WO2016072867A1

WO2016072867A1 - Connector for use with composite materials

Info

Publication number: WO2016072867A1
Application number: PCT/NZ2015/050185
Authority: WO
Inventors: Martyn Rohan Newby; Trent James MAINWARING; Malcolm Bruce MCLEAN; Jonathan David PAUL
Original assignee: Zenith Tecnica Limited
Priority date: 2014-11-05
Filing date: 2015-11-05
Publication date: 2016-05-12

Abstract

Metallic connectors or fasteners are often required in, or when making connections to, components or structures made of fibre reinforced composite materials. However, the location of these fasteners is often the site of structural failures due to corrosion or stress concentrations or other localised failures. This invention relates to an improved fastener or connector that provides improved integration with composite materials, and which can be used to minimise the possibility of corrosion damage while at the same time providing improved mechanical joints with reduced likelihood of stress concentrations leading to breakdown of the composite material surrounding the connector. The connector has a body section which has a graduated stiffness, the stiffness of the body section being greatest at a connection between the body section and a mechanical fastening section of connector, and the stiffness being least at the extremities of the body section. And the connector is made by electron beam melting allowing for cost effective use of titanium or titanium alloys to make the connectors, and providing for an improved strength to weight ratio and improved corrosion resistance.

Description

Connector for use with Composite Materials

FIELD OF THE INVENTION

This invention relates to a connector for use with composite materials, and in particular, but not exclusively to a metallic connector for use with fibre reinforced composite materials.

BACKGROUND

Fibre Reinforced Composite (FRC) materials, and components and structures made using these materials, are now common place in the aerospace, automotive, marine, military, extreme sports and prosthetic limb industries. Such articles typically have greater specific strength, stiffness, and toughness than similar articles those made entirely of metals. This is particularly so with respect to monocoque (stressed skin) structures.

A particular difficulty with components and structures made of fibre reinforced composite materials is that of conveying loads into- and out of- the components or structures efficiently.

By their very nature, connections and fastening systems tend to concentrate stresses in a structure. And at the same time, while FRC components generally have very good tensile strength, the FRC material usually has low bearing strength and is damaged all too easily by concentrated bearing loads. That is why the site of connectors or fasteners in composite articles is often the site of any failures in the articles caused by stress.

The stresses can become so concentrated at the location of the fasteners that even relatively strong composite materials will fail due to excessive loading. The failure mode will typically involve localised crushing or bearing failure, a separation between the fastener and the surrounding resin, or de-lamination between the layers of a composite material.

To overcome these difficulties, current practice is to sometimes clamp and bond the FRC material of an article between metal plates which are in turn attached to other parts of a structure or to a component that is to be connected to the article. These joints rely on friction or adhesive joints between the plates and the FRC article. Another method is to increase the wall thickness of the FRC article at fastener locations, and to drill and thread with conventional tools or utilise precision threaded inserts. Another method for thin FRC panel fabrications utilises two piece flanged bobbins which are inserted from either side of the panel and mechanically set together and bonded.

However, all of these solutions are time consuming in preparation, behave inconsistently with regards to fatigue and may still lead to undue stress concentration or to an uneven loading of the joint. In this specification unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.

OBJECT

It is therefore an object of the present invention to provide a connector for use with composite materials which will at least go some way towards overcoming one or more of the above mentioned problems, or at least provide the public with a useful choice. STATEMENTS OF THE INVENTION

Accordingly, in a first aspect, the invention may broadly be said to consist in a connector for use with composite materials, the connector having a body section configured for use in forming a connection to an article formed of composite material, and having at least one mechanical fastening section configured for use in mating the connector to a complimentary mechanical fastener, and the body section is connected to the or each mechanical fastening section, and wherein the body section has a graduated stiffness, the stiffness of the body section being greatest at the connection between the body section and the or each mechanical fastening section, and the stiffness being least at the extremities of the body section. Preferably the body section tapers in thickness from the connection between the or each mechanical fastening section and the body section, to the outer edge of the body section.

Preferably the body section is at least partly porous, or mesh-like.

Preferably the body section includes anns that are arranged in a substantially radial direction extending from the or each mechanical fastenmg section.

Preferably the body section includes webs extending between each radial arm.

Preferably each of the webs is porous.

Preferably each of the aims is porous.

Preferably the arms and the webs have a rough exterior surface. Optionally the webs have a mesh-like structure.

Preferably each of the anns is tapered, being thicker adjacent to the mechanical fastenmg section and thinner at an outer extremity of each arm.

