Improved stochastic methods for modelling imperfections for buckling analysis of composite cylindrical shells

Abstract

The important role of imperfections on decreasing the buckling load of structural cylinders has been investigated by scientists and engineers for the past century, yet there is currently no method that is able to thoroughly investigate and replicate realistic imperfections for a full account of possible buckling loads. This drawback impairs optimized design as shell designers are restrained to using an outdated and conservative lower-bound design philosophy that relies on empirical data from 1968. Modern manufacturing methods and materials such as high-strength, high-stiffness composites require new, optimized design measures to take full advantage of their greater efficiencies. Even when identical lay-ups, material and shell geometries are used, these cylinders exhibit a large scatter in buckling load levels due to imperfections introduced in their manufacturing process. Stochastic analyses can optimize and improve the robust design and reliability of such cylinders through accurate prediction of the range of conceivable buckling loads by realistic simulation of structural imperfections. A stochastic procedure which realistically models imperfection sensitive composite cylindrical shells is investigated in this paper. Monte-Carlo simulations of axially compressed cylinders are performed to show the combined effect of geometric and thickness imperfections on the scatter of the buckling load.