Mean stress effects

Another basic observation of metals subjected to fatigue loading is that the presence of tensile mean stress tends to shorten the fatigue life of materials and compressive mean stress tends to lengthen the fatigue life of materials as compared to the fully reversed (zero mean stress) loading case. The physical phenomenon is that the small cracks that are held open while in a tensile stress field grow faster that when they are held closed in a compressive stress field.

For the SN approach, these effects are taken into account by relating the stress amplitude at a non-zero mean stress level to an equivalent stress amplitude at a zero mean stress level based on equal fatigue lifetimes. Because of the scatter in fatigue test results for different materials and even for the same material, there have been several proposed methods for making the correction for mean stresses. In any method, however, the basic idea is to be able to use the original SN-curve in conjunction with the mean stress correction method to determine the fatigue life.

Options available in Specialist Durability to account for mean stress effects are the Goodman correction and multiple (3–5) segment corrections. Each method can be explained by examining a plot of mean stress versus stress amplitude.

Specialist Durability has provision to select different mean stress effects directly in the Mean Stress Correction durability simulation object.

In several application areas, SN-curves at different mean stress relations are required. This behavior can be estimated by various mean stress correction methods, but this is tedious.

Learn more

Mean stress correction for normal loads

Mean stress correction for shear loads

Mean stress correction for seam welds

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Mean stress effects, Simcenter 3D 2021.1 Series

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