12 Oct Strain Based Fatigue Analysis
Strain based fatigue analysis is one of three approaches to assess fatigue (https://fea-solutions.co.uk/fatigue-analysis/). It is also called critical location approach, local stress-strain analysis, strain-life approach, or crack initiation analysis. A strain based fatigue analysis concerns itself with describing the initiation or beginning of a crack.
Strain based fatigue analysis should be performed in the following scenarios:
- Low cycle fatigue problems, for structures that have to withstand less than 10,000 cycles during their intended lifetime.
- Peak stresses at or above the Yield Strength, hence possible plasticity.
- Components where crack initiation is the important failure criterion.
- If locating where crack initiation may happen is needed.
- Mostly defect-free components.
Strain based fatigue analysis is conducted when the life of a structure depends on the stress amplitude of the local strains at the location where crack initiation will take place. It is based on comparing the fatigue life of a component that has a notch to the life of an unnotched specimen which has been cycled to the same strains as the component at the notch root.
Strain based fatigue analysis requires knowledge of the elastic-plastic strains in the component. If only linear-elastic stress analysis results are available, they have to be converted using Neuber’s Rule (https://fea-solutions.co.uk/neubers-rule/).
Strain based fatigue analysis requires the availability of E-N curves (https://fea-solutions.co.uk/e-n-curves/) for all materials of the structure, using the strain to life cycle relationship. As E-N curves are generated using a mean stress of 0, stress correction may have to be used.
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