WO2009124354A1

WO2009124354A1 - Coupling with locking arrangements for tubular connections

Info

Publication number: WO2009124354A1
Application number: PCT/AU2009/000445
Authority: WO
Inventors: Luciano Papi; Stephen Pilt; Steven Smith
Original assignee: Lu Papi & Associates Pty Ltd
Priority date: 2008-04-10
Filing date: 2009-04-09
Publication date: 2009-10-15
Also published as: AU2009235954A1

Abstract

A structural assembly (10,30,40,50,60,70,80) comprises a plurality of tubes (100), which in one form are high strength stainless steel, and a coupling (11,31,41,51,61,71,81) that interconnect the tubes (100). In one form, the coupling comprises a plurality of spigots (13) inserted into respective ones of the tubes (100), and locking arrangements (25) interconnect respective ones of the tubes to the spigots inserted in those tubes so as to allow the assembly to accommodate loading across the coupling. In one form the locking arrangements comprise cavities (33,43,53,83) in the spigots which receive deformations (102,103,108,111,113) in the tube walls. Couplings, joints and methods of assembly are also disclosed.

Description

COUPLING WITH LOCKING ARRANGEMENTS FOR TUBULAR CONNECTIONS

Technical Field

The present invention relates to structural assemblies incorporating tubular members, to coupling systems for such assemblies, to joints and to methods of assembly. The invention has 5 been developed especially for use with tubes made from ultra-high strength materials, particularly ultra high strength stainless steels, and the invention is herein described in that context. However, it is to be appreciated that the invention has broader application and is not limited to that use.

Background 0 A major consideration in product development is often the overall weight of the product to achieve a required level of strength. In some areas weight considerations are a critical factor in the product design process. Examples include aircraft and motor vehicle design, high performance sports products such that used in bicycle components, sports racquets, and in mobile frame structures such as wheelchairs and stroller frames, where reductions in weight can5 substantially increase the user performance and experience.

New materials are continually emerging which have high strength to weight ratios. An example of one such material is ultra high strength stainless steels such as that manufactured and sold by Sandvik Materials Technology under the trade mark SANDVIK NANOFLEX™. This material is supplied in wire, strip, bar and tube and exhibits very high tensile strength o (greater than 1700MPa) and yield strength (greater than 1500Mpa) with excellent hardness and toughness. When provided in its tubular form, SANDVIK NANOFLEX™ has particular benefit in frame design. However, to maintain the strength properties of the tube and to simplify the manufacturing process, it is preferred if the tube is not subsequently worked or heat treated to any significant extent, but rather is used largely in its as delivered condition. This 5 may be problematic when the resulting component or product may involve a complex shape which requires bending and/or joining and/or welding of the tube sections.

Summary of the Invention

In a first aspect, the present invention provides a structural assembly comprising a o plurality of tubes, and a coupling to interconnect the tubes, the coupling comprising a plurality of spigots, each spigot being arranged to be inserted into a respective one of the tubes, and locking arrangements to interconnect respective ones of the tubes to the spigots inserted in those tubes so as to allow the assembly to accommodate loading across the coupling. In accordance with this aspect, a structural assembly is provided that incorporates sections of tube that are coupled together in a manner that enables loading to be accommodated. In this way changes in direction of the tubes can be provided for by the coupling (rather than directly by the tube) and jointing of the tubes can be made by interaction of the tubes with the 5 coupling rather than through direct interaction of the tubes. As such the amount of post working of the tubes that would otherwise be required and which may adversely impact on the properties of the tube sections can be reduced.

In one form, the spigots are arranged to be in intimate contact with the tubes in which they are fitted. By reducing the clearance between the tubes and the spigots so as to provide0 this intimate contact improves the structural characteristics of the coupling. In particular, the load carrying capacity of the coupling may be increased as the induced loading on the coupling and/or tube can be better distributed. To provide this intimate contact, in one form, the spigots are arranged to be shrink fitted into the tubes. In this arrangement, the size of the spigots is reduced temporarily (typically by a cooling process) and fitted in the tubes whilst they are in5 this reduced size. As the spigots expand on returning to their normal size, they are forced into intimate contact which effectively eliminates the clearance between the tubes and the joints.

