Spring with no compression stiffness

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mikail1
Posts: 2
Joined: Sun Nov 21, 2021 2:30 pm

Spring with no compression stiffness

Post by mikail1 »

Hello dear users,

I am looking for a way to simulate a string like structure using 2 node elements with spring setup which only have stiffness in tension but not in compression.

I found: SPRING1, SPRING2 and SPRINGA but no "no compression" option. Maybe a nonlinear spring with pre defined curve which is just zero in negative area?

I know for example in Abaqus there are spring type which can do something like that.

Unfortunately I cannot find such spring type in Calculix. Am I right or is there maybe a way to simulate something like this?

Also I want to ask you guys if there is an official user manual out there? When I search online I just find different sources from not official Calculix sources. Same for a website, is there one with official information? I really would like to do some nice projects with Calculix and this would be super helpful.

Or is this https://wiki.freecadweb.org/FEM_Workbench the offical manual?

Here's a picture of my current model, the nodes in between the green squares should be connected with the springs. This should be a 2D analysis, later on 3D using shell and in the end 3D with solids.
table.png
table.png (16.26 KiB) Viewed 2295 times
-> the picture is not visible for you or is it?

Thanks in advance :))
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NewJoker
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Joined: Sun Oct 11, 2020 7:49 pm

Re: Spring with no compression stiffness

Post by NewJoker »

In Abaqus there are several ways to do this (nonlinear springs, truss elements with no compression material or connectors). CalculiX offers less options for such cases. You will most likely have to use nonlinear spring elements and define proper force-displacement curve for these springs.

When it comes to manual, for FreeCAD FEM module use wiki that you’ve already found. For CalculiX itself there’s a manual on its official website: www.dhondt.de/ccx_2.18.pdf
This document is crucial if you want to work with CalculiX.

I can see the picture :-)
mikail1
Posts: 2
Joined: Sun Nov 21, 2021 2:30 pm

Re: Spring with no compression stiffness

Post by mikail1 »

Thanks a lot this is already super useful information!!!

One more thing I couldn't figure out right yet.. Is there a way to create quads instead of trias in a surface mesh?

Also for the abaqus approach, would you recommend beam elements or truss elements? please tell me why you choose this over that
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NewJoker
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Joined: Sun Oct 11, 2020 7:49 pm

Re: Spring with no compression stiffness

Post by NewJoker »

Currently supported meshers in FreeCAD (Gmsh and Netgen) can’t generate quadrilateral and hexahedral elements, they are limited to triangles and tetrahedrons.

If such an element is only supposed to work as a spring then beams aren’t necessary and trusses should be fine (discrete springs or connectors are even more convenient in such a case).
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