Preferably the thickness of the webs tapers, being thicker adjacent to the mechanical fastening section and thinner at the outer extremity of the webs. Preferably the body section also includes axial members, the axial members being generally aligned with a principal axis of the mechanical fastening section.

Preferably some or all of the axial members extend from the webs.

Optionally some or all of the axial members extend from the arms.

Optionally the axial members are porous. Preferably the body section includes one or more annular stiffeners.

Preferably the or each of the annular stiffeners is/are porous.

Preferably the pores of the porous nature of the body section are pores that extend right through the structure of the body section. Preferably the pores of the body section are holes having a diameter exceeding 0.3 millimetres.

Preferably the pores of the body section are holes having a diameter not exceeding 1.0 millimetres. Preferably the perimeter of the body section is substantially circular.

Optionally the perimeter of the body section includes a generally sinusoidal wave pattern.

Preferably the connector is made from a metal or a metal alloy, and ideally the metal is titanium or a titanium alloy.

Preferably the or each mechanical fastening section includes a thread form. Optionally the or each mechanical fastening section includes a bore configured to accommodate the shank of a bolt or rivet or similar mechanical fastener.

Optionally the or each bore of die mechanical fastening section includes a countersunk section.

Optionally the connector includes more than one mechanical fastening section and the principal axis of at least one of the mechanical fastening sections is at an angle relative to at least one other of the mechanical fastening sections.

Optionally the body section has a sintered construction, or a sinter-like construction.

Preferably a plane of the webs passes through or adjacent a mid point of a principal axis of the mechanical fastening section. In a second aspect, the invention may broadly be said to consist in a connector for use with composite materials comprising a threaded or plain boss with an annular mesh, radial stiffeners and axial stiffeners.

Preferably the connector is made from a metal, and preferably the metal is a titanium alloy to facilitate adhesion and inhibit corrosion. Optionally the connector is manufactured from a ferrous alloy, a nickel alloy, an aluminium alloy, a copper alloy, a cobalt alloy, a magnesium alloy, or a plastics material. Preferably the annular mesh is oriented in two planes.

Preferably the annular mesh is formed into a predetermined three dimensional shape.

Preferably the annular mesh is deformed into a three dimensional shape. Preferably the connector comprises multiple threaded or plain bosses oriented in different directions to each other.

Preferably the mesh size and orientation is sufficient to permit the passage of a liquid or reasonably viscous bonding agent.

Preferably the mesh size and orientation is sufficient to permit the passage of composite reinforcing fibres .

Preferably the mesh size, density and orientation varies from the threaded or plain boss to the outside of the connector in a continuous fashion.

Preferably the mesh size, density and orientation varies from the threaded or plain boss to the outside of the connector in a stepwise fashion. Preferably the outer shape of the mesh is shaped in a non circumferential shape, for example; wavelilce, sinusoidal or random.

Preferably the strength of the mesh and the threaded or plain boss are designed in such a ratio as to ensure failure occurs at the minimum or threaded section of the threaded boss, or of a bolt or stud passing through a plain boss. Preferably the radial stiffeners are oriented to prevent ripping or tearing of the anchor mesh.

Preferably the threaded or plain boss is level (flush) with the mesh or mesh-like structure.

Preferably the central plane of the mesh is midway along the tlireaded or plain boss, that is, mid-plane with respect to the boss. Optionally the central plane of the mesh is offset from the mid-plane of the threaded or plain boss.

Optionally the threaded or plain boss is substituted with a protruding screw, bolt, rivet or other mechanical fastener.

In a third aspect, the invention may broadly be said to consist in a method of connecting components made from FRC materials to other components wherein the method includes the use of a connector substantially as specified herein.

Preferably the method involves connecting components made from FRC materials to components made from metals or of plastics materials.

In a fourth aspect, the invention may broadly be said to consist in a method of manufacturing a connector for use with composite materials substantially as specified herein wherein the method includes the use of additive manufacturing (AM) via Electron Beam Melting (EBM) or Selective Laser Meltmg (SLM) or Direct Metal Laser Sintering (DMLS), or other additive manufacturing processes including plastics additive manufacturing processes.

Optionally the method of manufacturing of the connector involves the use of Metal Injection Moulding (MIM) or Spark Plasma Sintering (SPS), or metal stamping or forging or casting and machining.

In a further aspect, the invention may broadly be said to consist in a method of creating a hydraulic or pneumatic connection between components and overwrapped composite pressure vessels (COPV) using a connector substantially as specified herein.

