The three stages of fatigue failure in a component are: Crack Initiation Crack Propagation Rapid Fracture Crack initiation, sometimes called crack formation, occurs in areas of concentrated stress on the surface of a component, and in areas where surface defects can be found. As surface defects...
Rainflow Cycle counting is a method to determine the number of fatigue cycles in a load time history. For a load of constant amplitude, it is easy to calculate the fatigue due to cumulative damage (https://fea-solutions.co.uk/cumulative-fatigue-damage/) using the S-N curve (https://fea-solutions.co.uk/s-n-curves/) and Miner's Rule. In...
A fatigue load cycle is made of two components: Mean Stress – The average stress throughout the cycle. Alternating stress – This is the difference between the mean stress and the peak (minimum or maximum) stress in the cycle. A fatigue analysis is conducted assuming that...
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A fatigue analysis (https://fea-solutions.co.uk/fatigue-analysis/) is straight forward if the structure is subjected to just one load case, which can consist of several loads, but with the loading and unloading acting simultaneous for all of them. It gets more complicated if there is just one load case,...
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...
Stress based fatigue analysis is one of three approaches to assess fatigue (https://fea-solutions.co.uk/fatigue-analysis/). It is sometimes referred to as the stress-life approach. A stress based fatigue analysis should be performed in the following scenarios: High cycle fatigue problems, for structures that have to withstand more than...
The endurance limit, sometimes called the fatigue limit, is the stress level below which the material will never fail due to fatigue, no matter the number of load cycles it is subject to. Ferrous alloys (such as steel) and titanium alloys have a definite endurance limit....
Besides the surface factor (https://fea-solutions.co.uk/surface-factor/), the stress concentration factor or notch sensitivity is another key modification that could reduce the endurance limit. The stress concentration factor is used to account for the effect of irregularities or discontinuities such as holes, grooves or notches that are not...
The endurance limit (https://fea-solutions.co.uk/s-n-curves/) of a material is either obtained from a fatigue test (https://fea-solutions.co.uk/static-test-vs-fatigue-test/) or estimated using the ultimate tensile strength of the material if the test data is not available. Such an endurance limit does however not take into account the effects of...