Buckling and postbuckling of curvilinearly grid-stiffened variable-stiffness composite fuselage panels

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Due to their benefits and high structural performance in terms of strength, stability and damage tol-erance, grid-stiffened structures are used on a large scale in aerospace structures. Manufacturing of an integrated structure consisting of a tow-placed variable-stiffness composite skin and curvilinear stiffeners is possible using advanced techniques such as automated fibre placement and additive manufacturing (known also as 3D printing). In this proposed project, the buckling and postbuckling performance of curvilinearly grid-stiffened composite structures will be addressed. The variable-stiffness (V-S) concept based on the tow-placed steered fibres will be adopted to develop innovative tailored composite designs that are able to improve the buckling and postbuckling performance of aircraft structures. The primary objective of this research is to concurrently determine the optimal fibre paths of the skin and the optimal trajectories of the stiffeners for maximum buckling capacity taking into account the manufacturing constraints. In order to achieve this objective, as a first step, accurate yet fast semi-analytical solutions using energy-based approaches will be developed for ob-taining the buckling response of curvilinearly stiffened V-S composite plates and shells applicable to aircraft structures. Then, an optimization framework that includes different design tailoring scenari-os will be developed to investigate the effects of different parameters on the buckling performance of panels. The buckling performance of the designs obtained in each scenario will be compared with that for the traditionally stiffened straight design baselines. Additionally, the postbuckling behav-iour of the designs obtained in the previous scenarios will be addressed using the finite element method to assess the residual stiffness of the panels optimized for maximum buckling resistance.