Stress Intensity Definition 2

[mudmud35]

Corus wrote the following:

In general the stresses through a wall will be composed of primary membrane, primary bending, and a peak stress component. The primary stresses may of course be classed as secondary depending on whether or not they are strain dependent. ASME will give examples on the type of stress classification. In linearising the stress through the thickness the FEA code will remove the peak stress component (required for fatigue) to leave the primary plus bending stress at the surface which will be compared against some factor of the design stress (related to yield). The primary membrane stress can be considered as the average stress through the thiockness. Primary plus bending is the stress at the surface and is not an average as such.

This was a very good tip.

My question is where can I read more about what you mentioned here especially the following:

[The primary membrane stress can be considered as the average stress through the thiockness. Primary plus bending is the stress at the surface and is not an average as such.]

I mean I know that Stress=M/z and that stress is max on the outer fibers and zero at the neutral axis.

but the interpration of the these values in Ansys is another questions and I have been trying to interpret these values very carefully in my analysis of a Underground Buried Pipe core Support plate. Because this is not cleary explained in the ASME B31.3.

Thanks for the explanation and help.

 

[prex]

First have a look at faq794-982.
In what you quote above there is some mixup of different concepts:
-the concepts of membrane and bending stresses are only related to geometry factors, their calculation is per the FAQ above; note also that a bending stress is obtained from a surface stress only for a linear stress distribution, otherwise the procedure of the FAQ need be followed
-the concepts of primary and secondary stresses are related to the behaviour of the structure against the applied loads: a primary stress has the basic characteristic of being necessary to equilibrate the external loads (such as pressure, forces,...), a secondary stress has the basic characteristic of being self limiting when, with the increase of the loads, the material yields.
Unfortunately I don't know of any reference that treats this complex matter in a complete and authoritative manner: the only reference I can suggest is ASME VIII Div.2 App.4 (and other equivalent national standards).

prex

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[TGS4]

Well said prex. The only thing that I would add is that WRC-429 and the 2007 Edition of Division 2 both address this issue rather well.

 

[texag]

You might want to check out the following website:

http://members.aol.com/OLREngineering/olr.htm

I have taken the Designing to API 6A class and it is excellent, the instructor is an expert in the field of pressure vessel design and analysis.

 

[mudmud35]

Thank you for your replies. It is very helpful.