In a further aspect, the invention may broadly be said to consist in an article incorporating at least one connector for use with composite materials substantially as specified herein.

Preferably the article is a part of a vehicle.

Preferably the vehicle is an aerospace vehicle.

The invention may also broadly be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of the parts, elements or features, and where specific integers are mentioned herein which have Icnown equivalents, such equivalents are incorporated herein as if they were individually set forth.

DESCRIPTION Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

FIGURE 1 is a series of views of a first example of a connector for use with composite materials according to the present invention, FIGURE 2 is a series of views of a second example of a connector for use with composite materials,

FIGURE 3 is a perspective view of a third example of a connector for use with composite materials, and

FIGURE 4 is a perspective view of a fourth example of a connector for use with composite materials.

With reference to Figure 1, a first example of a single piece connector according to the present invention will now be described. The single piece connector is approximately circular- in shape; consisting of an open mesh structure on the outside (2), and a solid internally threaded boss or blank boss in the centre (1). The progression from open mesh to the central boss being topologically optimised in such a manner that ensures loads smoothly flow towards and/or away from the centre boss (depending on load sense and direction). Radial stiffeners (3) are incorporated to prevent ripping or tearing of the mesh.

Figure 2 shows an alternative connector having an outer extremity which is generally circular but with the outer perimeter having a sinusoidal wavey pattern. The connector is placed between layers of fibre mesh/fabric/roving and impregnated with the bonding adhesive. Once the assembly is cured, the connector becomes an intimate part of the structure. The material of the comiector ideally has a high specific strength, toughness and hardness. The material should also be sufficiently corrosion resistant with regard to the intended operating environment, and the adhesives and primers used within the FRC itself at the interface with the connector. Lack of corrosion resistance will lead to weakening of the connector and swelling of the joint with possible de-lamination. Examples of such materials are certain: titanium, nickel, aluminium cobalt, stainless steel alloys and inter- metallic aluminides.

The preferred method of manufacture of the comiector joint is by Additive Manufacturing (AM). This permits the smooth progression from open mesh structure through a finer mesh structure at smaller radii to solid metal at the central boss to be realised. The preferred method of Additive Manufacturing is Electron Beam Melting (EBM), however, other methods such as Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), or other additive manufacturing processes including plastics additive manufacturing processes could be used. A plane of the mesh structure (2), or webs, passes through a mid point of a principal axis of the threaded boss (1) or mechanical fastening section. This helps to centralise the transfer of loads between the mesh structure (2) and the threaded boss (1).

With reference to Figure 3, a third example of a connector for use with composite materials (11) will now be described. The connector or fastener (11) is designed for use in components or structures that are made from fibre reinforced composite (FRC) materials, for example Kevlar or carbon fibre car bodies, boat hulls or aircraft parts or structure. The connectors are used where it is necessary to make a mechanical joint between the composite article and another component, for example a bolted joint where a suspension member is attached to a racing car body. The connector or fastener (11) has a body section (13) that is configured to form a connection to an article formed of composite material. This body section (13) is designed to be integrated into the FRC component during the initial manufacturing steps. That is, the fastener (11) is inserted between the fibres, roving and/or fabric layers of the FRC component, and the body section (13) of the fastener (11) becomes completely covered or impregnated with the resin system or bonding adhesive of the FRC. When the FRC component is subsequently cured, the fastener (11) is embedded within the fibres and resin matrix of the component.

In addition to the body section (13), the connector (11) also has a mechanical fastening section (15) that is configured for use in mating the connector to a complimentary mechanical fastener. In this example the mechanical fastening section (15) is in the form of a boss (17) having an internal thread form (19). Alternatively the mechanical fastening section (15) could include a threaded stud, or a boss having a plain bore for receiving the shank of a bolt or rivet, a threaded nipple of a pressurised fluid connection, or a range of other mechanical fastening methods. The mechanical fastening section (15) can be counter-bored, or counter-sunk, to accommodate flush fitting fastener heads.

It can be seen in Figure 3 that the body section (13) includes arms (21) that are each arranged in a substantially radial direction extending from the mechanical fastening section (15). In this example, each of the arms (21) is tapered, being thicker adjacent to their connection to the mechanical fastening section (15) and thinner at an outer extremity (23) of each arm (21). The arms (21) can be solid, or they can be porous, and preferably they have a rough finish. The advantage of being porous is that the arms can become fully entwined within the fibre and resin matrix of the composite material.

