Separation of Primary & secondary stresses 1

[Umar107]

In elastic stress analysis by ASME sec VIII div 2, please explain how can I seperate primary stresses from total stress field?
Please suggest a good article or thread whatever might help.Thanks.
@TGS4 and other experts are requested to please guide a newbie here.

 

[TGS4]

Primary stresses are those that are required to satisfy equilibrium. Secondary stresses are those that are required for compatibility.

Beyond that, please refer to paragraph 5.2.1.2. Additional guidance can be obtained from Table 5.6.

 

[Umar107]

how can I seperate primary stresses from total stress field?

 

[TGS4]

5.2.1.2 For components with a complex geometry and/or complex loading, the categorization of stresses requires significant knowledge and judgment. This is especially true for three-dimensional stress fields. Application of the limit load or elastic–plastic analysis methods in 5.2.3 and 5.2.4, respectively, is recommended for cases where the categorization process may produce ambiguous results.

 

[Umar107]

You qoute this para many times already.
My question is regarding separation of primary stresses from total stress field.If you don't want to answer my question that's fine.

 

[prex]

If you start with a specific problem or example, it will be easier to help you. Often you don't separate the primaries from the total stress, you calculate the primaries by formula instead.

prex
[URL unfurl="true"]http://www.xcalcs.com[/url] : Online engineering calculations
[URL unfurl="true"]https://www.megamag.it[/url] : Magnetic brakes and launchers for fun rides
[URL unfurl="true"]https://www.levitans.com[/url] : Air bearing pads

 

[TGS4]

Who, at your company, can you get to mentor you so that you can leverage their significant knowledge and judgement?

It's not so much that I don't want you answer your question, it's that the question itself is, in effect, the wrong question to ask. I'm not trying to be obtuse or obstinate here.

If you really don't know how to properly categorize stresses, then you should obey the recommendation in the last sentence of that paragraph.

 

[Umar107]

@prex. Let's consider nozzle in shell and shell head junction. If we apply sustained loadings from piping on nozzle and internal pressure and run the FEA simulation. We expect primary (to maintain equilibrium) and secondary (at nozzle shell interface due to geometric discontinuiy) both stresses. So you mean we will compute primary stresses from hand calculations and primary plus secondary from FEA,right?
In shell head interface we will get primary plus secondary from FEA and primary stresses from hand calculations?
Can you please share a good source where I can learn all about elastic stress analysis? A good case study considering all failure modes will be very helpful.Thanks

 

[Umar107]

@TGS4, In my company they just use PV Elite and nobody is there to mentor me. I guess I have to try and learn by myself.

 

[IdanPV]

@Zeeshan107,

ASME PTB-3, Example E5.2.1 is a good place to start with.
Another good example may be found in

https://www.pveng.com/the-nuts-and-bolts-of-stress-linearization-post/

 

[GD2]

Zeeshan007,
Without having the knowledge on how how to separate stresses from FEA, you are bound to mess up the result.
Take some training course on stress linearization and separation. You won’t get a complete guidance through the group.

GDD
Canada

 

[NRP99]

Zeeshan107

Check this thread for simple example on stress classification.

Suggested reading-
Search this forum for stress classification
ASME PTB-1 (Specifically read Annex A-CRITERIA OF THE ASME BOILER AND PRESSURE VESSELS CODE FOR DESIGN BY ANALYSIS IN SECTIONS III AND VIII, DIVISION 2)

 

[Umar107]

Thanks NRP99, I have read this post some time ago and it really is a good explanation. Do you agree with my reply to prex?

 

[Umar107]

@ GD2, Thanks for your input. Can you share some free training material here? I don't think they can teach much in those 5 day DBA trainings.A good book on this topic can be better helpful, if there's any?

 

[GD2]

Try Becht. The Becht guys are heavily involved in ASME and PVRC.

GDD
Canada

 

[Umar107]

Anyone who came to this link looking for this topic, I will recommend to read asme criteria (at end of PTB-1) first and then example problem of elastic stress analysis in PTB-3 & PTB-5. IMO best source to understand the stress classification and criteria is " Design methods for power plant structure by David Burgreen"