Optimum Design of Composite Multilayer Shell Structures

Abstract

An improved method of structural optimization is presented which encompasses recent advances in nonlinear mathematical programming methods and methods of analysis for fibrous composite materials. The methodology is based on a transformation of an inequality constrained minimization problem into a sequence of unconstrained minimizations, by applying a penalty function formulation of the Fiacco-McCormick type. Advances include the formulation and solution of a composite shell design problem, including constraints on joint-discontinuity stresses and fibrous composite failure modes. The optimization method is first developed by considering a classic structural design application, the redundant three bar truss. Next, an application to a composite shell structure is demonstrated. Behavior constraints invoked for the shell include consideration of joint discontinuity stresses, shell buckling, deformation limits, and combined stress failure. The objective function is general enough to include both cost and weight criteria. Results for optimum sectional properties for the three bar truss, a composite pyrocarb cylinder and a carbon/aluminum cylinder joined with a composite hemisphere are obtained by this decision making technique.