Solver pivot warning in 3-point bending model
jinglun
Member
I am simulating a 1/4 model of a 3-point bending test, with symmetry regions applied. The sample is a shell from ACP while the crosshead and support are solids. The shell offset is set to "Top". The crosshead presses down on the sample along the Z axis. All contacts are frictionless, and "closed". The model worked fine when ACP was not used, everything else being the same (the sample was a simple midsurface shell). But with ACP I get many solver pivot warnings, with UX, UY, UZ of node 483 (highlighted in figure) repeatedly mentioned.
Note that in previous runs I used either all solid bodies, or all shell bodies. Here I have both solids and a shell body.
Please correct me if I am wrong, doesnt applying symmetry constrain the object in the corresponding directions? If so, why would this node be unconstrained in those directions (X and Y)? Furthermore, if I were to constrain the Z displacement of the sample, wouldn't it be unable to deform under the load?
May I know how should I constrain the model to solve these warnings? Or could it be a result of other ill-defined parts of the model? Hope someone can shed light on this, thanks in advance!
Comments
Heres the link to the project archive:
https://entuedu-my.sharepoint.com/:u:/g/personal/angj0054_e_ntu_edu_sg/EWmROcGhMBxBo2RTBP4c9I8BLk_pL8SfTd2uJKYT7eSJRA?e=eqKi84
Hi,
I see a gap between the sample and lower support, so that might lead to some initial rigid body motion before contact is established. I am not sure why the contact status is reported as "closed" when visually we can see a gap there. May be I am missing something? If the issue is rigid body motion at contact regions, you can use contact stabilization damping.
You are right about about the symmetry part. It is possible that the general rigid body motion results in a very high displacement at node 483. It need not mean that the issue is specifically at that node.
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Hope this helps,
Sai