Design Strategies
There are different strategies that can be used when designing components subjected to alternating loads. For example:
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Design for an infinite lifetime by keeping the stresses sufficiently low. “Infinite” should be interpreted as much longer than the service life of the component. The method can also be used for a material without a fatigue limit. This is the most common approach and it is preferred as long as it is not unfeasible.
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Design for a fixed life (with sufficiently large factor of safety), after which the component is replaced.
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Create a damage tolerant design where the structure is inspected for cracks at regular intervals. In this case, it is the growth rate of macroscopic cracks that sets the limit of the inspection interval, and fracture mechanics methods must be used in the analysis.