GB2054083A

GB2054083A - A Tensile/Compressive Member

Info

Publication number: GB2054083A
Application number: GB8019909A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1979-06-30
Filing date: 1980-06-18
Publication date: 1981-02-11
Also published as: DE2926493C2; DE2926493A1; GB2054083B; CH647833A5

Abstract

A tensile/compressive member comprises a tubular winding of reinforcing fibres of synthetic plastics material on a core 10 with two rounded traction end caps 11, on the rounded portions 17 of which the winding ends of longitudinal fibres extend around obliquely outwardly directed rigid pins 22, the core 10 being a fibre reinforced synthetic plastics tube fixed on the traction caps to assist in absorbing compressive or compressive and tensile loads. <IMAGE>

Description

SPECIFICATION Tensile/Compressive Member The invention relates to a tensile/compressive member by which we mean a member suitable for structural (i.e. static) applications or dynamic applications (e.g. as a link) in which the member is subject to tensile and/or compressive loads.

In one such member, described in German Patent Specification No. 21 46 783, the cylindrical part of the winding must be wound with a relatively large winding angle because the winding extends over a rounded shoulder part or geodetic pole cap face and because, furthermore, an external journal is provided. Therefore, when the tensile/compressive member is subject to tension and compression, the strength of the fibres is not utilised to a very high degree and furthermore optimum use is not made of the rigidity of the winding. The core is a solid core and in order to achieve minimum weight, it is made from foam material. When the tensile/compressive member is subject to a tensile or compressive loading, the core takes no part in absorption of the forces.

Also German Auslegeschrift No. 11 88 793 discloses a member having an internal pressure resistant tube having end flanges and comprising a winding disposed on a non-fibre reinforced synthetic plastics tubular core. The winding comprises peripheral fibres for absorbing the internal thrust and longitudinal fibres which are guided around pins at the end flanges. The tube is only subjected to loading by the internal pressure and is not subjected to or intended to be subjected to tensile or compressive loading. Only under increased internal pressure is there any tensile loading on the longitudinal fibres.The longitudinal thread with its very small winding angle undergoes, due to one pin in the crown, a change in direction to another pin in the crown which is disposed a few pins further on, around which pin it is then guided and passed bacle to the glange of other end. Where these radial pins and the thread supports provided at the deflection area are concerned, the change in thread direction is quite sharp, despite complicated alleviating means (inter aiia two rings of pins at each end of the tube, with the pins disposed in a staggered formation), so that the admissible tension on the fibres is relatively small. And this is quite sufficient, because the internal pressure is in the main absorbed by the peripheral fibres.

One subject of the invention is to enable greater tensions to be absorbed by the bonded fibre material and to enable the prop to bear greater tensile and compressive loads.

According to this invention we propose a tensile/compressive member comprising a tubular winding of synthetic plastics material reinforcing fibres on a core, with in each case, provided at each end and having a central external journal, a cap on a rounded portion of which the winding ends and which serves as a traction cap and with in each case, mounted on the external journal, a compression cap which encloses the rounded part of the winding, the winding has longitudinal fibres which are guided over the two rounded portions around pins disposed rigidly on the rounded portions and directed obliquely outwardly, the core being a fibre reinforced synthetic plastics tube fixed at each end on an inner journal of the traction cap and intended to assist in absorbing the comoressive or compressive and tensile loading.

The tension is here absorbed by the winding or by the winding and the tubular core while the longitudinal compression is absorbed by the tubular core and the winding. In contrast to known tensile/compressive members and to the known flange tube, where this prop is concerned, the core or tubular core also serves in absorbing forces when the prop is subjected to longitudinal stress, the tubular core being fibre reinforced which means that its force absorption capacity is relatively high.Greater tensile stresses in the fibre bonded material or in the winding are admissible in spite of the rounding and the outer journal, because longitudinal fibres are used and because these are deflected past the outer journal by pins, the pins being directed outwardly so that the angle of deflection at the pin and thus the shearing stress on the thread at that point is relatively small, smaller than with radial or axial pins and because the oblique pins are provided on the rounded portion; the greater the rounding or the radius thereof of the like in the area of the pins, the higher the loading on the longitudinal fibres in a longitudinal direction may be. The tensile strength of the longitudinal fibres is therefore capable of being utilised to a very high degree.Between the rounding part of the winding and the rounding, there is a form-locking effect in a longitudinal direction because with the member under tension, the fibres cling to the oblique pins and the rounding. The rounding and the oblique pins provided on it are ideally suited to deflecting the longitudinal threads during winding, in a fashion which is favourable from the manufacturing point of view. The longitudinal threads are unabie to slip off the pins. This also applies when the member is subjected to a tension loading. In either case, the oblique pins absorb the forces acting laterally on the longitudinal threads.

