ASME III, Division 1 - Plastic Analysis (FEA) using Ansys 13.0

[finkarma]

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

 

[TGS4]

If you are designing a vessel to Div. 1, then you are obliged to follow ALL of the applicable rules in Div. 1. Only in the event that there are no rules expressly permitting or prohibiting what are doing, then you may activate clause U-2(g). One could make an argument that elastic-plastic FEA is permitted under U-2(g).

Just a note, however. Good engineering judgment (coming from someone who does this for a living) says that you should follow the rules in ASME Section VIII, Division 2, Part 5 if you are to apply a design-by-analysis (of, course, only if you are permitted to, per U-2(g)).

Also, please note that the ASME Codes are software neutral. Any particular software package is neither permitted nor prohibited. The general rules to follow are in the Code, but it is up to the individual engineer to determine how/if their software properly applies the rules.

 

[finkarma]

I guess your are referring to ASME VIII Div.1 while I'm speaking about ASME III (Nuclear component).

In any case ASME VIII Div. 2 follows Von Mises criteria (§ 5.2.3.5).

Thank you the same for replying.

Fabio

 

[steris]

Hi Finkarma -

My company uses an outside firm for our FEA. They use Ansys 13 and report the Tresca stresses. I'm not familiar with Ansys so I can't tell you how to do it, but I know it can be done.

 

[finkarma]

Thank you steris.
I agree that with ANSYS you can report both stress intensities (Tresca) or Equivalent stress (Von Mises).
But in a non-linear analysis, elasto-plastic type, the method of failure used is the Von Mises one. In other words yielding occur when elemental mean stress, calculated as per Von Mises criteria, reach the yield stress of the material.