FR2764840A1 - ASSEMBLY SYSTEM FOR COMPOSITE SANDWICH STRUCTURES REINFORCED BY FIBERS IN MODULAR CONSTRUCTION - Google Patents

Abstract

An assembly system intended for fiber-reinforced composite sandwich structures in modular construction and which provides for connecting parts of the structures, in which the connecting parts (10, 20, 30) are provided on their front sides with lips of connection (21, 22; 31, 32) and there are provided connecting elements (40) which are formed in such a way that they fit or can fit between the connection lips (21, 22; 31 , 32) of abutting connecting pieces (10, 20, 30), and a press fit of the connecting pieces (10, 20, 30) is formed, characterized in that the connecting elements (40, are manufactured separately and are fixed, in particular glued, in the mating surfaces (26 and 36) to produce an assembly by force, and the assembly elements (40) have a casing (41, 51) completely encompassing with respect to the mating surfaces (26 and 36) Applications to the fields of aeronautical, naval and railway construction.

Description

I

  ASSEMBLY SYSTEM FOR SANDWICH STRUCTURES

  COMPOSITES REINFORCED BY FIBERS UNDER CONSTRUCTION

MODULAR

  The invention relates to an assembly system which is intended for fiber reinforced composite sandwich structures in modular construction and which provides structural connection pieces. The use of fiber-reinforced composite structures and large surfaces is becoming more and more important in the fields of aeronautics, naval and railway construction. Owing to the great solidity combined with the low weight of the structure, sandwich structures are often used, the manufacture of which for large areas, however, frequently poses technical problems. We therefore consider the modular construction of the overall structure from prefabricated semi-products to be an ideal solution. The prefabricated semi-finished products must therefore be assembled by an appropriate assembly technique to form composite structures reinforced by

fibers and large areas.

  A method is known which consists in providing a bevel with the connecting pieces designed in the form of prefabricated semi-finished products. The two connecting pieces are then bevelled at an angle of approximately 1:20, i.e.

  L = 20 H, where L is the length and H the height of the bevel.

  This bevel on the connecting pieces makes it possible to form an adherent assembly by force. This technique has proven itself in the specific case of repairs. The connection surface longer by a factor of 20 than the thickness of the part involves a large technical manufacturing cost which, in addition to the great requirements concerning the precision of the contours, is also linked to a large bulk. Due to its high cost, this technique

  unsuitable for mass production or mass production.

  In another context, Gerd Hintersdorf has already proposed in "Geklebte Konstruktionen in Wabenbauweise", Fertigungstechnik und Betrieb, 12th edition 1962, booklet 8, pages 503 to 537, to assemble two so-called honeycomb panels by removing the zones in honeycombs close to a frontal surface and by sticking a honeycomb bar in the free space thus formed. Document DE-GM 1 876 723 proposes a similar construction for the fixing of sandwich panels. It is also a question of assembling two completely flat sandwich panels frontally and it is proposed to insert between the projecting ends of the outer layers of the sandwich panels a sandwich panel intermediate piece corresponding in thickness and shape to their interior space. Patent DE 25 05 232 A1 also encourages the front assembly of shell construction panels in this way. Patent DE 94 18 409 U1 finally proposes to manufacture a tent floor panel in which a core is introduced between two outer layers, at least one of the outer layers being designed as a metal panel. This characteristic is here very

  important for keeping the panels completely flat.

  A connection between the core elements is provided, the

  connection profiles being linked to the outer layers.

  All these known forms of construction are neither intended nor suitable for the manufacture of composite sandwich structures reinforced by fibers in modular construction, which are also subjected to high stresses such as are encountered for example in the fields of aeronautical construction, naval and railway. All these proposals come generally from the field of building construction and are not designed for variable loads such as they may appear for example following

  influences exerted by movements or displacements.

  The object of the invention is therefore to propose a force assembly system which is intended for composite sandwich structures reinforced by fibers in modular construction and which implements a high degree of automation for low costs, constraints.

being also satisfied.