In another form, the intimate contact is provided by reducing the clearance through use of an intermediate material. In one form of this latter arrangement, the intermediate material may be an adhesive that also bonds the spigots to the tubes. In one form, a two part o polyurethane based adhesive may be used where one part (for example the curing activator), is applied to the surface of the spigot, whereas the other part is applied to the inner diameter of the tube. As will be appreciated other types of adhesives may be used. In that regard, a single component Methacrylate ester has been found suitable which offers high strength and low viscosity and is able to fill gaps up to 0.2.mm. 5 In one form, at least one of the locking arrangements comprises one or more interfϊtting projection and cavity, one of the cavity or the projection being disposed on the spigot, the other of the cavity or projection being formed on the tube.

In a particular form, the cavity is provided in the spigot and the projection is a deformation formed in the tube wall. In a particular form, to activate the locking arrangement o the spigot is inserted into its associated tube and the tube is subsequently deformed, (by a crimping, swaging or pressing operation) so that a deformation is produced as an inward projection that interfϊts within the cavity in the spigot.

In one form, the locking arrangements allow the assembly to accommodate torque and pullout (tensile) loading on the interlocked components. Various shapes of the cavity and/or interfitting projection may be used to allow the accommodation of this torque and pull out force.

In an alternative form, at least one the locking arrangements comprises a locking element such as a dowel or spring pin, mechanical fastener or the like that interconnects the spigot and the tube to allow the required transfer of force between those components.

In at least one form, at least one of the spigots incorporates an abutment shoulder which engages with an end surface of the tube in which the spigot is received so as to accommodate compressive loading applied to the structural assembly. hi one form, the tubes are formed from an ultra high strength material. In a particular embodiment the tube is an ultra high strength stainless steel having a tensile strength of greater than 1200MPa and in one form greater than 1500MPa. An advantage of using such high strength materials is that yielding of the tubes will typically not be the limiting factor on the strength of the resultant joint. Rather yielding of the coupling becomes the limiting factor. This then provides the opportunity to provide high strength joints through appropriate design and materials selection of the coupling and locking arrangements and by distributing the loading across the coupling through forming an intimate contact between the tubes and the coupling. hi one form, the coupling is made of metal although in alternative forms it is made from a polymeric material which may be reinforced.

In one form, the coupling is made in stainless steel. In another form the coupling is made in aluminum.

In a particular form, the spigot has a length so that the pre-insertion of the spigot into a respective tube is in the order of one to two times the diameter of that tube. In a particular form, the length is in the order of 1.5 times the tube's diameter.

The spigots may be disposed at different relative positions depending on the requirement of the resulting structure. For example in an arrangement where the coupling includes two spigots, those may be disposed at an included angle of less than 180 degrees so as to provide a bend in the resulting structure, hi another form, the coupling may include more than two spigots and these may be disposed in plane or out of plane depending on requirements. hi a particular form, the coupling further comprises a body from which spigots depend. hi one form, the body of the coupling may have an outer diameter which approximates the outer diameter of the at least one of the tubes thereby providing a continuity of appearance in the resulting structure, hi one form the coupling may be arranged to interconnect tubes of different diameter or shape so as to provide a reducer coupling in the resulting structure or to join - A - different profiles. In one form the plurality of spigots may merge together so that they effectively form portions of a common spigot. This latter arrangement may be particularly suitable when the coupling is used to form a linear joint between two tube lengths.

In a particular form, each spigot includes a central axis and wherein at least one of the spigots includes a plurality of axially extending ribs that are angularly spaced apart about the spigot axis. In this form the ribs of the spigot define the outer diameter of that spigot. In one form the ribs are equally spaced apart about the spigot axis. In a particular form at least one spigot includes three ribs. In an alternative form, at least one of the spigots includes four ribs. In a particular form where the locking arrangement includes a cavity formed in one or more of the spigots, both cavities are formed along the ribs of those spigots.

In a particular form, to assist in securing of the spigots within the tubes prior to activation of the locking arrangement, a fixing arrangement may be provided. In one form this fixing arrangement is in a form of an adhesive band provided on the respective spigot. The advantage of this fixing arrangement is that the adhesive may allow for adequate fixing of the tube to the spigot to assist in maintaining the tube and spigot in its correct position prior to and during the control buckling process to form the deformation on the tube to engage the locking arrangements.

In a further aspect, the invention is directed to a coupling for use in the system in any form described above. In a particular aspect, there is provided a coupling for joining two or more tubes comprising a plurality of spigots, the spigots being arranged to be inserted into respective ones of the tubes and including cavities that that interfit with corresponding projections in the tubes to form locking arrangements that allow the resultant joint to accommodate loading across the coupling. In one form the spigots each extend along an axis and wherein at least one spigot includes a plurality of axially extending ribs that are angularly spaced apart about the spigot axis, the ribs defining the outer diameter of that portion of the spigot that is locatable in the tube.

