GB2321941A

GB2321941A - Connection element for tubes or bars of different diameter

Info

Publication number: GB2321941A
Application number: GB9800995A
Authority: GB
Inventors: Rainer Schuetze
Original assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Current assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Priority date: 1997-01-17
Filing date: 1998-01-16
Publication date: 1998-08-12
Anticipated expiration: 2018-01-16
Also published as: GB2321941B; DE19701445C1; GB9800995D0; FR2758597B1; FR2758597A1

Abstract

A connection element 30 joins bars 10,20 of different diameter, the larger 20 of the bars being hollow in the region of the joint. The connection element 30 is circular, and conical with the greatest outside diameter equal to the inside diameter of the bar 20, and an inside diameter equal to the outside diameter of the bar 10. The connection element 30 is formed from four or six foam segments 32, with each segment 32 being covered with a fibre fabric tube 34 which is impregnated with resin. On curing of the resin, the tube sections between the segments form thrust walls 33. When the connection element 30 is used, another resin impregnated fibre fabric tube 40 can be stuck over the whole connection area.

Description

1 Conection Element 2321941 The invention relates to a conection element

orjoining member forjoining bars of different diameter, of which at least the larger bar is hollow at least in the region of the joint, the cross section of the joining member is circular, the outside diameter of the circular joining member is equal to the inside diameter of the bar of larger diameter, and the inside diameter of the circular joining member is equal to the outside diameter of the bar of smaller diameter. It also relates to a method of manufacturing those joining members and to an elongated structural element with those members.

Members for joining bars are known in many different forms. DE4330857C2Jor example, proposes a joining member made of a composite material with carbon fibres, whereby transverse or diagonal bars can be connected to a continuous spar member in frameworks. A joining member for an adhesion joint between two bars of round cross section at an angle to each other is known from DE 34 47 990 C2.

However there are cases Mere bars have to be connected to each other longitudinally rather than transversely or diagonally. Apart from standard transitions, e.g. by means of bushings or by welding, there is a need to join bar's of different diameter, where the joints are subject to not inconsiderable strains.

Short bars, Mere the possibility of buckling or bending can be excluded, can be loaded with the highest pressure. In the case of bars above a critical length, the maximum carrying capacity falls with the square of the length. If the requirement is to avoid buckling of the bar even with greater lengths, this can only be done by having greaterflexural strength Exi at the centre of the bar. An increase in flexural strength could thus be obtained by increasing the moment of inertia / or by increasing the modulus of elasticity, i.e. a characteristic of the material. With tubular cross sections, an increase of the bar diameter leads to an increase in the moment of inertia to the power of three, i.e. it is particularly effective.

If however large bar diameters were chosen right along the length owing to the danger of buckling, then correspondingly large force introduction members would have to be.provided at the ends. These are considerably oversize and consequently enlarge the bar dimensions appreciably.

A plastic joining member for coaxially joining a shaft to a pipe and a method of manufacturing it are known from DE-AS 1475 036. The member is inserted radially between the shaft and the pipe and has axially spaced annular raised portions at the outer periphery, Mich are resiliently deformable in the fitted condition. The shaft, Mich here has the smaller diameter, is pushed into the pipe by the joining member, and the joining member 2 itself is then pushed in intemally. The annular raised portions projecting radially outwards are deformed in the process and also clamp the joining member in the tube. This construction is very heavy and tends rather to yield to thrust. The resiliently deformable circular rings remain in their deformed and thus sensitive condition and are thus sensitive to changing or different stresses. Additional aids have to be provided to avoid penetration in the original direction of insertion.

A pipe with a non-detachable plug-type connection according to DE-GM 74 17 689 has similar disadvantages. The plug-type connection proposed therein is for quickly and nondetachably joining two pipes to each other or to a cylindrical body. A locking member is provided, in the form of a cylindrical hollow body with a plurality of locking edges arranged on a cylindrical surface and projecting axially inwardly or outwardly in the opposite direction. Here again an artificial, additional, part-elastic roughness is produced, intended to hold together the inside of a pipe of larger diameter and the outside of a pipe of small diameter. The weights are again considerable and the production process complex, as locking lugs have to be punched out inwardly and outwardly.

The present invention seeks to provide a member for joining bars of different diameter which reduces the weight.

According to the present invention, there is provided a connection element for joining bars of different diameter, of wflich at least the larger bar is hollow at least in the region of the joint, wberein the cross section of the conection element is circular, an outside diameter of the connection element is equal to the inside diameter of the bar of larger diameter, and an inside diameter of the connection element is equal to the outside diameter of the bar of smaller diameter, and wherein foam segments are provided, which are seperated from each other by thrust walls.

With the aid of such a transitional piece the longitudinal forces in a bar of small diameter can be passed to a bar of large diameter, and of course vice versa. Thus bars of different diameters can be joined concentrically. The joining member is also markedly lighter than the prior art constructions.

