ASME plastic coupled analysis

[Pawel27]

Dear all,

I have problem with ASME coupled analysis. I have one structure for which I performed coupled thermal-mechanical analysis (acc. to ASME, section VIII, Div 2, article 4-1). There can be used linear analysis. Everything seems to be clear for me.

Unfortunately I have another one structure where plasticity is reached for mechanical load (local stress concentration). Moreover the limits (Fig. 4-130.1) are not satisfied as it is mentioned in "4-136.5 Plastic analysis". There is some more explanations in this 4-136.5 section. I do not quite get it. Please explain shortly step by step this approach.

 

[LSThill]

Pawel27 (Structural)

What year of ASME SECTION VIII, DIV. 2 IS YOUR REFERENCE?

L S THILL

 

[Pawel27]

ASME 2004

 

[LSThill]

ASME SECTION VIII DIV 2 PART 5 2007 OR 2010

 

[DSB123]

LSThill,
If you read the response I beleive it says "ASME 2004" if I am not mistaken!!!

 

[Pawel27]

Yes, ASME 2004. There is Appendix 4 "Design basen on stress analysis". Interesting publications title are also desirable.

 

[DSB123]

LSThill,
You seem to have gone quiet now!!!! Looking for some "Cut and Paste" bibliography??

 

[Pawel27]

Men... such posts are not valuable and lead to nothing. I counted on more practical and advanced posts.

 

[DSB123]

Just trying to get an answer for you from this guy.... Women always whinging even when you try and help!!!

 

[TGS4]

Maybe I can help. The section that you are referring to is from an obsolete edition of ASME Section VIII, Division 2. The current edition (at the very least, the 2007 or newer edition) completely re-wrote the entire old Appendix 4.

The 2004 edition does not do a very good job of explaining how the calculations are to be performed, particularly with respect to performing FEA. However, that problem has mostly been resolved.

Therefore, rather than trying to explain to you the old rules, I would highly recommend that you review Article 5.2.4 in the newer editions. If things are not cleared up, then please come back here with questions.

 

[Pawel27]

Hmm... I did not read new 2007 ASME yet, because I am pushed on using Eurocode. I found similar method in EN 13445-3, Annex C. In fact used code is not so important (I guess) in this discussion. Some issues are discussed here thread727-211759. I would like to continue this discussion.
I have problem with stress categorization. At the connection pipe-hdr there is stress concentration. I hesitate between Local Membrane stress and Secondary stress. These are stress from mechanical loads. These "big stress" are locally mainly due to hdr twisting ("header" I mean this horizontal hdr at the picture). Actually I categorized all stress below 1.5f as Local membrane, and all stress above 1.5f as secondary stress
(i.e. stress which cause plastic deformations). Limits are on the basis of Table C-3, EN 13445-3.

Some comments:
material 16Mo3
f=157/1.5=104.6MPa (section 6 of EN 13445-3)
1.5f=157MPa

In fact it is not important what code we discuss. The most important is what to do with stress above yield limit in coupled thermal - mechanical analysis.

I would like to mention that on the picture are stresses from mechanical load. I would like to impose also thermal stress (at the next analysis stage). Thermal and mechanical Stress superpisition is not allowed due to plasticity.

 

[Pawel27]

I am sorry. Here below is right picture