When you select the Non-linear tab, the following dialog displays.
At the top of the dialog, the Label field lets you assing a name to a defined compatibility type.
Clicking Definition of non-linear model opens a dialog that lets you define a curve that determines the non-linear character of the compatibility. Curves defined in the Non-linear ModelDefinition dialog are visible on the selection lists in this dialog. The non-linear behavior of compatible nodes are defined by selection - for a given degree of freedom - of a non-linear model describing one of the following relations: force-displacement and moment -rotation. You can select the model after the appropriate direction is blocked.
Note: A non-linear model contains information about the degree of freedom (displacement or rotation); therefore, models are filtered. This means that a non-linear model with the force-displacement type set is not visible on the selection lists for RX, RY, and RZ.