The transitional piece, which could perhaps be described as a reducing piepe,_.ha'foam segments, the cross sections of which are sectors of a circle. These sectors are separated from each other by thrust walls. The Mole circular ring is arranged concentrically between the two bars which overlap in the transitional region, i.e. the "thin" and the "thick7 one.

The thrust webs are responsible for power transmission from the thin bar to the thick one. The transitional piece or joining member may respectively be joined in frictional engagement 3 to the inside of the outer, i.e. larger bar but also to the outside of the inner, smaller one, and in the assembled condition it is so joined.

If fibre composite or prepreg material is used, the joining member can be joined to the two bars in frictional engagement by adhesion, Which can be effected particularly reliably and at the same time cheaply and simply.

The thrust webs between the foam segments are preferably made by covering each of the foam segments with a.tube of fibre fabric, the tubes of pairs of adjoining foam segn, ents forming the thrusi wall located between the segments.

Each individual circular foam segment is thus covered with a tube of fibre fabric. It is preferably a tube of carbon fibre fabric and may also comprise more than one layer. Two tubes thus lie parallel between each pair of foam segments throughout the Whole region Mere the pair of segments meet.

The thrust webs preferably extend radially from the inner, thinner bar to the outer, thicker one.

The greatest thrust rigidity and thrust resistance are obtained When the fibres of the tubes form a fabric in which they are each at an angle of 45 to the longitudinal direction of the bars.

The number of sectors or segments into Which the circular rings are divided is a question of the Mole dimensioning of the bars. The preferred number is four or six. Thisrepresents an optimum combination of power supply line with complexity and simplification of manufacture for the joining member in most applications.

Division into smaller units results in a more uniform power supply, but the larger number of tubes of fibrous fabric makes the individual joining member more complex.

In order to allow a more even transition from the thick bar to the thin one, it is also preferable to taper the leading and trailing ends of the individual joining members. This allows the outer bar of larger diameter to have a smooth transition from its end to the outside of the inner bar of smaller diameter. The inner bar projects into the outer one so that an overlapping region is formed.

It is further preferable to provide an additional tube of fibre fabric covering the Whole transitional area. In this way the bar is also given a certain torsional rigidity. The structure of the tubes enables them to adapt to the different bar diameters.

4 Alternatively the additional tube of fibre fabric may cover the joining member but be inserted in the outer barwith it. Therewouldthen bean edge at the end of theouterbar.

Finally it is preferable for the joining members to be made in a process in which they are made as a long bar of a constant cross-sectional structure and are only then divided into individual pieces.

This is particularly useful from the manufacturing aspect, as the 1ong bars of constant cross section" item is relatively simple to produce and can then easily be divided into individual pieces. The whole long bar may then also be produced straight away with integral tubes of fibre fabric.

Joining members of the type according to the invention become particularly valuable in connection with force intrDduction elements for fibre composite bars known e.g. from DE 41 35 695 C2. This document describes force introduction elements which have a high loading capacity but the pressure resistance of which can only be fully utilised with short bars. In the case of longer bars with a danger of bending it is now possible, by inserting bars of larger diameter, to produce long bars with a high loading capacity throughout.

This can readily be done with the transitional pieces or joining members described above. They are preferably made of fibre composite materials.

It is clear from this example that force introduction member of correspondingly large dimensions vvould have to be provided, which would not be necessary with a long bar as intended.

In contrast, the use of joining members for joining two bars of different diameter concentrically and with an overlap, as discussed here, gives a very long bar which is very light throughout and yet has a high loading capacity. The diameters of the bar vary according to requirements and the respective bar sections are joined by the members according to the invention.

In this way an elongated structural element is formed, comprising two or more longitudinally coupled bars which are joined by joining members in accordance with the above considerations. The elongated structural element particularly has two bars of relatively small diameter vAth a third bar of substantially larger diameter between them, the bars having the same axes and being aligned longitudinally. The transitions between the different diameters are then provided by the joining members.

The joining members are each joined to the bars in frictional engagement, the exterior of the joining member to the inner surface of the outer bar and the interior of the joining member to the outer surface of the inner bar. The joint with frictional engagement is in particular an adhesion joint.

The field of application is primarily that of bars of carbon fibre reinforced plastics. However it would also be possible to join aluminium bars of different diameter in this way. Instead of sheathing the foam segments with tubes of resin-impregnated fibre fabric though, it would then be preferable here too to make the thrust walls of aluminium. In that case the foam segments are similarlly used to prevent denting of the thrust walls.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in Mich:

Fig. 1 is a perspective view of the region of a joint between two bars, Fig. 2 is a section taken along the line 11-11 in Fig. 1, and Fig. 3 is a section through a slightly modified embodiment.

A bar 10 of small diameter is at the left hand side in Fig. 1. Its cross section 11 can be seen to be filled with material, that is to say, it is not a hollow bar although it could be. The bar 10 is cylindrical, having an outside diameter 12 and a corresponding round external surface.

