composite panel and the metal panel:

a sinusoid of amplitude 4.5mm peak-to-peak and a wavelength of 2.5m, this defect corresponding to an overall shape tolerance of 4.5mm associated with a local shape tolerance of 0.2mm over 300mm; a sinusoid of amplitude 7.5 mm peak-to-peak and a wavelength of 5 m, this defect corresponding to an overall shape tolerance of 7.5 mm associated with a local shape tolerance of 0.1 mm over 300 mm.

For the curved composite panel of Figure 1 1, the validity requirements of the connection are ensured for more restrictive tolerances on the panels to be assembled, since the stiffness of the composite panel limits its ability to deform. The maximum defect justified corresponds to a sinusoid of amplitude 4.5mm peak to peak and a wavelength of 5m. This defect corresponds to an overall shape tolerance of 4.5 mm associated with a local shape tolerance of 0.1 mm over 300 mm.

It can thus be seen that, as expected, the assembly in the case of the curved composite panel requires that its shape tolerance be almost twice as low as that required for the assembly of the flat panel; and so that are cost is higher

In addition, to obtain compliance with the docking criteria under these conditions, the pawl length had to be lengthened to its maximum value, or 69mm to maximize the flexibility of the latter.

FIGS. 8A to 8C show a blind rivet that can be used to make the assembly of the invention.

In FIG. 8A, the rivet 30 is shown before being crushed to tighten an external part A on an internal part B, for example the support wall and the catches or catch tab and the first skin of the panel.

The rivet according to the example comprises a rod 31 terminated by a bulge 36, a head 32, here a countersunk head, a hollow body 33 receiving the rod and having a conical portion 33a, a helical washer 34 and a deformable sleeve 35.

The helical washer is disposed between the sleeve 35 and the conical portion 33a of the hollow body 33 and the deformable sleeve 35 is retained by the bulge 36 of the rod 31 against the washer.

In FIG. 8B, a pull on the rod 31 pulls on the bulge 36 which pushes the washer 34 and the sleeve 35 onto the body 33. The washer is expanded and the sleeve crushes longitudinally while widening while climbing on the part conical body. In FIG. 8C, the washer 34 abuts against the internal part B and is held by means of the crushing of the sleeve 35. Once the calibrated tightening force corresponding to the rupture of the rod 31 is reached, the latter breaks to leave an external surface without asperity.

For the rail car of Figure 9 comprising composite panels fixed with a lower metal structure, the side faces 300 of the car are riveted according to the invention on the body 200, structure located in the lower part of the car.

The invention is not limited to the examples shown and in particular a tubular reinforcement element or according to another profile such as an omega may be provided in the panel under the first skin 10 to the right of the piercing zones P1 receiving the rivets 30 for strengthen the panel. Similarly, the metal structure may be of varied height H, be straight or have a radius of curvature different from that shown.

Claims

R E V E N D I C A T IO N S

1 - end connection between two panels (1, 2, 200, 300, 300 ') each comprising two plates or skins (10, 1 1, 23, 26), defining external faces of said panels, connected by a solid core or honeycomb or box (12, 27), and having a termination edge, for which one of the plates or skins of each panel is extended by a tongue (17, 24), the tongue of a first of said panels coming, when of the connection between the panels, to be applied on the outside face of the skin or tongue-free plate (10, 26) of a second one of said panels and for which the edge of a first of said panels, said beveled edge ( 13), is made bevel with respect to said faces of the panel having it (10, 1 1) while the edge of the second of said panels, said right edge (22), is an edge substantially perpendicular to said face of the panel comprising it, so that the tongue of the panel with a straight edge, called catch tab (24), mporte in its width an end portion in support (b, c) and a free intermediate portion (a) capable of flexing to make up for differences in thickness between the panels while the tongue of the panel comprising said beveled edge, called tongue d support (17), bears substantially all of its width on the bearing portion (21) of the face of the panel receiving it.

2 - end connection according to claim 1, wherein said support tongue (17) defines a substantially rigid reference surface for the connection.

3 - end connection according to claim 1 or 2, wherein said straight edge (22) is at an angle of 90 ° ± 15 ° with respect to ux said faces of the skins or plates (23, 26) of the panel having it.

