Design of load-bearing anisotropic wing box panels ensuring static strength in the post-buckling state

The use of composite materials for the smooth load-bearing wing box panels of low-capacity aircraft can increase their weight efficiency. The present study considers thin smooth load-bearing panels of anisotropic structure, which can be used as the upper load-bearing wing box panels of forward-swept wings. The case of the maximum bending moment acting on the wing is considered, with wing box panels primarily subjected to compression at insignificant torque shear forces. The paper aims to develop a procedure for determining the thickness of thin anisotropic panels while allowing for the post-buckling behaviour under the action of near-expected compressive and shear flows. In accordance with the methodology for designing load-bearing panels for the post-buckling state, an analytical solution to a geometrically nonlinear problem was considered for anisotropic rectangular panels with hinged support; a procedure was proposed for designing panels that relies on the limiting static stresses of the composite cover exhibiting post-buckling behaviour. The obtained analytical expression was analysed to determine normal membrane stresses, and an expression was presented to ascertain the minimum thickness of the panel. A special attention was paid to the problem of determining the potentially critical points of an anisotropic panel exhibiting post-buckling behaviour, in which stresses can reach the maximum absolute values. The proposed procedure can be used to ascertain the thickness of thin load-bearing anisotropic panels under compressive and shear forces.