Would you please explain why the Ochtaderal calculated stress is almost half of the Tresca?
the difference should be something around 10%, is not it?
Thanks

A little background may promote a useful response.
I would agree that octahedral shearing stress (as a measure of distortion energy) would be similar to, and a little smaller than, maximum shear stress.

Dave,
I meant the Tresca/Von mises option in configuration page,
I assume when selecting Tresca the calculated stress in "extended stress" would be ~10% higher than of Von mises selection,
but in my case (I just applied some displacements to an empty system to check deflection) Von mises stress is almost double the Tresca.
I assume I am confusing some concepts here...
thanks for the advice

Tresca theory uses maximum shear stress to predict failure and von Mises uses octahedral shearing stress as a predictor of failure (related to energy of distortion). And I would say, too, that the piping codes use maximum shearing stress. While we are talking of maximum shearing stress, the codes generally use their stress intensity as the measure.
(Maximum shearing stress is the radius of Mohr's Circle while stress intensity (S.I.) is the diameter of Mohr's Circle.)
While max. shear stress may be limited to 1/2 of yield, S.I. would limited by yield. S.I. is an easier (slide rule) calculation.
Note the title of the column when using Tresca - it says stress intensity - and that's twice Tresca.
You say "Von Mises stress is almost double the Tresca". I would say you have it backwards. The model I ran shows that extra "extended stress" column for Tresca is double the stress listed when von Mises is selected in the configuration file. But look at the column titles: Max Stress Intensity (for Tresca) and OCTAHEDRAL Stress (for von Mises).

Thanks Dave,