Use of Quadratic Strain Interpolation Functions in a Mixed Quadrilateral Shell Element

In this paper a robust and effective shell element for the structural analysis of thin structures is presented. A Hu–Washizu functional with independent displacements, stress resultants and shell strains is the variational basis of the theory. Based on a previous paper an additional interpolation part with quadratic shape functions is introduced for the independent shell strains. This leads to a significant improved convergence behavior especially for unstructured meshes. The expanded element formulation proves to be insensitive to mesh distortion. Another essential feature of the quadrilateral element is the robustness in nonlinear applications with large deformations.