Material fatigue has famously led to several major mechanical disasters dating back to the Versailles train disaster in 1842 to two de Havilland Comet passenger jets that broke up in mid-air and crashed within a few months of each other in 1954, and a Norwegian semi-submersible drilling oil rig that capsized while working in the Ekofisk oil field in 1980 killing 123 people. The list goes on, some of them making headlines because people were killed in the incidents. But, material fatigue occurs in all mechanical equipment and is one of the areas design engineers have to focus on when developing new products. Fatigue occurs when a material is subjected to repeated loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form on the surface. Eventually a crack will reach a critical size, and the structure will suddenly fracture, usually leading to instantaneous and catastrophic failure.
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