An advantage of at least one form of the invention is that it provides a coupling and structural assembly that allows for interconnection of high tensile strength stainless steel tubes such as that sold under the trade mark SANDVIK NANOFLEX™ without requiring extensive working or heat treatment of that high strength material. The resulting joint is load bearing and in at least one form uses the inherent strength of the stainless steel to create a high strength joint that has as its failure mode yielding of the coupling rather than yielding of tubes. Also the arrangement allows for bends to be introduced into tubular lengths which have their centre line radius (CLR) not limited by the properties of the tube. In the case of the high stress stainless steels, they typically have a low value of elongation which makes obtaining a bend having a CLR of less than lOOrπm very problematic. If the bend is formed in the body of the coupling this problem is obviated. Whilst bending of these high strength tubes is restricted, local controlled "buckling" can be achieved by appropriate tools (such as hydraulic operated crimping tool) thereby allowing deformation of the tube wall to create the locking arrangements characterised above. In such controlled "buckling", the tube material is able to flow inwards in an unrestricted fashion until the wall of the tube conforms to the cavity in the coupling.

In another form, the jointing technique disclosed above may be used to join a tube to a member which is other than a tube. In this arrangement, the member incorporates a spigot and the resulting joint incorporates a locking arrangement, with both the spigot and locking arrangement being in any form disclosed above. A structural assembly is also provided by interconnection of the tube and the member.

In accordance with this further aspect, the present invention provides a joint formed between a tube and a member, the member including a spigot inserted into the tube, and a locking arrangement to interconnect the tube to the spigot so as to allow loading to be accommodated across the joint. In one form, the spigot and locking arrangement and tube is in accordance with any form described above in respect of the other aspects of the invention. In one form, the member is a coupling and in another aspect, the invention is directed to a coupling for use in that joint.

In accordance with a further aspect, the present invention provides a structural assembly comprising the interconnected tube and member according to the above aspect. In a further aspect, the invention is directed to a method of joining two or more tubes comprising: inserting a portion of a coupling into each of the two or more tubes, and deforming the tubes so that the tubes engage with those portions of the coupling.

In one form the spigots are shrink fitted to the tubes before they are deformed. In another form, the spigots are bonded to the tubes before the tubes are deformed. In a particular form, the portion of the coupling is inserted to a length which is between one and two times the diameter of the tube. In a particular form, the portions of the coupling include cavities therein and wherein the tube is deformed the tubes are deformed so that the deformations align with the one or more cavities.

Brief Description of the Drawings

5 Embodiments of the invention are herein described with reference to the accompanying drawings. It is to be appreciated that a particularity of the drawings and the related description is to be understood as not superseding the generality of the preceding claims of the invention.

In the drawings;

Fig. 1 is a perspective view of a structural assembly according to an embodiment of the0 invention comprising metal tubes (one of which is only shown in outline so as not to obscure features of the assembly) and a right angle coupling interconnecting of the tubes;

Fig. 2 is a perspective view of a structural assembly according to a second embodiment of the invention comprising metal tubes (one of which is only shown in outline so as not to obscure features of the assembly) and a right angle coupling interconnecting of the tubes; 5 Fig. 3 is a perspective view of a structural assembly according to a third embodiment of the invention comprising metal tubes (one of which is only shown in outline so as not to obscure features of the assembly) and a right angle coupling interconnecting of the tubes;

Fig. 4 is a perspective view of a structural assembly according to a fourth embodiment of the invention comprising metal tubes (one of which is only shown in outline so as not to o obscure features of the assembly) and a right angle coupling interconnecting of the tubes;

Fig. 5 is a perspective view of a structural assembly according to a fifth embodiment of the invention comprising metal tubes (one of which is only shown in outline so as not to obscure features of the assembly) and a right angle coupling interconnecting of the tubes;

Fig. 6 is a perspective view of a structural assembly according to a sixth embodiment of5 the invention comprising metal tubes (one of which is only shown in outline so as not to obscure features of the assembly) and a right angle coupling interconnecting of the tubes;

Fig. 7 is a perspective view of a structural assembly according to a seventh embodiment of the invention comprising metal tubes (one of which is only shown in outline so as not to obscure features of the assembly) and a right angle coupling interconnecting of the tubes; o Fig. 8 illustrates a structural assembly according to an eighth embodiment of the invention comprising four tubes and a coupling interconnecting those four tubes in a planar configuration; Fig. 9 illustrates a structural assembly according to a ninth embodiment of the invention comprising three tubes and a coupling interconnecting those tubes in a planar configuration; and

Fig. 10 illustrates various reducer couplings according to further embodiments of the invention for use in a structural assembly.

