Hi Domenico,
In order to use a custom material model, you would first need to program a usermat and then compile/link that to the Mechanical solver. This is discussed in the MAPDL Programmer's Reference 2.4.1. Subroutine UserMat (Creating Your Own Material Model). Please note that you will need an Intel Fortran compiler and Microsoft Visual Studios to compile and link your subroutine. These are third party software items which ANSYS does not provide. Also, you will need specific versions of these items based on which version of ANSYS you are running. This information can be found in the Installation Guide.
Regarding the Engineering Data GUI you've shown, this is only the GUI-based setup for initializing your custom material model parameters in light of having a subroutine compiled and ready to be incorporated by the Mechanical solver.
Lastly, you may want to check in the MAPDL Material Reference to see if there are any already-existing material models which closely replicate the behavior of your custom model.
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