Stimulating the realistic worst case buckling scenario of axially compressed unstiffened cylindrical composite shells

Abstract

The worst geometric imperfection is a mathematical concept which should deliver in theory a lower bound for the buckling load of unstiffened cylindrical shells. The corresponding knock-down factors could be used as base for improved shell design guidelines in order to reduce weight and cost of unstiffened shells. Commonly used worst geometric imperfections include eigenmode or axisymmetric imperfection pattern. However, experimental results show that buckling failure is induced by an isolated single dimple which can be classified as a realistic worst geometric imperfection. It is hypothesized that the interaction between single dimple motion and the deformation behavior in the pre-buckling range of cylindrical shells significantly influences the buckling load.A numerical model is proposed in order to study the before mentioned thesis. The results show that the proposed numerical model induces a physical meaningful and realistic buckling response in a cylindrical shell. It can be validated that the interaction between single dimple motion and the deformation behavior of a cylinder in the pre-buckling range significantly influences the buckling load. Based on experimental data it can also be shown that the lower bound of the buckling load is accompanied by a characteristic post-buckling pattern shortly after collapse.