Design sensitivity and optimization of composite cylinders

Composite cylinders are often used in both rotary- and fixed-wing applications where low weight and high strength are important design issues. This paper, the first of a two-phase study, addresses the failure of such cylinders, under axial compressive loading, using design optimization and sensitivity analysis procedures. Thin-walled cylinders made of different types of symmetric orthotropic laminates and several wall thicknesses are examined. Formal optimization techniques are used and the diameter and individual ply orientations are varied to maximize the critical buckling load of the cylinder. Constraints are imposed on the longitudinal, normal and inplane shear stresses of each ply. The optimization is performed using the nonlinear programming method of feasible directions. A two-point exponential approximation method is also used to reduce computational effort. Results are presented for Graphite/Epoxy, Glass/Epoxy and Kevlar/Epoxy composite cylinders with symmetric ply arrangements.