Choosing an Epoxy

[mtheo]

Hi, guys. I'm fairly new to FSAE and the forums so excuse me if I make any mistakes, but I chose the task of taking our suspension system from steel to carbon fiber tubes this year.
I've read many available papers, but a lot of them are outdated as epoxy technology has progressed throughout the years. I've been researching and so far I've come up with G/flex epoxy.
This seems like a strong and viable epoxy.

Which brings me to my questions:
-What epoxy is your team using?
-Are there any new papers out about a design I can reference to?
-Is an INSTRON test on inserts and epoxy enough validation for a judge?

[Z]

... I chose the task of taking our suspension system from steel to carbon fiber tubes this year.

Mtheo,

WHY?????

Z

[onemaniac]

Judge: "Hey, Why?" (pointing at the CF suspension tubes)
Student: "This carbon fiber suspension assembly reduced the toe compliance by xx.x% the camber compliance by xx.x% and unsprung weight by xx.x% so it's awesome"
Judge: "Cool. And by reducing the compliance by xx.x% and unsprung weight by xx.x%, how much performance gain (=lap time shavery) did you actually achieve?"
Student: "Doesn't matter BECAUSE RACECAR"
Judge: "Indeed" (turns around and walks away)

[mtheo]

Mtheo,

WHY?????

Z

One of our vehicle goals is to reduce weight, so I assumed that the next step would be to go from steel to carbon fiber.

[mtheo]

Judge: "Hey, Why?" (pointing at the CF suspension tubes)
Student: "This carbon fiber suspension assembly reduced the toe compliance by xx.x% the camber compliance by xx.x% and unsprung weight by xx.x% so it's awesome"
Judge: "Cool. And by reducing the compliance by xx.x% and unsprung weight by xx.x%, how much performance gain (=lap time shavery) did you actually achieve?"
Student: "Doesn't matter BECAUSE RACECAR"
Judge: "Indeed" (turns around and walks away)

I know what you're getting at here. And lets assume that the transfer from steel to carbon fiber provides a minimal gain in lap time. Even though that is true, I believe that if the team wants to reduce mass on the vehicle as a whole, a carbon fiber suspension system will only help.

[MCoach]

I know what you're getting at here. And lets assume that the transfer from steel to carbon fiber provides a minimal gain in lap time. Even though that is true, I believe that if the team wants to reduce mass on the vehicle as a whole, a carbon fiber suspension system will only help.

You could also cut weight off that massive aero assembly you guys run...

Have you done a calculation, just with respect to the mass loss of:

current car mass --> performance ---> lap time ---> competition points.
(current car - estimated mass saved) --> points delta.


I'm curious how much you want to save overall.

[Ahmad Rezq]

I know what you're getting at here. And lets assume that the transfer from steel to carbon fiber provides a minimal gain in lap time. Even though that is true, I believe that if the team wants to reduce mass on the vehicle as a whole, a carbon fiber suspension system will only help.

The fastest formula SAE vehicles don't have CF Control Arms.

[mtheo]

Can somebody inform me on why running a lighter unsprung mass would hurt the car's performance?

I mean, fundamentally a key goal to keep in mind is reducing mass. So, if a team can accomplish this efficiently and has the resources to do do, then why not?

[Z]

Mtheo,


One of our vehicle goals is to reduce weight, so I assumed that the next step would be to go from steel to carbon fiber.

Why not thinner steel? Namely a more "efficient" design of steel upright/control-arm/etc.?

Or better yet, why not just toss all the unnecessary junk on the car (I am sure there is a lot of it)?
~o0o~


...a carbon fiber suspension system will only help.

Really???

Have you followed FSAE for long? Do you know what CF-wishbones are famous for?
~o0o~


... why running a lighter unsprung mass would hurt the car's performance?

Because if you do not make it through Brake-Test (... because your CF-wishbone exploded!), then your dynamic points = a big fat duck-egg.
~o0o~

Put simply, you would make a very bad chess player. You are making moves that look wonderful for you, but you are ignoring their negative consequences. I doubt you would get ten moves into a game.

Anyway, try googling "cost-benefit analysis" or "return on investment". Pay special attention to what it says about the inevitable COSTS and INVESTMENTS, and how they can hurt you.

(In case this is not clear enough, the increased risk of failure inherent in CF-wishbones is a very significant COST.)

