Reinforcing a part with carbon cloth : Looking for advice

Hi community !

I am working on a hydrofoil design, and I know that the Formlabs resin will not be strong enough on it’s own.
The simplest way to reinforce my part would be to reserve an elongated cavity and insert a carbon rod inside, but that’s far less efficient than placing the fibers on the upper and under-skin of the part.
Therefor, I will have shear forces between the formlabs resin and my carbon cloth, and I wonder :
-If epoxy resin will stick to the Formlabs resin, or if I should use the same Formlabs resin to soak the cloth.
-If I should do some kind of texture on the skin of my part to improve adherence.
Any feedback from people having actually tried this out would be very appreciated !

Cheers,

Both ideas are great ideas. Epoxy works well with methacrylates and they sure are adequate for woven carbon fibers as you most probably know already. I think trying to soak the carbon fabric with UV-curable resin isn’t the best idea strength-wise and it will be a pain to cure fully.

I would personally design in such a way that the carbon fiber itself is strong enough to support the loads applied to the foils, such that the resin is only used as a mold. just like it’s done for RC gliders where the profile is usually cut from styrofoam. That way the resin’s mechanical characteristics aren’t important, as is the bond between the carbon and the resin core… this would also allow to print a hollowed part and thus make a core that is less heavy. I hope I’m not completely off, I’m assuming you are working on a hydrofoil board not a hydrofoil boat which is why I think a design where only the carbon takes the load is feasible.

Hi John,

and thanks for the feedback ! I’d love to see examples of your work.
I am indeed working on a hydrofoil intended to be strapped under a kitesurf board.
My design aims at solving the issue of depth regulation which makes foilboards so difficult to balance.

While writing my previous post I omitted a pretty important part :

I would personally design in such a way

I didn’t mean to imply that I was currently working on foils or with carbon fiber, although I did for a while help a friend during his studies who was working (among other things) on water propulsion efficiency and optimization so obviously hydrofoils were part of the work, and I did work with glass fiber fabric for a while. Never had the occasion of using an SLA printer which working on such projects though, it’s a very interesting idea !

Maybe you are aware of this but Hydros is hosting a yearly contest whose rules often bring participants to use hydrofoils, I went to several events when they were held in Switzerland and it was quite interesting to see what the students came up with.
http://hydrocontest.org

Hi John,

Thanks for the link to the Hydrocontest.
I watched the video ; very intreresting indeed.

I wish I was still a student and worked with a bunch of team-mates, but it’s quite the opposite :confused:

As long as you use a reasonable mold release epoxy will not stick to a mold made with standard Formlabs resin.

Infusion can be interesting with small parts but I would just wet out the layup and vacuum bag. I use infusion resin for wet layups now because it’s easier to pull the part down to the weight you need. You can make a male & female cavity mold if needed just be sure to add plenty of vents for the resin and air to escape from and vacuum bag over the entire mold.

Hi Fred,

I appreciate your suggestions, but my design implies that I will stratify on top of the printed part, using it as a core.
Therefor, adherence of epoxy to the Formlabs resin would be quite beneficial.
I don’t have the proper equipment to work with infusion, and weight is not such a big issue here, at least just for the purpose of validating my concept.

Again, thanks for the valuable advice ; it could be useful in later works.

Epoxy will stick to Formlabs resin (especially the standard resins). The standard resins are acrylic based so you could check compatibility with your favorite epoxy.

Hi Fred,

That’s good news because I don’t need the core to be very strong, and standard resins are cheaper :slight_smile:
I don’t have a favorite epoxy since I don’t do that type of work usually, but I will definitely check for compatibility with acrylics.

I would say that checking the compatibility for acrylics is a must thing for this.