While the concept of metal fatigue was not completely unknown in the 1800s by the scientific and engineering communities, it was a concept that was neither thoroughly observed nor investigated until the twentieth century. Metal fatigue is the term used to describe the weakened condition of metal parts used in machinery, aircraft, vehicles, etc. after extensive continuous use. The need for information on metal fatigue became increasingly important as aviation technology advanced. The metal parts of early aircraft sustained heavy damages--such as snapped-off wings and shattered propellers--now attributable to metal fatigue.

In 1914 Ambrose Swasey (1846-1937), a machine-tool builder living in Cleveland, Ohio, founded the Engineering Foundation to research metal fatigue common to aircraft specifically and found in other machinery as well. Hoping to determine stress limits, the foundation conducted thousands of tests and experiments on steel, aluminum, copper, bronze, brass, and all other metals used in...