The Shell interface has two fundamental types of material models. The first is represented by Linear Elastic Material,
Rigid Material, and
Section Stiffness. The other type of material models consists of
Linear Elastic Material, Layered,
Hyperelastic Material, Layered and
Piezoelectric Material, Layered. In either case, the dependent variables are the same, and exist only on the reference surface. The fundamental difference is that in the first group, the material properties are assumed to be constant through the thickness, so that stiffness and mass matrices can be computed by an analytical integration in the thickness direction.
In the Linear Elastic Material, Layered,
Hyperelastic Material, Layered and
Piezoelectric Material, Layered models, there is a numerical integration in the thickness direction. It is also possible to store states, such as inelastic strains, at different through-thickness locations. Thus,
Linear Elastic Material, Layered forms the basis for all nonlinear material models even if the shell is not layered as such. Use this material model if you want to write your own expressions as function of through-thickness location.
When the Nonlinear Structural Materials Module is available, Linear Elastic Material, Layered can be used to model plasticity, creep, and other nonlinear materials; and when the Composite Materials Module is available it can be used to model multilayered shells.
As this setting indicates, there is a virtual mesh in the transverse direction (the extra dimension). When there is a significant variation in the thickness direction, as is the case for plastic strains in state of bending, you need a good enough resolution.