Out of Plane (Z') Strain Tensor Components

Out of plane (Z') strain tensor components

Shell-like thick shells do not integrate the through thickness strain ( _ZZ' ), but this value may nevertheless be reported as non-zero. This is because the shell thickness may change, leading to a strain: its stiffness in this direction is based on volume preservation, but there is no stress associated with this.

Brick-like thick shells do calculate the through thickness strain.

Therefore principal strains also may not be confined to the plane of the element.