Carbon Fiber Questions: Help out guys

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#1

I am in the developing process of building a home built Tadpole (Reverse Trike) motorcycle with a target weight of around 550-650lbs and after much pondering i was thinking of trying out a hybrid design i came across on the FSAE forums, they built a frame out of 1/2" SAE1010 steel tube that was wrapped with 1 single layer of bidirectional 3k carbon fiber using carbon fiber sleeve material and their full build weight was 458lbs using an R6, 600cc motorcycle engine and having 4 wheels and supporting suspension. I am aiming for 550-650lbs as the max range using an R1, 1000cc motorcycle engine and only have 3 wheels, since there 1/2" setup with single carbon fiber layer was strong enough to last an entire race season, i am thinking of bumping up to 3/4" which is the normal tube size used on FSAE frames and wrapping it in an single layer of 3k carbon fiber sleeve material.

The questions i have is what is needed to protect the carbon fiber form the sun and elements? i ask this because i really like the look of the carbon fiber finished look and after thinking about it i was thinking i would find whatever finish coating i need and leave the carbon fiber as the “painted finish” instead of actually painting the frame. I built a Locost 7 previously out of 1" pipe that ended up weighing around 1200lbs that i had powdercoated black and the cheapest i could find within 100miles of me was $550 bucks, for as much pipe i would be using on this build i could single layer coat the pipe for less than half what i spent on powder coating previously.

My 2nd question is what kind of coating would need be between the carbon fiber and the steel pipe? Would the pipe be vulnerable to rust without painting the pipe layer first?

The way the FSAE group did it was they took all the pipe that they were going to build the frame out of and ran the carbon fiber sleeve across the length of the pipe, then they stuck it inside of a vacuum plastic material and vacuum’d it tell the resin cured, then when they built the frame the cut the already carbon fiber pipe to length and just handed back enough of the material to allow welding of the pipe together at the joints and such, then they used carbon fiber cloth to wrap over the areas that no longer had carbon fiber and the joints to strengthen them all.

#2

you wont need to paint the tubes first, as the epoxy from the carbon will seal the tubes

you will need to use a UV resistant clear coat … a 2k system will work perfect and is easy enough, or you can buy an epoxy with a UV already in it

its gonna be an expensive exercise … but it will look great once done

i presume you will be tig welding the frame together ?

#3

If you want to use carbon, you would be better off using carbon panels to fill in the gaps between the steel frame. These would act as shear panels and would improve the torsional stiffness of the chassis. Plus improve safety.

Also remember that FSAE cars are not designed for high speeds or high power (that R6 motor had a 20mm intake restriction).

#4

This isn’t totally correct, the epoxy in the laminate won’t insulate the carbon. If I am bonding metal to carbon in an environment that stands and chance of being exposed to moisture (read: anything that isn’t totally airtight, so most everything) then I put in a layer of fibreglass between them.

#5

But… would a single layer of 3k carbon fiber do any job at all??? Especially
When wraped around a steel pipe???

#6

So you’re going to wrap a steel pipe with carbon so you don’t need as much pipe? Wouldn’t it be better to use aluminium and carbon? Have you done some testing on what the actual benefit from this would be? Or maybe contact that FSAE team and ask them for their data, surely they must have done some destructive testing on their methods? I would think this approach wouldn’t be that beneficial… Testing would be a good first thing to do just to see if it will really make much difference quantitatively.

I would reccomend using braided sleeve, it would be the easiest to lay up on pipe and is much much stronger than using a regular fabric. Plus sleeve comes in a variety of weights and materials. If you did a sleeve, you could probably use a lighter weight pipe. After the pipe was assembled you’d probably want to do some layup over the joints so the loads could transfer across the welded areas. As moke said, panels linking the pipe would increase the strength greatly.

Another thing to be concerned about is galvanic corrosion. If this is a short term use vehicle, this might not be much of an issue. But if you want this thing to last, you’ll want to insulate the carbon with some sort of surface preperation. There are chemicals for this purpose. Or just don’t use carbon, use S glass/kevlar. You can get these in braided sleeve as well.

Really do some tests to start, or ask the team who built with this method if they did testing to verify that this method is worth it’s while. If not then, you might consider making a monocoque type setup instead. Or just use carbon tubes instead of metal.

sounds interesting :smiley:

#7

I’ll go along with a glass layer between tubing and CF (particularly if the OP adopts the idea of Al tubing) to make sure there is a dielectric barrier layer between to prevent electrolytic corrosion.

Additionally, I suspect that the Young’s modulus of the tubing and CF are sufficiently different that (depending on the specific loading) one component would take 100% of load stress and the other component would hold 0% of the load until the first fails; then the second would have to take up 100% of the stress.

In that context, a single layer of CF might as well not be there from an engineering standpoint, and has to be justified as solely a cosmetic “indulgence.”

#8

Sounds like a neat project but it also sounds like a lot of effort for a questionable return. I think you will find the hand work needed is far beyond what you expect, at least if you want it cosmetically acceptable. Moneywise, I doubt you’ll see much of a savings over your powdercoat expenditure.