Daniel Shaw
Ansys Employee

Ansys is not a testing company.  I recommend that you discuss this issue with someone more familiar with fatigue testing.  If the SN curve is developed from fatigue test data, typically an mean curve through the data is developed and used, but some industries require using the 1- or even 2-sigma curve from the test data. If the SN curve was developed from test data, it not clear why the UTS would affect it.  The SN curve is just a statistical fit to the actual test data.  SN curves can be estimated from physical properties (UTS, slope, transition points, etc.).  If SN curve is estimated from physical properties, then it would be affected by the UTS value.