Z

[onemaniac]

I know what you're getting at here. And lets assume that the transfer from steel to carbon fiber provides a minimal gain in lap time. Even though that is true, I believe that if the team wants to reduce mass on the vehicle as a whole, a carbon fiber suspension system will only help.

I think you're still off point.

Is your team's 'big picture' goal having the lightest car possible? Or is it reducing weight in order to gain performance to win the competition?
In other words - Why is your team wanting to reduce mass?

You're not entering Formula-so-you-think-your-car-is-light contest.

Also, nothing wrong with carbon fiber suspension. If you have time and money, go crazy with it.
But, when you're trying to implement something new that involves risk - this kind of project is better suited as a back-burner that you research on the side for the car to build a year or two later.
Learning things on the fly through expensive mistakes without suffering real consequences (i.e. losing your job) is the beautiful part of FSAE but also the worst pitfall at the same time.
It's good to be patient, take your time to thoroughly study your plans before jumping the gun.

[mech5496]

One of our vehicle goals is to reduce weight, so I assumed that the next step would be to go from steel to carbon fiber.

Totally unrelated, but we managed to reduce our chassis weight (not by a lot, but still) and cut cost and manufacturing time more than half by moving away from a carbon fiber monocoque and using an "inferior" aluminum folded structure. This (and similar decisions throughout the car) reduced overall weight by a good 25kg and led us winning cost in both competitions we entered. Sounding "better" does not mean it is, so try to quantify everything.

[BillCobb]

Pick a smaller lighter stronger driver. Maybe someone without massive test tickles, eh ?

[mtheo]

I think you're still off point.
Also, nothing wrong with carbon fiber suspension. If you have time and money, go crazy with it.
But, when you're trying to implement something new that involves risk - this kind of project is better suited as a back-burner that you research on the side for the car to build a year or two later.
Learning things on the fly through expensive mistakes without suffering real consequences (i.e. losing your job) is the beautiful part of FSAE but also the worst pitfall at the same time.
It's good to be patient, take your time to thoroughly study your plans before jumping the gun.

Fair point about patience. I'd like to get data on epoxies chosen, life of parts made, load failure of CF A-arms, lap sims, ect, and possibly execute this project next year if risk/reward/budget allows. So, I'm going to develop a test plan.

[Pat Clarke]

mtheo,

https://www.formulastudent.de/academy/pats-corner/advice-details/article/pats-corner-back-to-basics/

Pat

[Dunk Mckay]

What I've heard so far is:

"We're going to gain two thirds of bugger all in theoretical points by saving weight on our wishbones. Which won't make any difference to our overall ranking, and will double the likelihood of something breaking on our suspension.
In order to do this I'm going to spend loads of my time researching different types of epoxies, instead of just re-using a successful steel design which would give us more testing time (=better setup & faster drivers = many more points).
This epoxy research (instead of using a generic epoxy system) will allow me to increase the weight and stiffness gains even further, gaining an extra 5% on top of the two thirds of bugger all points previously mentioned."

STOP WASTING YOUR TIME RESEARCHING BLOODY EPOXY FOR IMMEASURABLY SMALL GAINS!! GET YOUR CAR BUILT EARLY AND ROBUSTLY AND GET IN ON A TRACK TO IMPROVE YOUR LAP TIMES!!!!

[Adam Farabaugh]

The easiest first-order solution is to at least make a pie chart of vehicle mass. How much do your current metal control arms weigh? How much will the CF ones weigh?
Could you achieve the same weight loss elsewhere faster, with less effort, and with less cost? This is engineering.

If you just want to learn more about composites and inserts and engineering of bonded joints, investigate
- material. are you laying up your own tubes or buying? or non-tubular layup? fiber stiffness? resin system? cure kinematics?
- if make, how are you tooling it? what layup? need to develop some sort of material properties for your layups, most likely by test
- how are you going to analyze the joint?
- fatigue. eopxies are brittle, need good process control or enough extra strength margin to not care
- galvanic couple
- bond prep
- stress distribution in the joint. what is the stress state within the adherends and the adherent? how can you design the joint to minimize stress?
- how are you tooling the bond? How do you ensure there are no voids? My suggestion would be to proof all the joints, but that means you need to develop loads to proof to
- damage tolerance
- thermal strength degradation. ends will likely be within decent radiation distance of your brake rotors. put some of your test coupons in a toaster oven immediately before testing or something

If you need somewhere to start, search for paste adhesives