That way I can just change the behavior on the outer ‘ring’ to be frictionless and force the top to be bonded: While this may work, let’s say I don’t want a single contact pair for the two dome-like structures, but 2. Just zooming in on one of the groups:īy default, when I generate contact for this group I’ll get two contact pairs: Now that you have all these connection groups, you can fine-tune the auto-detection rules to meet the ‘needs’ of those individual body groups. Rinse, lather, and repeat the process until you’ve created all the groups you want: I don’t have to worry about contact being generated between the bolt and plate.
In the image series above, I selected all the bolts and washers, clicked the connection group, and now I have created a connection group that will only automatically generate contact between the bolts and washers. Next, just select a group of bodies and click the ‘Connection Group’ button: So, how do you go about implementing this? Easy, first just delete the default connection group (right-mouse-click on it and select delete). I figured in the new alt-fact world with falsely-attributed quotes to historical leaders, I might as well make something up for the oft-overlooked FE-crowd. In the words of the original FE-guru, Honest Abe, it’s easier to manage things when they’re logically broken up into chunks. The other benefit to this is if you’re working in large assemblies, you can retain your sanity by having contact generated region by region. Or, what we could do is modify the auto-contact to be broken up into groups and apply appropriate rules as necessary. The brute force way to handle this would be to set the auto-detection value to be 0 and then go back and manually define the missing contacts using the options shown in the image above. But now let’s say that some parts of your assembly aren’t touching (maybe it’s bad CAD, maybe it’s a welded assembly, maybe you suppressed parts that weren’t important). So we can fix this by going in and specifying a value of 0, meaning that only surfaces that are touching will have contact defined. In the image above, we see that contact has been defined between the bolt head and a plate when there is clearly a washer present. However, what happens if you have a large assembly with a lot of thin parts? Then what you run into is non-sensical contact between parts that don’t actually touch (full disclosure, I actually had to modify the contact settings to have the auto-generated contact do something like this…but I have seen this in other assemblies with very thin/slender parts stacked on top of each other): Typically the default values do a pretty good job automatically defining contact. If you change the Tolerance Type to be ‘Value’ then you can just directly type in a number. You can play around with the slider value to change what the toleranceĪs you can see, the smaller the tolerance slider the larger the ‘acceptable’ gap becomes. So in the picture shown above faces that are 5.9939E-3in apart will automatically have contact created. What this controls is the face offset value for which Mechanical will automatically build contact. This can either ‘Slider’ or ‘Value’ (or use sheet thickness if you’re working with shells). It might look a little over-whelming, but really the only thing you’ll need to play around with is the ‘Tolerance Type’. In Mechanical contact is automatically generated based on a set of rules contained in the ‘Connection Group’ object: Sure, there were some macros somewhere on the interwebs that would go through and loop for surfaces within a particular offset, but for the sake of this stereotypical “old-tyme” rant, I didn’t use them (I actually didn’t, I was just TOO good at using ESURF to need anyone else’s help). Back in my day, I’d have to use the contact wizard in MAPDL or show off my mastery of the ESURF command to define contacts between parts. You kids don’t know how good you have it with automatic contact creation in Mechanical.