How to classified primary stress,secondary stress and peak stress?

[Lirock]

Hi,
I have a question about the classification of primary stress,secondary stress and peak stress in the postprocess after analysis with ANSYS.As we know, in the area displacement constrains applied or geometry discontidiscontinuity, some very large stress would appear, which usually contains secondary stress and peak stress. But how to recognize them? How to determine the range them impressed?

Thank you!

Rock Li

 

[cbrn]

Hi,
I don't mean that they are easy to understand and implement, but regulations ASME "B.P.V.C" VIII-2 Appendix 4 contain "everything" about that. On the net and in literature you will also find much material about the "interpretation" of these ASME Norms.
All that, provided that you are obliged to analyze a part with the stress categorization method: for example, EN-13445 "Design by Analysis" provides other ways which are much more "appropriated" for modern FEA. Unfortunately, they find difficulties to be "accepted", principally due to the fact that they are less conservative.

Regards

 

[TGS4]

I would also take a look at the 2007 Edition of ASME Section VIII, Division 2. Part 5 has a VERY in-depth discussion of stress classification.

BTW (and I know that this will come as a shock for many ANSYS fans), the ANSYS stress linearization routine does NOT (I repeat NOT) comply with the new rules in Part 5.

 

[cbrn]

Hi,
TGS4, ok, true, but I also wouldn't consider ASME as "THE Truth" without discussion. ASME BPVC was born so long ago that it had, and continues to have, extremely serious difficulties to keep up-to-date with the latest progresses both in material science and in stress-state calculations. EN-13445 allows, if used at full potentialities, savings in material weight ranging from 5 to... 15% (!!!) without loosing anything as regards security. Unfortunately, these "full potentialities" can be deployed only with very "complicated" and computer-consuming calculations. Moreover, customers will most probably find it difficult to accept that... Most of the time in my company we deal with "customer-made" rules which are, nowadays, completely absurd and even much more restrictive than ASME (one day someone should explain to me what they hope to obtain like that... probably a turbine with a null water passage area...).
To return to ANSYS: afaik, the linearization tool does exactly what it is called for: it discriminates the membrane part from the bending and the peak part. It DOES NOT CATEGORIZE these stresses: it's up to you to understand if it is general, primary, local, etc etc...

Regards

 

[TGS4]

cbrn, you're probably referring to the "old" Division 2. The "new" Division 2 is as current, if not more so than EN-13445.

When I said that the ANSYS linearization doesn't follow the Code methodology, I mean that it does not follow the procedure in 5.A.4.1.2., which is a mandatory part of the new 2007 Edition of Division 2.