Composite end connections

Abstract

A composite structural component made of a polymer matrix composite material includes an end connection that includes an end portion at one end of the composite structural component, comprising an internal surface comprising a plurality of ridges and grooves defining a first engagement surface along an axial direction and a metal interface component comprising an outer surface comprising a plurality of ridges and grooves defining a second engagement surface along the axial direction and an inner surface defining a mounting surface for attachment of an end fitting. The metal interface component is engaged with the internal surface of the composite structural component by mating of the first and second engagement surfaces. The structure also includes an outer annular component fitted around the end portion in axial alignment with the mating of the first and second engagement surfaces.

Claims

1. An end connection comprising: the end connection comprising: a composite structural component made of a polymer matrix composite material and comprising an end portion, the end portion comprising an internal surface comprising a plurality of ridges and grooves defining a first engagement surface along an axial direction and an outer layer of circumferential fibre reinforcement; a metal interface component comprising an outer surface comprising a plurality of ridges and grooves defining a second engagement surface along the axial direction and an inner surface defining a mounting surface for attachment of an end fitting; wherein the metal interface component is engaged with the internal surface of the composite structural component by mating of the first and second engagement surfaces; and an outer annular component fitted around the outer layer of circumferential fibre reinforcement of the end portion in axial alignment with the mating of the first and second engagement surfaces; wherein the outer annular component forms an interference fit with the end portion so as to preload the end connection with compressive radial forces.

2. An end connection according to claim 1, wherein the outer annular component forms an interference fit of about 0.1 mm with the end portion of the composite structural component.

3. An end connection according to claim 1, wherein the ridges and grooves defining the first engagement surface extend at an angle θ relative to the axial direction of the first engagement surface, wherein θ≤20°.

4. An end connection according to claim 1, wherein the outer surface of the metal interface component comprises a tapered portion and an engagement portion comprising the plurality of ridges and grooves, wherein the tapered portion tapers radially outwardly from an end of the metal interface component to the engagement portion.

5. An end connection according to claim 1, further comprising an end fitting attached to the mounting surface of the metal interface component.

6. An end connection according to claim 1, wherein the composite structural component comprises the end portion and a main portion; wherein the end portion has a first internal diameter and the main portion has a second, smaller internal diameter that substantially matches the internal diameter of the metal interface component.

7. An end connection according to claim 6, wherein the internal surface of the composite structural component tapers radially inwards from the end portion to the main portion.

8. An end connection according to claim 6, wherein the outer surface of the metal interface component comprises a tapered portion and an engagement portion comprising the plurality of ridges and grooves, wherein the tapered portion tapers radially outwardly from an end of the metal interface component to the engagement portion.

9. An end connection according to claim 6, further comprising an end fitting attached to the mounting surface of the metal interface component.

10. A method of forming an end connection for a composite structural component made of a polymer matrix composite material, the method comprising: providing a metal interface component comprising an outer surface comprising a plurality of ridges and grooves defining an engagement surface and an inner surface defining a mounting surface for attachment of an end fitting; forming an end portion of the composite structural component around the engagement surface of the metal interface component so that the metal interface component is engaged with an internal surface of the composite structural component at one end of the composite structural component; circumferentially winding fibres around the end portion of the composite structural component in axial alignment with the engagement surface so as to form an outer layer of circumferential fibre reinforcement; and fitting an outer annular component around the outer layer of circumferential fibre reinforcement of the end portion of the composite structural component in axial alignment with the engagement surface so as to form an interference fit with the end portion and preload the end connection with compressive radial forces.

11. A method according to claim 10, wherein the polymer matrix composite material comprises fibre reinforced polymer, the method further comprising: providing the metal interface component on a mandrel; and winding glass or carbon fibres around the mandrel to form the composite structural component and embed the metal interface component in the end portion of the composite structural component.

12. A method according to claim 11, wherein forming the composite structural component comprises winding glass or carbon fibres around the mandrel at a low angle θ between 8° and 15° and winding one or more layers of glass or carbon fibres around the mandrel at a high angle θ between 75° and 89°.

13. A method according to claim 10, further comprising curing the composite structural component; and removing at least some of the layer(s) of hoop fibre reinforcement before fitting the outer annular component.

14. A method according to claim 11, further comprising attaching an end fitting to the mounting surface of the metal interface component.

