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List Directions of Stress Tensor

Dear experts,


I need to list the values of directionals cosinus of stress tensor (eignevector) for each element of my model.

I know how to plot an arrows to see the tensor, but I need to extract this info to a file in order to perform a fatigue calculation.


Thanks in advance!




Re: List Directions of Stress Tensor

I don't know of a way to get the principal direction cosines out of NX. We supported this in I-deas 20+ years ago. I have to admit this is an area that needs improvement in NX. The data is there, but I don't know how to let the user see it from the UI. Maybe there is a way to get to it programmatically with NX Open and the results access API.





Mark Lamping

Simulation Product Management

Simulation and Test Solutions


Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

Re: List Directions of Stress Tensor

Thanks Mark for your sincerely response.


Now, I extract these values from tensor with an external calculation, so I will continue doing it like this.



Re: List Directions of Stress Tensor

Dear Pablo,

Well, the data you need is there indeed, simply ask to print results in the *.F06 file using the NX NASTRAN Output request setting Output Medium=PRINT and you will get for each 3-D solid element the following output:



The explanation of each field is available in the NX NASTRAN manuals, all is there, as always!!:



The explanation for each mark is the following:



  • This output is typical for the CHEXA, CPENTA, CPYRAM, and CTETRA elements.
  • Standard STRESS output, requested in Case Control Section.
  • The convention for the principal stresses are such that ""(A ≥C ≥B). In the case where the principal stresses are equal, the directional cosines are not unique, and the values of zero are output for the directional cosines.


Here you are the typical plot you can see in NX AdvSim V10 using a TENSOR plot for a simply cantilever beam meshed with CHEXA 8-nodes solid elements:




In 2-D Shell CQUAD4 elements the NX NASTRAN solver computes & write in the *.F06 file (with & without the corner data) the maximum, minimum & shear principal stresses in both TOP & BOTTOM faces together with the angle in the element coordinate system.



The explanation of every mark is the following:



The typical output for Shell CQUAD4 elements written in the *.F06 is the following (only showing results at center of the element, but available at nodes as well, of course):


The tensor result plot in NX AdvSim V10 for Shell elements is similar to the above for Solid Elements, but for FEMAP V11 users I want to inform that they can plot the Maximum Principal Stress Angle at TOP & BOTTOM faces for Shell elements as well because is an output vector available for postprocessing, coming directly from the NX NASTRAN *.OP2 file, then if FEMAP can postprocess this value then NX Advsim can do it as well in a future release, this is an important postprocessing feature to implement in the software, OK?.



Best regards,


Blas Molero Hidalgo, Ingeniero Industrial, Director
Blog Femap-NX Nastran:

Re: List Directions of Stress Tensor

Dear Blas,


thanks for your great response!

But...this info can´t help me, because I need to extract vectors from 2D shell elements and nastran only shows the angle between principal stresses.


Next screenshoot is an example (ANSYS output) of the info what I need: