Stress-Life
Use the Stress-Life node to calculate fatigue life based on a fatigue life curve that relates load cycle stress amplitude to life. The Stress-Life feature can be applied to domains, boundaries, edges, or points.
See Stress-Life Models for theory information.
Model Input
See Common Physics Interface and Feature Settings and Nodes for information about the Model Input.
Solution Field
From the Physics interface list select the physics interface where the load cycle was simulated.
If you select a Shell interface, also select a Through-thickness location — From shell interface, Top, or Bottom. This determines from which position in the shell stresses or strains are taken for fatigue evaluation. When you select From shell interface, the local z-coordinate given in the Default Through-thickness Result Location section in the settings for the Shell interface is used.
When you select the physics interface where the load cycle was simulated, the integration order of this interface will be automatically used to define shape functions used by the fatigue features.
Fatigue Model Selection
Select a Fatigue limit — S-N curve, Basquin, or Approximate S-N curve. This specifies the fatigue model to be evaluated. See S-N Curve Model, Basquin Model, and Approximate S-N Curve Model for details about these models.
Select how the stress is evaluated from the Stress σ list — Principal stress, Signed von Mises (principal), or Signed von Mises (hydrostatic).
When using S-N curve, also select a Modification — None or Stress factor. This determines whether a modification should be applied to the S-N curve or not.
Fatigue Model Parameters
S-N Curve
When S-N curve is selected as the Fatigue limit select a function from the list for the S-N curve fSN(N). The list contains all functions defined under Global Definitions. The Interpolation and Analytic functions are recommended for use with this model. If Stress factor is also chosen as the Modification then enter a value for k. The default is 1. The stress factor can be used for shifting the S-N curve. Typically, a value k<1 is used to compensate for effects like surface roughness.
Basquin
When Basquin is selected as the Fatigue limit, the material parameters Fatigue strength coefficient σf’ and Fatigue strength exponent b by default take values From material. For User defined specify other values in the fields as needed.
Approximate S-N Curve
When Approximate S-N curve is selected as the Fatigue limit, the material parameters Transition stress St, Transition life Nt, Endurance limit Se and Endurance life Ne by default take values From material. For User defined specify other values in the fields as needed.
Mean Stress Correction
Fatigue life is generally affected by the mean stress. This mean stress is defined as the average of the minimum and maximum values of stress during a load cycle.
Select a Method — None, Gerber, Goodman, or Soderberg. With None, the mean stress does not influence the fatigue life prediction. When you select Gerber or Goodman as mean stress correction method, you should also specify an ultimate tensile strength σu. When you select the Soderberg method, you should also specify a yield stress σys.
Evaluation Settings
When S-N curve or Basquin is selected as the Fatigue limit, enter a value or expression for the Cycle cutoff Ncut. The default is 1e10. This is the upper limit to the model prediction of the number of cycles to failure and is assigned as solution when the stress range is very small.