Stress Linearization

[dcattoni]

hi Guys

Can be possible that Membrane plus bending stress is higher than stress intensity (Tresca)?

thank!

 

[TGS4]

Unfortunately, your question makes absolutely no sense.

The stress intensity (or if you are using an Edition of ASME Section VIII, Division 2 more recent than 2004/2006, the invariant of choice should be equivalent stress or von Mises) is an invariant - a way of collapsing the stress tensor into a single quantity with no direction.

A membrane-plus-bending stress is typically a tensor representation of a stress state from an (pseudo-)elastic analysis along a stress classification line (SCL).

Perhaps some additional information can assist with getting a better answer to what you're actually looking for.

 

[dcattoni]

Ok TGS4

Here we go

I attached a .doc file when you can find what I want to say. There are 2 lines highlighted when it say:

SCL 6:
The Linearized Maximum Combined Membrane and Bending Stress is calculated as 80.187

The Maximum Tresca Stress along the SCL is 75.924

SCL7:
The Linearized Maximum Combined Membrane and Bending Stress is calculated as 101.769

The Maximum Tresca Stress along the SCL is 96.912

Thank!

 

[TGS4]

I don't use FEMAP, so I can't comment on what they're doing. Since you have posted this in an ASME forum, I am going to assume that you are performing an analysis in accordance with ASME Section VIII, Division 2 - is that correct?

If so, then your second SCL is completely invalid. Your first is valid.

The proper procedure for calculating primary-plus-secondary membrane-plus-bending equivalent stress (range) is to calculate the tensor of the membrane-plus-bending stress range, and then calculate the equivalent stress from that. You can't state that the membrane is X, and the bending is Y, so the equivalent (von Mises) is X+Y. That's not how tensors work.

Find out the basis of this calculation.

On the topic of membrane-plus-bending stresses - you may find my blog post on the subject enlightening -

https://becht.com/blog/asme-section...ic-analysis-discussion-collapse-vs-ratcheting

 

[dcattoni]

Yes TGS4 Sec VIII and III

I made a sub routine in matlab for calculate membrane, bending, membrane+bendig stress, using stress tensor components and I obtained the same result that in femap. But I have so many doubt about the procedure used for calculate the integrals shown in Sec VIII, Div2 Apendix 5A.

Do you have some papers or guide that estimate these integrals?

Thank!

 

[TGS4]

Just so that we're clear, ASME Section VIII, Division 2 uses von Mises (equivalent) as the invariant. Section III use Tresca as the invariant. The difference is important, so you need to ensure that you use the correct one for the appropriate Code.

ASME PTB-2 has sample problems for Section VIII, Division 2.

 

[pdiculous963]

I believe TGS4 is referring to PTB-3 for example problems, not PTB-2.

 

[dcattoni]

I'm using Tresca.

Thanks!!

 

[TGS4]

pdiculous963 - you are correct.

DomCattoni - I understand that you are using Tresca. However, if you are using VIII-2, then that is not a permitted invariant. Period.

 

[prex]

Coming back to your original question, DomCattoni, it is indeed possible that the maximum local stress intensity is lower than the M+b stress intensity. However you should not be concerned with the local stress intensity for verification purposes.

prex
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