Fibreglass with 1x carbon fibre layer for aesthetic body panels?

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#1

Hi All,

I have just been thinking about making some composite body panels for a project bike I’m working on. The panels aren’t very large at all, not load bearing in any way - basically they’re just there to stop the bike from looking really weird. :stuck_out_tongue:

I have been wanting to try out a few pieces in carbon fibre, but to make a 100% CF part is a bit beyond my budget at the moment. So I was thinking about maybe a CF outer layer, with the rest made up with fibreglass? I don’t know if this is even feasible, or a good idea… I have a lot of research to do but I just thought I would ask in case it’s just a flat out bad idea? If it’s better just to wait until I can afford to do a 100% CF part, I will wait.

The other thing I just wanted some clarification on - I have been reading about using CF with polyester resin, and how the resulting part will not be as strong and the resin will likely break down before the CF. How about making the exact same part using glass and poly resin? Is that combination somehow more durable? Or if I want to make durable, half decent parts do I need to use epoxy resin full stop?

I just want to get a bit more of an understanding on this before I dive in and start making plugs etc. Thanks very much for any info!

Cheers,

Conrad

#2

I’ve never had any problems with fiberglas as an outer layer with carbon. It depends on your working proces, when you use vacuum or infusion only use a woven fiberglas. The only issue is that you can see true the carbon (were the fibers cross), you can paint the back black to avoid the issue or use a black colored fiberglas as an outer layer.

My experience with polyester and carbon is: you can make good parts with it but they are not as hard and clear as when you use epoxy. Because polyester is more flexible the parts are in some cases “stronger” (impact resistens). For carbon fiber parts without any strenght function, I see not many issues. Maybe a vinylester is good alternative for you ? Carbonfiber in combination with a polyester resin is stronger than a polyester resin with glass if you use the same weight fabric(as far as i experienced).

#3

Using an outer layer of carbon for aesthetics over a fiberglass laminate is fine and much more cost effective than all carbon especially for a panel that is not load bearing. Depending on the size and thickness of your part you will have to watch out for warping if you do not use a symmetric laminate (mirror image from middle).

In terms of resin; you can use polyester resin with fiberglass or carbon fiber but you will not realize the full strength potential which is ok for a cosmetic panel I suppose. A vinyl ester will give better mechanical properties and is cheaper than epoxy.

Are you planning on infusing the parts or sticking with hand lamination?

#4

Thanks both for that info - glad to know that it would work out okay!

I have been thinking about vacuum infusion, I found what seems to be a really thorough vacuum bagging guide here: http://www.westsystem.com/ss/use-guides/
I am still reading about vacuum techniques, the trick is whether I can get good results with some “DIY” type equipment. I will see how much it would cost - but I really like the idea of vacuum to take some worry out of producing good parts with a great surface finish.

If the vacuum method turns out to be too tricky/expensive I was just going to go with what I know, wet layup/hand lamination.

Is using the CF likely to make the part more prone to warping? One other bit of info I read was that CF is so different to glass that any experience with glass basically doesn’t apply to CF. So I am planning to do at least a couple of different test parts anyway. And thanks for the vinyl ester tip, I will look into that as well.

On the subject of the fibreglass showing through the CF weave - I was thinking that I would use a black coloured resin after I put the CF down and fully wet it out. (From the last time I did any fibreglass work I am sure that resin colouring is available?) I wouldn’t have thought that painting the back of the part or using a black glass final layer would have helped any? Wouldn’t you still see the white glass if you’re looking through from the front/CF side of the part? Or is the CF weave so tight that it’s not an issue? I am also thinking about what will happen if the CF weave opens/distorts a little bit on curves etc.

#5

If the parts have some shape in it, do not worry about warping.

I would just use a transparent gelcoat (try and get that on nicely) then apply the carbon, with polyester resin, and after cure add the rest of the laminate (probably CSM) with black tinted resin. The part will not shine through, is easy to make, and has a nice gloss finish.

Once you master that, you will probably find other parts and uses, and can go more advanced, but right now all you need is a brush, a roller, some mixing cups and a bubble buster. (and personal protection)

#6

Thanks herman. Just on the subject of roller… that is what I have used previously with fibreglass, with really good success. I found that I could wet out each layer very well, and work in the resin, without using too much. But when using carbon, all the videos and discussion I have seen focussed on the use of a small flat spreader (squeegee)? Is it advisable not to use a roller, would that distort the weave? That is something I plan to test myself, but if a roller on carbon is prone to problems, I will save myself the hassle…

Cheers

#7

You should not have any problems rolling out the carbon using a roller to ensure that the carbon is fully wet out and all entrapped air is removed. The squeegee will help you remove excess resin which will help you achieve a higher fiber weight fraction, a good thing. FYI, you can use a squeegee on all glass laminates as well to remove excess resin.

#8

A squeegee is nice on more flat surfaces. It does not introduce as much air as a roller. For complicated structures a brush may be more appropiate.

#9

Ok, good to know! Thanks very much for all those tips & advice, I’m going to start planning out this job - looking forward to it!

#10

One more tip: do a small test of some 30x30cm, on a piece of glass or melamine board, so you get a feel for the materials. When you master that, you are good to go in more complicated parts.

Biggest concern is pinholes in the carbon layer. Make sure you use enough resin, and work out any bubbles well.

#11

Watch out when using any roller or squeegees with carbon. Woven fabrics are very prone to “bulk rebound”. As you press against the carbon the fibers will compact and the squeegee will push the excess resin ahead of it. The fibers will then rebound and suck air into the laminate. The key is to not use too much pressure. I recommend practicing on a piece of clear acrylic. This way you can flip the acrylic over and immediately see the results of different rolling/squeegee techniques.

#12

You may also be able to source black fiberglass, it looks very similar to carbon.

#13

Thanks HeyBen. I have heard about black fibreglass… not too concerned about that though, as I would just use a black pigment - problem solved!

And thankyou wyowindoworks for that tip on the squeegee use. I will definitely be doing small test pieces before going ahead with all of this, as carbon is completely new to me!

#14

I agree with wyowindworks. I roll with only the weight of roller, the same with squeegees.
I don’t use gelcoat because if there are air bubbles under it, you see all. And if there are big air bubbles (or if the fibre doesn’t follow the mold ), gelcoat has a different color of resin, so you see the repair. If you repair with only resin, you don’t see differences of color