Hello chiheb ben abdallah,
'Fatigue Tool' helps in getting the results regarding the life, damage, safety factor, etc.
You can also use a DesignLife Add-on to make the capacities of nCode DesignLife product in Mechanical.
You can also follow the sub-modeling approach to address the problem efficiently. (Performing Submodeling in Ansys Mechanical — Lesson 6 - ANSYS Innovation Courses)
For more information on dynamic analyses please check out (Random Vibration Analysis in Ansys Mechanical | Ansys Courses, Mode Superposition Transient Analysis | Ansys Courses)
The following references will help you to proceed with the details and steps to address the fatigue analysis. Also please find an example problem for the same.
Fatigue Tool (Group) (ansys.com)
Fatigue Results (ansys.com)
Chapter 1: DesignLife Add-on (ansys.com)
Chapter 60: Accelerated Thermomechanical Fatigue Analysis of Thermal-Barrier Coatings (ansys.com)
Hope this helps!