Carbon Fiber Skinning: materials question

[Kraftwerk]

I plan to take a deep-dive into the world of Carbon Fiber Skinning, have a f/g hood and duck-tail which I would like to carbon-fiber-skin.
Professor You-Tube is guiding the way.. (as with so many projects !)
There is a company makes a UV resistant resin ( right? ) which would be good for a final coat ( no? ) Others say automotive clear-coat for final finish. Personally, I like the idea of a polished-resin final coat. Can anyone reading this provide a list of supplies needed and where to find everything state-side, such as the black undercoat coat, final polish and a light carbon cloth? (I know where to buy sandpaper !) Would West System resin work for this? Since I have a hood and a trunk to do, the kits from England are too small, and shipping them is, anyway, cost prohibitive. The British seem to have this project under control. Here in the U.S. like the look of a company like Rock West Composites but theres not enough information on their very sexy web-site to get me launched into this project, which materials to buy. Pretty RWC won't exactly condone skinning... they are more technical, but could supply the cloth, I suppose..

[nota]

UV resistant resin is not UV PROOF

it will break down in direct sun over time
how much time depends on where you are and exposure time

sailboat masts were an early CF use and victim of UV degrading
most require paint for long life

for what you want a fake wrap CF print will be way cheaper lighter and eazyer to replace

btw while CF is very strong used correctly a single skin does very little
and the stuff is nasty to work with way worse then fiberglass dusts

[Kraftwerk]

Yeah, vinyl wrap, is a curious invention, would certainly save time / money & be super-easy, but not really my cup of tea. Both of these f/g lids need to be 'built out' on the edges, here and there, so there will be resin / gel coat work involved either way, even if i just go with a 'gray primer' finish. I have worked with Kevlar cloth and resin but not c/f cloth also restored a couple of f/g boats so I do know the toxicity and stink-factor of resin.

[otto_kretschmer]

I would say try a small part first before you dive deep and spend a lot of money. I buy most of my composite materials from here

Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc.

[nota]

https://store.acpcomposites.com/category/fabrics/woven

if you must

[island911]

Just get stickers.

Putting CF over an existing structure is a recipe for disaster. The differences in thermal expansion is pronounced (between CF and just about everything else).

[Kraftwerk]

'thermal expansion'.. when the the resin 'kicks' ?....or Just in day to day life? I would imagine the highest stress these parts see will be as the resin in the c/f heats up.... In normal freezing cold days or super hot summer-weather, wouldn't the f/g 'keep up' w/the carbon fiber? Both are 90% resin?

[otto_kretschmer]

Originally Posted by Kraftwerk

'thermal expansion'.. when the the resin 'kicks' ?....or Just in day to day life? I would imagine the highest stress these parts see will be as the resin in the c/f heats up.... In normal freezing cold days or super hot summer-weather, wouldn't the f/g 'keep up' w/the carbon fiber? Both are 90% resin?

Carbon fiber has a thermal expansion coefficient of almost zero. When it gets hot it doesn't expand. Steel will grow as it gets hot so if you put the two together you may have problems.

[nota]

Originally Posted by Kraftwerk

'thermal expansion'.. when the the resin 'kicks' ?....or Just in day to day life? I would imagine the highest stress these parts see will be as the resin in the c/f heats up.... In normal freezing cold days or super hot summer-weather, wouldn't the f/g 'keep up' w/the carbon fiber? Both are 90% resin?

no more like 50/50 fiber/resin ratio but varys
ratio is very important to strong work mini resin max fiber
they vacuum bag to get excess resin out
both for weight and strength

[javadog]

I cannot envision a good outcome where you take a finished fiberglass part and attempt to put on a fiberglass outer skin and make it look good. They had her skin needs to be laid up first, not last.

My advice would be to sell the parts you have and buy carbon fiber parts.

[Kraftwerk]

The skin would be going over f/glass not steel, so : thermal expansion differences would be nil, pretty sure. It won't be that much stronger ...or any lighter, heavier, in fact. Buying new c/f units would be the easiest route, easier in every way, except the wallet.

