Hand calc. possible for a brake disc?
Hand calc. possible for a brake disc?
(OP)
Hello Guys,
I'm trying to hand calc a brake disc to get some estimate of the stresses in the collar part(the part connecting the actual brake disc to the hub mounting face).
The stress state from FEA results prove very complex and multidirectional(basically a mess).
Does anybody have any experience with such a setup? Any thoughts, suggestions or assumptions to make are more than welcome.
p.s. thermal induces stresses are excluded, pure torgue loading
Thank you all.
I'm trying to hand calc a brake disc to get some estimate of the stresses in the collar part(the part connecting the actual brake disc to the hub mounting face).
The stress state from FEA results prove very complex and multidirectional(basically a mess).
Does anybody have any experience with such a setup? Any thoughts, suggestions or assumptions to make are more than welcome.
p.s. thermal induces stresses are excluded, pure torgue loading
Thank you all.






RE: Hand calc. possible for a brake disc?
If its a bolted flange and hub, for a purely torque loading I would do a hand calculation similiar to the calcs done for a shaft coupling.
see this link:-
h
strength+of+bolted+couplings&source=bl&ots=NoJE_egIw-&sig=_roMvkwFW4sQWMQymkQAd0QeH-0&hl=en&ei=7OKcS_jJNZKM0gSUz9jqAQ&sa=X&oi=book_
result&ct=result&resnum=7&ved=0CBgQ6AEwBjgK#v=onepage&q=
torsional%20strength%20of%20bolted%20couplings&f=false
desertfox
RE: Hand calc. possible for a brake disc?
first off thank you.
i suppose you're referring to the expression for shear strength of the hub-flange intersection:
d^2*f >= 2T/(pi * Sshear)
d=shaft dia.
f=flange thickness
T = torque
But this assumes torque effects on the complete circumference, which is not the case for a brake disc.
The pad only interacts on (let's say)a quarter of the circumference(90 deg).
Do you think one could simply divide the left part of the equation to counteract this effect?!
Some would probably shoot me for such's a remark, but i only need pallpark value's...
Again, thanks in advance!
RE: Hand calc. possible for a brake disc?
Yes your assumption about my post is correct.
Any chance you can provide a sketch, are you refering to the brake pad pressing against disc during operation? in which case you need to multiply the normal force by the coeff of friction to obtain the force acting tangentially.
Also with the resultant normal force you need to find where it can be considered to act radially from the hub centre, knowing that gives the radius at which the tangential force acts.
desertfox
RE: Hand calc. possible for a brake disc?
pls see attachment.
The problem is that i'm not sure how to correctly cope with the fact that the reaction (to the tangent pad force) is only coming from a part of the circumference(approx 90 deg), due to the pad contacting the disc locally.
RE: Hand calc. possible for a brake disc?
Have a look at this file I have uploaded, I assumed there was a hole in the centre of the collar though in my calculation.
desertfox
RE: Hand calc. possible for a brake disc?
If your collar was long compared to its diameter and you were looking far from the connection between disc and collar (at least a couple diameters) then you could expect the stress to be Tr/J regardless of how the torque is applied due to St. Venant's Principle. Since you are looking at stresses that are near the application of the load this won't be the case. I would expect that you would see shear stresses higher than Tr/J in the collar in areas close to the pad and lower than Tr/J in areas far from the pad (shorter distance -> stiffer -> carries more load).
RE: Hand calc. possible for a brake disc?
Terio makes a good point about the intersection between the disc and collar, you can use the stress concentration factors from this link below for torsion of a stepped shaft.
ht
you may need to scroll down to the case that you need.
This combined with the formula in my uploaded file should get you in the ballpark.
desertfox
RE: Hand calc. possible for a brake disc?
Ted
RE: Hand calc. possible for a brake disc?
htt
RE: Hand calc. possible for a brake disc?
i agree with you, the FEA results also prove your point.
I will try the suggestion from desertfox, regarding the stress concentration factors.
RE: Hand calc. possible for a brake disc?
Post back and let us know how you get on.
desertfox
RE: Hand calc. possible for a brake disc?
RE: Hand calc. possible for a brake disc?
Cheers
Greg Locock
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RE: Hand calc. possible for a brake disc?
Thanks for all the suggestions.
RE: Hand calc. possible for a brake disc?
i did a hand calc. based on the suggestion from TERIO(see attachment).
Not sure if's this simple though...although the result somewhat approaches the FEA.
Thought's more than welcome!
RE: Hand calc. possible for a brake disc?
I can't understand were the vertical reaction comes from, I am obviously missing something perhaps you can point it out.
desertfox
RE: Hand calc. possible for a brake disc?
the sole force that the brakepad/disc interface can create is tangent to the circumference, no two ways about it.
Since the pad is assumed on 3 o'clock position(and disc rotating clockwise), the reaction force is vertically upward.
The reaction force is counteracting the torque for equilibrium.
Besides the torque induced shear, there is also shear due to the vertical force, it's trying to shear the friction ring of the collar, upwards(credit to TERIO).
RE: Hand calc. possible for a brake disc?
RE: Hand calc. possible for a brake disc?
RE: Hand calc. possible for a brake disc?
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