Fatigue Plots
After you perform a fatigue analysis, you can plot life, damage and factor of safety plots for the model.
Suppose you run a static analysis and define a fatigue study with the static analysis being the only event that occurs N times. Consider the S-N curve for the material as shown:
The program, based on the loading ratio, determines a corrected alternating stress from the static study's stress value for each node.
In the graph above, the green dot represents the alternating stress (Y coordinate) and number of cycles for which the event occurs (X coordinate) for one node. One out of three possible outcomes can occur for each node:
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The dot lies above the curve. Fatigue failure is predicted at that location.
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The dot lies below the curve. Fatigue failure does not occur at that location.
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The dot lies outside the range of S-N curve. The highest corrected alternating stress in the model must be within the stress range of the S-N curve. Also, the number of cycles (N) should be within the cycle range of the S-N curve. Otherwise, instead of an intersection point, the program uses the S-N curve's end point.
Note: To simplify the discussion, we did not consider the scenarios where multiple S-N curves for a material and several events are defined.
See the table for meaning of Life, Damage and Factor of Safety
Related Topics
Mean Stress Correction
S-N Curve
Theory of Cumulative Damage
Performing Fatigue Analysis