Description

DETAILED DESCRIPTION

(1) One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures, in which:

(2) FIG. 1 shows an end joint of a composite rod according to a typical example of those found in the prior art; and

(3) FIG. 2 is an example of an end connection for a composite structural component according to the present disclosure.

(4) Referring firstly to FIG. 1, a cross section of an end joint of a composite rod 76 is shown according to a typical example of those found in the prior art, comprising a main section of a rod 55, an undulating joint portion 90, and an embedded insert 10b. The main rod section 55 tapers inwards towards the undulating joint portion of substantially constant diameter at its end 90. The outer diameter of the embedded insert 10b matches the undulations of the rod, and a portion of its inner diameter is threaded 24 suitable for attaching the assembly to other structures. A casing 88 fills in the annular channels in the joint portion 90 by winding layers of hoop fibres over the assembly before heating/curing the resin material.

(5) FIG. 2 shows an example according to the present disclosure, wherein a composite (e.g. carbon fibre reinforced composite) structural component comprises a composite rod 1 which in turn comprises a main portion 1A, a tapering portion 1B, and an end portion 1C. The end portion 1C has an internal surface 8 comprising a series of ridges and grooves which extend at an angle θ relative to the axial direction A generally defined by the internal surface 8. The ridges and grooves extend circumferentially around the axial direction A. The composite rod 1 may take the form of a tube.

(6) An end connection 20 for the composite rod 1 comprises the end portion 1C and an embedded metal insert 2, which is positioned interior to the tapering portion 1B and the end portion 1C of the composite rod 1. The embedded metal insert 2 has a constant internal diameter over its length equal to the internal diameter of the main rod portion 1A, and an outer surface 7 that follows the taper of the tapering portion 1B and comprises a series of ridges and grooves that match the ridges and grooves of the end portion 1C. The outer surface 7 of the embedded metal insert 2 mates with the internal surface 8 of the composite rod 1, such that the embedded metal insert 2 is engaged with the internal surface 8 of the composite rod 1. The outer surface 7 and internal surface 8 are first and second engagement surfaces of the end connection 20.

(7) The internal diameter of the insert 2 is equal to or slightly greater than the internal diameter of the main section 1A of the composite rod 1. A mounting surface 5 defined by an inner surface of the embedded insert 2 is threaded, in this example, to allow for attachment to a suitably threaded end fitting 6, for example a rod end, as is illustrated here. Of course, the mounting surface 5 could take other forms.

(8) Hoop fibres 4 are wound circumferentially around the end portion 1C, and subsequently a hoop ring 3 is fitted in an interference fit over the hoop fibres 4 and the end portion 1C, such that the end portion 1C of the composite rod 1 is preloaded with compressive radial forces, resulting in hoop compression. Compression of the end connection 20 results in a greater normal contact force between the rod 1 and the insert 2, such that the frictional force resisting relative movement of the outer surface 7 of the embedded insert 2 and the internal surface 8 of the end portion 1C is increased. A greater ability to resist relative movement minimises wear when the rod 1 is placed under axial tension or compression.

(9) When the end fitting 6 is put under tensile load in the axial direction, the threaded portion 5 acts to transfer this load into the embedded insert 2. The ridges and grooves of the end portion 1C at the surface 8 and the associated ridges and grooves at the surface 7 of the embedded insert 2 transfer this axial force into the composite rod 1 and in doing so produce a tensile hoop force on the end portion 1C of the rod 1. The compressive preloading of the end portion 1C by the hoop ring 3 allows for a greater axial load to be transferred to the rod 1 before a failure occurs due to excessive hoop force than if there were no preloading. Similarly, the compressive preloading performed by the hoop ring 3 allows a greater compressive axial load to be placed on the end fitting 6 before failure of the rod 1.

Example

(10) A composite structural component in the form of a rod or strut is well suited to high static and fatigue axial load requirements, typically in the range of 50 kN and above.

(11) For an axial load requirement of 250 kN, the internal diameter of the composite rod may be 45 mm with a wall thickness of 3 mm. Three tapered ridges with a taper angle θ of 15° are formed at the engagement surface with a metal insert, to aid manufacture of the rod and hence laminate quality. Compressive preloading of the end connection is achieved using an interference fit of approximately 0.1-0.15 mm between the hoop ring and machined composite rod surface. Without this compressive preloading, significant tensile hoop stresses would result under axial tensile and compressive loads of 50-250 kN.