An optimization procedure for maximizing the energy absorption capability of composite shells

Composite cylindrical shells are being used more extensively for structural applications in both rotary- and fixed-wing aircraft where low weight and high strength are important design issues. This paper addresses the energy absorption capability of such shells, under axial compressive loading. A design optimization procedure is developed to improve the energy absorption by maximizing the buckling and postbuckling characteristics of the shells. The sensitivity of both geometric and material properties is investigated by studying thin-walled shells of several thicknesses, made of different types of orthotropic laminates. Constraints are imposed on the longitudinal, normal, and in-plane shear stresses of each ply by utilizing a failure criteria. Design variables include shell diameter and ply orientations. The optimization is performed using the nonlinear programming method of feasible directions. A two-point exponential approximation is also used to reduce computational effort. Results are presented for Graphite/Epoxy, Glass/Epoxy, and Kevlar/Epoxy composite cylindrical shells with symmetric ply arrangements.