There is an entire field of study behind this...
But to answer your question briefly, you have to do a fatigue calculation. The result of that calculation will give you a value that must be below the S/N curve for the material. I suggest a book. Maybe this one: http://www.amazon.com/Shigleys-Mechanical-Engineering-Design-Mcgraw-Hill/dp/0073312606
Edit: I should also note that Solidworks Simulation Premium comes with a fatigue package that walks you through this. I use ALGOR, not Solidworks Simulation, but we hae the fatigue package, and it makes it pretty straight forward.
This kind of work would normally be undertaken by a suitable qualified mechanical engineer. The software is not a substitute for experience and knowledge in this field.
Just be aware,
You have to consider the loading Kf (multiplication factor due the loading type - bending, torsion). This will directly affect your FATIGUE results.
To analyse FATIGUe you'd have to run an FATIGUE analysis in SolidWorks using as event your available analysis! This will compare your loading cycles, stress data and results, and materia S-N curve!