Carbon Fiber Attachments

1) Mould whatever 'eye' you need in CF and bond (or bond and stake) it on.

2) If using a metal attachment, provide a decent, long spigot giving a surface area sufficient to take the load (knowing the bond shear strength). Design the wall thickness of the spigot to vary along it's length (taper it) so as to avoid a stress discontinuity at where the spigot runs out

In either case analysis (finite element) will help.

Be aware of the difference in thermal expansion of CF and your chosen material and your operating temp environment.

I am reminded of the adage about two peoples divided by their common language. So, please forgive my ignorance, but while I think I get it, would you please explain, in Texan, what is a spigot? Wikipedia send me off to tap for beer, while Google send me off to the UK for spigot rings. So, if I had a flat, circular plate to insert into the end of my tube, I might use a "spigot ring" to sandwich the CF between the ring and the plate? If so, do I need to beef up the penetrations that one might put through the CF for the screws? Thanks and Hook'em horns.

It would be easy if I could get a sketch off ms word into this message editor.

Have a thick metal tube with appropriate fittings which slides up over the dangling end of the tube..The hole in metal tube must be tapered... wider at its bottom end.

Then tap a tapered metal plug into the exposed bottom end of the CFtube, to expand it slightly...(may need a couple of slits to help, this could be pinned or glued. Then as you pull down on the thick tube and fittings it will slide back down and grip onto the expanded CF tube...the harder you pull the tighter it will get.

Or not...whatever...Blimey there's gotta be a better way...

Ha! yes... outer sleeve to support the tube (stop it splaying out)...Expanding sleeve up the middle with whatever fitting you like...

This discussion had some useful advice on carbon fiber bonding - http://cr4.globalspec.com/thread/10634/Carbon-Fiber

The load concentration might be a big deal. Sounds like you have a pre-made tube? Ask the company you got it from. The strongest interfaces are formed when you make the hook, or whatever your load interface is, an integral part of the piece - start with a sheet of carbon fiber and some epoxy, form it into the tube and whatever shape fits the tube side of your load interface, vacuum bag it while it cures. Same process as fiberglassing, not too hard.

This forum is full of surprises and I thank you all for your responses. We made the tube ourselves so in its next iteration we will work from a mandrel on which a slightly inwardly tapered end base can be turned. Once cast, we will insert a metal base plate to which a hook can be attached at the center. The plate will have a slight taper such that as it is pulled it will try to stretch the CF outward. If we add a "spigot ring" on the outside of the CF such that as the base plate is pulled it will compress the CF into the ring, we should have an even distribution of load around the base plate onto the ring. This would fit with Del the cat's suggestion as well.

Cheers, and thanks.

Del's suggestion is good, mechanical joint more reliable than bonding perhaps, but we now fly in planes 'glued' together (Hmm Crabtree thinking of another link here) and, some of us at least, do 200mph/300+kph between concrete walls in cars glued together.

Stupid really.

Ok it's done carefully, not like me and my Airfix (oops can I say that on the BBC?)

Getting back to spigots (died didn't he, the Jockey?), I envisaged your 'eye' having a tail extending up the inside or the outside of your tube say 2-3 times the tube's diameter. If it went up the inside it would be hollow, it would in effect be another tube inside the CF. The wall thickness of this inner (or outer) tube would vary from almost nothing at it's open end to whatever it needs to be to carry all of the load itself. It would also help if the CF tube tapered out as well. You could stake it too, for security.

Oh why so complicated? do what Del's said!

Actually it's not complicated, just wordy.

I think I got it, finally, except for the part about the "Jockey". Stay tuned, we will be building this in the next few weeks. I will let y'all know how it works.

Thanks and Cheers,

PS. I don't know how your going to do anything like 200 mph in the Midlands unless your in a boat.

Look forward to hearing, good luck with it. The jockey joke referred to Lester Piggott, with apologies to those outside Britain and Ireland. Don't know if he rode stateside but would guess he must have done sometime.