Definition and symbolization of fatigue terms
Fatigue of ferrous alloys - Definitions and diagrams

The stress taken into account during fatigue testing is a nominal stress. It is calculated in relation to the net cross-section of the part or specimen under consideration, using the usual resistance of materials (RDM) formulas for the elastic domain. It does not take into account stress concentration due to notches or other causes. Normal stress is expressed as $\sigma$ , and shear (or torsional) stress as $\tau$ .