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Endurance limit


Dear Sirs,

I've built a material's strain-life properties via UML. Looking at the "Static/Endurance" tab of the material I've found 5E5 as the number of cycles at the endurance limit.

I've exported the above mentioned material to the strain-life database.

I've built a material's stress-life properties using a a synthetic SN curve from strain-life, based on the strain-life properties formerly defined. Looking at the "Points" tab of the SN properties, I've found 3.5E5 as the NE value.

Would you mind letting know why the number of cycles at the endurance limit for strain-life and NE for stress-life aren't the same? Which value must I adopt to assess the safety factor?

Thank you very much


Best regards

Riccardo Testi


Re: Endurance limiit

Siemens Genius Siemens Genius
Siemens Genius

Dear Riccardo,


the synthetic SN curve is a tool that tries to identify an SN curve in the range of lifetime defined by the selected fatigue parameters.

For the identification we first subdivide the range into a set of lifetimes. For each we backcalulate the plastic stress and strain (from the material data) and then we use an inverse Neuber rule to back-calulate the elastic stress amplitude. Through these points we fit a log-log-linear SN curve.


For the endurance limit we do the same, i.e. we back calculate the elastic stress amplitude value that corresponds to the (plastic stress/strain) value in the strain material data. The SN curve then defines the number of cycles at this stress value.


So it's the same stress amplitude (back calculated to elastic stresses) that is used for the safety factor analysis.


Hope this helps





Dr.Michael Hack
Business Product Line Manager Durability
Simulation and Testing Solutions

Re: Endurance limiit



thank you very much. 

Let me take the chance to please ask you to send me an e-mail message, because I've lost your address.

Thanks again.