Finite Element (FE)
simulation is an engineering discipline that is applied in various ways in
industries such as aerospace, automotive, power train, customer goods and bio-engineering. It is commonly used to augment experimental testing to save
time and money at different stages in the product development process. More
recently, FE simulation is gaining ground in the field of Additive
Manufacturing to optimize and verify designs, or to simulate the AM process
itself.
Compared to traditional manufacturing procedures, AM allows for great
design freedom to produce complex and organic shapes enabling designers and
engineers produce designs that are very light while meeting structural integrity
requirements. To check requirements for service of very complex designs
produced by AM is often an impossibility based on experience and becomes quite
expensive if one has to do several test prints for experiments. Here, FE
simulation comes in handy to check a designs’ suitability for service before a
single cent was spent on the manufacturing process.
In most mid- to large-size companies it is quite common to have access
to commercial FE tools to optimize and check the suitability for service of
designs. However, in the Additive Manufacturing service industry access to
commercial simulation software may be limited or not possible due to a various
reasons. But what can one really do if they want use FE simulation to improve
their designs without having the opportunity to use commercial FE software?
Open Source Software has nowadays spread globally for pretty much all
application needs, and luckily, also for Finite Element simulation. There are
various websites that list comprehensively available Open Source FE software
such as the one from opennovation. For structural
simulation, and considering my Abaqus background, I have found the Open Source
FE software Calculix very convenient and
helpful to address a broad range of my simulation needs. To illustrate some of
Calculix’s structure-mechanical simulation functionality, I took the winner
design of the GE
Bracket challenge for Additive Manufacturing and generated a FE model to
determine the von Mises stress distribution. In addition to that, I ran the
same model with Abaqus
to demonstrate eventual differences in results between the Open Source and the
commercial FE software.
1.
In a first step I used the open source meshing software NETGEN to create
the FE mesh with 2nd order tetrahedral elements and to specify surfaces that
will be used for defining boundary conditions.
2.
Then I exported the model as INP file (Abaqus nomenclature) and manually
created a job file to apply boundary conditions and define analysis steps.
Generating the job file manually may require some exercise. However, Calculix
comes with decent documentation and examples that will help you to better
understand the syntax.
3.
After preparing the model and the job file I ran the analysis and
generated von Mises color plots.
The following plots show the von Mises stresses for the first three
loading scenarios:
The maximum von Mises
stresses in the Calculix version (images left) and the Abaqus version (images
right) are as follows:
Calculix
[MPa]
|
Abaqus
[MPa]
|
Difference
[%]
|
887
|
886
|
0.11
|
777
|
793
|
2.02
|
558
|
557
|
0.18
|
The comparison of the
von Mises stresses and their location showed that there is almost no difference
between the results of the Open Source and the commercial software. The biggest
difference occurs in the 2nd load case and is about 2%.
So, what is the
conclusion about this exercise? In this article I wanted to raise awareness
that there are accessible, alternative options to commercial FE software tools
if you want to optimize and check the suitability for service of designs e.g. via
maximum stress levels. There are of course downsides to free software tools;
commonly they are not as well supported as commercial ones, they may not
include the latest technology and methodologies or include other issues that
may raise the end-users’ concerns. Nevertheless, I found that for
structure-mechanical applications Open Source software such as Calculix works
very well and presents a great, low-cost alternative to commercial software to
investigate the integrity of designs.
If you have thought
that you want to share on this article, please leave a comment or send me a
message.
