FEA Design Tips #003

It’s high time to make another one of those : )

I recently got caught up with some urgent designs, and those required revisiting some stuff I did several years ago… but I think I will feature this in future advice!

Let’s go with the tips!

Pssst – there is also a video with those tips on YouTube : )

Freaking self-weight!

I think there are two layers here. The first one is pretty obvious. In most FEA software you will apply self-weight by defining the density of stuff… but also by defining acceleration (also known as the gravity!). And while applying density is pretty obvious (I’m pretty sure I managed to fail at this at least once!) the acceleration part is a nightmare!

Especially that in Femap, you have to define it in a “different place” than all the rest of the loads. Good luck with remembering that!

I had to redo my FEA at least seferal times wasting a lot of computing hours… simply becouse I failed to apply self-weight. No worries… at some time you will most likely do the same mistake, or maybe you already have? If so, definitely let me know in the comments : )

But there is more to it than that! And the more serious, and I think the more important lesson here is: Everybody makes stupid mistakes!

I know I have my share of them, and I’m pretty certain I will make more. Friends I talk to also say from time to time that some blunder happened, and something had to be fixed. It is life! No amount of experience will protect you from those stupid blunders that simply happen. I would say being nice to people is a really good strategy. Since when you make a mistake, someone might just as well be nice to you!

Apply enough load!

Often I get asked: “how should I interpret this nonlinear FEA outcome?”. It’s a tricky thing in itself, but you can tremendously help yourself with the task. Whatever load you have, apply more thank you should! I usually apply 10 times the load, simply because 0.1 load factor means “actual load” and it goes well with percentages and all : )

The point is to cause a failure in the model. If it won’t happen until the load of 10 times higher than what you should apply, you don’t have to worry. But most likely failure will happen, which is great – then you will know exactly how much bigger load than “yours” caused that failure… so you know how big safety margin you have on this design!

Also, in the FEA Guild Aleksei pointed out something:

So to clear this, I should point out, that always (unless I state otherwise) I will refer to structural design in FEA. You know, the calculations that help establish if something fails or not. It’s not only the civil engineering domain, but FEA can be used in a much broader spectrum of problems, and in some, my advice won’t do you any good.

Scaled and unscaled deformation

This is something I saw, but not something I struggled with.

There are programs which like to surprise you – i.e. I’ve seen outcomes from Robot that look perfectly fine… but displacements were almost in kilometers! If you wouldn’t check the values of that, and take a look only on normalized deformations… well everything else worked 

It’s good to pay attention 

Be friendly!

Oh, I’m really curious how you will react to this one!

A few years ago… I would laugh at the idea. But if I would meet myself from the past – I would punch myself 

Social interactions are so important, and at least here Universities don’t teach that at all! This is a real shame, and I would advise everyone (not only in FEA) to develop some skills here. Those can take you a long way!

Also, I really love the suggestion Robert made:

I admit that the title of D. Carnagies book sounds a bit scammy (the influence peopel part), but believe me, it’s worth your time. I can honestly say that this book changed my life! Get a copy today!

Avoid modeling welds!

It seems this is a hot topic. Tons of replies on Facebook and Linkedin. The general consensus is:

If you can, just do the hand calculations. You can calculate stresses by hand, or take some from FEA… just avoid modeling welds. But if you really need to do that (like a 3D detailed model)… it will hurt! There is no easy way around it!

Also, if you happen to know such an easy way around – definitely let us all know! You will be an instant superstar of FEA!

Final remarks!

Thanks for reading, I hope you enjoyed it!

Without a doubt, advice in FEA Design Tips will be about a lot of different stuff. If you prefer a bit more “organized” learning try a free online course I’ve created!

Free FEA essentials course!


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