I'm looking into building a carbon fibre monocoque frame and I was hoping I could get some feedback about how other teams met the rules. Specifically I'm curious as to how strict SAE is about proving equivalency (to a similar steel frame) and how other teams went about it.
I'm already working on it, but any help in this area would be greatly appreciated -- especially if any teams out there ran into problem meeting all the requirements.


Cheers

Kevin

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Carleton University FSAE

Well I'm in the process of doing the same thing at the moment for the next WWU car...I'm gonna send the first draft in this week, so I can only tell you what's been done in the past here and what I'll be submitting...

As far as I can tell, they just want a clear comparison of what you'll be using to the steel bar its replacing, we've done physical testing of our carbon parts, compared stress vs. strain curves of carbon and steel, and extrapolated, finding E and using that to compare the carbon to steel on paper...

If you ask me the physical testing should probably be the only thing considered since there are so many variables in composite parts, not the least of which being the students who made the part...but I think if you can take a guess at your E*I using the properties of the fibers used then you're probably going to be ok from what I've seen of past equivalency submissions....

We are using two ~6" OD carbon tubes as our main chassis components (similar to some of our older cars http://dot.etec.wwu.edu/fsae/v28/image016.jpg or http://dot.etec.wwu.edu/fsae/index.html) , and hopefully as most of our side impact protection...For testing I used some ~10" long sections trimmed off the end of the tube, applied a compressive load, recorded deflection, and then used a formula from Roark's to translate the deflection and load data to E....then compared the E*I of our tubes to that of the 1" steel tube its intended to replace. Additionally, I'll be submitting a full on 3 point bend test of a full tube (comprised of fewer layers, basically made of scraps just for testing) that was crushed to failure, with a graph a the steel tube of the same length loaded under the same conditions...

This is what our team has done in the past and its worked before, hopefully it will work again...I'd be interested in hearing what you're trying to get passed, and what you've been doing for your equivalency

Good luck

Travis Garrison
WWU

I don't know the extent of the safety equivalency Waterloo has used for our monocoque, but I know we have done some interesting impact tests. I remember last year we dropped a 60lb steel cylinder from about 4 ft onto a carbon sample. The carbon was supported between two cement blocks- the cement fractured and the carbon composite sample barely deformed.

I'm working on a composite chassis, hopefully out of carbon fibre. Can anyone tell me how to work out the stiffness of the fibre when i'm give the fibre construction with, Tex (at 3500) the ends (0.925), plain weave and a 660g/sq.m. and were using a polymer resin. is there anyway of working out the rigidity that this might give and the strength.

Thanks

Matt