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FreeCAD: Stress Analysis (2/3)

Update: July 13, 2021
FreeCAD 0.19

Condition settings

  1. Creating analysis case

    Switch workbench to FEM workbenchWorkbench_FEM and create new analysisfem-analysis.

  2. Material setteings

    We will set a material for analysis in this section. At first, select material setting toolfem-material. Then select "ABS-Generic" as "Material card" and click OK to close the dialog. ABS is a kind of resin and one of the most common material used in 3D printings.

    Material setteing dialog
    Material setteing dialog

    In addition to ABS, you can use Aluminum alloy, steel, concrete, glass, PLA or wood etc. as material. It is also possible to set any Young's modulus, Poisson's ratio, density, etc. values for material.

  3. Fixed condition settings

    Select fixed conditionfem-constraint-fixed. Select the face of the screw hole at the lower Y coordinate in the 3D view and click Add on the dialog to set fixed condition. Red pins will be shown on the face with fixed condition. After settings, click OK to close the dialog.

    Fixed condition setting dialog
    Fixed condition setting dialog
    Displaying on 3D view
    Displaying on 3D view
  4. Force condition settings

    Select force conditionfem-constraint-force. Select the face of the screw hole at the upper Y coordinate in the 3D view and click Add on the dialog to set force condition. Red arrows will be shown on the face with force condition.

    Enter "500" at "Load". The force unit is N (Newton).

    Force condition setting dialog
    Force condition setting dialog
    Displaying on 3D view
    Displaying on 3D view

    If you want to change the direction of the force, click Direction and then select the edge in the 3D view that you want to specify. You can also check "Reverse direction" to reverse the direction of the force.

    When all settings is done, click OK to close the dialog.

  5. Creating meshes

    Select the shape (Body) to be analyzed on model tree and run creating mesh with Netgen「Netgenによるメッシュ作成」アイコン.

    At first, set "Max. Size" to "5" on task tab. Then confirm that "Second order" has been checked. By this option, second-order elements with high computational accuracy (but costs more computational time) will be used.

    1st-order tetrahedron element
    1st-order tetrahedron element
    2nd-order tetrahedron element
    2nd-order tetrahedron element

    Confirm the mesh fineness has been set to "Moderate" and click Apply. If there is no problem with the mesh shown in the 3D view, click OK to close the dialog.

    Netgen meshing dialog
    Netgen meshing dialog
    Meshes for analysis
    Meshes for analysis

    The parameters are as follows:

    Parameters
    Max. SizeMaximum size of an element
    Second orderGenerate 2nd-order elements or not
    FinenessMesh fineness. Possible settings are "Very Coarse", "Coarse", "Moderate", "Fine", "Very Fine" or "User Defined".
    Growth RateGrowth rate for neighbor mesh
    Nbr Segs per EdgeNumber of segments per edge
    Nbr Segs per RadiusNumber of segments per radius
    OptimizeDo optimization or not
  6. The model tree after these settings

    The material and conditions are added under "Analysis" in the model tree. If you want to change these conditions, double-click the item in model tree and change parameters. If you want to delete these conditions, select the item in model tree and press Delete key.

    The model tree after these settings
    The model tree after these settings

Running calculation

Double-clcik "fem-solverSolverCcxTools" in model tree to show a dialog for running calculation.

Confirm that "Static" has been selected as analysis type.

Click "Write .inp file" to write input file and click "Run CalculiX" to start calculation. When the calculation is finished successfully, messages as "CalculiX done without error!" and "Loading result sets..." will be displayed in the text area at the bottom of the dialog, so click Close to close the dialog.

Dialog for running calculation
Dialog for running calculation

After calculation, "CCX_Results" and "ccx_dat_file" items will be added to model tree as analysis result.

The model tree after calculation
The model tree after calculation

The next step is to view analysis result and to improve the shape.

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