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'''Metal fatigue''' is caused by repeated cycling of a load on, or against, a piece of [[metal]].  Such fatigue is characterized by progressive localized damage due to fluctuating stresses and strains on the material.  Metal fatigue cracks initiate and propagate along an axis where the strain is most severe. 
   
The process of metal fatigue consists of three stages:

*Initial cracking
*Progressive crack growth across the material
*Final, sudden (if load remains in place) fracture of the remaining section