FEM ConstraintContact

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FEM ConstraintContact.svg FEM ConstraintContact

Menu location
Model → Mechanical Constraints → Constraint contact
Default shortcut
Introduced in version
See also
FEM Constraint fixed


Creates a FEM constraint for contact between 2 surfaces.


  1. There are several ways to invoke the command:
    • Press the FEM ConstraintContact.svg FEM ConstraintContact button.
    • Select the Model → Mechanical Constraints → FEM ConstraintContact.svg Constraint contact option from the menu.
  2. Select the master face.
  3. Select the slave face.
  4. Enter a contact stiffness.
  5. 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.


  • A very detailed CalculiX contact example. (link)
  • A very cool example found in the FreeCAD German subforum. (link)