FEM EquationDeformation

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FEM EquationDeformation

Menu location
Solve → Mechanical equations → Deformation equation
Default shortcut
Introduced in version
See also
Elasticity equation, FEM tutorial


This equation describes the nonlinear elastic deformation of solid bodies.

For info about the math of the equation, see the Elmer models manual, section Finite Elasticity.


  1. After adding an Elmer solver as described here, select it in the tree view.
  2. Now either use the toolbar button or the menu Solve → Mechanical equations → Deformation equation.
  3. Change the equation's solver settings or the general solver settings if necessary.

Solver Settings

For the general solver settings, see the Elmer solver settings.

The deformation equation provides these special settings:

  • DataCalculate Pangle: If the principal angles should be calculated.
  • DataCalculate Principal: If all stresses should be calculated.
  • DataCalculate Strains: If strains will be calculated. This will also calculate the stresses, even if DataCalculate Principal or DataCalculate Stresses is false.
  • DataCalculate Stresses: If stresses should be calculated. Compared to DataCalculate Principal the Tresca yield criterion and the principal stress will not be calculated.
  • DataInitialize State Variables: See the Elmer manual for more info.
  • DataMixed Formulation: See the Elmer manual for more info.
  • DataNeo Hookean Model: Uses the neo-Hookean material model.
  • DataVariable: The variable for the deformation equation. Change there the 3 to 2 if you have a 2D geometry. For the special case that you have DataMixed Formulation and DataNeo Hookean Model set to true, the variable number must be geometry dimensions + 1, so for 3D geometry the 3 must be changed to 4.


  • DataPlane Stress: Computes solution according to the plane stress situation. Applies only for 2D geometry.

Analysis Feature Information

The deformation equation takes the following analysis features into account if they are set:


  • Except for calculations in 2D, for all the above analysis features it is important that they act on a face. Features in 3D set to lines or vertices are not recognized by the Elmer solver.


The available results depend on the solver settings. If none of the DataCalculate * settings was set to true, only the displacement is calculated. Otherwise also the corresponding results will be available.