  The problem is solved according to the invention by an assembly system intended for composite sandwich structures reinforced by fibers in modular construction and which provides structural connection parts, according to which the connection parts are provided on their front sides with connecting lips and according to which connecting elements are provided which are formed in such a way that they adapt or can adapt between the connecting lips of abutting connecting pieces and that a force assembly of the pieces of connection is formed, characterized in that the connection elements are produced separately and are fixed, in particular glued, in the connection surfaces to produce a connection by force, and the connection elements comprise a completely encompassing envelope relative to the connecting surfaces. An assembly system is thus obtained, intended for composite sandwich structures reinforced by fibers in modular construction, which implements assemblies by determined and reproducible force. The exterior surface of the assembled sandwich structures of the fiber composite modules or connecting pieces is uniformly smooth and makes it possible to avoid harmful influences of a flow passing over the profile. The connection surfaces of the connection pieces advantageously allow automatic centering and therefore a high degree of automation with simple handling tools. Mass production or mass production can therefore take place with the system

assembly according to the invention.

  The fasteners fixed, in particular glued on the inside, between the connection lips in the area of the connection surfaces are produced separately and are surrounded by an envelope on all sides with respect to the connection surfaces. The envelope ensures an absolutely complete assembly and therefore a transmission of the forces of the assembly elements with all the connection surfaces of the two sandwich composite fiber structures placed end to end. All the proposals according to the state of the art assemble to the outer layers only certain partial areas of the assembly elements used. An envelope, on the other hand, allows a bonding, or equivalent fixing, of all

the sides.

  In principle, there is an assembly system, which is intended for fiber composite sandwich structures in modular construction and which provides connection pieces, in which the connection pieces are provided on their front sides with connection lips and in which connecting elements are provided which are formed in such a way that they adapt or can adapt between the connection lips of butted connection pieces and that an assembly by force of the connection pieces is formed. There is preferably provided an upper connecting lip and a lower connecting lip. The upper connecting lip is preferably arranged in the plane of the outer surface of the connecting pieces, while the lower connecting lip is arranged at an angle to the underside or inner surface of the connecting pieces so that obtain automatic centering of the connection surfaces of the parts

butted connection.

  The envelope surrounding each time the assembly elements can be provided in particular according to two

variants.

  A first variant of the assembly elements is designed such that a thin outer shell reinforced with fibers and a foam core surrounded by the outer shell reinforced with fibers is provided. The outer casing preferably has a fiber orientation suitable for the constraints. If it is to be protected against twisting, it preferably includes a 45 carbon fiber fabric. On the other hand, if the fibers are arranged with respect to each other at an angle of 90 as unidirectional layers, tensile or

  compression can be supported.

  The foam core preferably has a low density. Thus, in accordance with the requirements, it is very light.

  The outer envelope of the connecting elements can preferably be produced using a fiber weaving technique, mass production of the connecting element as a semi-finished product then being possible and very advantageous. The connecting element may also preferably comprise plies of sewn fibers or knitted and sewn fibers having moderate extensibility. Such moderate extensibility corresponds to values greater than the current calculation base of Skrit = 0.4% for composite structures reinforced by fibers used in aeronautics. A three-dimensional reinforcement by sewing the plies or the fabrics of fibers markedly improves the tolerance for damage to the structure because it prevents the propagation of possible tears. Therefore, extensibility can be

  increased for example to values of Ekrit = 0.7 to 0.8%.

  In another variant, a corresponding assembly element is manufactured such that a flexible fabric pipe previously impregnated with liquid resin is provided with an inner sheath. Such a fabric pipe with an inner sheath is inserted into the connection surface between the connection lips of two connection pieces placed end to end. Overpressure is produced in the inner sleeve. The overpressure is preferably produced by inflating the inner sleeve with a hot or very hot fluid, in particular hot air or very hot steam. The fabric pipe surrounding the inner sleeve thus rests on the contour of the connection surfaces of the connection pieces placed end to end. Preferably, the hot fluid intended to inflate the inner sheath makes it possible at the same time to adjust in a determined manner the temperature necessary for the curing of the resin of the fabric pipe. Thus, the resin of the fabric pipes advantageously assembles, and in particular sticks, the connection pieces in the area of the connection surfaces between the

  connection lips of the connection pieces placed end to end.

