This past week I had the opportunity to be reminded of a fundamental FEA principal relating to shell elements.

It is important to remember that in most FEA software, the z-axis in the shell element coordinate system is always NORMAL to the shell surface. This is by definition of a shell element.

So I attempted to rotate the element z-axis along the tube axis of my composite part to "calibrate" the model and I wasn't getting what I was expecting.

So after researching this topic for a while I finally realized the issue, created a 3D FE model (using hexahedrons), and reran the study and got what I was expecting.

In summary, if you ever want to orient your elements so that the z-axis is anything BUT normal to the shell surface you will likely not get the results you were expecting... instead use a 3D element (tet, hex, etc.).

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