Metal fatigue
Metal fatigue is a process by which a metal component is weakened by repeated bending or other cyclic stress, often to the point of fracture. The stress can be quite small, but over a large number of cycles the effect can be catastrophic. The process starts with a microscopic crack, called the initiation site, which then widens with each subsequent movement.Metal fatigue was discovered in 1954 after three de Havilland Comet passenger jets had broken up in mid-air and crashed within a single year. Investigators from the Royal Aircraft Establishment at Farnborough in England told a public enquiry that the sharp corners around the plane's window openings acted as initiation sites for cracks. All aircraft windows were immediately redesigned with rounded corners.
