# FEM EquationDeformation

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Menu location FEM EquationDeformation Solve → Mechanical equations → Deformation equation FEM None 0.21 Elasticity equation, FEM tutorial

## Description

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.

## Usage

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.
• 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.

Equation:

• 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:

### Note

• 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.

## Results

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.