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strain life approach for notched elements

NJ-AlJabar's picture

Hi

I am trying to calculate the Ni-number of cycles for crack initiation from noched steel specimens under multiaxial loading.  I start with the finite element to calculate the max stress and max strain at the notch and end with these questions: 

Assuming the isotropic hardening elastic-perfectly plastic model, and monotonic load equal to the maximum fatigue test loading (S-max in the cyclic loading). 

What is the explanation that the maximum stress-strain are not at the notch but a few mm from the notch?

 Do we need to consider the maximum stress and strain in the model or that in the notch assuming it's the critical point for crack initiation?

calculated strain is so sensitive to FE mesh far than the stress. what kind of sensitivity needed to cover here and how to ensure stable model knowing that I have different notches case needed different models?

how much accurately is the approximation above of the fatigue loading as a monotonic load in this method.

this approximation was a strat to avoid the need of the fatigue properties. I am using 300-grade steel, I am scanning the fatigue properties in the literature and need iteration study to find out which is the best fit to my specimens. 

Do you think that using the analytical method would be more accurate or better to overcome the strain sensitivity for element mesh that effect fatigue life correspondingly? using the Ramberg-Osgood model and Mason-coffin model

 

Your comments and suggestions are highly appreciated 

 

Thanks

 

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