AN OPTIMIZATION PROCEDURE FOR MAXIMIZING THE ENERGY-ABSORPTION CAPABILITY OF COMPOSITE SHELLS

Composite cylindrical shells are being used more extensively for struc tural applications in both rotary- and fixed-wing aircraft where low w eight and high strength are important design issues. This paper addres ses the energy absorption capability of such shells, under axial compr essive loading. A design optimization procedure is developed to improv e the energy absorption by maximizing the buckling and postbuckling ch aracteristics of the shells. The sensitivity of both geometric and mat erial properties is investigated by studying thin-walled shells of sev eral thicknesses, made of different types of orthotropic laminates. Co nstraints 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 perf ormed using the nonlinear programming method of feasible directions. A two-point exponential approximation is also used to reduce computatio nal effort. Results are presented for Graphite/Epoxy, Glass/Epoxy, and Kevlar/Epoxy composite cylindrical shells with symmetric ply arrangem ents.