What are Shell elements?
Shell elements in COSMOS are triangular thin shell elements with membrane and bending capabilities. Unlike in thick shell elements, the shear deformation effect is neglected for thin shell elements. Six degrees of freedom per node (three translations and three rotations) are considered for structural analysis. Only one degree of freedom per node, representing the temperature, is used for thermal analysis. In both thick and thin shell elements, a constant thickness is assumed throughout the element.
Why use Shell elements?
You may mesh any solid model with tetrahedral solid elements. However, meshing thin models with solid elements results in generating a large number of elements since you have to use a small element size. Using a larger element size can deteriorate the quality of the mesh and lead to inaccurate results. Although you can use mesh controls to reduce the number of elements, shell meshing is the natural choice for sheet metal and thin parts.