Determination of SN-curves

SN-curves should be determined from specimens made from the components directly, but you may also use SN-curves from tests with specimens made from the same material and with similar notches, or stress concentrators.

In Loading and local stresses, the concepts of load, nominal stress, and elastic notch stress have been introduced. You can conduct fatigue life analysis runs in the stress-life approach on either of these terms. But you have to be sure that the SN-curve you are using has been determined for the given terms.

If you are using the results of a finite element analysis for conducting a stress-life approach analysis, your SN-curve has to be determined for pseudo stresses like the material-based SN-curves in the Simcenter 3D materials. For more details, please refer to the description of Synthetic SN Curve from Strain Life in Creating durability material properties.

The characterization of fatigue endurance of engineering materials is usually made through uniaxial fatigue tests. The fatigue properties under such loading are readily available for most of the materials. In industry, often circumstances are encountered where the fatigue resistance of a component needs to be answered within a short time span; but fatigue data for the material is not available. The situation becomes even more difficult if the loading condition is multiaxial. Some multiaxial fatigue criteria require torsional fatigue data to determine all the parameters. To overcome the need to enter all the parameters, Bäumel and Seeger developed the Universal Slope Method. In this, it is required to select material and specify tensile strength for the same. For more details, please refer to the description of Universal Slope in Creating durability material properties.

Learn more

Defining SN-curves

Logarithmic nature of fatigue

How does the SN-curve definition via universal slope work?

Modifying factors of the SN-curve

Mean stress effects

Variable amplitude loading

Stress-life analysis in Specialist Durability

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