GB2579795A

GB2579795A - Composite material tubular member

Info

Publication number: GB2579795A
Application number: GB1820357.0A
Authority: GB
Inventors: Dewhirst Michael
Original assignee: Lentus Composites Ltd
Current assignee: Lentus Composites Ltd
Priority date: 2018-12-13
Filing date: 2018-12-13
Publication date: 2020-07-08
Anticipated expiration: 2038-12-13
Also published as: GB201820357D0; GB2579795B; WO2020120966A1

Abstract

Disclosed is a composite material (e.g. a fibre reinforced plastic with carbon-fibre or fibre-glass) member 10 including a wedge element 14 and a composite material shaft 16 formed, in part, over the wedge element. The wedge element has an inner surface 14a and an outer surface 14b that are parallel to one another over the majority of their length. The wedge element may be of prefabricated metallic form. Alternatively, it may be of prefabricated composite material form that is machined into shape. The shaft region overlying the wedge element may be machined to a uniform diameter, with an end fitting 12 pressed onto this region. The wedge element may have a region of tapering thickness adjacent its end of smallest diameter (see fig. 2). A reinforcing ring 20 may increase the stiffness and load bearing capacity of this region and may also be of prefabricated metallic or composite material form. A corresponding method of manufacture is also disclosed.

Description

COMPOSITE MATERIAL TUBULAR MEMBER

This invention relates to a composite material tubular member, and in particular to a composite material tubular member comprising a composite material shaft having an end fitting attached thereto to aid in the connection or cooperation of the tubular member to or with other components to allow the transmission of loads to or through the tubular member. In many applications, end fittings may be attached to both ends of the shaft.

One example application in which the composite tubular member may be employed is as a rotary drive shaft, the end fitting allowing the application of torque loads to or through the composite material tubular member.

GB2424464 describes a composite material tubular member that is formed by winding a fibre material onto a mandrel, the fibre material being impregnated with a suitable resin. Once the resin is cured, a tubular member taking the form of a shaft of good torque transmitting properties and of relatively low weight is formed. As described in GB2424464, the process of winding the fibre onto the mandrel includes a step of winding the fibre in such a fashion as to form a wedge shaped region. The purpose of the wedge shaped region is to cause the subsequently wound fibres of the shaft to be of gradually increasing diameter in the region of the wedge shaped region. During a subsequent step in the manufacturing process, the end part of the shaft, which overlies the wedge shaped region, is machined to be of uniform diameter. As a consequence, a number of the layers of fibres forming the shaft are exposed at the surface of the shaft. An end fitting is pressed onto the end of the shaft, the end fitting cooperating with the exposed parts of the layers of fibres. As a consequence, the transmission of torque loadings between the end fitting and the composite material shaft is enhanced.

The manner in which the end fitting is pressed onto the end of the shaft is such that an inwardly directed, compressive load is applied thereto. The wedge shaped region of the composite material shaft serves to react these loads. However, it has been found that the nature of the wedge shaped region is such that, in use, there is a tendency for parts thereof to deflect inwardly. As a consequence, the inwardly directed, compressive loads are not borne uniformly by the wedge shaped region, but rather tend to be concentrated towards specific parts thereof. The torque transmission loadings are similarly distributed. Accordingly, the maximum torque transmission loadings that can be carried by the composite tubular member are generally lower than would be expected, and so there is an increased risk of failure of the composite material member.

It is an object of the invention to provide a composite material member in which at least some of the disadvantages associated with known arrangements are overcome or are of reduced impact.

According to the present invention there is provided a composite material member comprising a wedge element and a composite material shaft formed, in part, over the wedge element, wherein the wedge element includes an inner surface and an outer surface, and over a majority of the axial length of the wedge element the inner surface and the outer surface are substantially parallel to one another.

It will be appreciated that in such an arrangement, the wedge element is of substantially uniform wall thickness over a majority of its length. The ability of the wedge element to withstand inwardly directed compressive loads is thus also substantially uniform along the length thereof. As a consequence, where the composite material member also includes an end fitting pressed onto the shaft, torque transmission between the shaft and the end fitting will be more uniformly distributed over the area in which the tubular shaft and the end fitting cooperate with one another. The risk of failure of the composite material member is thus reduced.

The wedge element may be of prefabricated form. By way of example, it may be of metallic form, machined to be of a desired shape. Alternatively, it could take the form of a composite material element that has been machined to take on a desired shape. Whilst the use of a prefabricated wedge element may be convenient, it is also envisaged that the wedge element could be formed as part of the same process as forming the shaft region, the wedge element being formed in situ on a mandrel immediately before forming the shaft region.

The part of the shaft region overlying the wedge element may be machined to be of substantially uniform diameter. An end fitting may be pressed onto the machined part of the shaft region.

The wedge element may include, adjacent its end of smallest diameter, a region of tapering wall thickness. As this part of the wedge element may be less well suited to bearing the applied compressive loads, in use, a reinforcing ring may be provided to increase the stiffness and load bearing capacity of this part of the wedge element. The reinforcing ring may be of prefabricated form. By way of example, it may be of metallic or composite material form.

A second end fitting may similarly be attached to an opposite end of the shaft.

The invention further relates to a method of manufacture of a composite material member comprising providing or forming a wedge element on a mandrel, winding a fibre material over at least part of the wedge element and at least part of the mandrel, and curing a resin material impregnated into the fibre material to form a composite material shaft formed, in part, over the wedge element, wherein the wedge element includes an inner surface and an outer surface, and over a majority of the axial length of the wedge element the inner surface and the outer surface are substantially parallel to one another.

The method may include a further step of machining a part of the shaft overlying the wedge element such that the said part is of substantially uniform diameter. The method may further comprise a step of pressing an end fitting over the said part of the shaft.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation illustrating a composite material member in accordance with an embodiment of the invention; and Figure 2 illustrates a modification to the composite material member shown in Figure 1.

Referring firstly to Figure 1, a composite material tubular member is illustrated, comprising a shaft 10 of a wound composite material to which an end fitting 12 has been attached. The shaft 10 is formed by locating a wedge element 14 upon a mandrel, the wedge element 14 being secured to the mandrel such that relative movement between the wedge element 14 and the mandrel is resisted. A fibre material 16, for example in the form of carbon or glass fibre, is then wound onto the mandrel, the fibre material 16 being wound over at least part of the wedge element 14 and over at least a part of the mandrel adjacent the wedge element 14. The fibre material 16 is impregnated with a suitable resin material, and upon curing of the resin material it will be appreciated that a composite material shaft 10 of generally tubular form is formed, the shaft 10 defining an integral outwardly flared region, the outwardly flared region resulting from the winding of the fibre material 16 over the wedge element 14. The manner in which the fibre material 16 is wound is such as to result in the formation of a number of layers 18 of fibre material 16.

The wedge element 14, in the arrangement illustrated, is of prefabricated form. By way of example, it may be of metallic form, machined to be of a desired shape. Alternatively, it could take the form of a wound or otherwise formed composite material element that has been machined to be of a desired shape. Regardless as to the material used in the formation of the wedge element 14, in the arrangement shown it is of hollow, frustoconical form defining an inner surface 14a and an outer surface 14b, both of which are of substantially the same cone angle. As a consequence, it will be appreciated that the surfaces 14a, 14b are substantially parallel to one another, and that the wedge element 14 is of substantially uniform wall thickness along its entire axial length. Whilst in the arrangement shown, the wedge element 14 is of substantially uniform wall thickness, it will be appreciated that small variations in wall thickness may be permitted and, in some arrangements, may be advantageous. By way of example, the inner and outer surfaces 14a, 14b may deviate from one another by an angle of, say, 5° or less.

The resin material may be introduced by, for example, passing the fibre material 16 through a resin material containing bath prior to winding the fibre material 16 onto the mandrel. Alternatively, it may be a so-called pre-preg material which already incorporates a resin material, or the resin material may be introduced into the assembly after winding. It will be appreciated that the manner in which the resin is introduced is not of relevance to the invention and that any suitable technique may be used without departing from the scope of the invention.

Similarly, the manner in which the resin is cured is not of relevance to the invention and may depend upon the nature of the resin material used.

As mentioned above, the cured composite material shaft 10 includes an outwardly flared region. Before attaching the end fitting 12 to the cured composite material shaft 10, a machining operation is performed upon the outwardly flared region to result in this region of the cured composite material shaft 10 being of substantially uniform diameter. As the layers 18 of fibre material 16 within the composite material shaft 10 in the vicinity of the flared region are themselves outwardly flared, it will be appreciated that the machining operation results in all or many of these layers 18 being exposed at the surface of the composite material shaft 10.

After machining, the end fitting 12 is pressed or pushed onto the machined end of the cured composite material shaft 10. The end fitting 12 includes a tubular part 12a having an inner diameter substantially the same as or slightly smaller than the outer diameter of the machined part of the composite material shaft 10. The part 12a is conveniently of inwardly splined form.

It will be appreciated that pushing or pressing the end fitting 12 onto the end of the composite material shaft 10 results in the part 12 contacting the layers 18 of fibre material 16 exposed at the surface of the composite material shaft 10. Accordingly, torque loadings may be efficiently and effectively transmitted, in use, between the end fitting 12 and the composite material shaft 10.

It will be appreciated that the application of the end fitting 12 to the composite material shaft 10 results in the end part thereof being subject to an inwardly directed compressive load. The load is reacted by the wedge element 14. As the wedge element 14 is of substantially uniform wall thickness along its entire axial length, it will be appreciated that all parts of the wedge element 14 have a substantially equal ability to bear the applied compressive loads. In contrast, in the arrangement described in GB2424464, the parts of the wedge element to one end thereof are of considerably smaller wall thickness than the parts at or close to the other end thereof. Consequently, in that arrangement, certain parts of the wedge element are able to bear the applied loadings without significant deformation thereof whilst other parts will tend to deform.

