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Fatigue Strength Reduction Factor

Fatigue Strength Reduction Factor

Does anyone know how to determine what the fatigue strength reduction factor should be for a fatigue analysis of a part or assembly?  I have read the help files both in the tech support section of the ptc web site, and by going through the help files in Pro, and have found nothing helpful at all.  Does anyone have any sort of guideline for determining this factor?

RE: Fatigue Strength Reduction Factor


There is no single answer. Fatigue analysis is very complicated and there are some sophisticated analysis packages for studying just this type of problem (nCode for example). Some questions to consider: Are you performing strain-life or stress life predictions? Will you be applying a Neuber correction factor?

Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Fatigue Strength Reduction Factor

It should be 1 (no reduction) unless you have a good reason to change it.  This factor modifies the elastic portion of the strain life curve. (It's also used to modify S-n curves, but that's not applicable to Mechanica.)  Sometimes people use it as a correction factor to account for welds. The only way to know what value to use is if you have data to correlate to (e.g. test or warranty data).  To understand more about how this factor works and how strain life curves are estimated from UTS (using Baumel and Seeger's uniform material law), you'll need a good reference on fatigue theory.

- Dave

RE: Fatigue Strength Reduction Factor

If you have a notch then you can find Fatigue strength reducton factor Kf from
Kf = 1+ q(kt -1) where kt is stress concentration factor.
Notch sensitivity factor q can be found from Peterson's guide or by using q=1/(1 + a/r) where a is a constant and given by a= ((300/Su)^1.8)/1000
Su = Ultimate tensile strength of the mtrl.

Hope that helps.

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