×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to locate primairy and secondary stresses with FEMAP

How to locate primairy and secondary stresses with FEMAP

How to locate primairy and secondary stresses with FEMAP

(OP)
We want to analyse pressure vessels with finite elements by using FEMAP. We analyse also the alternative way but that is not the isue.

We have problems to locate the primairy and secundary stresses according to ASME. I need to find the following stresses:
Pm membrane stress
Pb bending stress
PL local membrane stess
Q secundary stresses

In Femap I can generate the following stresses:
Principe stress
mean stress
Normal stress in X and Y
Von Misses

I use plate elements

Can anyone tell how to locate these stresses

RE: How to locate primairy and secondary stresses with FEMAP

Not to discourage you - but you are in WAY over your head.  I recommend getting your hands on WRC Bulletin 429, and the ASME "Criteria" document, and then, after you've done all that, hire a consultant for the first couple of times that you need to perform these evaluations.  Have them "mentor" you in how this is done.

Also, take a look through the eng-tips archives for discussions of this nature...

RE: How to locate primairy and secondary stresses with FEMAP

(OP)
We already ordered the bulletin. We also asked a mentor but they cannot explain how to locate these stresses. There is a API tool voor midplane membrane stress, however this gives more than one membrane stress situtation. I also used principal stress and von misses stress, but that ain't enough. These are all combined stresses.
ASME requires a separation of primairy stresses and so called secondary stresses.

It would be a lot easier if ASME gave a criteria in principal and von misses stress. But that ain't the case, so i 'll hope to get some straight answers here.

RE: How to locate primairy and secondary stresses with FEMAP

For starters, you are going to be dealing in component stresses, so I would forget about using any of the invariants.  Have you had the opportunity to peruse the 2007 Edition of Division 2?  In it, Annex 5A has a good discussion about stress linearization.

The classification of stresses - primary or secondary, have everything to do with the source of the stress - primary satisfies equilibrium, while secondary satisfies compatibility.  The techniques for linearization are in either the WRC Bulletin or Annex 5A (the WRC Bulletin has good explanations, so I use that extensively).

I take it from your questions that you are reasonably well versed in FEA, but not so much in the ASME/pressure vessel world.  I would try to find a mentor that excels in BOTH fields.  Good Luck!

RE: How to locate primairy and secondary stresses with FEMAP

Oh - and there are numerous technically valid reasons why the ASME rules are written as they are.  I suppose it would be a lot easier if the rules/criteria were written in a way that your general FEA program could apply them, but then the rules would be technically incorrect...  Ah the joys of pressure vessels...

RE: How to locate primairy and secondary stresses with FEMAP

(OP)
Thanks
We have 2007 Edition of Division 2. It is very difficult to apply this to femap. I can now locate the primairy membrane stress with a midplane stress tool. But the next question is how to find the local stress and how to recognize it. In other words, what is the definitation of a local area, how large are these areas and when is a stress spot peak and when local.

I'm  a little bit confused.
I'll hope that you can help me futher

RE: How to locate primairy and secondary stresses with FEMAP

Hi Ronski

This may already be known to you, but it contains a good discussion around primary and secondary stresses along with non-linear inelastic FEA approaches. I'm guessing that the consultant/mentors that TGS4 refers to would have practical experience in both of these approaches, and how applicable they are to ASME code.

Cheers.

http://www.nafems.org/resources/knowledgebase/


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources