Membrane and Bending stress components with Nastran Laminates

[EndeavourArg]

Hi everybody, this is my first post. I hope these topic could also help other people with same problem.

I can't find a direct way to obtain membranes and bending stresses of a laminate plate, which I need for a remaining life evaluation under cyclic thermal loads following API-579/ASME FFS-1 Section B1.5.5 Fatigue assessment of Welds, for a Coke Drum study. I'm using Siemens NX 10.0, SOL 106 (non-linear static analysis), since the intention is to study a low-cycle fatigue mechanism, and with stresses generated by temperature loads in quenching stage an ellastic-plastic model is found necessary.

The plate model consists in CQUADR 2D finite elements with two layers, assigned by a PCOMPS property: the external one of SA-387 material with a thickness of 40mm, and internal cladding of SA-240 410S material with a thickness of 3mm.

I have requested STRESS(PLOT,REAL,VONMISES,CENTER,CPLYBMT) = ALL . CPLYBMT parameter allows to obtain TOP and BOTTOM results for an equivalent shell, according to Nastran's QRG.
With NLSTRESS(PLOT) = ALL the outputs I obtain are Ply 1 Stress and Ply 2 Stress, but both are measured at mid-plane, which corresponds to membrane stress. However, I can't find results at top or bottom, or even more useful for this case, the bending stress.

I am also using PARAM,NOCOMPS,0. I think I am missing another parameter definition, or a laminate property. I've spent enough time trying to obtain Ply 1 and Ply2 middle/average, bending, top, bottom stresses, in the same way as is possible with the equivalent shell.
Could anyone guide me with the proper way of setting the paramenters, PCOMPS properties, and output requests for obtaining these stress components for a SOL 106?

Thank you very much in advance

José Piracés
Mechanical Engineer
Endeavour Ingeniería

http://www.edv-ing.com.ar

Argentina

 

[aerostress82]

Read below if no solution is proposed by anyone:

This part weirded me out previously on a project. I was using Hyperview to review an MSC Nastran analysis result, and somehow I wouldn't be able to see the ply stresses in Hyperview!!
What I did was - as I was dealing with 2 layers of isotropic materials - was to model these 2 layers as duplicate elements sharing same nodes and offsetting them according to their plane of stress in the "2 layered composite" structure.

Like you did, I was also dealing with SOL 106, and it is just plain weird.
I guess using an *.xdb output and using PARAM,POST,-1 with MSC Patran as a post-processor would be a different story than above. I would advise you to change your post-processor if your company has smt else (like Patran).

Or, if you have room to do so and you can't solve it otherwise, you may model them as duplicate elements (even triple elements sharing same nodes - or 4/5/6 elements sharing same nodes) and check the stresses by this way. But if your material is composite material with directional plies, then you would have to be very very careful on what you are modeling as composite has its own habitat and rules.



Spaceship!!
Aerospace Engineer, M.Sc. / Aircraft Stress Engineer