Fatigue R-ratio corrections

[Golum]

I have a requirement to relate SN curves for a material that has been tested with a R-ratio of 0.1 to my specific requirements which involve r-ratio 0f around 0.8.

Does anyone know of a mathematical correction method that could be applied to the original data curve.

I am trying to avoid time consuming and costly fatigue testing.

 

[rb1957]

it depends on the material ... the equivalent fatigue stress, Seq, is often expressed as Smax*(1-R)^m. for typical aircraft materials 0.5<m<1. a reference for this is Mil Hdbk 5 ... still available online (for free).

 

[metengr]

No, I don’t believe there is any direct mathematical correction factor. Take a look at the concept behind the Goodman diagram. You might be able to develop one with your limited SN data and calculate stress amplitudes based on various sigma tensile mean stress values (as a function of R).