Quote:
Originally Posted by DampRobot
I'm sure the OP has already figured this out, but for those newer members of the forums, there's a reason why the shaft snapped at a snap ring groove. Snap ring grooves (with their sharp corners) make what's called stress risers in the shaft. The shaft's much weaker where it has a smaller diameter (at the grove itself), and the sharp corners in the groove are great places for cracks to start.
For this reason, a lot of teams avoid snap ring grooves altogether, or at least stay away from them between places on a shaft where torque is being transmitted. I'm not sure exactly what the shaft that snapped was being asked to do, but I suspect that using spacers instead of snap rings to locate components on the shaft (with snap rings near the shaft's ends or screws tapped into the shaft's ends to retain the shaft in place) would have made for a bit stronger solution.
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This explanation is a good start, but not quite the whole picture. The implication you've made is that a snap ring anywhere on a shaft will weaken it, and that teams have good reason to avoid all snap ring use because of this. I don't want people to get the wrong idea here - in general, snap rings on the ends of a shaft will work just fine.
The shaft sheared cleanly right at the groove. This is almost certainly because torque was being transmitted through shaft components on either side of the shaft. (I feel like loading from other sources would result in a different looking failure?) The torsional load goes right through the section of the shaft with the snap ring groove, and the sharp corners the groove makes are stress risers - cracks are prone to form there under load leading to failure.
If torque is not being transmitted through a snap ring groove, this problem doesn't happen. No one sees numerous west coast drive axles failing because of snap rings on the ends. The takeaway lesson here is to not place stress risers on shafts between loads - not to avoid snap rings altogether.
(Aside: While the smaller diameter of the grooved area does make it weaker than other areas of the same shaft, the stress risers were probably the main reason this failed the way it did. The differences in maximum torque between a 1/2" round section and a 1/2" hex section are not *that* great...)
Full disclosure: Running on six hours of sleep and studying for a test, maybe none of this is correct / makes sense...