Stiffness matrix is singular / unstable structure in volumetric body

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1

Hello everyone,

I am currently working on a lifting device model in RFEM 6 using solid bodies (Volumenkörper).

I am encountering the following errors during the static analysis:

"BS1 enthält die fehlerhaften Fälle LK1"

"Die Steifigkeitsmatrix ist singulär | Die Struktur ist instabil | FE-Netzknoten Nr. 574497, in Richtung X, Inkrement 1"

I already tried:

  • fixing the supports completely,
  • increasing the number of iterations,
  • changing the load application method,
  • refining the STEP geometry and remeshing.

However, the instability error still appears.

Could someone please explain:

  1. What exactly causes this instability in my case?
  2. How can I correctly stabilize the model?
  3. Is this related to contacts between the pin and the plates, missing restraints, or an issue with the solid model itself?

This project is quite urgent, so I would really appreciate any help or recommendations.

2610029-1010-00-002.rf6 (2.1 MB)

Thank you very much.

3

Hi Alaeddine,

Welcome to the community.

You can find possible solutions here:

https://www.dlubal.com/en/support-and-learning/support/faq/005345

If you analyze the unstable model without loads first, ideally with a coarser mesh, you will find objects that are not connected:

image
image1920×1018 859 KB

Best regards
Stefan Hoffmann