  In order to explain the invention in more detail, below are described exemplary embodiments of an assembly system for composite sandwich structures reinforced by fibers in modular construction, with reference to the appended drawings, in which: FIG. 1 is a perspective view of a flat connecting piece with connecting lips according to the invention, Figure 2 is a sectional and perspective view of connecting pieces according to Figure 1 assembled with connecting elements according to l invention, FIG. 3 is a perspective view of a first embodiment of an assembly element according to the invention, FIG. 4 is a second embodiment of an assembly element according to the invention , and Figure 5 is a sectional and perspective view of a curved sandwich structure in modular construction with connecting lips and connecting elements

according to the invention.

  Figure 1 shows a perspective view of a generally flat connection piece 10 with connection lips 11, 12. The connection piece 10 is designed as a sandwich structure. On its outer edge, on all sides, the connecting lips 11, 12 project from the upper face 13 and from the lower face 14 of the connecting piece 10. The upper connecting lip 11 is arranged in the plane of the face upper 13 or outer surface of the connecting piece 10. The lower connecting lip 12 is disposed at an angle relative to the lower face 14 or inner surface of the connecting piece 10. The lower face of the upper connecting lip 11, an outer wall 15 of the connecting piece 10 and the upper face of the lower connecting lip 12

  together form a connection surface 16.

  Figure 2 shows a sectional and perspective view of the connecting piece 10 shown in Figure 1 with connecting pieces 20, 30 attached on both sides. The connecting pieces 20, 30 also each have an upper connecting lip 21, 31 and a lower connecting lip 22, 32. The upper connecting lips 11, 21, 31 touch in one plane. As the upper connecting lips lie in a plane, this results on the upper faces 13, 23, 33 of the connecting pieces

  overall structure which has a flat outer surface.

  No influence can therefore be exerted on the external contour of the individual modules assembled in the form of

  connecting parts for sandwich construction.

  The two connecting pieces 20, 30 also include lower connecting lips 22, 32 arranged at a certain angle relative to the respective lower face 24, 34 of the connecting pieces. Assembly elements 40 are inserted, fixed by cooperation of shapes and by force, in the connection surfaces 16, 26 and 16, 36 formed by the butted connection pieces 10, 20 and 10, 30 with

outer walls 25, 35.

  The connecting elements 40 are formed and fixed inside the connection surfaces in such a way that they allow the connection pieces 10, 20 and 10, 30 to be assembled by force. As is provided for the lower connection lips arranged at a certain angle with respect to the underside of the connecting pieces, there is an automatic centering of the connecting elements 40 in the

  Respective connecting surfaces 16, 26 and 16, 36.

  Preferably, the assembly elements 40 are glued inside the connection surfaces 16, 26 and 16, 36. The structure of the elements is described below using two examples shown in the following figures.

  assembly manufactured separately.

  Figure 3 shows a perspective view of a first embodiment of an assembly element 40 according to the invention. The assembly element 40 includes a

  outer shell 41 thin and reinforced with fibers.

  The outer casing 41 completely surrounds an inner foam core 42. The foam core 42 preferably has a low density. The fabric of the outer casing 41 preferably has a fiber orientation suitable for the constraints. For example, an orientation of 45 of a carbon fiber fabric is provided. The outer envelope 41 reinforced with fibers can be manufactured for example according to the woven fiber technique. Mass production is thus possible. A variant also consists in implementing this manufacture by means of sheets of sewn fibers or knitted and sewn fibers having moderate extensibility. In all cases, the outer envelope 41 reinforced by fibers must adapt to the shape of the core.

foam 42.

