18 months in service – the time it took for a window on the Comet aircraft to fail due to #fatigue #cracking in its corner (reconstructed window image below). The science of metal cracking had not been developed at that time. It was tragic.
It’s mainly due to fatigue damage in metals that the oblique windows on newer aircraft have their shape. Imagine that an airplane is like a balloon in the air, which inflates and deflates each time it is in the lower part of the atmosphere and then moves to a higher part of the atmosphere (and vice versa). This beh #design avior was simulated in 1955 in a water tank (picture of the black tank below). There was no other technique to test it.
Nowadays we use #FEA to check high-stress points for a fraction of the cost of full-scale model testing.