Importantly, the body section (13) also includes webs (25) extending between each radial arm (21). Each of the webs (25) is porous and the webs also have a rough exterior surface. As can be seen in Figures 3 and 4, the porous nature of the webs forms a meshlike or open mesh structure. Having said this, the webs (25) are not made of a wire or fabric mesh, they are formed integrally with the material that forms the remainder of the connector (11). The connectors (11) are single piece items, manufactured in one process and from a material that is largely homogeneous throughout. The thickness of the webs (25) can also be tapered, with each being thicker adjacent to the mechanical fastening section (15) and tlrinner at the outer extremity (23) of the webs (25).

The tapered radial aims (21), and or the tapered webs (25), give a graduated stiffness of the body section (13), with the body section (13) being stiffest adjacent to its connection to the mechanical fastening section (15), and less stiff at the outer extremity (23) of the body section (13).

The body section (13) also includes axial members (27), the axial members (27) being generally aligned with a principal axis of the mechanical fastening section (15), that is proti'uding perpendicular to the plane of the body section (13). In this example, the axial members (27) are relatively short and they extend from the webs (25), but in an alternative embodiment the axial members (27) could also, or alternatively, extend from the radial arms (21). The axial members (27) can also be porous.

In this example, the body section (13) also includes an annular member (29) which surrounds the mechanical fastening section (15) and links between the radial arms (21). The annular member (29) can also be porous.

The pores (31) of the body section (13) are pores that extend right through the structure of the respective webs, arms, axial members or annular stiffeners of the body section (13). The pores of the webs, arms, axial members or annular stiffeners are holes preferably having a diameter exceeding 0.3 millimetres, and preferably not exceeding 1.0 millimetre.

In this third example, the perimeter of the body section (13) is substantially circular. Figure 4 shows a similar connector or fastener (41) in which the perimeter (43) of the body section has a generally sinusoidal wave pattern.

The connectors according to the present invention can be used within the FRC material of a range of components or structures, for example boat hulls, bicycle frames, racing car bodies, aircraft or satellite parts.

It is also envisaged that the connector according to the present invention could be adapted for use as a pressurised fluid connector, for example a connector that could be incorporated into a hydraulic or pneumatic composite pressure vessel (COPV). The connectors (11) and (41) are typically made from a metal or a metal alloy, but could also be formed of a plastics material. As noted above titanium alloy is a preferred metal. Titanium is very strong, and relatively light in weight, but perhaps more importantly, it is relatively inert and does not corrode easily. This is particularly important for connectors or fasteners for use with carbon fibre FRC structures or components. Ferrous or aluminium based materials will typically corrode when placed along side carbon based products due to the high difference in the electrode potentials of each material, resulting in strong potential for galvanic corrosion. VARIATIONS

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

In the examples described above, the graduated stiffness of the body section (13) is primarily achieved by tapering the thickness of the radial arms (21), and/or the webs (25), with each tapering in thickness toward the outer extremities (23) of the body section (13).

In the second example, the graduated stiffness of the body section (13) is also partly achieved through the wavey pattern of the edge at the outer extremities (23) of the body section (13).

It is envisaged, that in an alternative embodiment, the graduated stiffness of the body section (13) could be achieved by graduating the porosity, or the density of the mesh-like structure, of the body section (13). For example, the porosity could be less, or the hole sizes of the mesh-like structure smaller, adjacent to the connection between the body section (13) and the mechanical fastening section (15), and the porosity or the hole sizes could be greater toward the outer extremities (23) of the body section (13).

The examples described above show connectors having one mechanical fastening section (15), but clearly the same principles could be applied to a connector having any number of mechanical fastening sections. In such an alternative embodiment, the important feature of the graduated stiffness would be graduated from each of the mechanical fastening sections and toward the outer extremities of the connector.

Optionally the connector could include more than one mechanical fastening section, with the principal axis of at least one of the mechanical fastening sections being at an angle relative to at least one other of the mechanical fastening sections.

Optionally the connector is manufactured from a ferrous alloy, a nickel alloy, an aluminium alloy, a copper alloy, a cobalt alloy, a magnesium alloy, or a plastics material. Optionally the connector, or at least the body section could have a sintered metal construction.

As an option to additive manufacturing, the connector could be manufactured using Metal Injection Moulding (MIM), Spark Plasma Sintering (SPS), or metal stamping or forging or casting and machining. DEFINITIONS

Throughout this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

The term "stiffness" used in this specification is intended to refer to resistance to deflection, or the degree of deflection under a given load, or as understood in the mechanical engineering field.

