Buckling capacity of composite panels with cutouts using continuous curvilinear fibres and stiffeners based on streamlines

Abstract In this paper a novel concept is proposed for improving the buckling capacity of composite aircraft panels with cutouts. The key idea is to adopt the streamlines of a fluid flow around a given body of arbitrary shape that represents the cutout to define both the fibre and stiffener trajectories. As such, fibres and stiffeners can curve around the cutout in a continuous fashion which may improve the structural performance of panels. The buckling performance of typical aircraft panels with cutouts is addressed. Circular cutouts with various sizes as well as elliptical ones with different sizes and alignments are considered. Unstiffened, longitudinally stiffened and grid-stiffened panels subjected to in-plane uniaxial compressive and shear loads are investigated. The critical buckling loads obtained using curvilinear fibres and stiffeners are compared with those obtained for conventional panels with straight fibres and stiffeners. It is shown that up to 30% improvement in the buckling performance of the unstiffened panels can be achieved. For the stiffened panels, replacing the straight-line format by a streamline format for the fibres and stiffeners yields tremendous improvements in the buckling capacity. The improvements may exceed 150% and 200% for longitudinally stiffened panels and grid-stiffened panels, respectively.