[1] The safe-life design technique is employed in critical systems which are either very difficult to repair or whose failure may cause severe damage to life and property.
Today, the curve is still consequential by experimentally testing laboratory specimens at many continuous cyclic load levels, and detecting the number of cycles to failure (Oja 2013).
This did not matter on an interim airframe designed for operations in the calm upper air, but at around 500 ft the loads and stresses were more volatile.
[2] In the current generation of Army helicopters, such as the UH-60 Black Hawk, composite materials make up as great as 17 percent of the airframe and rotor weight (Reddick).
Along with this application, it is the essential obligation that sound, definitive design criteria be industrialized in order that the composite structures have high fatigue lives for economy of ownership and good damage tolerance for flight safety.