Semi-analytical skin buckling of curved orthotropic grid-stiffened shells

With the introduction of composite materials to industrial aerospace applications, the research for innovative panel stiffening methods has gained significant interest. Possible candidates are grid-stiffened structures comprising of parallel and intersecting stiffeners forming regular polygonal patterns of skin fields. Since these thin-walled structures are critical to buckling, the structural stability is one of the driving criteria for minimum weight design. The present study investigates the local skin buckling of grid-stiffened structures known as orthogrid, isogrid, diamond grid and kagome grid with a semi-analytical Ritz energy method based on sets of trigonometric shape functions. The influence of the aspect ratio (stiffener angle), curvature and material orthotropy is shown for uni- and biaxial in-plane compression and shear. A self-stiffening effect of the grid-stiffened structures due to interaction with adjacent skin fields is identified, significantly increasing the buckling resistance of such structures. The presented results and trends support preliminary design tasks and the verification of detailed finite element analyses.