Stuck? 
support@mecway.com
support@mecway.com
Mecway
FEA
General Contact (Nonlinear, Hard Contact) in CCX
Hi, anyone has a suggestion on modeling general type contact (open and close without penetration and able to slide with friction coefficient defined) without doing trial and error the CCX contact parameters? The trial and error take alot of time waiting for the model to solve then do it all over again until a reasonable solution is reached. Thanks
Howdy, Stranger!
It looks like you're new here. If you want to get involved, click one of these buttons!
Comments
Regards
Here are two models with the same material properties, the same contact stiffness and about the same strains. The 1000x smaller one has about the same absolute penetration distance than the larger one, but since it's much smaller, one element goes about a third of the way through the other.
So perhaps a better rule of thumb might be 10 * Youngs modulus / thickness. This formula also has the correct units (force/length^3) so it's not limited to newtons and meters.
Also, in my (limited) experience with CCX, I often find it's useful to start with NODE_TO_SURFACE contact and no friction to get things working, as NODE_TO_SURFACE seems 3x-5x faster and more efficient at multithreading than SURFACE_TO_SURFACE, at least on my problems (v2.8p2 on Windows).
I usually add friction last, as it can cause convergence problems and sometimes requires really small steps. It's much easier if the penalty is already in the right range.
I think with most codes, you can plan 2-3 iterations to adjust contact parameters for the first solves with a new model involving complex contact.
This new contact CCX only feature and your suggested initial value are great! I've been trying to this example for some time and your feature is very easy to use. See YouTube video in the link below. Thanks!
By the way, I see the same issue when you postprocess as me. The first thing that you look for is the magnitude displacement (to check that the model is displacing a razonable value), but, you must press the select face or element button to remove the node "emphasis" representation that make hard to see the model. Would be great that in the postprocessing mode this balls would not be pressent, as they almost hide the model result colors, or at least that the default selection mode for postprocess be element or faces (to present to the user a clear image of the results).
Yes, I undertand that normally when postprocessing the more used feature is check values at nodes, but for complex meshes this balls almost complete hide the colors of the model.
Regards!
I do agree with your comment on all the nodes are selected cluttering the view. Basically we can't see anything useful there until click on select face icon to turn off the nodes display.
Have you tried with bolt preloading? I has made some examples very like you did but still not the bolt preloading in CCX.
Is very good your way to define the sets for contacts, first you define a set and rename it and then select the oposite side of the contact and define the contact feature. In that way you save to define and rename one of the sets (I made examples with 18 bolts with contact in both side, upper and lower side... and define/rename every set!!! I would save the half of sets in this way).
I always make a set of contact (or tie) for every bolt, but in case that have as you several bolts in the same plane, can be made only one contact set, with the lower sides of the several heads and only one face of the plate? My procedure is generate a partition on the plate surface for every bolt, then make an individual contact, but now I'm in doubt if is necessary or not.
Regards!
In the beam clip video, I could have used manual CCX feature to add the TIE but that require some typing to define the contact. Bonded contact in Mecway and TIE contact in CCX is the same except that TIE contact in CCX does not allow for large gap between the surfaces and Bonded contact in Mecway does (Victor told me that in another thread recently). This is just a thought: hopefully in the next release we also have something like "New Tied Contact (CCX Only)" and the original "New Contact (CCX only)" could be renamed as "New General Contact (CCX only)". You already requested for these and much more in your other post.
Victor,
Can you address Sergio question on selecting multi-surfaces and group them together to define contact. They seem to work for my test case but not sure if I also missing something. Thanks
Best regards!
Sergio, good point about errors vs warnings. I'll try to distinguish them more clearly. That one is only a warning and it's safe to do as long as you're aware of the limitations of *TIE. for coincident aligned surfaces, it should behave the same as Mecway's bonded contact.