Possible sources of error in fatigue testing?

[VelocityGirl]

Hey guys. I'm currently finishing up a lab report on fatigue testing and I was wondering if anyone has any ideas on sources of experimental error? I'm assuming it'll probably come down to calibration but any insights would be appreciated.

 

Cheers!

[Cap'n Refsmmat]

That all depends on how you performed the fatigue testing, and what instruments you used.

[baxtrom]

Hey guys. I'm currently finishing up a lab report on fatigue testing and I was wondering if anyone has any ideas on sources of experimental error? I'm assuming it'll probably come down to calibration but any insights would be appreciated.

 

Cheers!

 

 

Fatigue testing typically involves applying a known stress loading until the specimen breaks after N cycles. Counting the cycles would'nt present much of a problem, however knowing exactly the stress level could be. Presumably, the stress level in a test involving for example rotation bending is easier to keep track of than the membrane stress in a pure axial test. Rotation bending tests are typically performed applying a known static load to the end of a rotating shaft.

 

 

Knowing the RPM of the shaft gives you the cycles. An axial fatigue test requires a more complicated setup I guess, allthough I don't have experience from fatigue testing, just from fatigue calculation..

 

Good luck with your report!

[Enthalpy]

Fatigue is non-reproductible is this will overshadow the experimental errors.

 

The materials' fatigue behaviour depends heavily on the skin's chemical and thermal treatment (nitride, carbide, quenching), which is imprecisely known, and on the skin's roughness. Especially, final grinding parallel to the stress (axially in the drawing above) improves a lot.

 

I'd suggest to document at least the superficial hardness and the roughness.

[studiot]

Fatigue data is statistical in nature. By that I mean you have to repeat the measurements many times to get a good S-N curve.

 

This is fundamentally important, but this is your project so what do you think this means?