Articles about engineering

1. 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.

2. 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.

3. 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.

4. 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.

5. Resonance frequency of a composite tube

   Based on a question I ran into at work, I wanted to explore the influence of parameters like cross-section, wall thickness and laminate lay-up on the resonance frequency of a carbon fiber composite tube.

   The goal of this exercise is to determine which of the parameters are dominant.

6. Continuum properties of aluminium honeycomb

   Honeycomb cores are often used in composite structures as an alternative core material to e.g. polymeric foams or end-grain balsa.

   In FEA we want to be able to treat honeycomb as a continuous material instead of having to model individual cells. Otherwise even simple FEA models involving honeycomb would become unmanageably large.

7. Automating CalculiX with make(1)

   The make program is a staple UNIX development tool. In this article I will show how it can be used to automate and simplify the usage of CalculiX.

   My CalculiX projects are all kept in their own directories. In each of those directories there exists a Makefile. This contains instructions for the make program.

   By default, invoking make in this directory runs the pre-processor and the solver. But there are also specific sub-commands, for example:

   • “make mesh” shows the mesh used in the FEA.
   • “make disp” shows the deformed product in the post-processor.
   • “make stress” shows the stresses in the product in the post-processor.

8. Mooney-Rivlin rubber data for CalculiX

   Recently I was looking for material data for 60 Shore A rubber for a simulation. This article describes what I found and how I transformed that to material data.

9. FEA with Calculix (3)

   This is the third installment of a series of articles about how to analyze sandwich structures with FEA.

   It might be a good idea to read part 1 and part 2 first.

   In this part we will look at a simplified simulation of a three-point bending test of a sandwich panel.

10. FEA with Calculix (2)

    This is the second part in a series how to analyse sandwich structures with FEA. The first part is here. If you haven’t done so, you should probably read that first.

    In that part we built and analyzed a sandwich where the core and skins shared nodes. We saw how that leads to incorrect stress distribution images because of nodal averaging. In this article, we’re going to fix that by using *TIE constraints.