sliding contact sets and frictionless contraints in simulation environment

[Anonymous]

Hello team,

I have been having a lot of trouble creating a sliding contact/ constraint for a static stress analysis. In the model below (see screenshot), I want the sample/ beam to move freely over the dowels/ bearings as a load is applied. I have tried making the dowels both pin and frictionless, the samples frictionless and then changing the required contacts to sliding and separation without any luck. I can get the simulation to work when it is all fixed (albeit showing incorrect results) but when I try and put in the sliding fit, it either fails or produces unwanted results like   

Any help is much appreciated!!

Trying to select slider contact sets, but the pre-check suggests unconstrained bodies which leads to failed simulations:

When all contact sets are kept as rigid the simulation works (almost as supposed to be), except for the deflection where the beam and the bearing joins

Making the surfaces of the bearings and the beam frictionless leads to an incorrect result: 

[Anonymous]

Design file also attached below:

[alessandro.gasso]

Hi, 

As you can see in the video below, I've replaced the frictionless constraint with the pin one, that I believe is more appropriate for the movement the beam is supposed to do under the load due to the possible deformation. The pre-check warning is saying that the beam is free to move, and I believe this was the idea. The results the solver could generate without problems, make also sense to me.

https://autode.sk/3aV65qJ

Please, let me know if I've misunderstood the problem here.

Thanks!

[Anonymous]

Hi Alessandro,

Thanks for taking the time on this, it is very much appreciated. I have been plugging away at them and I find about half of the samples work and the other half fail with that constraint sets in place and I really can't work out why! 

I have attached the new file and as you will see from the last two simulation environments they have the same constraint set (pin and 2 sliding) but still don't work. Thanks again for your guidance!

[alessandro.gasso]

Hi Jeremy,

The circular solid bar 3 and 4 point tests works for me, as you can see in the image. I didn't modify your set up.

The setup for the square solid bar apparently generates a singularity that is causing the failure.

So, in this file (https://a360.co/2yfzNbG), I've added a constraint that fix the bar in two small areas around the points of contacts with the dowels, just in the X direction, that, considering the load resultant, shouldn't make a big difference for the configuration and this seems fixing the singularity issue.

I hope this helps.

Regards,

[Anonymous]

 

Hi Alessandro,

Thank you for taking this time to do this and sorry for the delay, I had to move on to some other projects, but now I have some time to finish this one! 

Unfortunately that file you provided also produced incorrect results on the simulation on my end. See below for example 1 photo (from the file you provided) which shows the bar doesn't slide like it would be expected to (like the example 2 photo). Do you think it could be something to do with the system settings on my machine regarding simulations? Sorry to be nitpicking on this one as well, I just can't send out an obviously incorrect simulation as a learning tool. 

Example 1 - incorrect behaviour

Example 2 - correct behaviour

[TheCADWhisperer]

I am not at my computer for the moment, but did you set the flag to detect and remove rigid body modes?

[TheCADWhisperer]

I didn't dig deep into this as I was confused why you have the test fixture included in the analysis, but I suspect that you should set Remove rigid body modes.

Even with symmetrical geometry, constraints and loads - the mesh may not be perfectly symmetrical which causes a non-symmetrical case and motion in the static analysis.  In other analysis software we might add a weak (or soft) spring to stabilize the model.  Having said that, I have had trouble in Fusion in the past not recognizing this flag.  As I recall - it used to work and then last time I checked (I only do this once a year in an FEA class) it was not working correctly.  I have not checked recently.  I might come back and check in more detail on you model once I understand why you have the fixture included in the analysis.