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Introduction

This page collects information on the CalculiX finite element solver, the default solver in the FEM Workbench for structural and thermo-mechanical analysis. Depending on the operating system you are working with, you'll need to install CalculiX before running your first simulation. Please see FEM Install.

The solver is able to do linear and non-linear calculations, for static, dynamic, and thermal problems. The solver operates on an Abaqus-like input file (.inp), which means it can be used with different pre-processors that support this format. The program includes its own graphical preprocessor which, however, is not used by FreeCAD, only the solver itself.

CalculiX is designed to run on Unix platforms like Linux and Irix computers but also on MS-Windows. CalculiX was developed by engineers from MTU Aero Engines, Munich, Germany, to assist them in designing machinery such as jet turbines. The software is currently released to the public on the terms of the GPL version 2.

Integration with FreeCAD

Interaction between the FEM Workbench and CalculiX is done through writing and reading text files. The sequence of operations is as follows:

1. A CalculiX input file is created with details required to run the simulation
2. The CalculiX solver is started with this input file
3. The output from the solver is logged
4. The output files from the solver are read, if they are available

The FEM Control Solver tool manages the whole process. User interaction in the process is possible.

Preprocessing interface

The input file that CalculiX uses can be prepared and edited before the solver is started. CalculiX doesn't use units and it's the user's responsibility to ensure that the same unit system is used consistently in the whole input deck. The units in which FreeCAD writes the input file are independent of the unit system set in FreeCAD's project or preferences. The input file is always written using the SI(mm) unit system:

• length: mm,
• force: N,
• mass: tonne,
• time: s,
• stress: MPa,
• energy: mJ,
• density: tonne/mm^3.

The CalculiX interface supports the following objects:

• 3D solid:
  • tetrahedral: C3D4, C3D10
  • hexahedral: C3D8(R), C3D20(R)
• 3D shell and membrane:
  • triangular: S3, S6, M3D3, M3D6
  • quadrilateral: S4(R), S8(R), M3D4(R), M3D8(R)
• 2D plane stress, plane strain and axisymmetric:
  • triangular: CPS3, CPS6, CPE3, CPE6, CAX3, CAX6
  • quadrilateral: CPS4(R), CPS8(R), CPE4(R), CPE8(R), CAX4(R), CAX8(R)
• 3D beam and truss: B31(R), B32(R), T3D2, T3D3

More details about the supported CalculiX elements can be found on the FEM Mesh CalculiX page.

Анализ

• Linear and nonlinear static analysis
• Frequency analysis
• Linear buckling analysis
• Coupled and uncoupled thermal-structural analysis, pure heat transfer analysis
• Electrostatic analysis

Материалы

• Linear elastic isotropic materials (uniform properties in all directions)
• Plasticity with isotropic or kinematic hardening

Postprocessing interface

The FEM Workbench loads CalculiX results into a result object which will contain:

• Displacements
• Stresses
• Strains
• Equivalent plastic strain (PEEQ) – if nonlinear material was used
• Temperature – for thermomechanical analysis

FreeCAD reads results from *.frd file which was created by CalculiX. If these results contain multiple time steps, each time step is imported to FreeCAD as a new result object. Same behavior applies for Frequency or Buckling analysis with multiple eigenvalues.

Reaction forces can be found in ccx_dat_file which contains reaction force components (fx, fy, fz) for each fixed boundary condition and for each displacement boundary condition which constrains translation degrees of freedom.

Related

• FEM Mesh CalculiX
• CalculiX page in the FEM Workbench preferences