What is the output convention for planar element internal stresses?

General stress results on shell type planar elements are s_xx, s_yy, s_xy, s_xz, and s_yz. Stresses s_ij (where "i" can be x or y and "j" can be x, y or z) are stresses that occur on the "i" face of an element on direction "j". For example, stress s_xx acts on the "x" face ("perpendicular" to the local "x" axis) and having the direction "x". Another example is s_xy, which is the stress that acts on the "x" face with the direction given by the "y" axis.

The following figure shows an example for all stresses that can appear on shell elements:

s₁ and s₂ are stresses on the principal direction:

The angle that gives the orientation of principal stresses is:

Advance Design computes, on three zones by thickness, the stresses of planar elements: superior face, middle and inferior face. In order to correctly identify the output, the rule is that the "z" axis orientation will always point to the superior face.

Advance Design will also compute the Von Mises equivalent stresses (compute by using the Strength of Materials formula):