Verify FEA outcomes: FEAchecklist!
(This is a 10min read. You may want to read it more conveniently on my blog)
Finally comes the time when your analysis converges, and you have the outcomes. As great as it feels, especially if there were convergence issues, now you have to deal with results!
However, this is not the end of fun! In the end, you need to see if your analysis results make any sense at all! Verification of FEA outcomes is a tricky thing - one I get asked about a lot! Let's take a look together at what you can do to verify them.
Sadly, there are so many different analysis, that it's impossible to make a "closed" list. But I do hope that this one will help you to verify FEA outcomes at least a bit!
Are the deformations ok?
This is a multi-part thing. All of those things are equally important and I've seen people ignoring either of them (or all!).
- Does the deformed model look "nice"? You've seen a lot of deformed models already! Also, since you're on this planet for some time you've seen a lot of things deform in real life. This means that you should have a general feeling of how deformations of your model will look like. The question is: do they look like you imagined? Note that sometimes you will have to INSANELY increase the scale of deformations to check that... but it's still a good idea!
- Are deformations reasonable? You know, a 1m beam should not deflect... 10 meters. It's a bit hard to do for the beam this short! If something goes wrong, such problems may happen. Maybe a nonlinear geometry should be used or your analysis didn't converge. Whatever the reason check the maximal deformations in your model. In some industries, maximal deformations are simply given in codes. But, even if this is not the case for you, set some "limit values" in your head and stick with them!
- Is the deformation in the direction I want? If your compressed model elongates... well, you are in trouble! You may think that the only way that this can go wrong is when you apply loads the other way around. And while this would be the most probable cause, I had an arc-length method "turning around" in stability analysis on me. So initially model was compressed but near the buckling load analysis "got dumb" and started to tension the model instead. At first it means less and less compression, but in the end, the model was in full tension! Stress levels on von Mises scale might be more or less ok... but it doesn't mean everything works as planned!
Don't forget about boundary conditions
I think this is the thing that people overlook the most. I know for sure I wasn't paying attention to this in first few years! However, when you make a model you make a lot of assumptions. Many of them are in boundary conditions. It makes sense to check if what you initially assume is actually still true!
- Do your simplifications still hold? Often you will ignore contact and just support something in both tension and compression (while contact carries only the compression). Do you get only compression in those supports?
- Check "soft springs" (aka "air hooks"). You may have added some weak, very elastic, supports to your system to stabilize it. A good example would be those 5kN/m springs you attache to an ISO container hanging on ropes so it doesn't sway. The usage of such elements is clear. Just check if you didn't get high reaction forces there. If you did... something went wrong!
- Do things fly "through" one another? Maybe you have ignored contact hoping that the deformations won't be high. Or maybe something went wrong in contact definition. Whatever the case may be, checking if elements of your model don't fly through other parts and supports makes sense!
- Are there any contact stresses in contact zones? Clearly, you defined contact for a reason. If there are no stresses there... something might have gone bad! It would be great to investigate this!
Checking stresses and more!
Read the full article on my blog!
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