Where in a steel member is there no fatigue observed?

The endurance limit refers to the value of stress below which a material can withstand an infinite number of loading cycles without experiencing fatigue failure. This is particularly significant in applications involving repeated or cyclic loading, such as steel structures subjected to traffic loads, wind loads, or vibrations.

When the stress level is maintained at or below the endurance limit, the steel member experiences negligible or no fatigue damage over time, making it a safe and reliable choice for structural applications. This principle is crucial in designing steel components to ensure they can operate effectively under expected service conditions without deteriorating over time due to fatigue.

The other scenarios do not guarantee the absence of fatigue. For instance, being above the yield point or under the ultimate strength exposes a member to conditions where plastic deformation can occur or high stress levels may lead to eventual fatigue failure. In the elastic region, while materials do not experience permanent deformation, repeated loading can still induce fatigue if the loads are high enough, particularly if they exceed the endurance limit. Therefore, the endurance limit is specifically the threshold beyond which fatigue is not observed.