Composite end connections
A fiber-reinforced polymer composite shaft for transmitting loads along a central axis. The composite shaft comprises a first interface surface extending along the central axis and comprising at least one helical groove and/or a plurality of circumferential grooves for engaging with at least one corresponding helical ridge and/or a plurality of corresponding circumferential ridges of a second interface surface of an end fitting. The at least one helical groove and/or the plurality of circumferential grooves comprises at least one flank with a flank angle of between 32° and 51°. In such an assembly, a preload structure is arranged to provide a radial biasing force to bias the first interference surface against the second interference surface.
1. A fibre-reinforced polymer composite shaft for transmitting loads along a central axis, the composite shaft comprising:
a first interface surface extending along the central axis and comprising at least one helical groove and/or a plurality of circumferential grooves for engaging with at least one corresponding helical ridge and/or a plurality of corresponding circumferential ridges of a second interface surface of an end fitting;
wherein the at least one helical groove and/or the plurality of circumferential grooves comprises at least one flank with a flank angle of between 32° and 41°, the flank angle being measured between the flank and a perpendicular to the central axis in a plane that contains the central axis.
2. The fibre-reinforced polymer composite shaft as claimed in claim 1 , wherein the flank angle is between 32° and 36°.
3. The fibre-reinforced polymer composite shaft as claimed in claim 1 , wherein the first interface surface comprises an average radius from the central axis of between 10 and 150 mm.
4. The fibre-reinforced polymer composite shaft as claimed in claim 3 , wherein the average radius is between 20 and 30 mm.
5. The fibre-reinforced polymer composite shaft as claimed in claim 1 , wherein the first interface surface is approximately 30 mm long.
6. The fibre-reinforced polymer composite shaft as claimed in claim 1 , wherein the first interface surface is an inner surface of the composite shaft or an outer surface of the composite shaft.
7. The fibre-reinforced polymer composite shaft as claimed in claim 1 , wherein the first interface surface is tapered relative to the central axis or the first interface surface extends parallel to the central axis.
8. An assembly for transmitting loads along a central axis, the assembly comprising:
a fibre reinforced polymer composite shaft as claimed in claim 1 ;
an end fitting comprising a second interface surface extending along the central axis and comprising at least one corresponding helical ridge and/or a plurality of corresponding circumferential ridges that is engaged with the at least one helical groove and/or the plurality of circumferential grooves so as to mount the end fitting to the fibre reinforced polymer composite shaft; and
a preload structure arranged to provide a radial biasing force to bias the first interference surface against the second interference surface.
9. The assembly as claimed in claim 8 , wherein the end fitting is metallic.
10. The assembly as claimed in claim 8 , wherein the coefficient of friction between the first and second surfaces is between 0.01 and 0.3.
11. The assembly as claimed in claim 8 , wherein the coefficient of friction between the first and second surfaces is 0.15.
12. The assembly as claimed in claim 8 , wherein the second interface surface is located radially inward of the first interface surface.
13. The assembly as claimed in claim 12 , wherein the preload structure comprises an annular member arranged to apply the radial biasing force to an outer surface of the composite shaft.
14. The assembly as claimed in claim 8 , wherein the second interface surface is located radially outward of the first interface surface.
15. The assembly as claimed in claim 14 , wherein the preload structure comprises a plug arranged to apply the radial biasing force to an inner surface of the composite shaft.
16. The assembly as claimed in claim 8 , wherein the preload structure is arranged in an interference fit with the composite shaft.
17. The assembly as claimed in claim 8 , wherein the end fitting is arranged to interface with another component.
18. A method of forming an assembly for transmitting loads along a central axis, the method comprising:
forming at least one helical groove and/or a plurality of circumferential grooves comprising at least one flank with a flank angle of between 32° and 41° in a first interface surface of a fibre-reinforced polymer composite shaft, the flank angle being measured between the flank and a perpendicular to the central axis in a plane that contains the central axis;
forming at least one corresponding helical ridge and/or a plurality of corresponding circumferential ridges in a second interface surface of an end fitting;
engaging the at least one helical groove and/or the plurality of circumferential grooves of the first interface surface with the at least one corresponding helical ridge and/or the plurality of corresponding circumferential ridges of the second interface surface so as to mount the end fitting to the composite shaft; and
subsequently engaging the composite shaft with a preload structure so as to bias the first interface surface against the second interface surface with a radial biasing force.
19. The method of claim 18 , wherein forming the at least one helical groove and/or a plurality of circumferential grooves comprises selecting a flank angle to minimise a performance measure that takes into account a total weight of the assembly and a sensitivity of the assembly to changes in friction between the first and second interface surfaces.