Creep function and pressure position dependance

Feature Requests
1

Hello everyone,

Hello Matej,

I am a thermal engineer and I have been using PrePoMax for the last few month: it is a great piece of software! Thank you so much for it. I had previously worked on Solidworks FEA Add-On, and PrePoMax is in my opinion far better!

I would like to request from you a creep calculation function. We are making very specific heating elements and we are trying to design a new generation that can withstand temperatures up to 1100°C. We expect inner pressure to reach up to than 100MPA and everything that is hollow will get crushed by creep inside.

When creep occurs, the pressure inside will slowly decrease, as the materials that are pushing because of themal expansion will be able to expand. Can you add an external pressure dependence on the strain of the part ?

Do you think you could add a creep function? i already saw your tutorial, and it would be great to include it in the GUI.

Thank you so much in advance, Thomas

1 Like
2

Features that can be added using the Keyword Editor have lower priority but I agree that creep and some other advanced material models (mainly orthotropic elasticity) would be great. However, creep also requires a special step type so it’s different in this regard. Another thing is that this material model often doesn’t work well in CalculiX. There are some known issues, mainly with convergence: Creep calculation and results - CalculiX (official versions are on www.calculix.de, the official GitHub repository is at https://github.com/Dhondtguido/CalculiX). but also a nasty bug with temperature dependence: Creep properties interpolation problem? - CalculiX (official versions are on www.calculix.de, the official GitHub repository is at https://github.com/Dhondtguido/CalculiX).

Dependence of applied load on the results is way more tricky as it requires the use of Fortran subroutines that have to be coded manually and recompiled with CalculiX and even then I’m not sure it would be doable in CalculiX (this part of the feature request is more for CalculiX itself: Issues · Dhondtguido/CalculiX · GitHub).

3

Thank you for your fast reply.

I understand. Are you planning to include creep in a foreseeable future? If so, when can we expect it? (Are we talking month or years you think?)

4

That’s the question for Matej so let’s wait for his reply but I wouldn’t expect it very soon due to the aforementioned order of priority. Using keywords for that is really not bad and CalculiX itself will likely be much bigger problem here. From what I’ve learned during the discussion linked above, I was lucky to get my simple example for the tutorial working. Creep is really hard to converge in CalculiX.

5

Ok, thanks . What i wanted to simulate is a complex assembly of 3 parts designed to collapse in one another during the creep process. If you’ve been lucky with your simple example, it will probably not work on my case.

6

Yeah, I can help you with this setup (just hit me up, you can send me a private message) but there’s a really great chance it won’t work in CalculiX. Might be good to try though. It’s just a few keywords to add creep and pretty much everything else can be done directly in GUI.

7

Thank you very much for your help, I will try to follow your tutorial first and I will ask your help if it does not work. (I first have to finish designing everything + find the mechanical properties of the material).

8

I had no plans to add creep in the following months. However, if there is a larger demand at some moment in time, the priorities can also change.

Since I have no experience with creep simulations in CalculiX, it is hard for me to justify its inclusion, but I trust @FEAnalyst in this regard.

And I am happy you like PrePoMax :slight_smile:

9

I see, thank you Matej :slight_smile: I think I might consider an experimental approach to my problem then. I’ll ty to follow FEAnalyst tutorial first .

Thanks guys.