Optimization of laminates with free edges under bounded uncertainty subject to extension, bending and twisting

The layup of the maximum strength of laminated composites with free edges under extension, bending, and twisting loads was optimized by genetic algorithm (GA). Interlaminar stresses, as well as in-plane stresses, were considered in estimating the strength of laminates. To calculate the interlaminar stresses of composite laminates with free edges, iterative stress-based method was applied. To consider the bounded uncertainty of material properties, convex modeling was used. Because interlaminar strength can change rapidly with respect to the scattered deviation of material properties values, a linear convex model is not suitable in considering bounded uncertainty. Thus, in the present study, two-point exponential approximation was used to build a convex set. In the formulation of a GA, a repair strategy was adopted to satisfy given constraints. In addition, a multiple elitism was implemented to efficiently and reliably search the optimum and near optimal designs as many as possible. Because uncertainties are always encountered in composite materials, they need to be taken into account in lightweight design of laminated composite structures. The combination of genetic algorithms and convex modeling is practical in accounting for the uncertainties and optimizing layup. (C) 2003 Elsevier Ltd. All rights reserved.