Articles about engineering

1. Contact analysis of a pin in a fixed sleeve

   Inspired by a recent question at work, I looked at the stresses developing in a steel pin when it is loaded under bending and partially placed in a fixed sleeve.

2. Element names in Calculix

   CalculiX consists out of two programs;

   • cgx: pre- and postprocessor
   • ccx: solver

   A minor annoyance is that the naming of element types is not consistent between them.

   Below is a table that provides a mapping between the two.

3. FEA based on STEP geometry using gmsh and CalculiX

   In this article an FEA workflow based on CAD geometry in the form of STEP files and gmsh for mesh generation and CalculiX as the solver will be discussed. This workflow is primarily suited for isotropic materials.

   If one is working with FreeCAD, the FEM workbench enables a similar workflow, if gmsh and CalculiX are installed. But the author prefers this method because it makes the details of the process more transparent and accessible.

   All the software used here is freely available. On UNIX-like systems (e.g. FreeBSD, Linux) it can generally be installed by the native package manager. Installing the prerequisites under ms-windows is outside the scope of this article.

4. Folded leaf spring ball joint flexure

   The Dutch-language engineering book “Constructieprincipes” by M.P. Koster contains flexure made out of four folded leaf springs that kind of acts like a ball joint.

   The point where the load is applied should rotate around a virtual center formed by the point where the fold lines meet. The goal of this article is to simulate that and see if it works.

5. Creating a rectangular tube in CalculiX

   Rectangular tubes are one of the standard shapes of beams. This article shows how to create them in CalculiX GraphiX.

6. Meshing a circle with hex elements in CalculiX

   In this article a methd of creating a second order hex mesh for circular cross-sections will be shown.

7. Corrugation against buckling

   Composite sandwich products loaded in bending tend to fail by buckling of the laminate under compression. The author’s intuition is that corrugating the surface under compression should help. So the question is; does it help, and how much. That is what will be investigated in this article.

8. Approximating elliptical arcs in CalculiX Graphics

   The line command in CalculiX Graphics can create lines, arc and splines but not elliptical arcs. This article describes how to approximate elliptical arcs using splines.

9. Hex versus tet meshes in FEA

   In this article the difference in the images of the stresses between a quadrilateral hexahedron (“hex”) mesh and a tetraeder (“tet”) mesh will be investigated. In both cases, second order elements will be used.

   Hopefully this will make it clear to the reader why hex meshes are generally preferred.

   The plate with a hole that was the subject of a previous article will again be used. The analyses will be done using CalculiX.

10. Singularities versus stress concentrations in FEA

    The way FEA works can lead to concentrations of high stress in single elements or even nodes. This article aims to show how such singularities can be recognized and when they can be safely ignored.