What element formulation should be used for a model with a length to thickness ratio of less than 5?

In structural analysis, the choice between thin and thick shell element formulations is crucial for accurately capturing the behavior of a model, particularly regarding its geometry and load conditions. When dealing with models that have a length to thickness ratio of less than 5, the thick shell element formulation is especially suitable.

Thick shell elements are designed to account for significant variations in stress through the thickness of the shell, which is essential when the thickness is not negligible compared to the other dimensions. This ensures that the element can handle bending, membrane, and shear effects appropriately. In cases where a model's thickness is comparable to its other dimensions, using a thick shell element will provide a more refined and accurate representation of the stress and strain distributions within the material.

Using a thin shell formulation in such cases could lead to inaccurate results, as it assumes that the thickness is slim enough to neglect through-thickness variations, which is not applicable when the length to thickness ratio is less than 5. This is why the thick shell element formulation is preferred for models with a lower length to thickness ratio, ensuring comprehensive and reliable analysis of structural behavior.