WO2020109766A1

WO2020109766A1 - Attachment of an end fitting to a composite material tube

Info

Publication number: WO2020109766A1
Application number: PCT/GB2019/053326
Authority: WO
Inventors: Michael DEWHIRST
Original assignee: Lentus Composites Limited
Priority date: 2018-11-26
Filing date: 2019-11-26
Publication date: 2020-06-04
Also published as: GB201819168D0; GB2579217A; GB2579254A; GB2579217B; GB2579254B; GB201820363D0

Abstract

An arrangement is described comprising a tubular component (10) of a composite material, the tubular component (10) including an end section (12), and an end fitting (22) attached to the end section (12), wherein the end section (12) is of stepped diameter form including at least a first region (14) of a first diameter, a second region (16) of a second diameter, and an intermediate region (18) interconnecting the first and second regions (14, 16), and the end fitting (22) includes an engagement section (24) including a first region (26) of diameter for engagement with the first region (14) of the end section (12), and a second region (28) of diameter for engagement with the second region (16) of the end section (12). A method of assembly of such an arrangement is also described.

Description

ATTACHMENT OF AN END FITTING TO A COMPOSITE MATERIAL TUBE

This invention relates to the attachment of an end fitting to an end of a composite material tube. By way of example, the invention may be employed in the attachment of an end fitting to a tube of a resin bound filament wound composite material.

Composite materials are in increasingly widespread use in a number of applications, and in particular in applications in which there is a desire to reduce the weight of components for efficiency or enhanced control purposes. By way of example, in a number of aerospace applications there is a desire to reduce component weight as doing so can result in the overall aircraft weight being reduced, and hence in the ability to make fuel efficiency enhancements. Weight saving may similarly be desirable in a number of automotive applications. Also, in applications in which components are required to rotate, in use, for example components used in drive trains, it can be desirable to reduce weight and inertia so that improved responsiveness to changes in a demand input can be achieved.

Whilst there is a desire to make weight savings in the applications identified hereinbefore, there is also a need for those weight savings not to come at the expense of reduced strength or load bearing capacity, or at the expense of significantly increased dimensions.

Many composite materials are of relatively low weight and relatively good strength or load bearing capacity. Accordingly, the use of such materials in the types of application outlined above are advantageous.

Whilst the use of composite materials may be advantageous in a number of applications, difficulties can be faced in attaching fittings to components manufactured from such materials as drilling holes into the materials to allow attachment of fittings thereto can result in significant weakening of the components. Fittings are often attached to such components by being press fitted thereto or clamped thereto. However, such attachment techniques can limit the size of load that can be transmitted using the assembly of the component and the end fitting.

It is an object of the invention to provide an arrangement or assembly in which at least some of the disadvantages associated with known arrangements are overcome or are of reduced effect. Another object of the invention is to provide a method whereby an end fitting can be fitted to a component material component.

According to a first aspect of the invention there is provided an arrangement comprising a tubular component of a composite material, the tubular component including an end section, and an end fitting attached to the end section, wherein the end section is of stepped diameter form including at least a first region of a first diameter, a second region of a second diameter, and an intermediate region interconnecting the first and second regions, and the end fitting includes an engagement section including a first region of diameter for engagement with the first region of the end section, and a second region of diameter for engagement with the second region of the end section.

By providing the component with an end section of stepped diameter in this fashion, and the end fitting with a correspondingly shaped engagement section, it will be appreciated that loadings may be transmitted more directly between the end fitting and inner and outer plies of reinforcing material contained within the composite material component, and hence that the load transmitting capacity of the assembly may be enhanced compared to an arrangement in which the end fitting cooperates only with outer plies of the component.

If desired, the end section and the engagement section may include respective third or further regions, potentially further enhancing the load transmitting properties of the assembly. The end fitting is preferably press fitted to the component. The engagement section of the end fitting is preferably provided with microspline teeth that, on attachment to the end section, dig into the composite material of the end section.

The stepped nature of the interface between the component and the end fitting may have the additional benefit that the assembly loads required to be applied during press fitting may be reduced.

An annular reinforcing member may be applied to the component prior to attachment of the end fitting thereto, the reinforcing member serving to resist radial expansion or contraction of the end section. The reinforcing member may be of wound composite material form, and is preferably of hoop wound form. It may be formed integrally with the component.

