Kevlar Body Construction

[Greg Davis]

I am considering using kevlar to construct a new center body section for my car to lose weight ( I'm about 25 lbs over) The weight of the current piece is 33+ lbs. I want to use kevlar because of strength and lightness, and I have read various articles that people have integrated e-glass in the construction process. Can anyone give me some guidance on the likelyhood of dropping enough weight to make this project worthwhile while using the kevlar/e-glass method? Also, any tips on typical mat thicknesses/weave type(s) and resin type(s) used would also be appreciated. Lastly, is there is a better method than what I'm considering? Thanks in advance for any advice offered.

[Ed Womer]

As long as you keep the amount of layers down and don't over saturate the cloth with resin you might make it. Yes you can mix different types of materials in the lay up, I do with the side panels on my car since you are required to have two layers of Kevlar in the side. The alternative is obviously carbon fiber since it only requires two layers and still is strong, but if you have any tight bens or corners you will need to vaccum bag to keep it there until it sets up. As for the kevlar you need two 5oz pieces in the side area but could use lighter weave else were to keep the weight down.
Ed

[Greg Davis]

Ed, Thanks for your input concerning my inquiry. I have aluminum side impact panels now, and because of the way my body has to be mounted, will probably keep them in place and use a lighter weight kevlar weave. Can you suggest an appropriate weight for this application? Thanks again for your time with this.

[vreihen]

How about making a sandwich core by just putting Kevlar on both sides of a thin piece of foam? Styrofoam-type material is sold by density (pounds per cubic foot), with the pink and blue stuff at Home Depot being between 1.5 and 2.0 lbs/ft^3. Kevlar and composite materials are measured by ounces per square yard, with 5 oz Kevlar weave being common. Modern composites need to use epoxy resin versus the cheaper polyester (Bondo-smelling) stuff, usually mixed 50/50 resin and hardener. There are formulas out there for estimating the resin-to-fabric ratio for wet layup, vacuum bagging, etc, but you can do the napkin math with these figures to see how much weight you can potentially shed from both your car and wallet. The resin will be the heaviest part, and actually provides the least strength.

I have never built a body to offer advice on material layers, but will point out that there have been entire FSAE monocoque chassis built from sandwich core composites that weigh less than the body panels that you're looking to replace.....

[Greg Davis]

vrehein,
I don't think the foam honeycomb would be too feasible because of the body shape (D-13), but I appreciate your input to my inquiry.

[hardingfv32-1]

Kevlar is not the correct material for the body. You add it in the appropriate areas as specified in the rules.

For maximum weight reduction you use carbon fiber with a thin layer (.125" or greater) of foam, like Rohcell, between the inner and outer skin. This is not inexpensive system, but if you WANT to reduce the weight of the body it is the best way. Vacuum bagging would also be a BIG help, but it might not be practical without a team of lay-up people. At best you will only have 2 hrs of pot life with the epoxy resin.

Brian

[kidkoh]

use thin sheets of aluminum and roll it out to match your existing body, it will take some work and you will probibly need to make it out of a few pieces but it can be done without a lot of specal tools and it will save you a ton of weight

[vreihen]

vrehein,
I don't think the foam honeycomb would be too feasible because of the body shape (D-13), but I appreciate your input to my inquiry.

Unless it is a hugely complex shape, you can cut kerf slots halfway through the backside of a bend using a razor knife or Dremel tool to allow thin foam to bend around some pretty sharp corners. I wouldn't use honeycomb for non-structural bodywork.....

[FV80]

FYI -
GCR 9.1.1.C.8.C. There shall not be frame/chassis rigidity or strength derived by
means other than the frame tubes. Stressed skin, monocoque, or
semi monocoque construction is not permitted, except that:
The firewall panel and undertray(s) may be rigidly attached to the
frame tubes.

Steve, FV80

[Ed Womer]

First question is do you have a mold? You can use any composit material to make the body but the cost is the reason for most applications. The cheapest stuff is mat which is most likely what yours is made from. Most people use it becuase it is chep and you can get it to fit all shapes but the big problem is it takes a lot of resin which is where the weight comes from. Next is the woven materials that come in various weights per yard and the heavier the threads the heavier the total weight. Kevlar is around $15 a yard and up and carbon $25 and up.

I have to disagree with Brian and kevlar is OK for bodywork since it is very tough stuff and is used in high abrasion applications like white water kayaks and I have seen it used on pro type bodywork. You need specially ground sissors to cut the stuff it is that tough. I actually put strips in the bottom of my noses to keep the wear down although even it will wear thorough from rubbing on the pavement.

Jereme Griener at Ski Motorsports makes carbon fiber bodywork for my cars using my molds and the parts are less than half the weight of mine using 4 layers of 10oz E glass cloth. But he only uses 2 layers of carbon and no gel coat.

Then you get into the resins and you have to choose from polyester, vylnester and epoxy and just like the cloth the price goes up with the better resin. I was using vylnester for a while because the guy I was bying from sold it so cheap that the increase of cost wasn't that much but he died and I now get my materials from Florida and a gallon of pojyester is around $30 with shipping. Someone said that you mix the resin with the hardner at 50/50 and I highly sugest you don't do that. It is supposed to be used at around 2% but it has a lot to do with air temp and humidity. I have to make a nose for someone and have been putting it off until it gets warmer so that I don't have to use so much hardner to get it to set up with the cold weather.

Ed

[vreihen]

Someone said that you mix the resin with the hardner at 50/50 and I highly sugest you don't do that.

50/50 is for most epoxy resins, which I suggested due to the superior strength over polyester and because polyester attacks certain types of foams. Here's a good quick summary of the resin choices:

http://sollercomposites.com/EpoxyResinChoice.html

[Ed Womer]

Yes I was talking about polyester and vynlester resins not epoxy. If you do a 50/50 mix with those two you could end up with it cathing on fire! I have wanted some to set up quickly and when it did it started smoking in the mixing pot. Although I haven't used epoxy they have pumps that provide the correct mixing ratio for the product. Trust me I do like the look of carbon but I just can't justify the cost and weight has never been a problem for me.

Ed

[Greg Davis]

I've been away from my computer for a few days and haven't been able to keep up with the responses to my questions, but I just wanted to thank all who have taken the time to give me their input on this subject.