FEM ConstraintContact

Constraint displacement

Constraint tie

FEM

FEM ConstraintContact
Menu location
Model → Mechanical Constraints → Constraint contact
Workbenches
FEM
Default shortcut
None
Introduced in version
-
See also
Constraint fixed

Description

Creates a FEM constraint for contact between 2 surfaces.

Usage

1. Click on or choose Model → Mechanical Constraints → Constraint contact from the FEM dropdown menu.
2. Select the master face.
3. Select the slave face.
4. Enter a contact stiffness.
5. Enter a friction coefficient.

Limitations

1. The contact constraint can only be applied to two faces.
2. Development for multiple contact at once: https://forum.freecadweb.org/viewtopic.php?f=18&t=15699&start=130#p303275

Notes

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.

CalculiX

• 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:
  • https://forum.freecadweb.org/viewtopic.php?f=18&t=23102#p180709 and following posts !!!
  • https://forum.freecadweb.org/viewtopic.php?f=18&t=20276
  • https://forum.freecadweb.org/viewtopic.php?f=18&t=21331
  • https://forum.freecadweb.org/viewtopic.php?f=18&t=15699 (initial contact topic)

• A very detailed CalculiX contact example. (link)

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

Constraint displacement

Constraint tie

FEM

FEM

• FEM Analysis

• Materials: Solid, Fluid, Nonlinear mechanical, Reinforced (concrete); Material editor

• Element geometry: Beam (1D), Beam rotation (1D), Shell (2D), Fluid flow (1D)

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