Detailed Description of the Drawings

Figures 1 to 7 illustrate embodiments of structural assemblies (10, 30, 40, 50, 60, 70, 80) that comprise a plurality of tubes 100 that are interconnected by couplings (11, 31, 41, 51, 61, 71, and 81). To more clearly illustrate details of the connections between the respective couplings and the tubes 100, in the embodiment of Figure 1 to 7, one of the tubes is shown in phantom.

In general, the structural assemblies are arranged to accommodate loading across the joint formed by the coupling. In this way, the assemblies can be used in load bearing situations such as in frames and the like. In the illustrated embodiment, the tubes 100 are a ultra high strength stainless steel such as that sold by Sandvik Materials Technology under the trade mark SANDVIK NANOFLEX™. Such tubes incorporate nano particles in the chemical composition and are cold formed using a seamless extrusion process and typically they have very thin wall thicknesses yet exhibit high levels of strength and corrosion resistance.

A primary purpose of the jointing system of the structure assembly shown is to introduce bends and to join the tube sections without subjecting the tubes to substantial working or heat treating which otherwise compromises the performance of the material. In each of the examples of the structural assembly shown in Figs. 1 to 7, a right hand bend is formed between the joined sections of tube. Thus the bend in the resulting assembly is introduced by the shape of the coupler and not by directly bending the tube. Further, by varying the shape of this coupler the resulting assembly can have almost a limitless variety of shapes with the tubes being inclined at different orientations and relative angles.

Moreover, through variations in the coupler design, it is possible to increase the number of tubes being connected at the coupling. Examples of structural assemblies having three or more interconnected tubes are shown in Figs. 8 and 9 and are described in more detail below. Turning now to the specific embodiment shown in Fig. 1 , the coupler 11 includes an elongate body 12 which is curved and includes two identical spigots 13 disposed on either end of the curved body 12. These spigots are located within the hollow cavity 101 of the tubes and in the illustrated embodiment, one of the spigots is obscured by tube 100 shown in solid line. Nevertheless it is to be appreciated that the following description of the spigot 13 not only applies to the spigot illustrated by also applies to the spigot obscured by the tube 100.

The spigot 13 extends along an axis 14 which when that spigot is disposed within the tube 100 is coaxial with the axis of the tube. In the illustrated form, the spigot 13 incorporates three axially extending ribs which are angularly spaced apart from each other by equal amounts. The ribs merge at proximal ends to form a central core 16 of the spigot whereas the outer end 17 of the ribs define the outer diameter of the spigot. A collar 18 is disposed at a proximal end of the spigot. The collar 18 is disposed radially inwardly of an end portion 19 of the coupler body 12 with a shoulder 20 formed between the collar 18 and the body end portion 19. The spigot 13 also includes a plurality of flanges 21 which extend from the ribs 15 to the collar 18. The flanges and collar are sloped inwardly so as to form an annular recess 25 at the join between the flanges 21 and the collar 18. Finally, the spigots also include cavities 22 which are formed in the end of the respective ribs 15 and which extend from a distal end 23 of the spigot and terminate midway along the spigot length. The body 12 of the coupling 11 incorporates a plurality of ribs 24 that extend between the opposite end portions 19 of the body. In the illustrated form, the ribs 24 define the outer diameter of the body 12 and this outer diameter is designed to correspond to the outer diameter of the connected tubes 100.

The coupling 11 may be made of various suitable materials and for example may be made from a polymeric material, or a metal such as stainless steel or structural grade aluminum.

In one form, the couplings are produced by injection molding using a metal or replacement polymer or alternatively by an injection molding process using metal injection molding. In another form, a lost wax process is utilised to form the coupler out of stainless steel. In yet an alternative form, a gravity process or die casting process is utilised to form the coupler out of structural grade aluminum.