Therefore, the winding is capable of absorbing greater tension. The core tube means that this tension may be even greater. Also, by reason of the longitudinal fibres, greater compressive stresses are acceptable in the bonded fibre material or in the winding. Therefore, the winding can also accommodate greater compression. By reason of the core tube, this compression may also be even greater. Furthermore, the rigidity of the prop or of the winding is greater than in the case of the known tensile/comprnssive member. Thus, the invention provides a hollow lightweight tensile/compressive member which is capable of meeting very exacting demands and yet involves relatively little expenditure.

Other features of the present invention are set forth in the appendent claims. Claim 2 indicates an angular range or angle for the oblique pin which is particularly favourable with regard to solution of the problem. In respect of the disposition of the oblique pins, the arrangement generally adopted is that defined in Claim 3. The single ring of oblique pins at each end is sufficient and is simple. The arrangement of Claim 4 provides for even greater admissible tension; the oblique pins and the pin supporting peripheral fibres extend radially generally almost to the outside diameter of the cylindrical part of the winding. Claim 5 provides a simple axial fixing of the tubular core under compression. As a result of the adhesive connection (a force-locking effect) defined in Claim 6, the tubular core absorbs a part of the tension.Should the adhesive connection possibly fail, the tension is absorbed only by the winding. With the arrangement of Claim 7, the sealing compound (mastic) can transmit compressive loads. It is a hardenable composition, particularly synthetic resin, e.g. epoxy resin, or a synthetic resin system consisting of synthetic resin and a hardener and possibly a hardening accelerator. This applies generally also to the synthetic plastic used for the winding and the tubular core. Longitudinal fibres in the synthetic plastic material of the tubular core (Claim 8) likewise contribute to increasing the acceptable compression and tension. The windings according to Claims 9 and 10 serve particularly as a safeguard against emergence of longitudinal fibres under compression.In general, the pin supporting peripheral fibres mentioned in Claim 4 are a radially inwardly thicker end of the winding according to Claim 9.

The reinforcing fibres are preferably carbon fibres. The said longitudinal fibres may be in the form of a longitudinal layer of threads or a plurality of radially directly consecutive layers of longitudinal threads, the said peripheral fibres being of the same type. Alternative dispositions are also advantageous.

The thickness of the winding is generally greater than the thickness of the core tube, e.g. more or less twice as great.

The tensile/compressive member may be employed as a lightweight rod or a lightweight rod element, e.g. for frame structures-for example a space platform, control linkages in aircraft and vehicle construction or a structure in satellite and rocketry engineering.

One embodiment of this invention will now be described by way of example with referecence to the accompanying drawings of which: Fig. 1 shows prop one end of a tensile/compressive member, in longitudinal cross-section; and Fig. 2 shows a detail A of the member of Figure -1 to an enlarged scale.

The strut has a core 10 in the form of a cylindrical tube, around which is a winding 12 and, at each end (are shown), a circular traction cap 1 a circular thrust cap 13 and an articulating rod head 14. The tubular core 10 and the winding 12 consist of fibre-reinfor6ed synthetic resin. The winding has an outside diameter of about 50 mm; its length being for example 220 mm, 400 mm or 1000 mm.

The tubular core 10 is produced on a winding mandrel, not shown, and consists of a layer of longitudinal fibres (unidirectional structure for the absorption of tensile and compressive loads, and, enclosing this layer, a layer of peripheral fibres. The wall thickness of the tubular core 10 is 0.5 mm.

Each traction cap 11 has a cylindrical inner journal 1 5, the external radius of which is smaller by the wall thickness of the core tube 10 than the radius of the cylindrical outer periphery of the traction cap 11 at 18 (i.e. between the step 1 6 and the commencement of the rounded shoulder 1 7 of the traction cap 1 1). The tubular core 10 is at each end and as far as the step 16 glued to the inner journal 15.

