The Underlying Stress Analysis
The Fatigue Module provides the ability to postprocess stress and strain results, which have been computed using one of these physics interfaces:
•
Solid Mechanics
•
Shell
•
Plate
•
Membrane
•
Multibody Dynamics
•
Solid Rotor
Since fatigue is caused by the variation in stress and strain, it is necessary to have at least two sets of results from a stress analysis available for postprocessing. If the unloaded state is a part of the load history, then the trivial stress free state must be computed as well. Fatigue analysis can be done on results from the following types of studies:
•
A Stationary study with at least two load cases
•
A Stationary study using the parametric solver, which has at least two parameter values
•
A Time Dependent study, either direct or modal, having results at least in two time instances
•
A Frequency Domain study, either direct or modal.
In all cases, it is one full load cycle that is used for fatigue analysis. Often, several load cycles need to be computed before a steady state is reached. From that point, each consecutive cycle repeats the stress-strain response and such a cycle is representative for the fatigue life.
If the Fatigue interface has already been added before computing the stresses, then the physics interface should be disabled in the Physics and Variables Selection section of the study step for the stress analysis.
For an example about how to set up an analysis having a shake-down to a stable cycle, see Elastoplastic Low-Cycle Fatigue Analysis of Cylinder with a Hole: Application Library path Fatigue_Module/Strain_Based/cylinder_with_hole_plastic.
•
The Fatigue Interface
•
Theory for the Fatigue Interface
•
Applying Loads in the Structural Mechanics Module User’s Guide
In the COMSOL Multiphysics Reference Manual:
•
Using Load Cases
•
Studies and Solvers
•
Physics and Variables Selection