Elasticity Solutions for the Buckling of Thick Composite and Sandwich Cylindrical Shells Under External Pressure

Abstract

Thick composite and sandwich shells are used in many naval submersible structures and in other applications such as space vehicles. Stability under the prevailing high external pressure in deep ocean environments is of primary concern. In many other applications the loading involves a combination of external pressure and axial compression. It is well known that for these structures the simple classical formulas are in much error, due to both the large thickness and the large extensional over shear modulus ratios of modern composite and sandwich materials. Although there exist several advanced theories, such as first order shear and higher order shear theories, each based on a specific set of assumptions, it is not easy to determine the accuracy and range of validity of these advanced models unless an elasticity solution exists. This paper presents the research performed over the last 15 years on benchmark elasticity solutions to the problem of buckling of (i) orthotropic homogeneous cylindrical shells and (ii) sandwich shells with all constituent phases i.e., facings and core assumed to be orthotropic. The paper focuses on uniform external pressure loading. In this context, the structure is considered a three-dimensional body. The results show that the shell theory predictions can produce in many cases highly non-conservative results on the critical loads. A comparison with the corresponding formulas from shell theory with shear included, is also performed. The present solutions provide a means of accurately assessing the limitations of the various shell theories in predicting stability loss.