In engineering applications the two main metallurgical features of importance to an alloy's fatigue performance are heat-treatment ad defect content.Heat-treatment and thermochemical or mechanical processing are used to generate favourable microstructures and residual stress distributions such as those found in 'surface-treated' components.The defect content,deriving from features of the alloy's processing,often determines the initial flaw size which subsequently grows by fatigue mechanisms.The materials engineer has to be aware of the features which control fatigue life,and then has to be able to exert metallurgical control to imporve properties.The use of fracture mechanics has made it possible to quantify the effects of such improvements.reducing the need for a 'such it and see' philosophy; this not only leads to a general speeding-up of the design process but should also eliminate the costly process of taking forward a design prototype-test stage and then finding that the component does not meet its fatigue life.
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