uniaxial fatigue testing - hollow cylinder 2

[zerow3]

Hi, I have been talking to someone about uniaxial (tension-tension) loading fatigue testing. They told me that hollow cylinder specimen is a lot harder to work with than solid cylinder specimen in terms of fatigue. I just want to know the reason for that. Is it because the cross section of the hollow cylinder will warp during testing (making it hard to control the load)?

 

[BobM3]

How would you grip it? I way to hold it and not have the grip influence the stress would be difficult.

 

[CoryPad]

If you are loading a hollow cylinder to the point that it has large deflection (warping), then you are testing in a very short cycle fatigue regime.

You can internally thread the hollow specimen and connect it to the load train using an externally threaded rod.

 

[zerow3]

Thanks

 

[BobM3]

Make sure that however you hold it, the holding mechanism doesn't influence the stresses in the area of interest. The mechanism must also be stronger than the area of interest (so the mechanism doesn't fail first).

Standard test specimens are necked down (to make them weaker than the connection area) and the gage length (area of interest) is located far from the holding mechanism (usually threaded or hydraulically clamped).