×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Corner Radii vs Notch Factor

Corner Radii vs Notch Factor

Corner Radii vs Notch Factor

(OP)
We have been working on a part that is shaped like a horse shoe with machined bosses on the ends. Where the bosses connect to the horse shoe we have a generous 3/16 radius. When we run the fea we are getting very high stress concentrations on the corner radii. When we modify the model and reduce them the stress levels drop significantly. Obviously there is a trade off between too small a radius and too large. Although I would not have expected too large to make that much difference. I would have thought a 3/16 radius would be better for fatigue and notch factor than a 1/16 radius but it sure doesn't look that way on the results. Any thoughts?

RE: Corner Radii vs Notch Factor

I agree with your intuition. However, are you applying forces or displacements as a load case?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Corner Radii vs Notch Factor

I'd check that you are getting sufficient mesh density with the smaller radius fillet. The problem with FEA is that it underestimates the stiffness the coarser the mesh. If you've used a coarser mesh for the smaller radius then you may get lower stresses.

corus

RE: Corner Radii vs Notch Factor

Generally, stresses will be higher for a smaller radius fillet, not lower. I agree with the first and last sentence by corus. And, see if you have stress averaging across elements turned on or off, to see if that's making your results seem unintuitive.

Just one comment on the second sentence by corus. I thought a coarser mesh overestimates stiffness, since it has fewer dofs (assuming typical shell or solid elements).

RE: Corner Radii vs Notch Factor

(OP)
We are appling forces to our model. I will check and see if we have refined the mesh in the higher stress areas.

Thanks

RE: Corner Radii vs Notch Factor

The problem of the re-entrant corner was examined by M. L. Williams (ASME JAM Vol 74, pp 526, 1957).  This work is based upon the assumption of a symmetric stress tensor.  If the FEM program is also based upon this assumption, then a stress singularity will be encountered, no matter the density of the mesh.  As radius of curvature is increased, some relief can be attained.  You can use Peterson's Stress Concentration book for estimates associated with radius curvature.

There have been some investigations as to determining the stress level when considering a mixed-boundary condition.   A group of Italians examined this problem and published their work : "Mathematical Theory of Elastic Equilibrium", by G. Grioli, 1962, Academic Press.  Finite stress levels have been predicted when the non-symmetry of the stress tensor is assumed.  Also, one should examine: "An Application of the Lagrangian Multiplier method to a Mixed Boundary Value Problem", by R. L. Citerley, J. Franklin Institute, Vol. 281, No. 4, April 1966 and the documentation associated with MSC Nastran's crack element.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources