The fatigue notch factor

For notched components the use of the elastic stress concentration factor Kt alone may lead to too conservative results. As shown in the figure below, the difference in fatigue life between the notched and un-notched component gets smaller as the applied loads get higher. This is due to the fact that locally plastic deformations will occur that lower the local stresses. To reflect this phenomenon the fatigue notch factor is introduced. The fatigue notch factor is the ratio of fatigue strength of a specimen with no stress concentration to fatigue strength of a specimen with a notch. The fatigue notch factor is usually lower than the theoretical stress concentration factor because of stress relief due to plastic deformation.

It may be extended to the finite life region by:

It may also be called in some literature. Keep in mind that Kf depends on the number of sustainable cycles to failure. In the following, we will call the value at endurance limit Kf if not stated differently.

Property	Symbol	Formulae
Fatigue notch factor	Kf

Comparison Between the Fatigue Behavior of an Unnotched Component Compared to a Notched Component

The fatigue notch factor is used as a basis for taking into account a range of non-local and surface effects. For more details, please refer to How to account for size effects in the topic Examples for size effects.

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The fatigue notch factor, Simcenter 3D 2021.1 Series

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