In RFEM, there is an option to couple surfaces with the stiffness types "Membrane" and "Membrane Orthotropic" with the material models "Isotropic Nonlinear Elastic 2D/3D" and "Isotropic Plastic 2D/3D" (add-on module RF-MAT NL Add-on Module for RFEM 5 erforderlich).
This functionality enables simulation of the nonlinear strain behavior of ETFE foils, for example.
