Solver pivot warning in 3-point bending model
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!