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Discussion Starter · #1 · (Edited)
Hey Everyone,

At my work we have lots of cars that run on track all day, many of these cars are work horses doing over 50 laps a day, and their brakes take a beating. I've made a small collage of the life cycle of the brake rotor.The goal is to change the rotors before the cracks reach the outer edge of the rotor. I figured you may find this interesting, that way you all know when its time to change your rotors. You can always change your rotors sooner to be on the safe side, but brake rotors are often good for track use until they are heavily cracked. Enjoy!

The cars in the pictures are as follows

Cayman GTS --- Gallardo Superleggera
Mclaren 12c ---- Ferrari F430 Challange Car
Ferrari F430 Challenge car ---458 italia

Product Light Ceiling Lighting Metal
 

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Interesting.

I see the cracks in the Ferraris and McLaren, but not in the two on top... Do I need glasses?

Hey Everyone,

At my work we have lots of cars that run on track all day, many of these cars are work horses doing over 50 laps a day, and their brakes take a beating. I've made a small collage of the life cycle of the brake rotor.The goal is to change the rotors before the cracks reach the outer edge of the rotor. I figured you may find this interesting, that way you all know when its time to change your rotors. You can always change your rotors sooner to be on the safe side, but brake rotors are often good for track use until they are heavily cracked. Enjoy!

The cars in the pictures are as follows

Cayman GTS --- Gallardo Superleggera
Mclaren 12c ---- Ferrari F430 Challange Car
Ferrari F430 Challenge car ---458 italia

View attachment 54273
 

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Discussion Starter · #3 ·
I was showing a progression, so the top left is a used but non cracked rotor, the one to the right of that is starting to show signs of cracking, the middle left cracking appears, middle right more cracks, bottom left cracks, bottom right heavily cracked
 
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The cracks radiating from the drilled holes are 'stress risers' and actually mulitply the stress applied and can fail catastrophically
The other 'cracks' appear to be surface and without any NDE, I can't tell but may or may not be detrimental
In any event, a catastrophic brake rotor failure at speed is NOT something I want to experience, so my rotors have no cracks.-Richard
 
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The cracks radiating from the drilled holes are 'stress risers' and actually mulitply the stress applied and can fail catastrophically

Richard, You are correct the holes are stress risers. This can (and does) initiate the onset of cracks earlier. You can see in the photo the cracks radiating from the holes are much longer (and hence older) than the cracks starting away from the holes. Crack propagation and catastrophic failure are determined by the stress intensity at the crack tip. Once a crack has initiated and the crack tip (the end of the crack) has progressed away from hole the presence of the hole has no impact on the stress intensity at the crack tip and hence no impact on the progression of the crack propagation. In other words a drilled rotor with a crack x long is no more or less likely to catastrophically fail than a non-drilled rotor with a crack x long.

I don't mean to pick nits I just didn't want some one to misinterpret your comment to mean that a cracked rotor without holes is less likely to fail than a cracked rotor with holes. Once the cracks are present the holes don't matter anymore.

Cheers! :cheers:
 
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Discussion Starter · #7 ·
its interesting that our Mclaren 12c came with drilled rotors, you would think mclaren would know something about this.
 

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I bet they're cast that way and not drilled.
 
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FWIW, the outside "holes" on the 981 rotors are really dimples that do not go completely through the rotor--different from the 987 rotors. I'm thinking they changed this so a crack would take longer to get to the outside edge.

Interesting that the slotted rotors have cracks in the rotor, independent of the slots.

To the original poster--any idea if these rotors have the similar numbers of laps on them?
 

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Richard, You are correct the holes are stress risers. This can (and does) initiate the onset of cracks earlier. You can see in the photo the cracks radiating from the holes are much longer (and hence older) than the cracks starting away from the holes. Crack propagation and catastrophic failure are determined by the stress intensity at the crack tip. Once a crack has initiated and the crack tip (the end of the crack) has progressed away from hole the presence of the hole has no impact on the stress intensity at the crack tip and hence no impact on the progression of the crack propagation. In other words a drilled rotor with a crack x long is no more or less likely to catastrophically fail than a non-drilled rotor with a crack x long.

I don't mean to pick nits I just didn't want some one to misinterpret your comment to mean that a cracked rotor without holes is less likely to fail than a cracked rotor with holes. Once the cracks are present the holes don't matter anymore.

Cheers! :cheers:
I appreciate the detail.
As a Nuclear Engineer and Metallurgist, I generally keep things simple on Forums but Petch has done a lot of work in this area.
http://folk.ntnu.no/christth/papers/stateofart-april02.doc
 

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Discussion Starter · #11 ·
FWIW, the outside "holes" on the 981 rotors are really dimples that do not go completely through the rotor--different from the 987 rotors. I'm thinking they changed this so a crack would take longer to get to the outside edge.

Interesting that the slotted rotors have cracks in the rotor, independent of the slots.

To the original poster--any idea if these rotors have the similar numbers of laps on them?
No they have all different amount of laps on them. Some of the cars' brakes take more of a beating because they are faster on the same track. The F430 challenges, mclaren, and 458 italia all reach 130 mph on our straight versus the Cayman's 110, so those faster cars naturally will have their brakes degrade faster.
 

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I appreciate the detail.
As a Nuclear Engineer and Metallurgist, I generally keep things simple on Forums but Petch has done a lot of work in this area.
http://folk.ntnu.no/christth/papers/stateofart-april02.doc
Thanks for the link. I'm actually familiar with Petch as a portion of my post-grad study was in fatigue and fracture mechanics. Small world as you mention nuclear engineering. I also am a nuclear engineer, at Millstone power station. I tend to focus on fatigue, piping and reactor vessel structural integrity (surveillance capsule, p/t limits, etc). Might you be at Point Beach, now that Kewaunee is decommissioned?
 
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