Temperature dependent thermal conductivity + Stress Linearization

Hi guys,

Foremost, thank you so much for this software. It has a clear, straight forward GUI, works nice with SALOME, and in each version gets more and more sophisticated.

I have two questions:

  1. I do a lot of study with temperature dependent material values in pressure vessel engineering. When I define a material in PPM, there is option for “temperature dependent data points” for thermal expansion but not for thermal conductivity. Is this missing because of some limitation of Calculix, or it hadn’t been implemented yet? This feature would be extremely useful for e.g. a hot-box calculation.

  2. I know, it was asked many times, STRESS LINEARIZATION. Doing this with Code-Aster is a nightmare, Mecway, hm yes, it has this module but somehow I’m not happy with the GUI. Jump to Paraview is not the best option either (I couldn’t figure out, why isn’t working). I read here Freecad too, I never tried (didn’t find anything about it, except the wiki page…)

In pressure vessel business “normal” FEA values are nice, colored pictures, we need membrane and bending stress - regardless it is ASME or EN design. Seriously, this program is great

Thank you again your continuous commitment.


Both thermal expansion and thermal conductivity can be set as temperature-dependent:



Stress linearization is indeed not yet supported but, as you said, FreeCAD can do it and the GUI is quite user-friendly. This page describes how to use it so give it a try: FEM PostFilterLinearizedStresses - FreeCAD Documentation

If you need any help with it, ask on the FreeCAD FEM forum and we will try to assist you: FEM - FreeCAD Forum

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Thank you, I didn’t notice the “Data points” sub-menu, my bad :slight_smile:

I made a benchmark in FreeCAD and I used the STRESS LINEARIZATION. But I can remember it was not possible with Sxx (FreeCAD 0.20.2) so I had to use P1 instead.

(Section/Paragraph numbers in the following are from ASME BPVC.VIII.2-2021)

ASME Section VIII, Division 2 allows three methods of showing protection against plastic collapse of a pressure vessel.

  • 5.2.2 Elastic Stress Analysis
  • 5.2.3 Limit-Load Analysis Method
  • 5.2.4 Elastic-Plastic Stress Analysis Method

Elastic Stress Analysis is the only one that requires stress linearization, and only one of the three methods needs to be satisfied. 5.2.3 is considered more accurate than 5.2.2, and 5.2.4 is considered more accurate than 5.2.3.

The Elastic Stress Analysis method requires stress categorization and linearization. This process is quite subjective and requires interpretation of the category descriptions. The difficulty of this process is one of the main reasons we switched to PrePoMax. The non-linear capabilities of PrePoMax allows use of the Elastic-Plastic method. With this method, safety factors are applied to the loads, and specified load combinations are analyzed. For each load combination, if the analysis solves (meaning the structure does not collapse) the design is sufficient. The elastic-plastic stress-strain curve can be determined using Annex 3-D of Division 2.

If those reviewing and approving the analysis will accept the Elastic-Plastic method, it may be worth considering using it.