  The foam core 42 is formed in such a way that it adapts optimally in the connection surfaces between the assembled connection pieces. The foam core is therefore in the form of a bar and has a substantially pentagonal section. Three sides of the pentagon are arranged with angles of 90 relative to each other. The two remaining sides together form an obtuse angle and are about half the length of the opposite side. As these two lower sides together form an obtuse angle, they reproduce the angle of the two lower connecting lips with respect to each other and with respect to the vertical outer walls 15, 25 and 15, 35 of the pieces of

  connection 10, 20 and 10, 30 according to Figure 2.

  Figure 4 shows a second embodiment of an assembly element 50 according to the invention. FIG. 4 shows at the same time the assembly element 50 inserted inside the connection pieces 10, 20 and 10, 30 according to the

figure 2.

  The connecting element 50 comprises an outer fabric pipe 51. An inner sheath 52 is provided on the inner face of the fabric pipe 51. The fabric pipe 51 is produced in the form of a flexible part and impregnated beforehand with liquid resin. The fabric hose with inner sheath has first, when not inserted

  in the connection surfaces, a round section.

  For the forced assembly of the connection pieces 10, 20 and 10, 30, the fabric pipe with inner sheath is inserted into the connection surfaces 16, 26 and 16, 36.

  then produces an overpressure in the inner sleeve.

  The overpressure is preferably produced by a hot or very hot fluid. For example, hot air or very hot steam is blown into the inner sheath and the latter is thus inflated. The fabric pipe 51 surrounding the inner sleeve therefore rests on the contour of the connection surfaces 16, 26 and 16, 36 of the connection pieces 10, 20 and, 30 placed end to end. By blowing in hot or very hot fluid, the temperature necessary for hardening the resin of the fabric pipe 51 is produced. By correctly choosing the heating fluid intended to be blown and to inflate the pipe, a temperature can be determined in a determined manner. wanted. The resin of the fabric pipe is thus heated and assembles, that is to say glue, the connecting pieces 10, 20 and 10, 30 in the region of their connecting surfaces 16, 26 and 16, 36. The resin

  therefore contributes to the stability of the assembly element 50.

  After inflation and after the resin has hardened, the connecting element 50 has a shape which corresponds to the hollow space between the connection surfaces 16, 26 and 16, 36. This shape also corresponds to the external shape of the assembly element 40 according to the previous figure. FIG. 5 shows a variant of the embodiment of the middle connecting piece in the form of a curved connecting piece 60. The curved connecting piece 60 also includes an upper connecting lip 61 and a lower connecting lip 62. The upper connecting lips 61 and 21 or 61 and 31 placed end to end form the flat outer surface of the overall structure. The lower connecting lip 62 protrudes, at a certain angle, from the lower face 64 of the curved connecting piece 60. Connecting elements 70 are inserted in the connecting surfaces 66, 26 and 66, 36 thus formed. These assembly elements generally correspond to those of FIGS. 3 or 4. Due to the external walls 65, provided with a slight inclination relative to the vertical, of the curved connecting piece 60, the assembly elements 70 are also provided a corresponding inclination of their walls adjacent to these outer walls 65. The rest of the structure of the assembly elements corresponds to the assembly elements of FIGS. 3 or 4. A variant also obviously consists in providing, instead of the structure according to Figure 3, a structure of the assembly elements according to Figure 4, namely a fabric pipe with an inner sheath. A design of the assembly elements according to FIG. 4 proves to be very advantageous precisely because of the inclined outer walls 65 and the other angles thus formed.

by the connection surfaces.

  By providing the corresponding connection lips on the connection pieces in the form of upper and lower connection lips, the various connection piece modules can therefore be assembled by gluing in a sandwich structure to form complete structures. In the field of lightweight constructions from fiber-reinforced composite materials,

  the connecting elements according to the invention with the upper and lower connecting lips on the various connecting pieces are very useful auxiliary means15 for the construction of light sandwich structures.

  Such global structures, composed of modules, in sandwich construction from fiber-reinforced composite materials, are used with many advantages in the field of aeronautics,

  railway and shipbuilding.

  Although the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be readily understood by those skilled in the art that modifications in form and in detail can be made

  without departing from the spirit or the field of the invention.