The engagement section of the end fitting may be adapted to encircle the end section of the composite material component, in which case the reinforcing member, if provided, may be located within the end section. Alternatively, the engagement section may be located within the end section, in which case the reinforcing member, if present, may encircle the end section.

The invention also relates to a method of attaching an end fitting to a tubular component comprising the steps of forming the tubular component with an end section, the end section being of stepped diameter form including at least a first region of a first diameter, a second region of a second diameter, and an intermediate region interconnecting the first and second regions, and attaching an end fitting to the end section, wherein the end fitting includes an engagement section including a first region of diameter for engagement with the first region of the end section, and a second region of diameter for engagement with the second region of the end section.

The end fitting is preferably attached by being press fitted to the end section. The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view illustrating an arrangement in accordance with a first embodiment of the invention; and

Figures 2 and 3 are views similar to Figure 1 illustrating alternative embodiments.

Referring firstly to Figure 1, a part of a composite material tubular component in the form of a wound fibre composite material hollow shaft 10 is shown. The shaft 10 include an end section 12 of stepped outer diameter, including a first region 14 of a first, relatively large diameter, and a second region 16 of a second, smaller diameter. The first and second regions 14, 16 adjoin one another at an intermediate region or step 18. Whilst the end section 12 is only shown as including regions of two different diameters, it will be appreciated that three or more different diameter regions may present, if desired. Conveniently, the stepped nature of the end section 12 is formed by machining the end part of a shaft of uniform diameter. Flowever, it will be appreciated that this need not always be the case, and arrangements in which the shaft is manufactured in such a manner as to have an end section of stepped form is possible without departing from the scope of the invention.

The shaft 10 is manufactured by winding layers or plies 20 (illustrated diagrammatically in Figure 1) of a suitable reinforcing fibre onto a mandrel, the fibre being impregnated with a suitable resin material either prior to winding onto the mandrel, during the winding operation or after winding. The angles at which the layers or plies 20 are wound are chosen depending upon the application in which the shaft 10 is to be used, for example to result in the shaft being of a desired torque transmitting capacity, stiffness, strength or the like. The resin material is then cured or allowed to cure and, if required, finishing operations are undertaken to produce a shaft of the desired form. As mentioned above, the end part of the shaft is then machined to take the stepped form mentioned above. It will be appreciated that the presence of an end section 12 of stepped form results in the layer or ply of fibres exposed at or adjacent the surface of the first region 14 being different to the layer or ply exposed at or adjacent the surface of the second region 16.

An end fitting 22 is press fitted to the end section 12. The end fitting 22 is conveniently of a metallic material and includes parts or features shaped for cooperation with other components, for example to motors, gear boxes, or components to be driven for rotation. The end fitting 22 further includes an engagement section 24 of hollow tubular form. The engagement section 24 is of internally stepped diameter, including a first region 26 of a diameter selected for cooperation and engagement with the first region 14 of the end section 12, and a second region 28 of a diameter selected for cooperation and engagement with the second region 16 of the end section 12. The first and second regions 26, 28 of the engagement section 24 are provided with a series of microspline teeth. Such teeth are of small radial height, for example of height less than 2mm, preferably less than 1mm, and may be in the region of 0.5mm or less. By way of example, they may be of height less than 0.25mm.

The arrangement further comprises a reinforcing member 30 of wound fibre composite material form. The winding angle of the fibres of the reinforcing member 30 is preferably chosen such that radial compression of the reinforcing member 30 is resisted, such winding sometimes being referred to as hoop wound.

During assembly, the reinforcing member 30 is pressed into the end of the end section 12, providing support to the end section 12 resisting radial compression thereof. Subsequently, the end fitting 22 is press fitted onto the end section 12, the engagement section 24 thereof encircling the end section 12. Once fitted in this manner, it will be appreciated that the first region 26 of the engagement section 24 engages the first region 14 of the end section 12, cooperating with the layer or ply 20 exposed at or adjacent the surface thereof, and that the second region 28 of the engagement section 24 engages the second region 16 of the end section 12, cooperating with the layer or ply 20 exposed at or adjacent the surface thereof. Loads applied to the end fitting 22, in use, can thus be efficiently and effectively transmitted into shaft 10, or vice versa. The nature of the attachment of the end fitting 22 to the shaft 10 thus allows relatively large loads to be transmitted, in use. The stepped nature of the interface between the end fitting 22 and the shaft 10 may further allow a reduction in the size load that must be applied to achieve press fitting of these components to one another.

