Hi @phi195014 . Welcome to the Inventor Nastran forum.
A life of 9E9 seconds is close to infinite life.
- Maybe the stress is too low to cause fatigue?
- Maybe the mesh is too coarse to calculate accurate stress?
- Maybe the geometry that causes a stress concentration is missing? Are there fillets between the different sections of the shaft?
Keep in mind that the legend (for fatigue solid life) always goes from red (minimum life) to blue (maximum life), whether the range is 9E9 to 1E10 or the range is 1 to 1E10. The color represents the values that are calculated. If the colors are wrong, the analysis is probably wrong. (Fatigue life is somewhat different since 1E10 is a very large value, and often the low value is between 1E4 and 1E6. Hopefully the design is good and most of the model will be in the blue end of the legend.)
Hope this helps.
John
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided, indicate the version of Inventor Nastran you are using.If the issue is related to a model, attach the model! See What files to provide when the model is needed.
