pic: Broken Output Shaft

[Alan Anderson]

Originally Posted by mplanchard

You have a large aspect ratio in this problem - long shaft and short, small keyway.

What keyway?

[mplanchard]

sorry - tried to answer this on my iphone. maybe it is a grove?

[JamesCH95]

Learning how to use COMSOL 4.0 at work (an excellent FE program for those who are interested, much better than COMSOL 3.5) I decided to see if it could show the stress risers in this particular situation, and it did so quite well. I've attached two plots. One plot is of the surface stresses, which does indeed show the stress concentrations in the groove. However, I find the slice plot much more illuminating as to why this groove is a stress riser. If you look at how the shear stress flows through the part you can see that it likes to stay near the outside surface, but the snap ring groove abruptly forces stress towards the middle, compressing the stress (if you will) around the groove.

Pay no attention to the magnitude of the stresses, I just picked a load number out of the air that was close-ish.

PS- I hope no one is too upset about reviving an older thread.

[JamesCH95]

Stress plots posted above.

[kibbs425]

No FEA is necessary. Contrary to popular belief. A lot of good analysis can be done with a book, pencil and a napkin! All good ME design books will have a reference to Stress concentrations. They are generally relatively simple to use as long as you can read a chart.

Engineers edge (www.engineersedge.com) is the 1st pass that I usually take when I'm looking and I don't have my book handy and the internet is available. Here is the section on stress concentrations: http://www.engineersedge.com/calcula...tion-shaft.htm

This won't give you the stress unless you know the rest of the numbers, but you can at least compare Kts for the known geometry to determine what has less of an impact.

Shigley's Mechanical Engineering Design is my text book of choice. It was required in my college ME Design class. It is still something that I use regularly and has a lot of great references.

Good luck!