Applying a genetic algorithm to the optimization of composite patches

This paper describes the application of genetic algorithms (GAs) to the optimization of a composite patch bonded on a metallic structure. The objective is to reduce the stress level in a given area under some constraints such as a maximum surface of the patch and some forbidden zones which cannot be covered by the patch. GAs are presently used for optimizing ply orientations of the stacking sequence as well as for the location and the shape of the patch which is modelled with a spline function. The design variables are ply orientations and coordinates of interpolation points which define a closed plane spline curve. Stress field calculations in the structure are carried out using the Ansys finite element package. The structure considered in this study is an aluminium plate with a circular hole around which the stress level must be reduced by bonding the composite patch. Shapes and ply stacking sequences resulting from the optimization procedure enable a local reinforcement in the neighbourhood of the patch and also a long-distance effect which consists in a deviation of the stress flow adjoining the area over which the stress level must be reduced.