Buckling of aerospace structures under combined loadin

One of the main components utilised in aerospace structures is the stiffened thin-web panel. It is widely used throughout aircraft construction for its ability to carry in-plane loads with an efficient use of material whilst also providing smooth surfaces for aerodynamic considerations. A design issue for thin-web stiffened panels is that compressive components of in-plane loading can result in instability in the form of buckling. Current AIRBUS wing design philosophy is to integrally machine stiffened panels within the wing spar component. Increases in the size of aircraft manufactured by AIRBUS has led to increases in size of wing spars and thicker section spar webs. It is shown that bending of the larger wing spars results in the thicker section webs carrying significant in-plane direct compression in addition to the expected shear loading. The objective of the research undertaken in this thesis was to introduce a new design methodology for the analysis of plates and panels buckling under combined compression and shear. An automated Finite Element method was verified against theoretical and experimental methods and then used to further investigate buckling behaviour. Initial buckling interaction curves were predicted for a range of plate aspect ratios having various combinations of idealised boundary conditions under combined compression and shear. Artificial Neural Networks and other methods of function approximation were then used to determine the function relating the plate configurations to initial buckling loads. The ABAQUS non-linear Finite Element software package was verified for its ability to accurately predict the posbuckling behaviour of AIRBUS spar panels. A Genetic Algorithm was combined with the FE method to determine geometric configurations for maximum increases in postbuckled strength of an AIRBUS spar, through minimal increases in weight. Artificial Neural Networks were also utilised to significantly increase the efficiency of the GA optimisation process.