Brake Disk thickness

[Phil1988]

Hey Guys,

got a question about the Brakes.
How thick are your Disks? Our last years car the disks were 5mm thick! Thebrakes did not get really warm. Only about 100 deg.

Our Plan is to go down to 3.5mm thickness. But we don't really get realistic results of temperature simulation.. Does anyone have some experience ??

Regards Phil

[Jon Burford]

we have used 4mm and (I think) 3.5mm on the front.
We used 3.2 mm overall vented disks in a twin brake setup on the rear.

[TMichaels]

I am not a brake guy, but isn't that depending on many more factors than just thickness?
For example:
disc material, pad material, hole pattern, diameter, ducting, vehicle weight, latitudinal load transfer, tires etc.

Just going down/comparing your setup to other teams will not help you in any way. Not talking about trouble in design judging.

[Jon Burford]

I agree with Tobias.
I am just sharing, I am not saying that our spec will work for you!

[Phil1988]

Thanks for the Information...

I know that we can't use the values of other teams.
Only to get some feeling of this value and so on. Not to take the thickness of other teams.

Thanks

[MCoach]

5mm thick? Steel? I've seen 5mm thick aluminum rotors work on a FSAE car, just saying.
That being said, our rotors this year were 5mm thick steel. As mentioned in previous threads, 800 F was common for us.



Your simulation can consist of something as simple as this:

Assume rotors absorb all energy with none sent to other components (pads, fluid, etc)
Assume cooling is nill per stop.
Assume your own calculated (read guessed) cooling coefficient during non-braking events.


1/2m*v^2 = Cp * (delta)T * rho * V

variables as listed in order of appearance:
m - mass of vehicle
v - velocity of vehicle
Cp - brake disc specific heat
(delta)T - temperature gain in brake disc
rho - density of disc material
V - volume of brake disk

There's the heating part of it, which can at least get you an idea of what is going on with your discs.
The cooling part is up to you.

This is about as simple as it gets.

[RobbyObby]

Originally posted by MCoach:
5mm thick? Steel? I've seen 5mm thick aluminum rotors work on a FSAE car, just saying.
That being said, our rotors this year were 5mm thick steel. As mentioned in previous threads, 800 F was common for us.



Your simulation can consist of something as simple as this:

Assume rotors absorb all energy with none sent to other components (pads, fluid, etc)
Assume cooling is nill per stop.
Assume your own calculated (read guessed) cooling coefficient during non-braking events.


1/2m*v^2 = Cp * (delta)T * rho * V

variables as listed in order of appearance:
m - mass of vehicle
v - velocity of vehicle
Cp - brake disc specific heat
(delta)T - temperature gain in brake disc
rho - density of disc material
V - volume of brake disk

There's the heating part of it, which can at least get you an idea of what is going on with your discs.
The cooling part is up to you.

This is about as simple as it gets.

^^^This!^^^

Last year we put together a nice little Excel sheet based on a simple energy balance like one you described. We included just simple convection cooling in static ambient air (for worst case scenario) and calculated the temperature change over a few laps based on somewhat representative on track performance. We saw similar numbers as you after only a few laps (Albeit in simulation. We weren't able to correlate on track numbers). FWIW, in 2011 we had temp stickers put on our top hats for comp and I believe we saw something like 600F right near where the top hat was attached to the rotor. The rotor temp would've been higher. We also had 3/16" (4.75mm) steel rotors all around.

But in all honesty, it depends on alot of things. Are you using just 1018 Mild, or something else (Aluminum, Cast Iron, MMC)? Can your material handle those high temperatures? Will it even affect performance? Can your pads take that amount of energy transfer with predictable results? All these need to be taken into consideration as well.

