Definitions, objectives and precautions
Fatigue testing – High Cycle Fatigue domain

Experience shows that, if the amplitude and number of repeated (cyclic) stresses are sufficient, the result is progressive cracking followed by fatigue failure. Fatigue fracture generally occurs suddenly, without precursory elongation, and the fracture presents two distinct zones: a smooth zone, which is the fatigue crack itself, on which successive stop lines can generally be observed as it propagates, and a pull-out zone, which corresponds to the final instantaneous fracture. This failure can occur at applied stresses well below the static failure load, and even below the apparent yield strength.

While fatigue is the accepted term for the cause of in-service failure, endurance is the ability to resist fatigue.