4 - end connection according to claim 1, 2 or 3, wherein said beveled edge (13) is at an angle of 45 ° ± 15 ° relative to the normal to said faces (10, 1 1) of the panel having it.

5 - end connection according to any one of the preceding claims, wherein said bevel edge (13) is made by folding a first skin (10) at a first inclination at the beginning of the bevel and then at a second inclination at the end of the bevel where the first skin (10) joins the second skin (1 1) of the panel to form the first tongue called the support tongue ( 17) at the end of said beveled edge.

6 - end connection according to any one of the preceding claims, wherein said straight edge (22) is a wall connecting the two plates (23, 26) of the right-sided panel and disposed at the end of a first of these plates (26), said catch tab (24) of the panel comprising said right edge (22) being constituted by an extension of one second of its plates (23) cantilevered with respect to said right edge (22).

7 - end connection according to any one of the preceding claims, wherein the panel (2, 200) having said right edge is a panel or a metal structure.

8 - end connection according to any one of the preceding claims, wherein said catch tab (24) is made so as to have a flexibility adapted to make up the differences in thickness of the panels by bending of its free intermediate portion ( at).

9 - end connection according to any one of the preceding claims, wherein, by making a retraction tab (24) and a bevel (13) sufficiently long, the free intermediate portion (a) is sufficiently deformable to come into contact with the face of the panel receiving it and allow riveting while minimizing the stresses induced by the assembly.

10 - end connection according to any one of the preceding claims, wherein the connection comprises a substantially rectangular triangular section day, said beveled edge (13) constituting the hypotenuse of said section, the right edge (22) and said free intermediate portion (a) constituting the other two sides of said section.

1 1 - Assembly of two panels by means of a connection according to any one of the preceding claims which comprises between the two panels a riveted connection comprising at least a first line of rivets (P2, 120) for fixing the tongue of support (17) of the panel comprising said bevelled edge (13) on a support face (26, 21) of the panel comprising said right edge and at least a second line of rivets (P1, 1 10) for fastening said portion terminal of said catch tab (24) on a bearing face (10) of the panel comprising said bevel edge.

12 - Assembly according to claim 1 1 for which the bearing wall (21) of the panel comprising said right edge is advantageously a recessed edge of the face (26) devoid of tab of said panel so as to compensate for the thickness of the support tongue for having the outer plane faces (26, 1 1) to the two panels in continuity.

13 - An assembly according to claim 1 1 or 12 wherein the bearing wall of the panel comprising said straight edge is advantageously a recessed edge (21) of the tongue-free face of said panel and connected to said face by a heel (25). ) forming a stop for the support tongue (17).

14 - Assembly according to claim 1 1, 12 or 13 wherein the catch tab (24) is preferably adapted to bend under the action of the assembly of the first panel and the second panel is towards the first panel (- y) in the opposite direction (+ y).

15 - An assembly according to claim 14, wherein the flexibility of said catch tab is calculated to allow it to flex by a distance at least equal to the sum of the tolerances of the layers that constitute each panel.

An assembly according to claim 14, wherein the flexibility of said catch tab is calculated to allow it to flex by a distance at least equal to the quadratic sum of the tolerances of the layers that constitute each panel.

17 - Assembly according to claim 16, wherein for the quadratic sum we take the square root of the sum of the squares of the uncertainties of each layer.

18 - assembly according to claim 15, 1 6 or 17 for which the deflection of said catch tab is measured at the point of docking between said tongue (24) and the face (10) of the panel on which it is applied.

19 - An assembly according to any one of claims 1 1 to 18, wherein a first of said panels is a composite panel and a second of said panels is a metal structure. The assembly of claim 19, wherein the composite panel is the panel having said beveled edge and the metal structure is the panel having said right edge.

21 - An assembly according to claim 19 or 20, wherein the composite panel comprising a core (12) between a first skin (10) and a second skin (1 1), the core has a beveled edge starting from the first skin to extend towards the second skin, the first skin marrying the slope of the beveled edge to join the second skin and achieve the support tongue.