Bonding 2-piece carbon fibre wing

Talk Composites - The Forum for Advanced Composites

Back

Bonding 2-piece carbon fibre wing

Author	Message
Hanaldo	Hanaldo posted 11 Years Ago HOT Topic Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Hey all, Done a bit of reading, and I know this topic has been covered several times before but I couldn't find the answer I was after. I'm currently building a rear wing blade using a 2-piece split mould. Originally I was going to do 2 layers 2x2 twill weave carbon, one layer of 3mm Soric, then one more layer of the twill weave. I was then simply going to bond the two halves together using a strong epoxy adhesive. However, I had a thought this morning about making some strengthening ribs to go inside the two halves, probably out of balsa wood. Then use expanding polyurethane foam to bond the two halves together. My thought trail was this will give me both a very high strength bond, as well as a bit more structural reinforcement. A bit more added weight sure, but it's not going to be super heavy anyway. However, I'm a little unsure as to how I would go about using the foam. I've played with the stuff before, and it has the potential to make quite the mess if I don't get the two halves together in time. Would I be better off leaving the parts untrimmed before bonding, then trim them after? To limit mess and make sure the foam doesn't spill out of the part and lock them into the mould? Or is there a better way to prevent foam leaking out? Or should I just stick with the idea of bonding the two halves together? Thanks for any help, Martin.
	Reply Like 6
wozza	wozza posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 688, Visits: 5.4K	For the ribs I lay up a cored sheet using closed cell foam and then cut it into the rib shapes. These are then bonded into one half off the wing and then finally the two halves are bonded together with ET515. I have tried filling the void with expanding foam and then clamping the two halves together. The problems I found was judging how much foam to put in, not enough and it won't fill the void too much and it can actually distort the wing. I also found that you can end up with pockets of foam that haven't cured fully. One method that did work was to put the foam into each half off the wing, let it expand and cure. Then trim the foam back to the split line, you now have a nice big flat area to bond the two halves together. Just make sure that the adhesive you use wont attack the cured foam. Hope that helps. Warren Carbon Copies Ltd
	Reply Like 6
Hanaldo	Hanaldo posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Hmmm, now there's an idea. Although, it almost defeats the purpose of doing it. I suppose it will still give me greater bond strength and a reinforced core. I just like the idea of the wing being as close to one piece as I can get it. Unfortunately I think I would run into the same problems as you Warren, I won't be able to work out how much foam I need to put into the void.
	Reply Like 6
Zorongo	Zorongo posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 40, Visits: 330	You can calculate it. You need two data. The density of the foam ONCE EXPANDED. And the volume to be filled. density = weigth / volume. So: requiered weigth = volume x density (mind units) Mix that weigth and if the density is correct, it will expand to the expected volume. I've used that estimation for bouyancy reservoirs on boats. As density is normally not accurate, it´s advisable (sorry if not correct) to leave exits for foam excess. If not, expansion pressure may damage the joint. By the way, keep in mind that expanded PU foam is not an structural surface to act as a bonding surface, as it may suffer cohesive breakage (debonding bet ween PU particles) I would do: First half + bond ribs + bond second half. Much ligther and good acess to make a propper epoxy bonding half to half. Suggest: On the lines where the ribs will seat, laminate one +/- 45º stripe about 100 to 150 mm wide. This will avoid local stress on the surfafe, will distribute the rib´s strength into a wider area. (just an outsider´s opinion ) Edited 11 Years Ago by Zorongo
	Reply Like 5
Hanaldo	Hanaldo posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Thanks mate, very useful opinion! I think I will stick to doing it as an open mould, filling the void with foam and then trimming the excess. The design of my wing does not allow for any holes for venting, so I suspect a closed mould could well lead to damage or uncured foam.
	Reply Like 5