In the longitudinal section illustrated, the rounded shoulder 1 7 is circular and its radius amounts to about 1/6th of the outside diameter of the cylindrical part 18 of the traction cap 11, in other words about 8 mm. The rounded shoulder 1 7 merges into a steeply conical surface 1 9 which forms an obtuse angle with the boss extending in the direction 23 (on the axis 20 of the tubular core 1 0) outwardly at the end of the strut as shown in the drawing.Rigidly fitted in the part 21 of each cap 11 on which the rounded shoulder 1 7 is formed, are straight metallic pins 22 arranged in a single ring around the cap 11 and directed obliquely outwardly, at an angle a to the said longitudinal axis 20, the angle a being approximately 30 . The pins 22 are closer to the radially inner end of the rounded shoulder 1 7 than to the radially outer end thereof. The traction cap 11 has an external journal 24.

The winding 1 2 is produced on the tubular core tube 10 and traction cap 11 assembly and consists of a layer 25 of longitudinal fibres (rovings) and, enclosing the layer 25, a layer 26 of peripheral fibres. The longitudinal fibres are wound at a very small angle to or are parallel to the axis 20. The thickness of the cylindrical part of the winding 12 amounts to 1 mm. The longitudinal fibres of the winding 1 2 are wound continuously over the rounded shoulder 1 7 and around the pins 22, the longitudinal fibres being passed around one pin and then closely past the outer journal 24-see longitudinal thread portions 27-to another pin 22 around which it is passed before leading back to the rounded shoulder 1 7 and the pins 22 on the other traction cap 11 at the other end of the member.

The peripheral fibres 26 in the filler 28 serve to support the pins 22. The thrust cap 13 is screwed onto the outer journal 24 into contact with a hardened sealing compound 29. A hollow cylindrical part 30 of the thrust cap 13 is glued to the end of the cylindrical part of the winding 12.

The articulating head 14 is screwed through the traction cap 11 and clamped to the outer journal 24 by a nut 31. The force initiating elements, i.e. the traction caps 11 and the compression caps 13, are formed from metal, particularly a light metal, e.g. aluminium.

The tensile strength of the bonded fibre material of the winding and of the tubular core is greater than the compressive resistance of this material. In the preferred embodiment, it is 50% greater; the maximum tensile force being equal to the maximum compressive force or the product of tensile strength and the cross-sectional area of the winding 12 (assuming that the tubular core 10 is no subject to a tensile loading) is equal to the product of the compressive strength and the cross-sectional area of the winding 12 and of the tubular core 10.

(Pmax traction=Pmax compression=atension F12=compression . F 12+10)

Claims

1. A tensile/compressive member comprising a tubular winding of synthetic plastics material reinforcing fibres on a core, with in each case, provided at each end and having a central external journal, a cap on a rounded portion of which the winding ends and which serves as a traction cap and with in each case, mounted on the external journal, a compression cap which encloses the rounded part of the winding, the winding has longitudinal fibres which are guided over the two rounded portions around pins disposed rigidly on the rounded portions and directed obliquely outwardly, the core being a fibre reinforced synthetic plastics tube fixed at each end on an inner journal of the traction cap and intended to assist in absorbing the compressive or compressive and tensile loading.

2. A member according to Claim 1, wherein the oblique pins are set on angle of between 450 and 150, in particular about 300, relative to the longitudinal axis of the member.

3. A member according to Claim 1 or 2, wherein the oblique pins are disposed on the rounded portion in the form of a single crown.

4. A member according to Claim 1, 2 or 3, wherein the oblique pins are braced in respect of the longitudinal traction of the longitudinal fibres by peripheral fibres which are wound around the longitudinal fibres on the rounded portion axially inwardly beside the pins.

5. A member according to any one of Claims 1 to 4, wherein there is a step at the commencement of the inner journal, forming an axial abutment for the tubular core.

6. A member according to any one of Claims 1 to 5, wherein the tubular core is glued to the inner journal.

7. A member according to any one of Claims 1 to 6, wherein the space between the rounded portion of the winding and the pins on the one hand and the thrust cap on the other is filled with a hardened sealing compound.

8. A member according to any one of Claims 1 to 7, wherein the tubular core has longitudinal fibres.

9. A member according to any one of Claims 1 to 8, wherein the peripheral fibres are wound around the longitudinal fibres between the oblique pins on the traction cap at opposite ends of the member.

10. A member according to Claim 8, wherein the tubular core has peripheral fibres which are wound around the longitudinal fibres thereof.

11. A tensile/compressive member constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.