Composite structural component with tension/compression mechanical joint

Abstract

A composite structural component includes an elongate member made of a polymer matrix composite material. The elongate member generally extending along an axis of the composite structural component from an end portion thereof. The component also includes an end fitting forming a mechanical joint with the end portion. The elongate member includes a first member extending from the end portion along the axis of the composite structural component and a second member extending from the end portion along the axis of the composite structural component. The end fitting is constrained in the end portion by the first and second members such that the first member is preloaded with a compressive stress in the axial direction and the second member is preloaded with a tensile stress in the axial direction.

Claims

1. A composite structural component comprising: an elongate member made of a polymer matrix composite material, the elongate member generally extending along an axis of the composite structural component from an end portion thereof; and an end fitting forming a mechanical joint with the end portion; wherein the elongate member comprises: a first member extending from the end portion along the axis of the composite structural component; a second member extending from the end portion along the axis of the composite structural component, wherein the second member comprises an axisymmetric dome in the end portion; and wherein the end fitting is constrained in the end portion by the first and second members such that the first member is preloaded with a compressive stress in the axial direction and the second member is preloaded with a tensile stress in the axial direction.

2. A composite structural component according to claim 1, wherein the first member comprises an end face in contact with the end fitting.

3. A composite structural component according to claim 1, wherein the first member is axisymmetric.

4. A composite structural component according to claim 1, wherein the first member is a filament wound structure comprising multiple layers wound at different angles.

5. A composite structural component according to claim 1, wherein the second member comprises a tension band that wraps around the end fitting in a direction that is perpendicular to the axis.

6. A composite structural component according to claim 5, comprising a further end fitting forming a mechanical joint with a second end portion of the elongate member, wherein the tension band forms a continuous loop extending along the axis and around the end fitting and the further end fitting of the composite structural component.

7. A composite structural component according to claim 5, wherein the end fitting comprises a groove in an outer surface that extends in a direction perpendicular to the axial direction and receives the tension band.

8. A composite structural component according to any of claim 5, wherein the tension band is made of a polymer matrix composite material consisting of fibre reinforcement extending at an angle of 0-5 to the axis.

9. A method of forming a mechanical joint for a composite structural component comprising an elongate member made of a polymer matrix composite material, the elongate member generally extending along an axis from an end portion thereof, the method comprising: providing a first member of the elongate member; positioning an end fitting in contact with the first member in the end portion of the elongate member so as to preload the first member with a compressive stress in the axial direction; providing a second member of the elongate member in contact with the end fitting to form a mechanical joint with the end portion, wherein the second member comprises an axisymmetric dome in the end portion; positioning the end fitting so as to be constrained in the end portion by the first and second members and so as to preload the second member with a tensile stress in the axial direction.

10. A method according to claim 9, wherein providing the first member comprises winding fibres or filaments around a mandrel to form the first member.

11. A method according to claim 9, wherein providing the second member comprises winding fibres or filaments around the end fitting.

12. A method according to claim 9, wherein providing the second member comprises applying a tension band around the end fitting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(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) FIGS. 1A-1E show various partial views of a composite structural component according to a first example;

(3) FIGS. 2A-2E show various partial views of a composite structural component according to a second example;

(4) FIGS. 3A-3D show various views of a composite structural component according to a third example;

(5) FIGS. 4A-4C show various views of a composite structural component according to a fourth example; and

(6) FIGS. 5A-5D show various partial views of a composite structural component according to another example.

DETAILED DESCRIPTION

(7) There is seen in FIGS. 1A-1E a first example of a composite structural component 2. The composite structural component 2 comprises an end fitting 8 and an elongate member, which itself comprises a compression member 4 and a tension member 3, i.e. a twin member. The tension member 3 comprises a hollow, filament wound CFRP cylinder portion along with a domed axisymmetric portion 10 in an end portion 5 of the elongate member 3,4. The end fitting 8 comprises a matching axisymmetric dome portion 6 which sits inside the domed end of the tension member 3 in the end portion 5 of the elongate member 3,4. The end fitting 8 may be a metal e.g. steel component. A further element of the end fitting 8, in this example a rod end, protrudes from the end portion 5 of the elongate member 3,4 in an axial direction, through an opening in the domed portion 10 of the tension member 3.

(8) It can be seen, particularly from FIG. 1A, that the domed portion 10 at the end of the tension member 3 does not extend fully through 90. There is a gap 7 between the end face of the domed portion of the tension member 3 and the end fitting 8. This ensures that the composite material of the tension member 3 does not come into contact with the surface of the metal end fitting 8, especially a threaded surface. It will be appreciated that the dome portion 6 may have a screw connection with the end fitting 8, which can assist in applying a preload stress.

(9) The compression member 4 comprises a hollow, filament wound CFRP cylinder with an outer diameter equal to the inner diameter of the tension member 3. The compression member 4 is interior to the tension member 3 and is entirely enclosed by the tension member 3 and the end fitting 8, such that the dome portion 6 of the end fitting 8 is constrained between the tension member 3 and the compression member 4. This forms a mechanical joint between the end portion 5 of the elongate member 3,4 and the end fitting 8.

