Phenomenological description of the fatigue strength

In the previous sections, we discussed the failure mechanisms of the different material classes. Using the example of metals, we discussed in some detail how cracks may be initiated in a component and how they propagate, until final fracture occurs. To safely design components, we need tools to describe and assert their life time. Two different approaches can be used  

However, even if no cracks are initially present in the component, it is not exempt from fatigue failure. Microcracks may, for example, form at the surface of the component, propagate, and cause ultimate failure as described in section 10.2 for the case of metals. Thus, we also need methods to assert the life time of uncracked components. 

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Phenomenological description of the fatigue strength Table 10.2. Approximate fatigue limit of some metals... 

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