FR2720795A1 - Straight bars for transmitting longitudinal forces based on reinforced composite materials. - Google Patents

Abstract

Straight bar transmitting longitudinal forces composed of two or more coaxial partial bars (4, 6) which are respectively connected by a sleeve (16) by joining them end to end. The object of the invention is a means for simply assembling individual bars based on fiber-reinforced composite materials with high flexural strength and a thin wall in long bars by means of a connector by sleeve without significant difference in rigidity.

Description

! "Straight bars of longitudinal force transmission based on

  reinforced composite materials "The present invention relates to a straight bar transmitting longitudinal forces which consists of two or more coaxial partial bars which are respectively connected by a sleeve by assembling them

end to end.

  By DE 1 871 814 El, it is known to connect metal pipes by assembling them end to end by a sleeve threaded on the smooth ends of the pipes and encroaching on the location of the joint, sleeve which is connected by gluing to the ends of the pipes. For copper pipes, we know

  join the ends of the pipes and the sleeve by brazing.

  By DE 38 18 066 A1, we know how to connect carbon or graphite pipes to each other on a coaxial plane by gluing. The pipes are then fitted to

  the front of cones that fit together and glued together on the faces of the cones.

  A carbon fiber cuff impregnated with a thermoplastic is stretched over the outer end of the conical slot. The cuff is then

  preferably wound on the pipes.

  DE 23 26 628 discloses a connector made of glued sleeve shells for pipes and tubular elements. The juxtaposed edge portions of the rigidly designed sleeve shells are arranged so that they overlap to enlarge the adhesion surface of the

junction point.

  Bars of high flexural strength based on fiber-reinforced composite materials with a thin wall are ideal materials for lightweight constructions, particularly in the aeronautics and astronautics sectors. With such bars, it is possible, for example, to make three-dimensional lattices with a low weight such as those described in DE 42 30 857. In aeronautics and astronautics, such beams are required with great lengths, for example lengths greater than 10 m. Bars of this length with diameters of the order of 20 mm can only be produced in a single block with large equipment. A problem then is in particular the hardening in the rectilinear position required. Shorter bars with lengths up to 6 m can be manufactured advantageously with the high precision required. Such bars can only be used with very long load-bearing structures if they can be assembled into fairly long bars with small stiffness differences. The assembly of bars of fairly short length into bars of fairly large length can, for example, lead to advantages in terms of manufacturing technique even for manufacturing

of truss beams.

  The object of the invention is a means for simply assembling individual bars based on fiber-reinforced composite materials with high flexural strength and a thin wall in long bars by means of a connector by sleeve without gap

important stiffness.

  This problem is solved by an assembly composed of two or more coaxial partial bars which are respectively connected by a sleeve by joining them end to end, characterized in that there are provided as partial bars bars very resistant to bending based on composite materials reinforced with fibers, with a thin wall, at the junction point, a bonding sleeve with a thin wall, split along a generatrix parallel to the axis, based on reinforced composite materials, is bonded to the outside with fibers, which has an inner layer based on unidirectional fibers, parallel to the axis and distributed at the periphery, the rigidity of which corresponds essentially to the rigidity of the layer of unidirectional fibers, transmitting the longitudinal forces, partial forces and which presents on the outside on the inner layer based on unidirectional fibers a winding of fiber s with fibers crossing with respect to the axis at an angle greater than 20 and on the outside, on the connecting sleeve, a hose made of high-strength fiber-based fiber fabric is laminated in a resin matrix synthetic, pipe that extends on both sides over the ends of the connecting sleeve and is laminated in the areas protruding outside on

partial bars.

  Bars assembled according to the invention can be used as spar bars for very wide load-bearing structures. However, the bars can also be used in control rods transmitting traction and pressure forces in which these bars are guided radially by suitable housings and are therefore

  free from buckling stress.

  The realization of the bar in several parts made possible by

  assembly can also have advantages during assembly.

  With a bar according to the invention, the bar elements to be connected can also be for example bar elements which are produced at one end with connecting elements. Such bar elements produced with connection elements can be produced practically continuously, for example in fairly short lengths with connection elements arranged on both sides, as described in DE 41 35 695 A1. Such bar lengths produced with connection elements can then be subsequently connected, for example also on a support structure produced with the bars.

  transverse and diagonal bars.

  With assemblies according to the invention, it is also possible to connect partial sections of such load-bearing structures to one another, which makes it possible to discount assembly reliefs with load-bearing structures very stretched in length. This can also be an advantage in cases where it

  there is no problem when it comes to making bars.

  An important advantage is the low weight and low volume of

  the assembly in conjunction with a high load capacity of the assembly.

  The invention is illustrated for example in the drawing and described below

  in detail using the drawing.

  Figure 1 shows in longitudinal section an assembly between two

  partial bars by means of an external connecting sleeve.

  Figure 2 shows a connecting sleeve in side view.

  Figure 3 shows the connecting sleeve according to Figure 2 seen from the front left. Figure 4 shows the connecting sleeve in an unfolded state for mounting. The bar shown in Figure 1 is composed of two partial bars 4, 6 or more coaxial which are shown here in the form of thin-walled bars and are connected assembled end to end. A connection between two coaxial partial bars is shown in Figure 1. The

  walls of the partial bars 4,6 are made of plastic reinforced with fibers.

  As the fiber, glass fiber, carbon fiber or very strong plastic fiber can be used in known manner. They must have at least one layer made of unidirectional fibers which extend parallel to the axis 10 of the bar and absorb the tensile and pressure forces. This layer of unidirectional fibers is masked by a layer of fibers with fibers crossing at an angle relative to the axis 10, preferably with an angle greater than 20 relative to the axis 10. These two layers of fibers, for which different fibers can also be used, are coated in a matrix of synthetic resin and together form in a fiber reinforced composite construction, the tubular bar body 12. The tubular wall rests in a known manner, in the embodiment shown, on a pressure-resistant foam core which is produced in such a way that it has a high resistance to deformation in the transverse direction to

Axis 10.