The bar 10 is to be joined to another bar 20 of larger diameter. The bar20 is hollow, as can be seen from the cross section 21 shown in a dashand-dot line at the right hand side of Fig. 1. Both the outside diameter 22 and the inside diameter 23 of the hollow bar 20 are larger than the outside diameter 12 of the inner bar 10. The bar 20 is also cylindrical and, like the bar 10, is preferably made of a fibre composite material or prepreg.

A joining member 30 is provided to join the bars 10 and 20. The member 30 has a constant cross section 31, which can be seen especially from Fig. 2, over most of its length. The outside diameter of the member 30 is as large as the inside diameter 23 of the outer bar 20 and is joined to and frictiionally engaged with it, for example by adhesion, in Fig. 1. The outermost ring with the outside diameter 22 and the inside diameter 23 of the bar 20 can also be seen from Fig. 2 and in the same way from Fig. 3.

The joining member 30 is primarily made up, particularly in respect of its volume, of a plurality of foam segments 32. These are shaped as segments of a circle; the individual ones can clearly be recognised as mathematically exact segments in the embodiments shown in Figs 2and 3. This means that their edges all adjoin each other radially.

6 The individual foam segments 32 are each separated by corresponding radial thrust walls 33. An arrangement other than the radial one would be possible.

The thrust walls 33 extend from the interior of the joining member 30 to its exterior, thus joining the inner bar 10 to the outer bar 20, and are used for force transmission.

The thrust waHs 33 are formed by having each individual foam segment 32 surrounded by a tube or braided nose 34 of fibre fabric. The tube may in turn be made up of a plurality of coatings or layers. The tubes 34 of pairs of adjoining or adjacent foam segments 32 then form the thrust wall 33 in each case.

The tubes 34 of fibre fabric naturally also form precisely the two regions which fie externally on the outer surface or the outside diameter 12 of the inner bar 10 and those which lie internally against the inner surface or the inside diameter 23 of the outer bar 20 and support the latter. They thus have a multiple function. Again details can be found especially in Figs 2 and 3. The number of foam segments is four in the Fig. 2 embodiment but six in Fig. 3. There is of course exactly the same number of thrust walls 33.

The tubes 34 of fibre fabric are impregnated with resin. Impregnation may take place either before or after the tubes are pulled over the foam segments 32. The ensuing curing process then produces the rigidity acquired by the walls 33.

It will also be seen from Fig. 1 that the cross section 31 of the joining member 30 becomes smaller from right to left, so that a conical region 36 is formed. The conical region 36 begins exactly where the outer bar 20 ends, as seen from the right hand side, and its diameter decreases evenly and continuously until the outside diameter 12 of the smaller bar 10 is reached. In addition the smaller bar 10 naturally extends a certain distance 15 into the outer bar 20, as can equally be seen dearly from Fig. 1.

The transitional region, i.e. the conical region 36 but also the immediately adjoining sections of the inner bar 10 and outer bar 20, are surrounded externally by a tube 40 of fibre fabric. This gives the whole transitional region torsional strength and also protects the part of the joining member 30 wflich it surrounds.

There is another useful alternative embodiment which is not illustrated. In this alternative, the tube 40 of fibre fabric - also impregnated with resin, see above - similarly surrounds the whole joining member. However the tube with the joining member is then stuck into the hollow bar 20, that is to say, the outside of the tube 40 is stuck internally onto the inner surface of the outer bar 20. In this alternative embodiment there is indeed a step-shaped 7 edge at the end of the bar 20, but this does not detract from the structural rigidity or other advantages of the invention.

8

Claims

1. A connection element for joining bars of different diameter, of which at least the larger bar is hollow at least in the region of the joint, wherein the cross section of the connection element is circular, an outside diameter of the connection element is equal to the inside diameter of the bar of larger diameter, and an inside diameter of the connection element is equal to the outside diameter of the bar of smaller diameter, and Merein foam segments are provided, which are separated from each other by thrust walls.

2. A connection element according to claim 1, wherein the foam segments are each covered with a resin-impregnated tube of fibre fabric, the tubes of pairs of adjoining foam segments forming the thrust wall located between the segments.

3. A connection element according to claim 1 or 2, which with the adjoining regions of the bars is covered externally with a further resinimpregnated tube of fibre fabric.

4. A connection element according to claim 1 or 2, which is covered with a further resinimpregnated tube of fibre fabric and is sunk into the outer bar of larger diameter together with the tube.

5. A conection element according to any of claims 2 to 4, wherein the fibres of the tubes form a fabric in which they each form an angle of 450 to the longitudinal direction of the bar.

6. A connection element according to any preceeding claim, wherein four or six foam segments are provided.

7. A connection element according to any preceeding claim which has a conical region at one side, whereby the transition from the bar of larger diameter to the bar of smaller diameter can be evened out.

8. A connection element substantially as herein describes with reference to Figs 1 and 2 or to Figs 1 and 3 of the accompanying drawings.

R A method of manufacturing connection elements according to any preceeding claim. wherein they are made as a long bar of a constant crosssectional structure, and are only then divided into individual pieces.

9 10. An elongated structural element comprising two or more bars which are fitted together longitudinally and which are conected by conection elements according to any of claims 1 to 8.