Surface Contact Extension

[lancef]

Hello,

I'm having a bit of difficulty creating surface constraints in ABAQUS. Currently, I have an imported mesh of a knee generated from ScanIP. I set up contacts in ScanIP, and so when I import it, ABAQUS recognizes the contact nodes from the original mesh. However, I'll be putting a load at the top of the knee, and my parts will slide past these predefined contact points. Thus, I want to extend my contact zones to cover entire surfaces (i.e. medial femoral cartilage --> medial meniscus).

I tried to do this by going to tools -> surface -> manager -> edit

I edited each contact area by selecting the entire surface of my parts using the "select by angle" mechanism. However, when I run the model, it's pretty evident I've made a mistake because my femur is not recognizing the contact underneath it and is sliding all the way through my tibia. I'm getting warning messages saying that node constraints are being removed.

If anyone has any advice or insight into this, I would be much appreciative!

Lance

 

[corus]

Are you using surface to surface contact after defining the sliding surfaces?

 

[lancef]

corus - Yes, I'm using surface to surface contact. This one issue of surface extension seems to be my only fault right now. I've isolated every change I've made to my model recently, and everything runs as it should. But once I start manipulating my contact zones...it's game over, folks.

 

[IceBreakerSours]

Have you defined the interaction property in the normal direction?

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[lancef]

Hmm.. Probably not.. How can I check/do that? And is it problematic to select the entire surface when extending my zones. For example, I know my femoral cartilage will only slide along the superior portion of my meniscus, yet I'm selecting the entire surface of the meniscus as a contact zone (including the inferior portion that surely does not communicate with the femoral cartilage).

 

[IceBreakerSours]

You probably specified the interaction behavior only in the tangential direction when you were setting it up in CAE.

You should avoid selecting regions (for contact surface assignments) that are not expected to come in to contact. Otherwise, the contact solver is forced to keep track of normals on surfaces which will never come in to contact; it is an unnecessary expense. In small models, this is nothing to bother about but, in large or complicated models, one has to pay attention to the details. When it comes to biomechanics, it doesn't take too long before the models become complicated.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[lancef]

Ok, so I checked my contact behavior, and I do, in fact, have normal behavior defined. The error message I'm getting is "Node 14134 Instance Part-1-1 is common between the contact pair (zone1_with_zone2, zone2_with_zone1). No constraint is formed for this node." I get this message for a countless number of nodes.

The problem is, as far as I'm aware of, everything in my model (that I'm concerned with) is disjointed, so there shouldn't be any part in my model that's sharing a node. My cartilage is completely disjointed from my meniscus, so when I select each surface as a contact zone, there shouldn't be any nodes that are "common between 2 contact pairs".

I do not get this error when I keep the original contacts as is from the original imported mesh. Thus, the problem specifically is when I attempt to extend these zones.