Before you run an analysis: #FEAchecklist!

(This is a 13min read. If you prefer, you can read it on my blog!)

My friend and employee Asia just started a maternity leave. Since she was also responsible for training our new team member, in her "casual-self" brilliance she left her an "FEA with no stress" checklist. I've read it, and it's so awesome that I simply have to share it with you! It also gives me a chance to say that I'm really proud of Asia and that I will miss her a lot : )

All right - let's get to it!

A. The geometry

Usually, you will mesh geometry rather than building a mesh from "scratch". If that is the case, it's always a good idea to check if the geometry is ok. There are some things that seem trivial (like surface overlap). But not fixing that can cause trouble elements in some places... thing really difficult to find in postprocessing!

Check those before you run an analysis, or even before meshing:

• Are all surfaces have normal in the same direction? We do a lot of shell models and it's nice if all the "top" surfaces are on the same side. Makes displaying outcomes much quicker!
• Are there any overlapping surfaces? However accurate you do stuff... things just happen. Just check if all is nice and move on!
• Delete all unnecessary lines and points! This is only 2 clicks in Femap (such a cool tool BTW). They don't get translated into the input file, but better not to have them "flying around" if they are not needed!
• "Rebuild model" - check for errors. Yet another Femap tool. You can "rebuild" your model, and if Femap finds some errors it will throw them at you. This is a nice way of checking if you won't translate some stupid stuff into your analysis model!

B. Material properties

Setting material parameters can take seconds. In more complex problems far more of course! In either case, it's important to be aware of the unit system you are using... and the freaking self-weight! Just check those and you should be fine:

• Do orders of magnitude of material parameters align? When you decide on a unit system this is usually pretty simple. You just use meters, inches or whatever while defining the geometry and your "unit of choice" when you define loads. This is not as simple, however! All those choices "combine" in material properties, where you can get some bizarre units for density or Young's Modulus. This has to be checked and verified!
• Is the self-weight applied? Don't get me started on that! In most civil-engineering software self-weight is automatically applied. In FEA you most likely have to input density and gravity acceleration somewhere. I had to redo the calculations several times because I missed this! This is such an important thing to check!
• Does material fit the analysis? As you know there are many approaches to material parameters. You can go with the linear or nonlinear material. The nonlinear models can be pretty sophisticated. Some analyses require first using the linear and then nonlinear approach in second analysis run. Geometric nonlinearity is similar, but you can decide if you want to have linear or nonlinear geometry in solver settings. Material nonlinearity is defined... in material properties. It is easy to forget to change the linear for nonlinear material while defining analysis (there are no switches in solver settings that does that!) - hence the checkpoint!

C. Properties

This point might depend on your software a bit. In most FEA packages, you first define the geometry and then assign "properties" to shells, solids, and beams. In some, the properties (like thickness or material) are assigned WHILE creating geometry. If that is your case checking would be a bit different. However, it is still valid to verify if the model is made from materials and thicknesses that should really be there!

• Are properties defined correctly? The fact that the property name says "10mm" does not necessarily mean that it is defined as such. Sometimes you can misclick, sometimes you change something (thinking that you will remember about it!). This way or another it is worth checking if all thicknesses are actually what they should be!
• Are correct materials assigned? This is a rather straightforward check. Usually, when you create a property you will assign material to it. Just make sure you did assign a correct one : )
• Are properties correctly assigned? So we took care that properties have good values, and that good material is assigned to each of them. Now it's time to check if actual parts of the model have correct properties assigned!

D. Loads

It is already assumed that you have the correct load values. If you don't check that may take some serious time (depending on the code you are using I guess). However, if the values are calculated/estimated correctly it's not the end! You still need to check if the load is applied correctly. Let's take a look:

• Are the loads applied everywhere they should? A simple miss-click and you are in trouble... better to check then!
• Do the loads have good values/directions? Even if you have calculated the load values correctly, you still need to check if they have those values in FEA! A choice between total load/load on area/load on element can greatly influence this - so be careful with what load "type" was applied as well!
• Is the self-weight applied? Yup! It was already mentioned. And it is mentioned again! Go check - this can save you a lot of time later on redoing the analysis!
• Are coordinate systems ok? You may use scripts to create loads. In such cases, you will most likely base the load on a coordinate system. Is it the correct system, and does it have a "zero point" where it should be? Are the axis directions in your model in accordance with what you have assumed in your script?

Boundary conditions, mesh and more:

Read the full article on my blog!

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