(10) The inner end of the dome portion 6 of the end fitting 8 comprises a narrower cylindrical section with an outer diameter that matches the inner diameter of the compression member 4, and the compression member 4 is arranged such that the narrower section of the dome portion 6 of the end fitting 8 extends into the compression member 4. This prevents the compression member 4 and the end fitting 8 from moving relative to one another during manufacture and use. The dome portion 6 of the end fitting 8 is therefore in contact with an end face of the compression member 4.

(11) During manufacture, the compression member 4 is preloaded with axial compressive stress, and the tension member 3 is preloaded with axial tensile stress. As a result, all of the components within the composite structural component 2 are held firmly in contact with one another such that they cannot move relative to one another during use, without the use of any adhesive (although this does not preclude the use of adhesives).

(12) In use, the end fitting 8 delivers an axial load to the end portion 5 of the elongate member 3, 4, wherein a compressive load is resisted by the compression member 4 and a tensile load is resisted by the tension member 3. Whilst in this example the compression member 4 and the tension member 3 are illustrated as having substantially the same wall thickness, this, along with their stiffness, can be tuned in order to give the composite structural component 2 the tensile and/or compressive strength required for a particular application.

(13) Although FIG. 1 only shows an end portion 5 at one end of the elongate member 3, 4, it will be appreciated that the composite structural component 2 may have the same structure at both ends, with an end fitting at either end or both ends.

(14) There is seen in FIGS. 2A-2E a second example of a composite structural component 22. The composite structural component 22 comprises an end fitting 28 and an elongate member, which itself comprises a compression member 24 and a tension band 23. The end fitting 28 may be a metal e.g. steel component. The end fitting 28 comprises a first, outer end which has the shape of a solid axisymmetric dome with portions removed so as to form a cylindrical eyelet with longitudinal axis running perpendicular to the axis of symmetry of the dome, and two planar surfaces at the entrance and exit of the eyelet. The end fitting 28 further comprises a second, inner end, which has the shape of a cylinder aligned with the axis of symmetry of the dome, but has a smaller diameter than the outer diameter of the dome.

(15) The compression member 24 comprises a hollow, filament wound CFRP cylinder with an internal diameter that matches the diameter of the cylinder portion of the end fitting 28. The compression member 24 is positioned such that the cylinder portion of the end fitting 28 extends into the end of the compression member 24 so that there is no relative movement of the compression member 24 and the end fitting 28 during manufacture or use.

(16) The composite material (e.g. CFRP) tension band 23 runs along the edge of the compression member 24 in the longitudinal direction, around the curved end of the end fitting 28 and back along the opposite side of the compression member 24 again in the longitudinal direction. As a result the end fitting 28 is constrained between the compression member 24 and the tension band 23 and a mechanical joint is formed between an end portion 25 of the elongate member 23, 24 and the end fitting 28.

(17) While the tubular compression member 24 may be formed using a standard filament winding process to include both low angle and high angle fibres, the tension member 23 is preferably formed from axially extending 0 fibres to maximise its tensile strength.

(18) During manufacture, the compression member 24 is preloaded with axial (longitudinal) compressive stress, and the tension band 23 is preloaded with tensile stress. As a result all of the components within the composite structural component 22 are held firmly in contact with one another such that they cannot move relative to one another during use, without the use of any adhesive (although this does not preclude the use of adhesives).

(19) In use, the end fitting 28 delivers an axial load to the end portion 25 of the elongate member 23, 24, wherein a compressive load is resisted by the compression member 24 and a tensile load is resisted by the tension band 23. In this example the tension band 23 has the same thickness as the wall of the compression member 24, but has a width that is significantly smaller than the circumference of the compression member 24. The thickness, width and stiffness of the tension band 23, and the thickness and stiffness of the compression member 24, can be adapted for each particular application to provide the composite structural component 22 with the tensile and/or compressive strength required.

(20) Although FIG. 2 only shows an end portion 25 at one end of the elongate member 23, 24, it will be appreciated that the composite structural component 22 may have the same structure at both ends, with an end fitting at either end or both ends. In particular, the tension band 23 may form a continuous loop extending along the axis of the component 22 and around an end fitting 28 at each end of the component 22.

(21) In FIGS. 3A-3D, another example of a composite structural component 32 is shown that comprises an elongate member and an end fitting 38. The end fitting 28 may be a metal e.g. steel component. The composite material (e.g. CFRP) elongate member comprises a tension band 33 and a compression member 34 and, similarly to other examples, a mechanical joint is formed between an end portion 35 of the elongate member and the end fitting 38 due to the tension band 33 and compression member 34 being in tension and compression, respectively. In this example, the diameter of the compression member 34 is smaller than that of the end fitting 38 such that tension band 33 is never in contact with the compression member 34. The end fitting 38 has a different shape to accommodate the radial spacing between the compression member 34 and the tension band 33. The smaller diameter of the compression member 34 may reduce the weight of the composite structural component 32 in applications for which a lower degree of compressive strength is required.

