Elastic imperfect cylindrical shells of varying length under combined axial compression and bending

This paper presents a comprehensive computational investigation of the elastic nonlinear buckling response of near-perfect and highly imperfect uniform-thickness thin cylindrical shells of varying length under combined uniform compression and bending. In particular, the elastic ovalization phenomenon in cylindrical shells of sufficient length under combined compression and bending was systematically investigated with finite elements for the first time. The study considered a representative range of practical lengths up to very long cylinders in which ovalization is fully developed under uniform bending and Euler column buckling controls under uniform axial compression. The imperfection sensitivity of the system was studied by introducing a single idealized axisymmetric weld depression imperfection at the midspan of the cylinder. The predictions permit an exploration of the nonlinear mechanics of the generally unfavorable interaction between bending and axial compression at the elastic nonlinear buckling limit state in thin long cylinders. The interaction is at its most unfavorable in cylinders where Euler column buckling is about to become critical, and is qualitatively very different from the favorable moment-force interaction at the reference plastic limit state of circular tubes. A simple closed-form algebraic characterization of the interaction is proposed considering both imperfections and ovalization.