September 12, 2023 at 5:01 pm
Alberto Bensi
Subscriber

Hello Bill,

first of all, I would like to thank you for the time you took to help me.

In order: 

  • Yes, I activated the large deflection option for this analysis.
  • "Sez_triang_Alt2.part" is the tool, and I'm pretty sure that problem is the way i tried to lock the tip. Because in the past when I did the first attemps with this kind analysis (with a more straight tube) I had the same problem, so as soon as the third substep (related to twisting) began, the tip of the instrument exploded, literally. It was because I initially thought that by imposing everything equal to zero, I was saying that from that moment when the remote displacement was activated would work as a fixed support and the tip would be locked. But, actually, I was imposing to bring the tip of the instrument back to the absolute origin. I am explaining this because it looks to me like something similar is happening also now. I think there is a better way to impose that portion of the tool remains locked with the  remote displacements equal to zero relative to the last position reached in the previous substep, no? Such as a coordinate system integral to the center of mass of the tip as it moves. This way I just impose everything equal to zero with respect to that coordinate system and only activate it in the third substep.
  • I already reduced stifness factor to 0.05.
  • I tried to use Normal Lagrange method and it worked well for the part of inserting the tool into the tube. I can try also with pure penalty. 
  • I already select asymmetric contact, because i know that is for case when it's clear who is the contact and who is the target. Like you said, tool is the contact and tube is the target.
  • The tube material is linear. Instead the material of tool is non lineart. Is a nickel-titanium alloy with the property of superelasticity.
  • As for the convergence criterion, on the other hand, I did not know, I will try to make the changes you suggested.

I thank you again for the answer you have already given me, and I hope you can clarify my thoughts about the tip lock, to confirm whether what I have done is right or something else can be done.

Best regards,

Alberto