This option models the problem using a plane stress assumption. A plane stress assumption is valid when one of the principal stresses is so small compared to the other two that it can be neglected. Using this option, you can model thin slabs with one dimension smaller than the other two. The forces acting normal to the section plane should be negligible.
The figure shows a thin slab subjected to in-plane tensile, compressive, and shear forces. The model dimension in Y is much smaller compared to the X and Z dimensions. For this example, you select a section plane parallel to the XZ plane, specify the thickness, and apply loads and fixtures to the edges.
The following simplifications are valid for the simulation results.
- Displacement and Temperature
- Displacement and temperature do not vary along the thickness. For the slab:
where u is the displacement vector,
Py=0, where Py is the load along Y direction.
and 
where T is the temperature.
- Stress
- Out-of-plane stress components along thickness direction are zero. For the slab:
where σ represents normal stress and τ represents shear stress.
- Strain
- All strain components are non-zero. However, out-of-plane strain components do not play an important role in the simulation.