Safe-Life Structure
Not all structure need exhibit crack initiation to ensure safety of operation. Some structures operate under the safe-life design principle, where an extremely low level of risk is accepted through a combination of testing and analysis that the part will ever form a detectable crack due to fatigue during the service life of the part. This is achieved through a significant reduction of stresses below the typical fatigue capability of the part. Safe-life structures are employed when the cost or infeasibility of inspections outweighs the weight penalty and development costs associated with safe-life structures. An example of a safe-life component is the helicopter rotor blade. Due to the extremely large numbers of cycles endured by the rotating component, an undetectable crack may grow to a critical length in a single flight and before the aircraft lands, result in a catastrophic failure that regular maintenance could not have prevented.
Read more about this topic: Damage Tolerance
Famous quotes containing the word structure:
“When a house is tottering to its fall,
The strain lies heaviest on the weakest part,
One tiny crack throughout the structure spreads,
And its own weight soon brings it toppling down.”
—Ovid (Publius Ovidius Naso)