(22) In such an example, one or more stiffening elements 49 may be employed to mitigate vibrations of the tension band, as seen in FIGS. 4A-4C. In this example, a composite structural component 42 is shown that comprises an end thing 48 and an elongate member comprising a compression tube 44 and a tension band 43. The tension band 43 follows the outer surface of the end fitting 48 but does not extend from the end portion 45 along the surface of the compression member 44. Such a large portion of the band 43 being unsupported can lead to potentially damaging radial vibrations of the tension band 43, as illustrated by the double head arrow in FIG. 4B. In the example illustrated here the stiffening element 49 comprises an annular component in the form of a clamp-type fitting placed around the compression member 44 and two radially extending arms which are shaped to constrain the radial position of the tension band 43 at a point approximately halfway along the composite structure.

(23) In FIGS. 3 and 4 the entire composite structural component 32, 42 can be seen. The same end fitting 38, 48 is provided at both ends of the component 32, 42.

(24) FIGS. 5A-5D illustrate another example of a composite structural component 52. The composite structural component 52 comprises an end fitting 58 and an elongate member, which itself comprises a compression member 54 and a tension band 53.

(25) The end fitting 58 comprises an outer cap 57 and an inner fitment 56. The end fitting 58 may be a metal, e.g. steel, component. The outer cap 57 comprises a hollow cylinder with one open end, and is axially symmetric, whereas the inner fitment 56 comprises a solid cylindrical portion 56A with a longitudinal axis running perpendicular to the longitudinal axis of the compression member 54. The outer cap comprises two sections, a wider section and a narrower section wherein the narrower section has a smaller outer diameter than the wider section. The solid cylindrical portion 56A is attached at one end to a connecting arm 56B, which in turn is connected to the outer cap 57 of the end fitting 58. The other end of the solid cylindrical portion 56A is not connected to anything, such that the cylindrical portion 56A and the connecting arm 56B form a hook. As will be explained below, the hook of the inner fitment 56 allows a tension band 53 to be attached to the end fitting 58. The inner diameter of the outer cap 57 is substantially constant along its length, and may be threaded to allow for connection to other components.

(26) The compression member 54 comprises a hollow, filament wound CFRP cylinder, with an internal diameter that is equal to the outer diameter of the narrower section of the outer cap 57. The compression member 54 is positioned such that the end fitting 58 extends into the end of the compression member 54 with only the wider section of the outer cap 57 extending beyond the compression member 54. This prevents relative movement of the compression member 54 and the end fitting 58 during manufacture and use.

(27) The composite material (e.g. CFRP) tension band 53 lies internal to the compression member 58 and is entirely enclosed by the compression member 54 and the end fitting 58. A portion of the tension band 53 is in contact with the inner fitment 56 of the end fitting 58. The portions of the tension band 53 that are not in contact with the inner fitment 56 run parallel to the longitudinal direction of the compression member 54, and the portion that is in contact follows the cylindrical cross section of the inner fitment 56, such that the tension band 53 is connected to the hook of the inner fitment 56. As a result the end fitting 58 is constrained by the compression member 54 and the tension band 53 and a mechanical joint is formed between the end portion 55 of the elongate member 53, 54 and the end fitting 58.

(28) During manufacture, the compression member 54 is preloaded with axial (longitudinal) compressive stress, and the tension band 53 is preloaded with tensile stress. As a result all of the components within the composite structural component 52 are held firmly in contact with one another such that they cannot move relative to one another during use, without the use of any adhesive (although this does not preclude the use of adhesives).

(29) In use, the end fitting 58 delivers an axial load to the end portion 55 of the elongate member 53, 54, wherein a compressive load is resisted by the compression member 54 and a tensile load is resisted by the tension band 53. In this example the tension band 53 has a greater thickness than the wall of the compression member 54, but has a width that is significantly smaller than the circumference of the compression member 54. The thickness, width and stiffness of the tension band 53, and the thickness and stiffness of the compression member 54, can be adapted for each particular application to provide the composite structural component 52 with the tensile and compressive strength required.

(30) In this example the tension band 53 is not in contact with the compression member 54, i.e. they are radially spaced apart, but in other examples the tension band 53 may be in contact with the interior surface of the compression member 54. In examples where the tension band 53 is not in contact with the compression member 54, one or more stiffening elements, although not shown here, may be used to mitigate vibrations of the unsupported tension band 53 (e.g. as described above).

(31) Although FIG. 5 only shows an end portion 55 at one end of the elongate member 53, 54, it will be appreciated that the composite structural component 52 may have the same structure at both ends, with an end fitting at either end or both ends. In particular, the tension band 53 may form a continuous loop extending along the axis of the component 52 and around an end fitting 58 at each end of the component 52.

(32) Although not shown in the Figures, in any of these examples the compression member may be provided with an outer hoop ring at the end forming the mechanical joint. The outer hoop ring, for example a metal ring, may act to resist delamination of the composite material where the end face of the compression member is subjected to compressive loads.