As mentioned above, the resulting structural assembly 10 is designed to accommodate loading across the resulting joint. This loading may take the form of compression loading, or tensile loading (which results in a force which tends to pullout the tube from each resulting spigot), as well as to accommodate torque. In the embodiment of Fig. 1 these loading conditions are at least partially accommodated by locking arrangements 25 formed between the interconnected tube and spigot. These locking arrangements comprise depression 102, 103 which extend inwardly from the tube and engage with components of the spigots (being in this form the flanges 21 and run out cavities 22). Further, in the illustrated form, the depressions 102, 103 formed on the tube are made through deforming the tube after the tube end is inserted over the spigot.

In particular, in the embodiment shown in Fig. 1, the tubes 100 fit tightly over the spigots 13 until an end surface 104 of the tube butts against the shoulder 20. The abutment of the end surface 104 of the tube 100 against the shoulder allows the resulting assembly 10 to accommodate compression. Depressions 103 are formed around the tube 100 which locate within the annular recess 25 to form the locking arrangements 26 to enable the coupling to accommodate tensile loading. Longitudinal deformations are formed along the tube proximal of the end 104. These longitudinal deformations 102 are typically formed by a crimping operation and correspond in position to the run out cavities 22 in the spigot 13 to form locking arrangements 20 to enable torque to be accommodated across the structural assembly 10. The crimping operation may be carried out by any suitable tool such as a hydraulic actuated tool with settings for speed and force. The crimping detail is designed to keep the thinning of the material (as occurs in bending of the tube) to a negligible quantity. To further assist the accommodation of loading in the assembly 10, the spigots 13 are arranged to be in intimate contact with the inner walls of the tubes 100. As a result of this intimate contact, there is effectively no clearance between the tubes and the joints. This intimate contact may be provided in various forms. In one form, these spigots 13 are shrink fitted into the tubes. This involves a process whereby the size of the spigots is reduced, typically by rapidly cooling of the coupling 11 and inserting the spigots into the tubes whilst in this reduced state. Thereafter, the tubes are allowed to expand to take up any clearance between the spigots and the tubes. In another form, these spigots are bonded to the inner wall of the tubes using a separate adhesive. The approach of shrink fitting these spigots to the tubes is particularly suitable in a factory environment, whereas the use of an adhesive is more suitable for on site use. In either case, the resulting intimate contact between the spigots and the tubes found to significantly improve the capacity of the assembly to accommodate tension and torque loading.

Fig 2. illustrates a further embodiment of structural assembly 30. As the embodiment 30 of Fig. 2 includes many of the features of the earlier embodiment like features have been given like reference numerals.

The main difference between the embodiment shown in Fig. 2 and that shown in Fig. 1 is that the construction of the spigots 32 of the coupling 31 has been modified. In particular, the spigot 32 incorporates four equally spaces apart ribs 15 rather than the three ribs configuration as shown in Fig. 1. Moreover rather than including the run out cavity 22, the ribs incorporate notches 33 midway along the rib length. These notches 33 form part of a locking arrangement 34 to resist both torsion and tensile loading as will be discussed in more detail below.

As in the first embodiment the tubes 100 are fitted over the spigots 32 until an end of the tube butts against the shoulder 20 on the spigot so as to allow the resulting assembly 30 to accommodate compression. To accommodate both torsion and tensile loading two or four equally spaced H-shaped depressions 105 are formed in the tube. These depressions 105 are arranged to align with the notches 33 formed on the ribs whereby the cross arm 106 of the H- shaped depressions 105 extends into the notches to accommodate tensile loading in the assembly 30 whereas the longitudinally extending component 107 of the H-shaped depressions 105 extend on either side of the ribs 15 thereby capturing the ribs therebetween so as to enable torque to be accommodated across the assembly 30.

Fig. 3 illustrates yet a further embodiment of structural assembly 40 incorporating yet a further modified coupling 41. Again the embodiment of the Fig. 3 has many similarities to the earlier embodiments and like features are given like reference numerals. In a similar arrangement to the coupling 31 shown in Fig. 2, the coupling 41 incorporates a spigot 42 incorporating four equally spaced apart ribs 15. Furthermore, the ribs include intermediate notches 43 disposed inward of the ribs 15.

Unlike the earlier embodiment whereas the notches 33 where disposed in each of the ribs, in the embodiment shown in Fig. 3 the notches 43 are only incorporated in two of the ribs 15. The notches 43 form part of a locking arrangement 44 and cooperate with annular depressions 108 that are formed in the tube 100.

