Optimization of Ply Drop Locations in Variable-Stiffness Composites

Abstract

A method for optimizing ply drop locations in composite laminates is developed using ideas from topology optimization. The design is parametrized using a fiber angle and fictitious density distribution for each ply. The solution proceeds using a successive conservative convex approximations strategy. Starting from a feasible point, the algorithm converges to a local minimum. The structural responses are approximated separately in terms of the angle and fictitious density distributions of each ply. Explicit penalization of intermediate densities is used to force the densities to either one for ply coverage or zero for no coverage. Ply drop locations are identified as the boundary between regions having densities near one and those near zero. The ply drop optimization is combined with fiber angle optimization by alternating the optimization between the corresponding sets of variables. Optimized variable-stiffness variable-thickness composite laminates, with a prespecified ply drop order, are obtained. Initial results show that large improvements in the buckling loads of flat plates can be obtained by combining ply drop and fiber angle optimizations.