Optimization of composite cylindrical panels for buckling by ranking

Fibre-reinforced composites are used in many engineering structures with cylindrical panels being a typical component. Buckling is one of the important modes of failure of such a panel. The work presented in this paper deals with optimizing the orientation of plies in a simply supported composite cylindrical panel so as to achieve maximum buckling load. The panel is assumed to be composed of a repeated sublaminate construction. In this type of construction the basic sublaminate has a smaller number of plies, for example, 8, 6, 4 or 2, and the full panel is obtained by repeating the basic sublaminate. Such a construction is used to avoid manufacturing errors and to produce damagetolerant panels resulting from maximum splicing of plies. The buckling loads have been found using an energy method, and optimization of ply orientations in the basic sublaminate is achieved by using the ranking technique proposed by Tsai. The following configurations are considered in the paper: (i) solid laminated panel, (ii) sandwich panel, and (iii) stiffened panel. The sandwich or stiffened panel may have sinusoidally corrugated sheet, hat-type corrugated sheet or regular grid as core or stiffener respectively. The computer program developed was first checked for accuracy by comparing with results available in the literature for isotropic and orthotropic cylindrical panels. Then it was used to optimize the ply orientation in the sublaminate for any specified geometry, material, loading and boundary conditions. It was found that significant gains in buckling loads can be had by choosing the optimum lay-up scheme and that quasi-isotropic lay-up in many cases is far from the optimum.