Fatigue limit
![Representative curves of applied stress vs number of cycles for steel (in blue and showing an endurance limit) and aluminium (in red and showing no such limit).](/Images/godic/202501/11/S-N_curves4503.PNG")
Fatigue limit, endurance limit, and fatigue strength are all expressions used to describe a property of materials: the amplitude (or range) of cyclic stress that can be applied to the material without causing fatigue failure. Ferrous alloys and titanium alloys have a distinct limit, an amplitude below which there appears to be no number of cycles that will cause failure. Other structural metals such as aluminium and copper, do not have a distinct limit and will eventually fail even from small stress amplitudes. In these cases, a number of cycles (usually 10) is chosen to represent the fatigue life of the material.