Enforcing tie constraint

Dear iMechanica users,

I have a problem which I would appreciate any input on how to solve. I have an indentation problem, in which I indent a cell with an enclosing membrane. Therefore, I create contact between the (rigid) indenter and membrane, and tie the membrane and intracellular solid elements together. The model is an axisymmetric model, with CAX3 and CAX4R making up the intracellular axisymmetric solid elements and SAX1 the axisymmetric membrane.

However, the tie constraint does not seem to be enforced very well. I am not sure if there is something I am misunderstanding here. From the manual:

"A surface-based tie constraint can be used to make the translational and rotational motion as well as all other active degrees of freedom equal for a pair of surfaces." I took this to mean that the tied nodes should be given the same translational and rotational motion? But that is not what appears to happen (see attached figure). Does this mean that Abaqus tries to make the motion of the actual surfaces equal, and not the nodes (not that this seems to be the case either). I am not sure what I am missing here.

Any help would be much appreciated. Thanks!

Best regards

Björn Fallqvist