First I just wanted to say thanks to everyone here for some awesome info. I haven’t had too much experience with composite materials in the past, but I’ve learned a lot just reading threads on here.
I’m working on a SAE mini baja car for my university, and while we have experience using fiberglass to make body panels, we want to extend our use of composites to the belly pan as well. Typically the belly pan is made out of something like .032 aluminum or .020 steel (thicker for teams that don’t obsess over every pound of weight, but we do obsess), but I think we can get a lighter, stronger, and hopefully tougher part with a composite piece. Because it will need to withstands hits from rocks, I assume Kevlar will be a necessity. What sort of layup should I be going for here. Is there anything I need to know about working with Kevlar? Members on our team only have experience with fiberglass and carbon fiber.
Perhaps look at carbon/Kevlar hybrids for a floor pan that’s going to take a lot of abuse. Kevlar is good at resisting impacts but not as great as carbon when bonding with epoxy for example so the hybrid cloth will be good for bonding & resisting impacts/delaminations. Possibly also look at twintex if you can get some nearby
Kevlar can be a pain to cut, get some serrated scissors. Not sure how much weight you’d save by using kevlar/carbon. Is weight savings of a pound that big a deal in off road? Maybe body panels from kevlar/carbon might save some weight over fiberglass?
Thanks for the opinions guys. A belly pan that’s 3 layers thick of carbon/kevlar would save approximately 2 lbs over an .032 aluminum belly pan. The plan is to use carbon on the body panels as well this year. I know Kevlar is difficult to cut, we would definitely invest in some scissors designed to cut it.
We have no minimum weight, so every pound we can remove helps. Last years car was 445 lbs, this year our target is 360. It looks like we should be able to reach that, or really close. The top cars are around 300, but we don’t have the quite budget, facilities, or experience the top teams have yet.
does anyone do carbon tubing or carbon suspension members or other structural types of components?
I’ve seen some companies make their springs for the shock assemblies of carbon and of course there are companies that make composite leaf springs. Though I doubt you use leaf springs.
Though it sounds like a lot of trouble to go through to save two pounds. That’s usually aerospace or track car type mentality. With that mind set you gotta consider how much paint weighs and maybe find a female driver. The weight of the tires must kill you to think about!
anyway… the belly skin at 3 plys is pretty flimsy. So be aware of that. We’re building a belly skin coincidentally of 3 plys right now as well. Not sure what kevlar you’re using, but the stuff I have is pretty light weight and not all that strong compared to carbon. Having some geometry to the part will make a huge difference in it’s rigidity.
A few people do use carbon for suspension members. We plan to use carbon tubes for the steering column (about 1.25 lb over steel) and tie rods (another 1 lb+), but our suspension arms are A-arms, so that would be more difficult than a straight tube.
It is a little more trouble than cutting a sheet of aluminum, but if we’re already making composite body panels, why not make a belly pan? It’s just a flat sheet, not hard to make at all. If it breaks we have plenty of aluminum for a backup. The plan was to use the hybrid carbon/kevlar material. It’s a little difficult to figure out exactly how many layers will be required, because it’s so dependent on the course layout. The belly pan will be a trapezoid type shape with several lateral members which can support it.
You mentioned paint and a female driver, who needs paint on a carbon body panel? And we have a female driver <100 lbs. Hopefully she can drive fast! The ATV tires are super heavy, the best we’ve found are 13.7 lbs for the rear, a little lighter (smaller) for the front.
If the belly pan is flat that does make it easier in one sense, however you tend to have more issues of rigidity with a flat piece. Were you planning on using some core or maybe hat stiffeners to keep it more rigid? Or is rigidity even an issue? Even screwed down to the lateral members its gonna vibrate and what not.
and yah paint… Unless your team color is black on black, you might have an issue! Of course you could always just add a racing stripe. but it does look cool with paint that is masked to show the carbon under neath.
Rigidity isn’t really much of an issue. The goal of the belly pan is just to keep rocks out, so it just has to stay in 1 piece during the race, doesn’t matter if it flexes.
There isn’t actually very much area the body panels cover, we will probably throw some vinyl graphics on them.
Racer3207. Which university are you working with? When I was in my undergrad I worked on the FHSAE team so I’m always curious about the SAE competitions in general
