Need some help ake composite fins

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#1

Hi,
I need some help. I want to make carbon/fiberglass diving fins. On pictures you can see what I am talking about.

It’s only a flat plate that has good flexibility. I want to know what materials would be best to use for this purpose, and what process to use ? Is vacuum bagging ok for this ?

Maybe some one knows how to achive sort of performance that you can see on this video :

Diving fins video

And some view of what am after you can see at the pictures bellow :


By lovre at 2008-02-15


By lovre at 2008-02-12


By lovre at 2008-02-12


By lovre at 2008-02-15

#2

I’ve used flexible polyurethane resins with carbon fiber and with kevlar to create flexible objects. The resin is Huntsman/Ren 6434 which also has an additive which lets you vary the flexibility depending how much additive you add.
I’ve also used a flexible epoxy; Huntsman Rencast3266. Depending on the ratio of parts A and B, the flexibility can be varied.
I used it with the wet-preg system (vacuum bag). The polyurethane system is quite low viscocity, but has a short pot-life, the epoxy has a very high viscocity.
Let me know if you want any making.

#3

What about sea water resistance of polyurethane resin ?

From what I know all manufactureres use epoxy resin ? I don’t know why to be honest, but I guess there is some reason.

Why using kevlar ?

How much layers and what cloth you think I should use ?

#4

3 or 4 layers of carbon, using epoxy or at least vinylester. i dont think you need infusion for such a thing, laying them on glass or a 2 piece sandwitch mould (for having both sides looking sweet)

#5

the problem with carbon is, it will crack of bend too much, like the rolled up one in the pics.
I can possibly say a good starting point would be 3 layers. unidirectional. 90-0-90, this way, the outside layers will be orientated in the flexible direction.
Or carbon on the outsides, and kevlar/vectran on the inside. (will aid in flexibility and lessen any fatigue cracking)

but it also comes down to the resin, which I don’t kno wmuch about, but PUR seems like a good idea.