SCL for ratcheting assessment

[Paulettea]

TGS4 please help me understand an issue regarding SCL's as per VIII-2 Part 5. In one of your previous posts you mentioned something that I have doubt if I got the point or not. It is in thread794-412084

I would ignore the intermediate points. They are merely points along a straight line. The intermediate points are not calculated by anything other than y=mx+b. Figure out how to do the linearization first.

Does this mean that the only valid points to be accounted for membrane or bending stresses are the ones that are actually element nodes and other points along the path are not valid for linearization?

 

[TGS4]

The context of that specific post was that the OP was trying to calculate the "Bending" stress at each node - as opposed to asking a SCL. What their software was doing was then attributing that so-called bending to each node, but only in the context of y=mx+b.

To answer your specific question - no. Your software will be able to interpolate the stresses inside an element in order to provide a good result.

 

[Paulettea]

TGS4 What is meant by the meridional stress in the following:

Bending stresses are calculated only for the local hoop and meridional (normal) component stresses, and not for the local component stress parallel to the SCL or in-plane shear stress.

Does this mean the stress which is normal to the SCL and lies in the SCP?
Is it necessary to consider multiple SCL around the stress concentration region or just one will do?
Is there any guide regarding the orientation of the SCL? Are the following SCL's appropriate?

 

[TGS4]

Meridional is also analogous to longitudinal. Both the hoop and meridional directions are generally mutually perpendicular, and generally mutually perpendicular to the through-thickness direction.

Regarding your SCLs - red, yes; blue - no.

The requirement of the Code is that the stress limits must be met "everywhere". You can use engineering judgement to reduce the number the SCLs, but you need substantial experience in order to be able to exercise that judgement.

As far as guidance goes, see WRC 429. We're working on additional guidance for the 2019 Edition. Might not make it, though... You'll get good guidance here.

 

[Paulettaa]

Thank you TGS4.

I have another nozzle which is on the shell (the previous one was on head).

For this nozzle two SCL's similar to the previous one are considered. here the blue SCL gives the Pm+Pb+Q to be 303 MPa and the red one is 185 MPa. Do I have to ignore the results of the blue SCL for this case or shall I take it into account because it seems to be more critical.

Second, I want to know that am I right for not categorizing stresses in elastic ratcheting analysis. Since secondary and primary stresses are to be considered, I used the FE results as such and linearize them to exclude peak stresses.

Is it OK to use tetrahedron mesh or do they have to be hexagonal?

That really is good news: additional guidance on new edition

 

[TGS4]

Your blue SCL is still wrong. Especially for that geometry, try to have the SCL perpendicular to both the inside and outside surfaces.

I generally don't care about the element shape, so long as the results are independent of the mesh. You need to ensure that you have enough elements through thickness to develop a proper linearized distribution.