Estimate Shear Fatigue Strength from data in MMPDS

[DrDave88]

MMPDS-01 has S/N curve for Inconel 718. I believe that this is axially loaded. I need to know (or estimate) the shear S/N curve. Does anyone know of a good method to estimate shear fatigue strength based upon normal fatigue strength.

Also, is stress ratio defined as mean stress / alternating stress or max stress / min stress or something else?

Thanks for your help.

 

[salmon2]

If you don't have S/N curve specific for shear, I would transform your shear stress to the equivalent tensile stress as in a axial load case by using either von Mises or Tresca criteria. Then you can use the S/N curve you got. Tresca will be slightly more conservative than von Mises.

Fatigue stress ratio is defined to be (min stress) / (max stress).

 

[metengr]

http://www.egr.msu.edu/classes/me471/thompson/handout/class13_2005SFatigue.pdf