  The bars can however also be produced without a core and be produced for example according to the known winding technique or also in the form of pipes subjected to pultrusion. The fibers transmitting the longitudinal forces can also be the fibers of a braided fiber-based sheath which is arranged with a large extension with an angle of the fibers less than +/- 15 relative to the axis of

bar.

  At the junction point, the two partial bars 4 and 6 are separated

  transversely to their axis 10. They can touch each other by their faces 14.

  However, a space is preferably provided.

  To connect the two partial bars 4, 6, a connecting sleeve 16 is provided which surrounds the two partial bars on the outside and is supported in the connection zone and is glued to the external face of the partial bars to be connected. The length of the connecting sleeve is chosen so that the ends of the bar are covered respectively over an area L equal to at least 2D. On the connecting sleeve 16, a flexible hose based on fiber fabric 18 is laminated, which is preferably made of carbon fibers and is coated in a matrix of synthetic resin. This pipe protrudes from the ends of the connecting sleeve respectively over a length L. In this zone, the braided fiber sheath 18 is laminated on the external face of the partial bars. The connecting sleeve 16 is a fiber-reinforced composite element with an internal layer 20 based on unidirectional fibers parallel to the axis and a layer 22 arranged above based on a thin fiber mesh, for example a sheath braided in fibers based on glass fibers. As a result of the manufacture of the connecting sleeve 16, it is possible to manufacture a bar with a core of pressure-resistant foam and, arranged thereon, the two layers of fibers mentioned in a composite technique with fiber reinforcement. From such a bar, one can then detach lengths depending on the required length of the connecting sleeve. Starting from these bar sections, the foam core 8 is then emptied. The tubular sleeve thus formed is cut along a generatrix 24 parallel to the axis, then unfolded by at least 90, but preferably of 180, as shown in FIG. 4. It then breaks in the layer of unidirectional fibers mainly in front of the separation cut 24. The two parts remain connected in the manner of a hinge by the outer layer of fabric 22. The location of the break and therefore of the assembly in the manner of a hinge poses no problem. For the consistency of the unidirectional fibers, a circumferential winding can also be provided

instead of a fabric pipe.

  After the adhesive has been applied to the external face of the two partial bars 4, 6 and / or the internal face of the connecting sleeve 16, the unfolded connecting sleeve can be placed on the partial bars and bent again to have the shape initial tubular. By an appropriate dimensioning of the internal diameter of the connecting sleeve, one can then respect a desired adhesive thickness. The connecting sleeve 16 is produced in such a way that the solidity of the unidirectional fibers of the layer of fibers 20 corresponds essentially to the longitudinal resistance of the two

partial bars 4, 6.

  Through the connecting sleeve 16, a section of fabric pipe 18 is slid previously slid over one of the partial bars 4, 6, based on high-strength fibers, preferably carbon fibers, and it is laminated on the external face of the connecting sleeve 16 and the zones L '

  bordering on the two partial bars 4, 6.

  The laminated fiber fabric pipe reduces the stiffness differences on the

  two ends of the connecting sleeve.

  Connecting sleeves like those shown in Figures 2 to 4 can also be used for repair in the event of material damage to the bars by applying a connecting sleeve of appropriate length to the damaged sections. In the case of a repair, a severely damaged section of a bar can also be removed and a suitable bar can then be inserted into the damaged bar by means of two connecting sleeves. In this case, you can also insert and

  laminate appropriate sections of fabric pipe.

  Of course, the invention is not limited to the examples of embodiment described and shown above, from which other modes and other embodiments can be provided, without going beyond the ambit of the invention. .

Claims (3)

  1. Straight bar transmitting longitudinal forces composed of two or more coaxial partial bars which are respectively connected by a sleeve by joining them end to end, characterized in that partial bars are provided (4,6; 4 ', 6') bars very resistant to bending on the basis of composite materials reinforced with fibers, with a thin wall, 10 at the junction point, a bonding sleeve (16) with a thin wall, split along a generator (14) parallel to the axis, based on fiber-reinforced composite materials, which has an inner layer (20) based on unidirectional fibers, parallel to the axis and distributed at the periphery, the rigidity corresponds essentially to the rigidity of the layer of unidirectional fibers, transmitting the longitudinal forces, partial forces and which presents on the outside on the inner layer based on fibers unidirectional a winding of fibers with fibers crossing with respect to the axis (10) at an angle greater than 20 and outside, on the connecting sleeve (16), a fiber fabric pipe (18) to high strength fiber base is laminated in a synthetic resin matrix, pipe which extends on both sides over the ends of the connecting sleeve (16) and is laminated in the areas beyond   the outside on the partial bars.   2. Bar according to claim 1 or 2, characterized in that the connecting sleeve (16) has a length equal to at least 4D of partial bars.   3. Method for manufacturing a connecting sleeve for bars according to claim 1, characterized in that, starting from a bar provided with a core of pressure-resistant foam with a diameter corresponding to the outside diameter of the bars partial (4,6) to be connected and a thin wall resting thereon made of a fiber-reinforced composite material with a layer, resting on the foam core, of unidirectional fibers parallel to the axis and an outer layer with fibers crossing at an angle greater than 20 relative to the axis of the bar, removing the foam core, cutting the wall of the sleeve thus formed along a generatrix parallel to the axis and unfolding the sleeve so that the unidirectional fiber layer (20) breaks in the area opposite the partition (24) parallel to the unidirectional fibers.