Is it possible to specify different stiffnesses for the x- and y-directions of a surface?
Yes. To do this, you can specify the orthotropic properties either for the material or for the surface.
Orthotropic Material (Figure 1)
Specify the moduli of elasticity for both surface directions (if you don’t have a license for the add-on module RF-MAT NL, only the "Isotropic Linear Elastic" and "Orthotropic Elastic 2D/3D" material models are available). Next, assign the material to the surface.
Orthotropic Material (Figure 2):
Define the stiffness type of the surface as "Orthotropic." Then, you can specify the coefficients of the local stiffness matrix according to various criteria.