I'm trying to model a capacitive force sensor with a bilayer configuration of polymer - Si on Mechanical APDL 16.2 .
I have a 0.2 mm layer of Si deposited on 0.005 mm of polyimide polymer. My goal is to find out the the length change in polyimide for an exerted force of 3 mN. For that purpose, I plot the displacement curve along x direction (origin to the edge). However, I obtain a nonlinear result.
I can't understand the origin of this nonlinearity. In my opinion, the polymer has to obey Hooke's law. What could be its reason?
Here is the model code.