Trying to understand Von Mises a bit better

[DRW75]

A little while ago, we contracted a small local FEA company to give some assistance with a solid FEA analysis we were carrying out. The contractor had made the statement that the material will begin yielding upon reaching sqrt(3)*Fy or 1.73 * yield strength of the material under a generalized stress condition. He stated that this is the allowable von mises stress and he mentioned that it was analogous to the Pythagorean theorem in 3 dimensions comparing it to the von mises ellipse for planar stress expanded to 3d...

I know that whenever I've done FEA modeling, that I usually first look to the max von mises stress state as a measure of 'closeness' to the yield strength of the material as a first assessment of the stress state. I then usually carry on with hand calculations of allowable stresses for plate buckling given the geometry etc...

I have not been able to find the (3)^.5 * Fy anywhere... what is up? Does this have something to do with solids versus shell elements?

thanks for any insight

DRW

 

[johnhors]

Out of pure curiousity, why did you not go to your FEA division/experts in the first place?

 

[DRW75]

Fair comment - and funny story to boot. We put in a proposal for our guys to do the work, however the client decided to save 20% and go with the other guys...

 

[rb1957]

arh, so now you're in for a huge bun-fight ... you don't like the client's FEA, the client won't pay for more analysis (without suing someone's a$$), the client's FEA people are happy with their model and think you're overly conservative.

good luck