Endurance Limit (Se)
Definition - What does Endurance Limit (Se) mean?
Endurance limit (Se) is the stress level below which a specimen can withstand cyclic stress indefinitely without exhibiting fatigue failure. Rigid, elastic, low damping materials such as thermosetting plastics and some crystalline thermoplastics do not exhibit an endurance limit. On the other hand, steel exhibits a high endurance limit.
If the tensile stress never exceeds a minimum level in most materials, fatigue failure does not occur. Therefore no crack or corrosion occurs.
Endurance limit is also known as fatigue limit.
Corrosionpedia explains Endurance Limit (Se)
In fatigue testing, the maximum stress which can be applied to a material for an infinite number of stress cycles without resulting in failure of the material is applied and measured. Some authors use endurance limit for the stress below which failure never occurs, even for an indefinite number of loading cycles, as in the case of steel. Below a certain stress level, the steel alloy never fails due to cyclic loading alone.
Typical values of the endurance limit for steels are 1/2 the ultimate tensile strength. For iron, aluminum and copper alloys, Se is typically 0.4 times the ultimate tensile strength.
The endurance limit is due to interstitial elements, such as carbon or nitrogen in iron, which pin dislocations. This prevents the slip mechanism that leads to the formation of microcracks. Care must be taken when using the endurance limit since it can be reduced due to:
- Periodic overloads (which unpin dislocations)
- Corrosive environments (due to fatigue corrosion interaction)
- High temperatures (which mobilize dislocations)
The effect of periodic overloads relates to smooth specimens. Notched components may have completely different behavior, due to the residual stresses set up by overloads. Most nonferrous alloys have no endurance limit.