  List of part numbers connection piece 11 upper connection lip 12 lower connection lip 13 upper face 14 lower face external wall 16 connection surface connection piece 21 upper connection lip 22 lower connection lip 23 upper face 24 lower face external wall 26 connecting surface connecting piece 31 upper connecting lip 32 lower connecting lip 33 upper face 34 lower face external wall 36 connecting surface connecting element 41 outer casing 42 foam core connecting element 51 fabric pipe 52 inner sheath 60 curved connection piece 61 upper connection lip 62 lower connection lip 63 upper face 64 lower face external wall 66 connection surface connection element

Claims (11)

  1. Joining system for composite sandwich structures reinforced by fibers in modular construction and which provides structural connection pieces, in which the connecting pieces (10, 20, 30, 60) are provided on their sides front of connecting lips (11, 12; 21, 22; 31, 32; 61, 62) and in which there are provided connecting elements (40, 50, 70) which are formed so that they '' adapt or can be adapted between the connection lips (11, 12; 21, 22; 31, 32; 61, 62) of connection pieces (10, 20, 30, 60) butted and a force assembly of the pieces connector (10, 20, 30, 60) is formed, characterized in that the connecting elements (40, 50, 70) are produced separately and are fixed, in particular glued, in the connection surfaces (16, 26 and 16, 36; 66, 26 and 66, 36) to produce a force connection, and the connection elements (40, 50, 70) have a completely encompassing envelope (41, 51) pa r compared to   connection surfaces (16, 26 and 16, 36; 66, 26 and 66, 36).   2. An assembly system according to claim 1, characterized in that an upper connection lip (11, 21, 31, 61) lies in the plane of the outer surface of the connection pieces (10, 20, 30, 60 ), and a lower connecting lip (12, 22, 32, 62) is arranged at an angle relative to the inner surface or lower face (14, 24, 34, 64) of the connecting pieces (10, 20, 30, 60) so as to obtain automatic centering of the connection surfaces (16, 26, 36, 66) of connection pieces (10, 20, 30, 60) placed end to end end.   3. Assembly system according to one of previous claims,   characterized in that the connecting elements (40) comprise a thin outer shell (41) reinforced by fibers and a foam core (42). 4. An assembly system according to claim 3, characterized in that the outer envelope (41) has an orientation of fibers suitable for the constraints and the foam core (42) has a low density.   5. Assembly system according to one of previous claims,   characterized in that the outer casing (41) of the connecting elements (40) is produced using a fiber weaving technique. 6. Assembly system according to one of claims 1 to 5,   characterized in that the outer casing (41) of the connecting elements (40) consists of sheets of sewn fibers or knitted and sewn fibers having extensibility   moderate, notably from Ekrit = 0.7 to 0.8%.   7. Assembly system according to one of claims 1 to 3,   characterized in that the connecting elements (50) comprise fabric pipes (51), flexible and impregnated beforehand   liquid resin, with inner sleeves (52).   8. An assembly system according to claim 7, characterized in that the fabric pipes (51) with the inner sleeves (52) are inserted in the connection surfaces (16, 26, 36, 66) between the connection lips. (11, 12; 21, 22; 31, 32; 61, 62) and an overpressure can be produced or is   produced in the inner sheath (52).   9. An assembly system according to claim 7 or 8, characterized in that the fabric pipe (51) bears against the contour of the connection surfaces (16, 26, 36, 66) when the inner sleeve (52) is swollen with hot or very hot fluid, especially with hot air or steam very hot.   10. Assembly system according to one of claims 7 to 9,   characterized in that, by means of the hot or very hot fluid intended to inflate the inner sheath (52), the particular temperature conditions for the curing of the resin of the fabric pipes (51) are determined in a determined manner. 11. Assembly system according to one of claims 7 to 10,   characterized in that the resin of the fabric pipes (51) joins, or sticks together, the connecting pieces (10, 20, 30, 60) in the region of their connecting surfaces (16, 26, 36, 66) between the connecting lips (11, 12; 21, 22; 31, 32; 61, 62)