Boundary condition to bring nodes together?

[biopolvo]

Hello brilliant FEBio community!

Another way to ask the question: Is there a way to simulate bringing a volume-less "suture" together?

In the linked model, the goal is to bring nodes 1 and 2 in contact with nodes 7 and 8, respectively, as a boundary condition under the control of a load curve. The load curve would specify the length of the "suture" (i.e., the distance between the nodes where 0 is touching/contact). It would be a bonus to measure the tension in the "suture" throughout the steps. The suture need not have a volume nor any properties per se; it is only there to bring the nodes together. I do not wish to specify a force (magnitude nor direction) nor a displacement because I won't know them ahead of time, but shortening/contracting an element/material is fine.

Sorry if this has been asked and answered previously - I tried to search the forum.

Thank you!

N.B. For reference, the linked model has a discrete element to illustrate the "suture" before bringing it together.

[maas]

Hi biopolvo,

I wasn't able to access the google drive, but I think I understand your question. There is an undocumented feature called a "node distance" constraint that enforces a user-defined distance between two nodes. I actually had to make a few tweaks to this feature in order to get it to work, but I think it's doing what you intend.
First, make sure to update to the latest development version to make sure you have this fix.
Then, take a look at the attached file and give it a try.
Let me know if this works for you and if it's what you had in mind.

Best,

Steve

[biopolvo]

Nice - it works well. Thank you for making the tweaks and for uploading the sample model, Steve!