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Originally Posted by AU N EGL
Try this little calculator that lets you know the stress concentration factors of a plate with holes. Put in the radius of the hole, the distance to the hole from another hole or edge and see how much faster the holes will make your rotors fail. We all know all rotors will fail, it is a matter of when and this will give you a factor of 2-4x less life before cracking. BTW, slots do a similar concentration factor. This is especially true in a brittle material like cast iron. Use the case of an infinite plate with 2 circular holes. For the case of 2mm radius holes 25mm apart, the stress is 2.91 times the "usual" rotor stress. Or to put it another way, you willl crack 2.9 times sooner.
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Did you notice, if you play with this calculator thing, that if you make the 2mm radius holes bigger, the stress gets lower? Stress is reduced to 2.82 from 2.92 when you go to 5mm radius holes. Weird, huh?
Bye the way, are our rotors in parallel or perpendicular tension - and is it one of these rather than the other that makes the cracks appear?