Base neutral surfase selection for optimal design of structurally-anisotropic aircraft panels made from composite materials with refined buckling theory restrictions

The aim of this study is the approach to the optimal design of structurally-anisotropic aircraft bearing surface panels with the restrictions according to the refined buckling theory for the optimal size-weight design implementation. The panels are subjected to the distributed constant compressive loading applied to the edges in the skin plane in the longitudinal direction. The panel contour boundary conditions are assumed to be the particular case with conformable boundary restrictions for the plane problem and problem of bending. The optimal design problem statement and analytical solution are formulated to determine the geometry parameters of a flat rectangular multilayer panel made from composite materials with the eccentric longitudinal and lateral stiffening set being of minimal mass. The equal-buckling condition is the optimal design base. The general bending mode of buckling and multi-wave torsion mode of buckling must have the same occurrence probability while the buckling margin tends to one. The optimal design problem is reduced to the mathematic conditional extremum investigation of the goal weight function with multiple variables using the analytical and numerical methods. New mathematic model relations for the buckling problem investigation of structurally-anisotropic composite panels are presented. The primary scientific novelty of this research is the further development of the thin-walled elastic rib theory related to the contact problem for the skin and rib with an improved rib model. The analytical solution is reduced to determine the displacements of a base neutral surface that may be select arbitrarily. The schematization of the panel as structurally-anisotropic one has been proposed as a design model when the critical forces of total bending mode of buckling are determined. For a multi-wave torsion buckling study, one should use the generalized function techniques for the discrete stringer stiffness. The solution of the strained surface differential equation of an eighth order is designed by a trigonometric series in the closed form. The results of the optimal design with the refined buckling restrictions based on refined buckling analysis calculations offer opportunities to reduce and optimize the weight characteristics of aircraft elements.