As in the earlier embodiments, the tube fits tightly over the spigots 42 and butts up against the shoulder 20 so as to allow compressive loading across the assembly 40. Annular depressions 108 are pressed into the tube so that these depressions are broken by sections 109 which are arranged to correspond to the positions of the un-notched ribs 15. With this arrangement, the annular depressions 108 extend through, and cooperate with, the notches 43 whereas the unbroken ribs 15 locate in the sections of tube 109 between the depressions 108 thereby capturing the ribs between the depressions 108. In this way tensile loading is accommodated by inter-engagement of the depressions 108 with the notches 43 whereas torsion is accommodated by the captured ribs 15 in the sections 109.

A further embodiment 50 of a structural assembly is described in Fig. 4. Again the assembly 50 includes many of the features of the earlier embodiments and accordingly like features have been given like reference numerals. As in earlier embodiments, the spigot 52 is formed from four equally spaced ribs 15. As in the first embodiment, the spigot 52 incorporates an annular recess 25 that is formed between collar and flanges 21. These flanges are broken by recesses 53. In this embodiment, the annular recess 25 and the recesses 53 form part of the locking arrangement 54 to allow the resulting assembly 50 to accommodate loading conditions. The locking arrangement 54 also includes a U-shaped depression 110 which is stamped into the tube 100.

In the embodiment, the tube 100 again fits tightly over the spigots 52 and an end 104 of the tube butts up against the shoulder 20 so that the resulting assembly 50 can accommodate compression. Two or four equally spaced U-shaped depression 110 are stamped in the tube. The arms 111 of the U-shaped depressions 110 locate on either side of a respective rib 15 whereas the base 112 of the depression 110 locates within the annular band 21. In this way, the interconnection of the depression 112 within the annular band 25 allows the assembly to accommodate tension, whereas the capturing of the rib 115 between the arms 111 of the depression 110 enable the resulting assembly 50 to accommodate torque. Fig. 5 illustrates yet a further embodiment of structural assembly 60 so that again like features have been given like reference numerals.

In the embodiment of Fig. 5, the coupling 61 includes a spigot 62 incorporates a plurality of spaced apart ribs 15 that extend along the axis 14 of that spigot. However unlike the earlier embodiments, the spigots 15 are disposed only along a distal portion of the respective spigot and an annular recess band 63 is divided between the ribs 15 and the collar 18. This recess band 63 forms part of the locking arrangement 64 that enables loading to be accommodated across the assembly 50. The other part of the locking arrangement 64 is a wide annular clip 113 which is formed within the tube 100.

In use again the tubes 100 fit over the respective spigots 62 so that an end 104 of each tube 100 abuts the shoulder 20 so that compression is accommodated in the structural assembly. The wide annular crimp 113 is applied to the tubes 100. These crimps 113 are aligned with the recess band 63 so torsion in the resulting coupling is restricted only by the frictional forces applied between the crimp 113 and the band 63. Torque tension is accommodated by an edge surface 114 of the crimp 113 bearing again a distal abutment shoulder 65 formed between the ribs 15 and the recess band 63.

Fig. 6 illustrates yet a further embodiment of a structural assembly 70. In this embodiment, the spigots 72 of the coupling 71 incorporate a pair of centrally located bosses 73. These bosses are formed in opposite ribs 15. These bosses are generally frustoconical and incorporate depression cavities 74 in an outer surface. The bosses 73 form part of the locking arrangement 75 for the structural assembly 70. In use, as in the earlier embodiments the tubes 100 locate over these spigots 72 so that an end 104 of each tube abuts against a respective shoulder 20 of the coupler 71 to thereby allow the assembly 70 to accommodate compression. Two opposing annular depressions 115 are formed in the tube 100. These depressions mate 5 with the cavities 74 formed in the respective bosses thereby capturing the tube so as to resist both tension and torsion. In an alternative form (not shown) a mechanical fastener such as a press-fit-pin or a screw may be inserted through the screw (such as through a pre billed hole) so as to inter engage with the boss 73 to provide a new locking arrangement 75 for this structural assembly. o Fig. 7 illustrates yet a further embodiment of structural assembly 80. As the assembly

80 shares many of the features of the earlier embodiments, like features have been given like reference numerals. hi the embodiment of Fig. 7, the coupling 81 includes spigots 82 (only one of which is shown) that incorporate a plurality of spaced apart ribs 15 that extend along the axis 14 of the5 respective spigot. However unlike the earlier embodiments, the spigots 15 are interrupted along their length by laterally extending depressions 83. However, it is to be appreciated that the spigot may include less than four depressions 83, for example only two disposed on opposite ribs. The depressions 83 form part of a locking arrangement 84 that enables loading to be accommodated across the assembly 80. The other part of the locking arrangement 84 is a radial o depression 116 formed in the tube 100. hi the embodiment of Fig. 7, the tube 100 again fits tightly over the spigots 82 and an end 104 of the tube butts up against the shoulder 20 so that the resulting assembly 80 can accommodate compression. The radial depressions 116 are stamped in the tube 100. The depressions 116 mate with the lateral depressions 83 within the spigot 82. In this way, the5 interconnection of the depression 116 within the depressions 83 allows the assembly to accommodate tension and torque.

