Fatigue - Options
The Options tab of the Fatigue dialog box allows you to set options for the active fatigue study.
You can define studies with constant amplitude events or variable amplitude events. You cannot mix constant and variable amplitude events in a study.
The ASME Boiler and Pressure Vessel recommends this option. It is more conservative (predicts higher damage) than the No interaction option.
For studies with fatigue events referencing to multiple studies, the program calculates peak stresses based on the Random option even if you select the No interaction option.
Using a large number distorts the variable amplitude record and results in underestimating the damage. For accurate damage prediction, the highest alternating stress filtered out should not be larger than the equivalent endurance limit of any associated S-N curve.
These methods are used only if all associated S-N curves are based on fully reversible environment (zero mean). The software calculates the mean stress in addition to the alternating stress for each cycle and then it evaluates the corrected stress using the specified method. The correction becomes significant if the applied fatigue load cycles have large mean stresses compared to the stress range. If you define multiple S-N curves with different load ratios, the program interpolates between the curves linearly to account for mean stresses and no correction method is used. If you define one S-N curve with a stress ratio other than -1 for a material, the curve is used without correction for that material.
Fatigue strength reduction factor (Kf). Use this factor, between 0 and 1, to account for differences in test environment used to generate the S-N curve and the actual loading environment. The program divides the alternating stress by this factor before reading the corresponding number of cycles from the S-N curve. This is equivalent to reducing the number of cycles that cause failure at a certain alternating stress. Fatigue handbooks suggest numeric values for the fatigue strength reduction factor.
This value is only used for S-N curves for which the maximum number of cycles is less than the specified number.
What is Fatigue Analysis...