Buckling analysis and minimum-mass design procedures for composite wing-box structures

Abstract

This study investigates the minimum-mass design of composite wing-box structures employing a syntactic film core (SynCore™) as a partial replacement for carbon-fiber material. Special attention is given to the balance between buckling strength and the limiting strain constraints of the two materials. Symmetric and antisymmetric angle-ply stacking sequences, with specially orthotropic properties, are combined to form the special orthotropic laminate skin of the wing box. Computer modeling accounts for continuity of the skin over composite curved root-channel-section spars, which are assumed to be connected by a single line of closely spaced bolts. Emphasis is also placed on the level of sophistication of the modeling and the level to which modeling approximations may be safely applied. The effects of analyzing a panel with its true skewed shape, rather than approximating it as rectangular in plan, are compared with the infinitely long panel representation on which the optimization study is based. Two design strategies are adopted in the study whereby either skin-ply thickness is the independent variable and the outer mold line of the wing box is maintained by linking the spar depth (dependant variable) or the spar pitch is the independent variable and all plies are held at their correct physical thicknesses