The structural assemblies utilizing the couplings and tubes may be provided in an almost unlimited variety of angles and directions and be configured to interconnect any number of tubes and different sizes of tubes. As examples, Fig. 8 illustrates a further variation of o structural assembly 90, where a coupling 91 is provided that is arranged to interconnect three tubes 100. The coupling 91 includes the spigot 13 and locking arrangement 27 of Fig. 1 with the tubes 100 having both the depressions 102 and 103. The coupling is disposed in a Y-shape with a branch connection 92 extending from the main coupling body 12. Fig. 9 illustrates another example where structural assembly 95 has a coupling 96 that provides a four-way connection. Again the coupling 91 includes the spigot 13 and locking arrangement 27 of Fig. 1 with the tubes 100 having both the depressions 102 and 103. Fig. 10 illustrates coupling 97 that is designed to interconnect tubes 100 of different sizes. The couplings include spigots 98 of different sizes to fit within the different sized tubes 100 and include tapered bodies 99 that interconnect those spigots. Whilst the spigots are designed in the form as described with reference to Fig. 5 any form of the above described spigots could be used. Also these "reducer" couplings 98 may be designed at any variety of angles and modified to accommodate any number of tubes.

Finite testing analysis was conducted on a joint formed from a NAONFLEX™ tube and a coupling 81 (having a spigot design as shown in Fig. 7) made from a polymeric material

(DURALON N66 33CF HS BK106) which has a yield strength of 256 MPa. In this test it was assumed that there was effective intimate contact through use of an adhesive between the tube and the spigot. In this testing a tension load of 1668kg was able to be accommodated by the joint. At this load the yield limit of the coupling material was reached. The same joint was able to accommodate a torque load of 100Nm. In a second finite analysis test where it was assumed that there is a slightly loose fit between the tube and the spigot, the maximum tension load before yielding of the coupling material was 660kg and the torque lad was 53Nm. In both cases the resultant joints were load bearing. However the arrangement where the coupling was in intimate contact with the spigot allowed better distribution of stress in the coupling which accounted for the greater load that was able to be accommodated by the joint before yielding of the coupling.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the invention.

Claims

We claim:

1. A structural assembly comprising: a plurality of tubes;

5 a coupling to interconnect the tubes, the coupling comprising a plurality of spigots, each spigot being inserted into a respective one of the tubes, and locking arrangements to interconnect respective ones of the tubes to the spigots inserted in those tubes so as to allow the assembly to accommodate loading across the coupling.

2. A structural assembly according to claim 1, wherein the interconnected spigots and l o tubes are in intimate contact with one another.

3. A structural assembly according to claim 2, wherein the intimate contact is provided by an adhesive bond between the spigots and the tubes.

4. A structural assembly according to claim 2, wherein the intimate contact between the spigots and the tubes is provided by temporarily reducing and subsequently increasing the size

15 of each spigot following insertion of that spigot into its respective tube.

5. A structural assembly according to any preceding claim, wherein the locking arrangements allow the assembly to accommodate torque and/or tensile loading.

6. A structural assembly according to any preceding claims, wherein at least one of the locking arrangements comprises one or more interfitting projection and cavity, one of the cavity

20 or the projection being disposed on the spigot, the other of the cavity or projection being formed on the tube.

7. A structural assembly according to claim 6, wherein the cavity is in the spigot and the projection is a deformation formed in the tube wall.

8. A structural assembly according to any preceding claim, wherein the spigots each 25 extend along an axis and wherein at least one spigot includes a plurality of axially extending ribs that are angularly spaced apart about that spigot axis, the ribs defining the outer diameter of the portion of the spigot that is locatable in the tube.

9. A structural assembly according to claim 8, wherein the ribs are equally spaced apart about the spigot axis.

30 10. A structural assembly according to claim 8 or 9, wherein the at least one spigot includes three ribs.

