Understanding Stress Concentration Factor in FEA for Stepped Shafts

[k.udhay]

Hi,
I want to understand how stress concentration factor or notch factor is considered in FEA method.
Lets assume a case of stepped shaft which has got the left end of the shaft fixed with rigid wall and the other end being pulled by an axial load.
In the case of conventional calculation method, stress is given by load over area. At the location of the step, the stress found is multiplied by a stress concentration or a notch factor based on some guideline.

If it is done using any 3D FEA package, the software, by its own, shows the highest stress at the step.

How does FEA find out a suitable stress concentration factor? Can someone help? Thanks.

 

[paisiello2]

I believe the stress concentration would come directly from the analysis itself.

 

[k.udhay]

Yeah I understand that... But what is the actual mechanism behind calculating it? I mean what portion of the matrices of FEA formula calculates it?

 

[paisiello2]

I think you would do just what you originally described: calculate by hand the average stress at the section of interest, then compare it to the value from the FEM.