Use the Vibration Fatigue node to define the solution field, load history definition and fatigue evaluation parameters for vibration fatigue evaluation. The Vibration Fatigue feature can be applied to domains, boundaries, edges, or points.

See Common Physics Interface and Feature Settings and Nodes for information about the Model Input.

From the Physics interface list select the physics interface where the stress response to the forced vibration is 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.

To define how the frequency history is prescribed, select the Frequency history — Time duration, Number of cycles, Linear frequency sweep or Logarithmic frequency sweep.

If Time duration is selected, also specify Time history. The Time history entries define the duration of the excitation at each excitation frequency. The number of excitation times in the table must correspond to the number of excitation frequencies selected in the settings for the Fatigue or Stationary study step.

If Number of cycles is selected, also specify Cycle history. The Cycle history entries define number of cycles experienced at each excitation frequency. The number of cycle entries in the table must correspond to the number of excitation frequencies selected in the settings for the Fatigue or Stationary study step.

If Linear frequency sweep is selected, also specify the Rate of change, C, which is the rate of frequency change per unit time

If Logarithmic frequency sweep is selected, also specify the Logarithmic rate of change, Cl, which is the frequency doubling rate

Under Direction select how the stress is evaluated from the Stress σ list — Directional stress, or Signed von Mises.

If Directional stress is used, also select how the direction is evaluated from the Direction definition list — Direction vector, or a predefined coordinate system. The list contains all coordinates systems that have been defined under the Definitions node in the model tree, except those of the Scaling System type.

If Direction vector is selected, also define the Direction vector, nσ. The default direction is along the X-axis. The normal stress in this direction is used for the fatigue evaluation.

If a predefined coordinate system is selected, also specify its Direction axis — First, Second, or Third. The normal stress along this axis is used for the fatigue evaluation.

Under Material select the S-N curve σa(R,N) from the list. It contains all functions defined under Global Definitions. Also enter a value for the Cycle cutoff Ncut. The default is 1010. Based on the S-N curve, the Cycle cutoff implicitly provides the highest stress value that gives no contribution to the fatigue usage factor. From the evaluation point of view this stress can be seen as the endurance limit.