ADVANTAGES

Thus it can be seen that at least the preferred form of the invention provides a connector for use with composite materials which has numerous characteristics that aid the integration with the FRC:

1. The mesh pores are sufficient, at all sizes, to permit the diffusion of the FRC glue or resin.

2. The mesh cell size is sufficient to resist load and stresses in two dimensions.

3. The mesh has integrated into it extra solid reinforcement to resist progressive failure of the mesh, i.e. ripping. The mesh thickness tapers in cross section from the central threaded or plain boss outwards to the edge. The mesh pores at the edge are sufficiently large to peimit the manual integration via interweaving with fibre. The connector can be interwoven with fibres prior to assembly, impregnation and curing to aid in load distribution. The mesh has small upright elements or prongs that are perpendicular in relation to the surface of the completed FRC component - to facilitate integration via interweaving with the fibres. Optimisation of the pore size, or mesh cell size, density change rate, and orientation relative to principle loads can be done during design - such that design loads can be dealt with in a minimum total structural weight solution known as topological optimisation. The thickness of the mesh and the central boss may be designed in any such ratio so as to provide a predictable margin over any limit load or combination of load conditions desired by the designer and whatsoever failure load to be expected into/from the structure at the minimum or threaded section of the central boss (or combination of threaded bosses/blank bosses). Multiple threaded bosses or bosses may be designed and manufactured together with the intervening region being a topologically optimised mesh network that takes due account of the multiple attachment sites, discrete and shared loads and the geometry between these. Due to the versatility of the AM method employed, the mesh stracture may be contoured to other than plain flat surfaces in order to place or orientate bosses in any direction desired by the designer at, for example, comers, edges, curved faces, ends or other such features used in FRC monocoque construction.

Claims

CLAI MS

1. A connector for use with composite materials, the connector having a body section configured for use in forming a connection to an article formed of composite material, and having at least one mechanical fastening section configured for use in mating the connector to a complimentary mechanical fastener, and the body section is connected to the or each mechanical fastening section, and wherein the body section has a graduated stiffness, the stiffness of the body section being greatest at the connection between the body section and the or each mechanical fastening section, and the stiffness being least at the extremities of the body section.

2. A connector as claimed in claim 1, wherein the body section tapers in thickness from the connection between the or each mechanical fastening section and the body section, to the outer edge of the body section.

3. A connector as clamed in cl m 1 or clam 2, wherein the body section is at least parti y porous, or mesh-l i ke.

4. A connector as claimed in any one of claims 1 to 3, wherein the body section includes arms that are arranged in a substantially radial direction extending from the or each mechanical fastening section.

5. A connector as claimed in claim 4, wherein the body section includes webs extending between each radial arm.

6. A connector as claimed in claim 5, wherein each of the webs is porous.

7. A connector as claimed in any one of claims 4 to 6, wherein each of the arms is porous.

8. A connector as claimed in any one of cl ms 4 to 7, wherein each of the arms is tapered, being thicker adjacent to the mechanical fastening section and thinner at an outer extremity of each arm.

9. A connector as claimed in any one of claims 5 to 8, wherein the thickness of the webs tapers, being thi cker adj acent to the mechani cal f asteni ng secti on and thi nner at the outer extremity of the webs.

10. A connector as claimed in any one of claims 1 to 9, wherein the body section also includes axial members, the axial members being generally aligned with a principal axis of the mechanical fastening section.

11. A connector as claimed in claim 10, wherein some or all of the axial members extend from the webs.

12. A connector as claimed in any one of claims 6 to 11, wherein the pores of the porous nature of the body section are pores that extend right through the structure of the body section.

13. A connector as claimed in claim 12, wherein the pores of the body section are hoi es havi ng a di ameter exceadi ng 0.3 mi 11 i metres.

14. A connector as claimed in claim 12, wherein the pores of the body section are holes having a diameter not exceeding 1.0 millimetres.

15. A connector as claimed in any one of claims 1 to 14, wherein the perimeter of the body secti on i ncl udes a general I y si nusoi dal wave pattern.

16. A connector as claimed in any one of claims 1 to 5, wherein the connector is made from ti tani urn or a ti tani urn al I oy .

17. A connector as claimed in any one of claims 1 to 16, wherein the or each mechani cal f asteni ng secti on i ncl udes a thread form.

18. A vehicle incorporating at least one connector substantially as claimed in any one of claims 1 to 17.

19. A method of connecting components made from FRC materials to other components wherein the method includes the use of a connector substantially as claimed in any one of claims 1 to 17.

20. A method as claimed in claim 19, wherein the method involves connecting components made from FRC materials to components made from metals or of plastics materials.