Although as described hereinbefore the reinforcing member 30 takes the form of a separate component pressed into the shaft 10, it could, if desired, be formed integrally with the shaft as part of the manufacturing process for manufacturing the shaft. In such an arrangement, it would take the form of a filament wound structure, and may have the same inner diameter as the remainder of the shaft.

Whilst Figure 1 illustrates an arrangement in which the engagement section 24 of the end fitting encircles the end section 12, the reverse is also possible, for example as shown in Figure 2. In each case, if desired and if the end of the shaft is of sufficiently good strength, the reinforcing member may be omitted. As with the arrangement of Figure 1, the reinforcing member 30 could be formed integrally with the remainder of the shaft, if desired.

In the arrangements described hereinbefore, the layers or plies 20 all extend substantially parallel to the axis of the shaft throughout the full length of the shaft 10. However, this need not always be the case. By way of example, Figure 3 illustrates a modification in which as an initial part of the process for manufacturing the shaft 10, a wedge 32 is formed over which the layers or plies 20 making up the majority of the shaft 10 are wound. A consequence of the presence of the wedge 32 is that, at the end section 12, two or more layers or plies 20 may be exposed or located adjacent to each of the regions 14, 16. As a consequence, further enhancements may be made to the load transmitting properties of the arrangement. As shown in Figure 3, the wedge 32 may be made up of a series of steps. However, other arrangements are possible in which the wedge is of smooth form. Furthermore, whilst forming a wedge 32 of wound form as part of the manufacture of the shaft 10 may be convenient, the wedge could be of prefabricated form, for example of metallic or composite material form positioned onto the mandrel before winding of the remainder of the shaft 10. It will be appreciated that the description hereinbefore is of specific example embodiments of the invention and that a wide range of modifications or alterations may be made thereto without departing from the scope of the invention, and that the invention may be employed in a wide range of applications.

Claims

CLAIMS:

1. An arrangement comprising a tubular component of a composite material, the tubular component including an end section, and an end fitting attached to the end section, wherein the end section is of stepped diameter form including at least a first region of a first diameter, a second region of a second diameter, and an intermediate region interconnecting the first and second regions, and the end fitting includes an engagement section including a first region of diameter for engagement with the first region of the end section, and a second region of diameter for engagement with the second region of the end section.

2. An arrangement according to Claim 1, wherein the component includes a plurality of layers or plies of reinforcing material, and the stepped nature of the end section allows transmission of loads between the first region of the engagement section and a first layer of the reinforcing material, and between the second region of the engagement section and a second layer of the reinforcing material.

3. An arrangement according to Claim 1 or Claim 2, wherein the end section and the engagement section include respective third or further regions.

4. An arrangement according to any of the preceding claims, wherein the end fitting is press fitted to the component.

5. An arrangement according to any of the preceding claims, wherein the engagement section of the end fitting is provided with microspline teeth that, on attachment to the end section, dig into the composite material of the end section.

6. An arrangement according to any of the preceding claims, further comprising an annular reinforcing member applied to the component prior to attachment of the end fitting thereto, the reinforcing member serving to resist radial expansion or contraction of the end section.

7. An arrangement according to Claim 6, wherein the reinforcing member is of wound composite material form.

8. An arrangement according to Claim 7, wherein the reinforcing member is of substantially hoop wound form.

9. An arrangement according to any of Claims 6 to 8, wherein the reinforcing member is integrally formed with the component.

10. An arrangement according to any of the preceding claims, wherein the engagement section of the end fitting is adapted to encircle the end section of the composite material component.

11. An arrangement according to any of Claims 1 to 9, wherein the engagement section is located within the end section.

12. A method of attaching an end fitting to a tubular component comprising the steps of forming the tubular component with an end section, the end section being of stepped diameter form including at least a first region of a first diameter, a second region of a second diameter, and an intermediate region interconnecting the first and second regions, and attaching an end fitting to the end section, wherein the end fitting includes an engagement section including a first region of diameter for engagement with the first region of the end section, and a second region of diameter for engagement with the second region of the end section.

13. A method according to Claim 12, wherein the end fitting is attached by being press fitted to the end section.

14. A method according to Claim 13, wherein an annular reinforcing member is applied to the component prior to attachment of the end fitting thereto, the reinforcing member serving to resist radial expansion or contraction of the end section.