The Fatigue Study
The Fatigue study () is a dedicated study step for fatigue evaluation. It processes a load cycle and evaluates a fatigue criterion specified in The Fatigue Interface. Before a Fatigue study can be calculated, a load cycle must be simulated. This is done in a Stationary, Time Dependent, or Frequency Domain study step, where the structural response to several loading events is analyzed. The following selection must be made in the Fatigue study step:
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In the Study Settings section, the setting for Include geometric nonlinearity should match the setting that was used in the simulation of the load cycle.
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In the Values of variables not solved for section, Settings should be User controlled.
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From the Method list, select Solution.
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From the Study list, select the study containing the load cycle to be used in the fatigue analysis.
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Depending on the type of study, you will get a different type of list to choose from; time steps, parameter values, or load cases. From the list, select the appropriate option for the load cycle definition. The option All evaluates fatigue using all load events of the study selected in the Study list. Use options From list or Manual to evaluate fatigue on only a part of a load history. With the option From list, select also the load cases, time steps, etc. that define the load cycle. Alternatively, you can use the option Manual to select also the load cases that define the load cycle. Here the load cases have an ordering number with the first load case being one, second load case being two and so on.
If large deformations, such as rigid body rotations, are modeled during the load cycle simulation, it is important to select Include geometric nonlinearity also in the Fatigue study step.
Fatigue analysis can also be performed using a Stationary study step. The evaluation options are then somewhat limited as compared to a Fatigue study step, and the following settings must be made for the study step:
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Make sure that only Fatigue interfaces are selected in the Physics and Variables Selection section.
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In the Values of variables not solved for section, Settings should be User controlled.
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From the Method list, select Solution.
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From the Study list, select the study containing the stress cycle to be used in the fatigue analysis.
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From the list of solution steps, select All. This means that you do not have the option to select only part of the load history for the fatigue analysis when using Stationary study step.
You can add as many Fatigue interfaces as needed and solve them in the same study.
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Applying Loads in the Structural Mechanics Module User’s Guide
In the COMSOL Multiphysics Reference Manual:
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Introduction to Solvers and Studies
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Fatigue and Stationary (studies)
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Using Load Cases
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Values of Dependent Variables
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Physics and Variables Selection