Originally Posted by Dodge Guy
Yes, but what happens when you bend a piece of metal a few thousand times? think of a coat hanger!
Good question - just remember that airplanes ( and rotorcraft) have a great amount of engineering go into the certification process before they are certified for use.
That's one reason that wings are stressed to their breaking load. The wings are highly instrutmented and data recorded during the process. I'm not an enginner, but I know that the data recorded during the process is recorded and used to come to what the wings are capable of hand,ing.
In addition,aircraft are certified with a maximum service lift - that being the amount of flight hours and cycles that it can be flown before it has to taken out of service. This service life is often extended though data recorded during operation and with FAA approval,is extended.
Also certain components of an aircraft are listed as "lift limited parts" and these parts have to be replaced when they reach a certain point.
In addition,the aircrafts maintenance programs will contain requirements to keep the aircraft airworthy.
So in summary - aircraft are not ever just rolled out the factory door never to be seen again - the FAA,the manufacturer and the airline are constantly monitoring it.
These much more to this and if you wish to know more,PM me and I will provide reference to the regulations covering this.