If the response of the system is harmonic in nature, not random, the application uses the maximum stress response for a either a single target frequency or sweeping multiple target frequencies, along with the duration of exposure to calculate the fatigue effects.
There are three different options available for Harmonic fatigue calculations:
Single Frequency: The stress at the defined Frequency is considered for the fatigue analysis. This stress is used along with the defined SN Curve to interpolate for the fatigue life.
Multiple Frequencies: You can manually specify frequency values and their corresponding Exposure Durations. Stresses at each of these distinct frequencies are considered for the fatigue analysis and fatigue damage is accumulated.
Sine Sweep: You can manually specify frequency values and their corresponding Scale Factors. A Sine Sweep analysis is performed from the lowest to highest frequency value in steps of 0.5 Hz using the Sweep Rate (to account for total exposure time) and the appropriate amplitude scaling at each step. The fatigue damage is accumulated.
Note: In the Harmonic Response fatigue analysis, the:
S-N Curve Table will take precedence and it will be used if available. If the table is not present, then the solver will use either the Linear/Bilinear parameters, whichever is present, to construct a pseudo curve and that will be used for the interpolation.
Stress is always assumed to be fully reversed.