This deformation results in the compressive load applied between the end fitting and the composite material element being unevenly distributed, and consequently in the torque loading applied between the end fitting and the composite material element also being unevenly distributed. As mentioned before, this may lead to failure of the component. In the arrangement shown in Figure 1, as the wedge element 14 is of substantially uniform wall thickness along its entire length, it will be appreciated that the distribution of the compressive load, and hence the torque loading applied in use, is considerably more uniform. The risk of failure is thus reduced.

Whilst in the arrangement of Figure 1 the wedge element 14 is of substantially uniform wall thickness along its entire axial length, this need not always be the case and many of the advantages of the invention may be achieved in arrangements in which the wedge element 14 is of substantially uniform wall thickness over a majority, but not necessarily all, of its length. By way of example, Figure 2 illustrates an arrangement in which the wedge element 14 is of modified form to include a small diameter part of tapering wall thickness. Such an arrangement may be advantageous in that manufacture or fabrication of the composite material shaft 10 may be simplified as a mandrel of uniform outer diameter may be used (the arrangement of Figure 1 may require the use of, for example, a stepped mandrel or a multipart mandrel). In the arrangement of Figure 2, as the tapering wall thickness section of the wedge element 14 may be prone to deflection upon the application of compressive loadings, a reinforcing ring 20 may be pressed into the interior of the composite material member prior to attachment of the end fitting 12 to aid in resisting such deflection.

The reinforcing ring 20 may be of prefabricated form. By way of example it may be metallic or of machined composite material form.

It will be appreciated that other than at the tapering wall thickness section, the wedge element 14 is of substantially uniform wall thickness, being of substantially uniform wall thickness over a majority of its axial length, and so many of the benefits described hereinbefore may be achieved, and the presence of the reinforcing ring 18 may counter the disadvantages of this embodiment compared to that of Figure 1.

Whilst in the embodiments described hereinbefore the composite material member includes an end fitting 12 fitted to one end of a shaft 10, in many embodiments a second end fitting may be similarly attached to the other end of the shaft 10.

In the arrangements described hereinbefore the wedge element 14 is of prefabricated form. It will be appreciated that this need not always be the case and that the invention could employ a wedge element 14 fabricated as part of the same process by which the remainder of the composite material shaft 10 is formed. By way of example, substantially the method described in GB2424464 may be used, the method being modified to use a modified mandrel including a tapering diameter region shaped to result in the formation of a wedge element when a uniform thickness of fibre material is wound thereon. After forming the wedge element in this manner, the remainder of the fibre material of the composite material element is wound, and the impregnated resin is cured.

Whilst specific embodiments of the invention are described hereinbefore, it will be appreciated that a wide range of modifications and alterations may be made to the arrangements described hereinbefore without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS: 1. A composite material member comprising a wedge element and a composite material shaft formed, in part, over the wedge element, wherein the wedge element includes an inner surface and an outer surface, and over a majority of the axial length of the wedge element the inner surface and the outer surface are substantially parallel to one another.
2. A member according to Claim 1, wherein the wedge element is of prefabricated form.
3. A member according to Claim 2, wherein the wedge element is of metallic form.
4. A member according to Claim 2 wherein the wedge element is of composite material form, machined to be of a desired shape.
5. A member according to any of the preceding claims, wherein the part of the shaft region overlying the wedge element is machined to be of substantially uniform diameter.
6. A member according to Claim 5, wherein an end fitting is pressed onto the machined part of the shaft region.
7. A member according to any of the preceding claims, wherein the wedge element includes, adjacent its end of smallest diameter, a region of tapering wall thickness.
8. A member according to Claim 8, further comprising a reinforcing ring to increase the stiffness and load bearing capacity of the tapering wall thickness part of the wedge element.
9. A member according to Claim 8, wherein the reinforcing ring is of prefabricated form.
10. A member according to Claim 9, wherein the reinforcing rings is of metallic or composite material form.
11. A member according to any of the preceding claims, further comprising a second end fitting similarly be attached to an opposite end of the shaft.
12. A method of manufacture of a composite material member comprising providing or forming a wedge element on a mandrel, winding a fibre material over at least part of the wedge element and at least part of the mandrel, and curing a resin material impregnated into the fibre material to form a composite material shaft formed, in part, over the wedge element, wherein the wedge element includes an inner surface and an outer surface, and over a majority of the axial length of the wedge element the inner surface and the outer surface are substantially parallel to one another.
13. A method according to Claim 12, further comprising a step of machining a part of the shaft overlying the wedge element such that the said part is of substantially uniform diameter.
14. A method according to Claim 13, further comprising a step of pressing an end fitting over the said part of the shaft.