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|Model → Mechanical Constraints → Constraint contact|
|Introduced in version|
|FEM Constraint fixed|
Creates a FEM constraint for contact between 2 surfaces.
- There are several ways to invoke the command:
- Select the master face.
- Select the slave face.
- Enter a contact stiffness.
- Enter a friction coefficient.
- The contact constraint can only be applied to two faces.
- Development for multiple contact at once: https://forum.freecadweb.org/viewtopic.php?f=18&t=15699&start=130#p303275
- Because multiple meshes are currently not supported, contact must be applied to faces that are separated by (at least) a small distance. If the faces were touching (no gap between them), the result of a boolean union or boolean fragments operation (necessary to avoid having multiple meshes which is not allowed at the moment) would be a continuous mesh and thus no need to use contact anymore. See Forum discussion.
Tips for modeling
- from https://forum.freecadweb.org/viewtopic.php?f=18&p=340874#p340494
- Better use linear elements otherwise calculations are very time consuming
- master/slave assignment:
- The larger of the two surfaces should act as the master surface.
- If the surfaces are of comparable size, the surface on the stiffer body should act as the master surface.
- If the surfaces are of comparable size and stiffness, the surface with the coarser mesh should act as the master surface.
- The contact stiffness should be 10 times the young's modulus of the material for hard contact. The higher the value for contact stiffness, the harder the contact between surfaces.
- The slave face is the face which penetrates into the master face, and therefore experiences more deformation.
- The *CONTACT PAIR card is used for modeling contact in CalculiX. The constraint uses Face-to-Face penalty contact and the contact formulation is explained in detail at http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node112.html
- Overview for different contact types: https://forum.freecadweb.org/viewtopic.php?f=18&t=15699&start=90#p188736
- Further interesting informations:
- A very detailed CalculiX contact example. (link)
- A very cool example found in the FreeCAD German subforum. (link)