11. A structural assembly according to claim 8 or 9, wherein the at least one spigot includes four ribs.

12. A structural assembly according to any one of claims 8 to 11, wherein at least one of the locking arrangements comprises one or more interfitting projection and cavity, the cavity being formed in one or more of the ribs of the spigot.

13. A structural assembly according to any preceding claim, wherein at least one the spigots incorporates an abutment shoulder which engages with an end surface of the tube in which the spigot is received so as to accommodate compressive loading applied to the structural assembly.

14. A structural assembly according to any preceding claim, wherein the coupling further comprises a body from which the spigots depend.

15. A structural assembly according to claim 14, wherein the body comprises one or more cylindrical members having an outer diameter that is substantially equal to the outer diameter of at least one of the tubes of the assembly.

16. A structural assembly according to any preceding claim, wherein the tubes are formed from a metal having a tensile strength of greater than 1200MPa.

17. A structural assembly according to any preceding claim, wherein the tubes are formed from a metal having a tensile strength of greater than 1500MPa.

18. A coupling for use in a structural assembly according to any preceding claim.

19. A coupling for joining two or more tubes comprising: a plurality of spigot, the spigots being arranged to be inserted into respective ones of the tubes and including cavities that that interfit with corresponding projections in the tubes to form locking arrangements that allow the resultant joint to accommodate loading across the coupling.

20. A coupling according to claim 19, wherein the spigots each extend along an axis and wherein at least one spigot includes a plurality of axially extending ribs that are angularly spaced apart about that spigot axis, the ribs defining the outer diameter of the portion of that spigot that is locatable in the tube.

21. A coupling according to claim 20, wherein the ribs are equally spaced apart about the axis of the at least one spigot.

22. A coupling according to claim 20 or 21 , wherein the at least one spigot includes three ribs.

23. A coupling according to claim 20 or 21, wherein the at least one spigot includes four ribs.

24. A coupling according to any one of claims 19 to 23, wherein the cavity is formed in one or more of the ribs of the spigot.

5 25. A coupling according to any one of claims 19 to 24, wherein at least one of the spigots incorporates an abutment shoulder which engages with an end surface of the tube in which the spigot is received so as to accommodate compressive loading applied to the structural assembly.

26. A coupling according to any one of claims 19 to 25, wherein the coupling further comprises a body from which the spigots depend. 0

27. A joint formed between a tube and a member, the member including a spigot inserted into the tube, and a locking arrangement to interconnect the tube to the spigot so as to allow loading to be accommodated across the joint.

28. A joint according to claim 27, wherein the interconnected spigot and tube are in5 intimate contact with one another.

29. A joint according to 27 or 28, wherein the locking arrangement allows the joint to accommodate torque and/or tensile loading.

30. A joint according to any one of claims 27 to 28, wherein the locking arrangement comprises one or more interfitting projection and cavity, one of the cavity or the projection o being disposed on the spigot, the other of the cavity or projection being formed on the tube.

31. A joint according to claim 30, wherein the cavity is in the spigot and the projection is a deformation formed in the tube wall.

32. A joint according to any one of claims 27 to 31, wherein the spigot extends along an axis and includes a plurality of axially extending ribs that are angularly spaced apart about that5 spigot axis, the ribs defining the outer diameter of the portion of the spigot that is locatable in the tube.

33. A joint according to any one of claims 27 to 32, wherein the tubes are formed from a metal having a tensile strength of greater than 1200MPa.

34. A joint according to any one of claims 27 to 33, wherein the tubes are formed from a o metal having a tensile strength of greater than 1500MPa.

35. A joint according to any one of claims 27 to 34, wherein the member is a coupling.

36. A coupling for use in a joint according to claim 35.

37. A method of joining two or more tubes comprising: inserting a respective one of a plurality of spigots of a coupling into each of the two or more tubes, deforming the tubes so that the tubes engage with the spigots of the coupling.

38. A method according to claim 37, wherein at least one spigot is bonded to its respective tube before that tube is deformed.

39. A method according to claim 37, wherein the size of at least one spigot is reduced and then subsequently increased following insertion of that spigot into its respective tube.

40. A method of joining two or more tubes according to any one of claims 37 to 39, wherein the spigots are inserted into the tube to a distance between one and two times the diameter of the tube.

41. A method of joining two or more tubes according to any one of claims 37 to 40, wherein the spigots of the couplings include cavities and the tubes are deformed so that the deformations align with the one or more cavities.