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Thanks for the replies. One thing I could add is that the shaft is rotating and failed in a matter of hours - about 200,000 cycles. Just worked through possible stresses and looks like the possible bending stress is much higher than torsional stress. There is a 3/8" weld about 3/8" away so...

Last pic. Thankshttp://files.engineering.com/getfile.aspx?folder=1d5fce58-67fd-4d7f-97a7-a91b18f9ce77&file=_DSC0764_6979_1.jpg

Second pichttp://files.engineering.com/getfile.aspx?folder=3903f5db-54a4-4b0d-b0e0-744f61d6926c&file=_DSC0759_6974_1.jpg

Hello, Anyone care to look at this failed shaft? - I'd like to know if it is fatigue or something else that might cause it to break like this? I'm a little baffled because I can't see any beach marks or similar looking breaks from any books I have. It is 1045 material 1" diamter. It's load...

We broke 12 of these and the cracks did start at that high concentration. Juvinalls book suggested adjusting the mean stress down to account for the material over yield and that brought it just under the life range that was observed, of course it too warns against using this as anything more...

Yes - we are only testing the worst case loading as that is what we are interested in. What is bad about the part is the geometry/loading is a smaller surface is highly stressed (10 times the average), yet the rest of the large cross section is low stress. Perhaps that area just yields then the...

This is a forging. The peak stress does go over ultimate so plasiticity would happen - does that rule out any typical SN type calculations to predict life like I was looking at? We are going to cycle test a bunch of these and would like to have a calculated life going in. We have some initial...

Thanks for the link desertfox - I will have a read. Sounds like the rainflow method is what I need to do. I was using the Marin equation from Mark's to determine the endurance limit. It states the following about stress concentration reductions - this really confuses me for finite life...

I need to estimate the mean life of a cross section that has a very significant stress concentration (approx 10X average stress) The loading in the section cycles from 25 to 100% and I expect it to fail around 100,000 cycles so infinite life does not apply. What is the correct approach to...

How can the tensile fatigue limit be estimated in a 1.25 inch shaft that has been butt welded assuming it has been properly prepared and welded? I've looked in British Standard 7608 and a couple other machine design books and do not see any examples of that kind of connection in a shaft, only...

Sorry, I should explain better - the key here is that the original design had weld at the high stress area, and the press fit design removes the weld from the high stress zone increasing life. I suspect as you both point out it still falls short of a properly radiused one piece design but I am...

I need to design a hub/shaft on a roller that is subjected only to high bending stresses that can lead to fatigue failures of the shaft. Which design is best from a fatigue point of view? - machine a single piece hub and stub shaft with a large radius (actually a compound radius) in the...