Knee Joint Abaqus.

[Aravindkj]

Hi,
I am Aravind working with Abaqus for last few months. I am working on developing a knee implant. I am trying to do FEA analysis with ABAQUS. I am using TIE feature with femur and tibia and implant plates as well. I get the following errors.

The volume of 102 elements is zero, small, or negative. Check
coordinates or node numbering, or modify the mesh seed. In the case
of a tetrahedron this error may indicate that all nodes are located
very nearly in a plane. The elements have been identified in element
set ErrElemVolSmallNegZero.

NODE 26 INSTANCE TIBIAPLATE1-1 IS COMMON BETWEEN THE TIED PAIR
(ASSEMBLY_SCREW, ASSEMBLY_TPLATE2). NO CONSTRAINT IS FORMED FOR
THIS NODE.

***WARNING: 1169 nodes are common between the tied pair. no constraint is
formed for these nodes. The nodes have been identified in node set
WarnNodeCommonTiedPair.

And how to calculate the tolerance from Master to slave?

It would be of great help if you can help me with this, as I am trying for almost a month.
Thanks in advance

 

[IceBreakerSours]

As the error message - implicitly - suggests, you need to improve your mesh.

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

 

[rstupplebeen]

Aravind,

Usually when I see this error it is because the geometry has small slivers. This is especially true if the geometry is from scan data or STLs. Without seeing the model it is difficult to suggest how to fix this though. I hope this helps.

Rob

Rob Stupplebeen

http://www.optimaldevice.com

 

[Aravindkj]

Thank you so much for your reply. I have attached the image here in the link. I am not sure how I can make contac

http://www.eng-tips.com/viewthread.cfm?qid=366562t

pairs on the plates with Femur and Tibia. I tried using the Tie feature. I selected the inner surface of the plates(Slave) with the femur and tibia(Masters) accordingly. I also tried selecting the whole plate as slave and Femur and tibia. I am getting same errors and slave node lies outside the tolerance level of the master surface. I am not sure how to go about tolerance value as I am randomly trying with numbers.

Initially I had a very fine mesh and since I am trying to see the working functionality I have a very course mesh.

Thank you for your support and gesture. Its been a nice learning curve from this forum.

Cheers
Aravind

Link to image

http://files.engineering.com/getfile.aspx?folder=45d41fb8-026d-4204-9e43-b766c0a30826&file=1_(1).png

 

[IceBreakerSours]

I am a little confused here:

Do you want to allow contact (i.e., interaction) between two surfaces or do you want to constrain the movement of a surface with respect to another surface?

By the way, if you use the Query tool to figure out the distance between nodes, then a more reasonable number for the tolerance should pop into your mind.

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

 

[Aravindkj]

I want to allow contact between the plates and the bones(Shear Forces). And Thank you for your reply.

 

[rstupplebeen]

It looks like your mesh does have many slivers.

Try using Mesh>Verify to find the bad elements.

Then Tools>Virtual Topology>Automatic Create. Virtual topology does slightly modify the base geometry typically to combine faces or edges together.

I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

 

[Aravindkj]

Thank you Rob. I tried Virtual Topology feature. I get the following error. "Failed to create automatic topology feature no entity to be ignored was found."

 

[IceBreakerSours]

In virtual topology, as per Rob's suggestion, try ignoring some 'ignorable' features, if any. In geometries from imaging software packages, there tend to be some tiny features which can easily be ignored. Also, you could edit the geometry itself in a SolidWorks or some other package in order for the mesh to be of, at the very least, acceptable (for the solver, not you) quality.

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