Morning to All

We are designing a pressure vessel according ASME III, Division 1.

I'm checking the possibility of performing a plastic analysis using software ANSYS 13.0 but we have a concern: may I use this software?

In effect, at NB-3212, the Code specify that the teory of failure used is the maximum shear stress theory (Guest-Tresca), while ANSYS is based on Von Mises theory.

Thank you in advance for any suggestion.

Fabio

I have not used Ansys but it seems that you can choose whether you want to use Tresca or Von Mises:

http://ansys.net/ansys/tips_sheldon/STI03_Yield_an...

You can choose either ANSYS or other valid finite element software... If you want to see the result contours, the default form is shown base on Von Mises, but you can choose your criteria,,,,and don't forget to normalized the stress result through the thickness.

Actually you can't choose tresca as failure criterion in ansys. By the way, NB-3212 is intended to use with stress classification method and linear analysis.

Rules for the plastic analysis are given at NB-3228 and the paragraph doesn't force any particular theory of failure. In my opinion the von-mises rule could be used in spite of tresca as a failure criterion is used through out the code. However, use of tresca criterion might lead to numerical difficulties in plastic analysis (unfortunately I couldn't find any quote from the web..) and that's why it's not supported by ansys or abaqus.

If you are not strictly forced to follow the ASME code, you probably could use additional 15 % safety factor for yield strenght and von-mises failure criterion which is always conservative approach. See EN 13445-3 Annex B for example. I also suggest you to contact technical help of ansys.