I saw several reports like that when I did my internship in college. Broken gears and shafts in the aircraft industry generates a LOT of analysis reports.
Although, that is one of the better written ones I've seen.
I believe that is one of the reasons many manufacturers have switched to the laser etching for manufacturing markings. The affected depth is much shallower.
Well that is a good write-up of a duh example. Any time you induce a stress riser you have a path for stress crack initiation. A critical crack analysis would have shown that. I'd also have to question the hardness of the 300m shafts. Rc 54-56 is too hard for that application where the premium zone to be in would Rc 47-49. We shoot for 48 but have to allow for minor deviations. Toughness and ductility have a large role in an input shaft. And never ever stamp numbers like that. Laser etch is the desired for longevity, but rubber ink stamping is also applied. We have run critical crack analysis on large parts that have show that even the scratches we put on the surface from instalation have lead to a stress crack failure - I mean small nick type scratches less than 0.010" deep.
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