[MCoach]

Last year we put together a nice little Excel sheet based on a simple energy balance like one you described. We included just simple convection cooling in static ambient air (for worst case scenario) and calculated the temperature change over a few laps based on somewhat representative on track performance. We saw similar numbers as you after only a few laps (Albeit in simulation. We weren't able to correlate on track numbers). FWIW, in 2011 we had temp stickers put on our top hats for comp and I believe we saw something like 600F right near where the top hat was attached to the rotor. The rotor temp would've been higher. We also had 3/16" (4.75mm) steel rotors all around.

But in all honesty, it depends on alot of things. Are you using just 1018 Mild, or something else (Aluminum, Cast Iron, MMC)? Can your material handle those high temperatures? Will it even affect performance? Can your pads take that amount of energy transfer with predictable results? All these need to be taken into consideration as well.


Completely agree, the energy transfer equation is just as good as a huge simulation with more inputs, if guesses go well and taken with a grain of salt.
I've gone a bit farther than that now and honestly, the numbers haven't changed a whole lot. I have a higher confidence in my current values and can get closer to "optimizing" designs for cars (should have seen the final design of the rotor used for the 2012 car), but thicknesses aren't that different. It's really all in the slot design (leading edges for extra friction, spiral to degas pads during fade, cross drilling and slotting to increase cooling.


This is only good for a VERY simple thermal analysis, compared to what has been mentioned in previous threads of buckling concerns and/or fatigue calculations, all which must be taken into account. And not just taken into account seperately, but by "optimizing" for operating temperature, how high has the stress risen? Is it going to fail instantly, in a few days, never?


Yup, more things to think about.

But again, it's a simple, easy to test way to do it.
I would also recommend "The Brake Handbook" in the books to read list on the front page of the forums here.

[zrcjdxc]

Originally posted by MCoach:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Last year we put together a nice little Excel sheet based on a simple energy balance like one you described. We included just simple convection cooling in static ambient air (for worst case scenario) and calculated the temperature change over a few laps based on somewhat representative on track performance. We saw similar numbers as you after only a few laps (Albeit in simulation. We weren't able to correlate on track numbers). FWIW, in 2011 we had temp stickers put on our top hats for comp and I believe we saw something like 600F right near where the top hat was attached to the rotor. The rotor temp would've been higher. We also had 3/16" (4.75mm) steel rotors all around.

But in all honesty, it depends on alot of things. Are you using just 1018 Mild, or something else (Aluminum, Cast Iron, MMC)? Can your material handle those high temperatures? Will it even affect performance? Can your pads take that amount of energy transfer with predictable results? All these need to be taken into consideration as well.


Completely agree, the energy transfer equation is just as good as a huge simulation with more inputs, if guesses go well and taken with a grain of salt.
I've gone a bit farther than that now and honestly, the numbers haven't changed a whole lot. I have a higher confidence in my current values and can get closer to "optimizing" designs for cars (should have seen the final design of the rotor used for the 2012 car), but thicknesses aren't that different. It's really all in the slot design (leading edges for extra friction, spiral to degas pads during fade, cross drilling and slotting to increase cooling.


This is only good for a VERY simple thermal analysis, compared to what has been mentioned in previous threads of buckling concerns and/or fatigue calculations, all which must be taken into account. And not just taken into account seperately, but by "optimizing" for operating temperature, how high has the stress risen? Is it going to fail instantly, in a few days, never?


Yup, more things to think about.

But again, it's a simple, easy to test way to do it.
I would also recommend "The Brake Handbook" in the books to read list on the front page of the forums here. </div></BLOCKQUOTE>
Have you done the realistic results of temperature simulation by Ansys?

[MCoach]

as an engineer, don't confuse realistic, complicated, and simulation. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[typeh]

disc thickness is restricted by caliper.
we do simulation for the worst case maybe even worse so it's ok to have results better than simulation.

[MCoach]

Maximum thickness is limited by caliper, and minimum thickness is only "limited" by the caliper manufacturer's recommendation. We were under 3mm thickness this year...

Validating that limit is just as important as calculating it.