Metal fatigue

Metal fatigue isprocess by whichmetal componentweakened by repeated bending or other cyclic stress, often topointfracture. The stress can be quite small, but overlarge numbercycleseffect can be catastrophic. The process starts withmicroscopic crack, calledinitiation site, which then widenseach subsequent movement.

Metal fatigue came strongly tonoticeaircraft engineers1954 after three de Havilland Comet passenger jets had broken upmid-aircrashed withinsingle year. Investigators fromRoyal Aircraft Establishment at FarnboroughEngland toldpublic enquiry thatsharp corners aroundplane's window openings acted as initiation sitescracks. All aircraft windows were immediately redesignedrounded corners.