Consider constant load in fatigue analysis

It is often asked how to apply a constant load to a fatigue study (continuously acting on a structurally non-changing load, rather than generating alternating stress changes or dynamic loads)
The figure below shows the alternating stress and the average stress, both of which are important for the life of the material.


Usually the input data for a fatigue study is the stress amplitude, but the picture below shows that the average stress is also very important for the life of the material. The higher the average stress, the shorter the life expectancy.


Although the constant load does not change but contributes a lot to the average stress, it is also important to consider in the fatigue analysis. So what should I do?
Alternating load analysis
For general fatigue analysis, the load defines the maximum stress, Smax is calculated by static calculations, and then Smin is defined by the load ratio (R = Smin/Smax).


E.g:
• Select "based on 0" to indicate that Smax is from a static study, but Smin=0
• Select “Complete Inversion” to indicate Smin=-Smax
• Selecting “Load Ratio” means that any ratio of Smin to Smax can be customized. The appropriate static example can be selected by the fatigue analysis setting to apply the alternating stress value using the load ratio, and then the life or damage cloud map can be obtained by comparison with the SN curve.

Constant Load Analysis Constant load values ​​are fixed without alternating factors, which means they have a non-zero mean stress. As discussed above, this value has an effect on the life of the structure and must be considered in the analysis. This part of the value cannot be applied directly in SolidWorks Simulation.
This part of the impact can be considered by using the "Find Cycle Peak" method. This method calculates the damage by selecting the peaks under multiple loads, so first create a static study with peaks.

Therefore, if all one alternating stress and one constant load, two examples need to be established:
• Static Study 1 contains Smax and constant load • Static Study 2 contains Smin and constant load as shown below. Instead of defining Smax and load ratio definition Smin by an example, two separate examples are used, one containing Smax. One contains Smin and both studies contain a constant load.


Finally, in the fatigue study, the two examples are used to calculate by the method of “finding the peak of the period”. This method uses Smax+constant load and Smin+constant load to calculate the fatigue life.

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