ttAmerica RoadsterAWD

Looking into possibilities of getting some body parts for my car. Anybody know specifics pros/cons between kevlar and CF? Which is stronger, which is more elastic, which is lighter, How "brittle" is one over the other, etc., Also, where can I get Kevlar parts??

Jaime

robmug

Jaime - I think much of it has to do with the manufacture process.

They both start the process as woven cloth, and Kevlar in particular can come in all sorts of varieties (woven in different directions, same direction etc).

Both need a resin to cure the shape, and much of the weight of the finished oart is the weight of resin - which varies on the manufacture process.

I don't know enough to comment further, only that FIA approved race seats can come in either material, but the carbon ones tend to be slightly lighter (we're talking 10% ish) for the same strength.

grankin

He's right, y'know. Think of it this way: you're buying a piece of plastic - reinforced with a fabric. The fabric may be glass, kevlar, or carbon fibers.

When I was closer to boatbuilding (small, light, Olympic-class stuff), the way to test for quality was to burn a laid-up and cured sample, and the smaller the difference in weight before & after was the better measure. The resin is what burned away. The Grand Plan was to have only enough resin in the lay-up to keep the water out, which meant one had not much in the way of panel stiffness. Stiffness was gotten by directional fabric in the layup, and only where it was needed. The stress of racing tended to make the hulls last only about one season ... which was long enough.

Gene Rankin

frankvan

IIRC from my surfboard building days:
Kevlar is tough - you put it where you want resiliance - we would reinforce our skeg boxes with a layer of kevlar.
CF is stiff and light and, depending on the resin used can be fairly, fragile (in contrast to kevlar which is used in body armour) - we put a strip of it down the centerline of the board in lieu of using a wood stringer to provide longitudinal stiffness.
Neither has any strength if not well impregnated with a resin such as epoxy or polyurethane - the cloth provides a "matrix". At least that is what my surfin sensai taught me

BLK964

I asked my brother who works in composites and this is what he had to say:

--It depends on the application, I’m not aware of anyone using Kevlar for body parts. Kevlar has a strong tensile strength that is why it is used in abrasive conditions, such as gloves, ropes and things. When it is laminated with resin it becomes molded to a shape, the problem with Kevlar is that it absorbs a lot of moisture and delaminates or if it is left in the dry state with cloth it basically rots, hence the expiration date on bullet proof vest.--

So you can make your panels bulletproof, but they will expire... If you want your transmission bullet proof, drive a TIP. I know bulletproof isn't what you're after, but I had to throw that in there.

Best of luck. I love your car, by the way.

Heirsh

When we made panels for a solar car in college we used cf on one side and kevlar on the other. The idea was to keep the kevlarin tension and the cf in compression. The orientation varied from piece to piece as they analyzed the forces involved and its mounting locations (I came in after the analysis and almost all the fabricating was done). As far as I know, the moisture absorption was not considered. Though on a street car with more than a couple yr life expectancy that sounds like a good plan (considering absorption).

Didn't I read about some stock kevlar body panels on race cars from porsche? Particularly the wing/engine bonnet?

ttAmerica RoadsterAWD

Guys, you are amazing! Thank you very much for the info. First hand experience is very helpful. Kevlar has been used in Porsche racing products, and some high end shops (FVD, Gemballa etc.,) still make kevlar/CF hibrid body parts. I've read somewhere that Porsche used strictly kevlar in the old days. But now that there is CF, I wondered if kevlar was better or CF. Looks like it's "6 of one or half dozen of the other".

anybody else with anecdotal info between kevlar and CF?

Jaime

chris walrod

Kevlar is great for some applications such as bullet proof vests, sailboat sail ropes etc., but a terrible choice for automotive body panels. Its difficult to trim, doesnt like to bond to anything, absorbd moisture, does paint well etc. To good news is that a hybrid Kevlar/CF laminate does well in that the Kevlar will hold together an otherwise brittle CF piece that has been fractured.

Kevlar is also non-conductive and can be transmitted/received through.

JasonAndreas

Porsche's composite hood for the 964 was made of kevlar.