FEM tutorial

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Freecad.svg Tutorial
Topic
Finite Element Analysis
Level
Beginner
Time to complete
10 minutes + Solver time
Authors
Drei
FreeCAD version
0.17 or above
Example files
None
See also
None

Introduction

This tutorial is meant to introduce the reader to the basic workflow of the FEM Workbench, as well as most of the tools that are available to perform a static analysis.

FEM tutorial result.png

Requirements

  • FreeCAD version 0.17 or above.
  • Netgen and/or GMSH is installed on the system (included in the FreeCAD instalation).
  • Calculix is installed on the system (included in the FreeCAD instalation).
  • The reader has the basic knowledge to use the Part and PartDesign Workbenches.

Procedure

Modeling

In this example a Cube is used as the study object, but models created in the Part or PartDesign Workbenches can be used instead.

  1. Create a new document (press on the Std New.svg button).
  2. Activate the Workbench Part.svg Part Workbench.
  3. Create a Cube.
  4. Change its Dimensions to the following:
    1. Length: 8.000 m.
    2. Width: 1.000 m.
    3. Height: 1.000 m.

Now we have a model with which to work with.

Creating the Analysis

  1. Activate the Workbench FEM.svg FEM Workbench.
  2. Select the Model → FEM Analysis.svg Analysis container‏‎ option from the menu.

Constraints and Forces

  1. Hide the mesh from the Tree View.
  2. Show the original model.
  3. Select FEM ConstraintFixed.svg Create FEM fixed constraint.
  4. Click Add, select the back face of the Cube object (face on the YZ axis) and click OK.
  5. Select FEM ConstraintForce.svg Create FEM force constraint.
  6. Click Add, select the front face of the Cube object (the face parallel to the back face) and set the Load [N] value to 9000000.
  7. Set the Direction to -Z by selecting one of the face edges parallel to that direction.
  8. Click OK.

We now have established the restrictions and forces for our static study.

Material

  1. Select FEM MaterialSolid.svg Material for solid and choose Calculix-Steel as the material.
  2. Click OK.

Meshing

It is recommended to make a mesh as the last step in the analysis preparations due to association to a geometry in FreeCAD. Depending on FreeCAD installation, there can be Netgen or GMSH meshers, you can use any of them.

Netgen

  1. Select the model.
  2. FEM MeshNetgenFromShape.svg FEM mesh from shape by Netgen: Generates a finite element mesh for a model using Netgen.
  3. In the meshing dialog, click Apply and OK.

You can also drag and drop a mesh to a Mechanical Analysis that does not have a mesh within the Tree view.

GMSH

  1. Select the model
  2. FEM MeshGmshFromShape.svg FEM mesh from shape by Gmsh: Generates a finite element mesh for a model using Gmsh.
  3. In the meshing dialog, click Apply and OK.

We have now meshed our object and are ready to add constraints and forces.

Running the Solver

Standard Procedure

  1. Select the solver object FEM SolverCalculixCxxtools.svg contained in the Analysis container.
  2. Select FEM SolverControl.svg Solver job control from the menu.
  3. Select Write .inp File.
  4. Select Run CalculiX.
  5. Click OK.

Quick Procedure

  1. Select the solver object FEM SolverCalculixCxxtools.svg contained in the Analysis container.
  2. Click on FEM SolverRun.svg Run solver calculations.

Analyzing Results

  1. From the Object Tree, select the CCX_Results object.
  2. Select FEM ResultShow.svg Show result.
  3. Choose among the different Result types to view the results.
  4. The slider at the bottom can be used to alter the mesh visualization. This allows us to visualize the deformation experienced by the object, keep in mind that this is an approximation.
  5. To remove the results select FEM ResultsPurge.svg Purge results.
Comparison to previous example file

If you select the Z displacement result type, you can see that the obtained value is almost identical to the test example provided by FreeCAD. Differences may occur due to the quality of the mesh and the number of nodes it possesses.


We are now finished with the basic workflow for the FEM Workbench.