Stress States in Highly Flexible Thin-Walled Composite Structures by Unified Shell Model

Abstract

This work deals with highly flexible laminated shell structures. The main focus is to provide an advanced model for the accurate prediction of the interlaminar three-dimensional stress state of shells subjected to large displacements/rotations, buckling, and snap-through phenomena. In this context, a two-dimensional shell finite element based on the Carrera unified formulation (CUF) is formulated in an orthogonal curvilinear reference system. Thanks to CUF, the governing equations are expressed in terms of fundamental nuclei, which are invariant of the shell theory approximation order. Thus, classical theories of structures to layerwise approaches can be implemented with ease and in a unified manner. The full Green–Lagrange strain tensor is employed because far nonlinear regimes are investigated. Furthermore, the geometrical nonlinear equations are written in a total Lagrangian framework and solved with an opportune Newton–Raphson method along with a path-following approach based on the arc-length constraint. The results demonstrate that classical theories may bring to wrong and unconservative stress predictions, especially in nonlinear equilibrium states, where the use of advanced and layerwise approaches shall be recommended.