[otto_kretschmer]

Originally Posted by Kraftwerk

The skin would be going over f/glass not steel, so : thermal expansion differences would be nil, pretty sure. It won't be that much stronger ...or any lighter, heavier, in fact. Buying new c/f units would be the easiest route, easier in every way, except the wallet.

you can take the fiberglass part and use it as a master and make a mold and then make a carbon fiber part

its a lot of work but I've done it

[Zeke]

A smooth shiny look is achieved by laying up composites on a smooth shiny surface, like a mold. The backside of any F/G or CF part you see is rough unless it's a cavity mold. Very rare in cars but used in furniture manufacturing. The original early Corvettes were smooth on both side making repairs easy to spot.

So, after bonding the CF to your existing fiberglass parts, you will have an endless task of spraying on a clear sandable product to get a decent finish. This will tend to cloud your CF fabric unless you use water clear coats which don't sand well at all.

I ran a fiberglass operation early in life and although this is possible, I wouldn't touch a job like that.

[Kraftwerk]

Wow, now I am really considering going back to just spraying a nice coat of paint on the fiberglass lid & duck tail.....

[island911]

Originally Posted by Kraftwerk

The skin would be going over f/glass not steel, so : thermal expansion differences would be nil, pretty sure....

Nope. CTE is higher with Glass FRP than with steel.
You would be creating the classic "unbalance" composite.

Also what Milt said.

And I will add that CF is used mostly for its stiffness, not strength. As far as UTS goes, S-glasses are up there with CF and typically provide more toughness than CF. But CF starts out stiffer. To get the same stiffness out of glass, more glass will be used. (more weight)

Fiberglass is fantastic stuff. So is CF. But adding CF to a stiff enough tail is only adding weight, expense, and inviting problems.

[island911]

One more thing... CF weaves are almost always bling.

Engineered CF looks boring, as it will be unidirectional lam's.

Reason being; CF performs best when straight, or at least minimal curvature. Weaves kink the crap out of the fibers. This also leads to a whole bunch of stress concentrators to the lam's underling.

[Bill Douglas]

Always remember carbon fibre is a VERY hazardous substance to work with.

[Captain Ahab Jr]

Only reason to do this would be for your own enjoyment which is a good enough reason as any

Glass and carbon as island911 correctly pointed out create an unbalanced laminate which could cause distortion. I couldn't say by how much as it is very dependent on the shape, ratio of carbon and glass, type of weaves, stacking sequence and fibre orientation of the laminate

I've used this combination of materials to create a temperature dependent morphing structure on a F1 car, was very effective at creating deflection but in practice didn't add any car performance so the idea was dropped

As both your ducktail and hood will have an internal structural frame and the added carbon fibre content won't be much I'm not sure you'll notice any distortion problems. If you're going to have a distortion problem it will be on the hood as it is the larger part with the least shape to it. The ducktail may get hotter but it's smaller and has a stronger, more self supporting shape. I'd suggest doing the hood first as it should be the easier than the ducktail.

I think making the un-moulded external surfaces shiny and smooth will be your biggest problem

The uni-directional engineered laminates island 911 refers to only really work on large curvature parts such as aeroplane wings etc. Uni-directional materials are frequently used in automotive/motorsport but are always mixed in with woven fabrics. This added complexity is not even worth considering for your project.

I'd suggest using a woven 200 gsm 2x2 twill for drape-ability, cost and looks. A heavier fabric would work but won't wrap well around the panel edges. Also use a UV resistant epoxy resin if you can as it will be more durable than a polyester resin and should give an improved adhesion strength between the carbon and original fibreglass. Very important also to well abrade and degrease your f/g panels before laminating on the carbon. Something like a 400 grit wet and dry should be fine.

Please post up your progress as I'm interested to see how you get on

[Kraftwerk]

The 'skinning' technique is really just for looks, it is not far from a vinyl wrap, a bit stronger, pretty sure it would not compete adversely with the already built f/g part, which is rather 'stout'. The c/f is just one very thin and yes drape-able layer. It's cosmetic, of course, paint would be easier /cheaper ( am all about cheaper! ) always liked the look of c/f parts, who doesn't?

[island911]

Like I said, stickers. Get some CF-look vinyl wrap.

https://www.amazon.com/LZLRUN-Stickers-CarInterior-Waterproof-Anti-Scratch/dp/B0895SMVJQ

Not that I like the look, but at least it won't completely ruin an otherwise good tail.