How are notch or stress concentration factors in FEA of shaft strength considered?
How are notch or stress concentration factors in FEA of shaft strength considered?
(OP)
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.(pic. attached)

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.
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.(pic. attached)
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.





RE: How are notch or stress concentration factors in FEA of shaft strength considered?
FEA is used when your data is out of the typical range used for Peterson's handbook etc. However, without modelling any transition radius, whatever your program spits out is useless at the 90deg step.
If you use a small radius I recommend using strain criteria, because you will most likely have local yielding. Obviously try to incorporate as large of a radius as possible if you are concerned about life of the part. Unless you have a fit, and then you probably need to use FEA to design an undercut with a suitable radius.
RE: How are notch or stress concentration factors in FEA of shaft strength considered?
you can mesh the crap out of the concentration, and run non-linear (as the peak stress is probably plastic).
if a purely static problem, you can say that the highly localised yielding has a negligible reduction on gross section allowable load.
you can run you FEA and extract gross section stresses, then use a Kt solution to determine the peak stress 9though this is likely plastic).
another day in paradise, or is paradise one day closer ?
RE: How are notch or stress concentration factors in FEA of shaft strength considered?
RE: How are notch or stress concentration factors in FEA of shaft strength considered?
it sounds like you need to review a text on FEA method ...
another day in paradise, or is paradise one day closer ?
RE: How are notch or stress concentration factors in FEA of shaft strength considered?
If you had a plate with a hole in it, you could use FEM to find the stress concentration factor. That geometry doesn't have a discontinuity, so repeatedly refining the mesh would give results that asymptotically approach the true stress. In general, a brute force way to determine if you are getting good results from any finite element model is to keep refining the mesh until the critcal stresses don't change very much.
People forget that FEM was originally developed to determine load distribution between multiple load paths. Engineers then plugged those load results into closed-form equations for various joints to do sizing, life prediction, etc. Nowadays people (especially managers) expect FEM to do everything and overlook its limitations.
RE: How are notch or stress concentration factors in FEA of shaft strength considered?
another day in paradise, or is paradise one day closer ?