The first principal direction for each structured shell element is relative to the direction of decreasing K for each element, as shown in Figure 2.10: Material directions defined in IJK-space for 3D structured Shell. The material directions will coincide with the co-rotational directions of the shell element.
The material directions will also coincide with the co-rotational directions of the shell element when the I-J-K option is used for unstructured shell elements.
Using the I-J-K option you can define initial material directions that are aligned with the shell elements. This can be useful when modelling shapes such as cylinders where the principal directions are aligned with the major axes of the body.
