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Fatigue Analysis Certainty of Survival

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Dear all,


What is the equation for dropping test data in a fatigue analysis with standard deviation (Se) and certainty of survival (SurvCert). In our understanding this equation should be:


LogS(new) = LogS(data) + Se*Cert


Where Cert=-1 for 84% SurvCert, -2 for 97.7% SurvCert  and -3 for 99.9% SurvCert


However the results we are getting are not what expected, and we can't validate what we see from the results.

Also, in the manual we cannot find the used equation for dropping the data.


We would appreciate any help on the matter, or if someone can confirm what optistruct is using (what equation) to drop the data.


Many thanks.

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Hi @inasiopo


Can you share the results of analysis and reference so that we can have a look and check where the problem is?

Please use the file transfer link in my signature to share the model file



As per the OptiStruct document SVERCERT ranges from 0 to 1.

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