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The Workbench Fatigue Module uses Neuber's rule to convert elastically, calculated stress, and calculated strain to total stress and strain. According to Neuber`s rule, the total strain (used to access the strain-life curve) is the nominal elastic strain multiplied by the ratio of the nominal elastic stress to the local stress. The nominal elastic stress and strain are the calculated values from the ANSYS linear-elastic analysis.
The Fatigue Module calculates the local stress using the nominal elastic strain and the elastic-plastic stress strain life curve developed from the inputted material parameters. If the elastically-calculated strain exceeds yield, the local stress will then be less than the nominal elastic stress, and the total strain will be greater than the nominal elastic strain. The effect of Neuber's rule is more pronounced for low-cycle fatigue. For high-cycle fatigue, the total stress is almost all elastic, so Neuber's rule has a minimal effect. You can assess the amount of plastic stress and placing a hystersis object in the Fatigue Tool.
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