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NUMERICAL AND EXPERIMENTAL STUDY OF BUCKLING OF ADVANCED FIBRE COMPOSITE CYLINDERS UNDER AXIAL COMPRESSION R S PRIYADARSINI 1 , V KALYANARAMAN 2 Department of Civil Engineering, Indian Institute of Technology, Madras Chennai 600 036, India 1 [email protected] ; 2 [email protected] and S M SRINIVASAN 3 Department of Applied Mechanics, Indian Institute of Technology, Madras Chennai 600 036, India 3 [email protected] ABSTRACT Advanced lightweight laminated composite shells are increasingly being used in modern aerospace structures, for enhancing their structural efficiency and performance. Such thin-walled structures are susceptible to buckling when subjected to static and dynamic compressive stresses. In this paper, details of a numerical (FEM) and an experimental study on buckling of carbon fibre reinforced plastics (CFRP) layered composite cylinders under displacement and load controlled static and dynamic axial compression are reported. The effects of different types of loadings, geometric properties, lamina lay-up and amplitudes of imperfection on the strength of the cylinders under compression are studied. Accurate measurement of imperfections in the cylindrical surface is carried out in the specimens tested. It is shown that the buckling behaviour of thin composite cylindrical shells can be evaluated accurately by modeling measured imperfections and material properties in FEM. 1. Introduction Composite cylindrical shells, used in weight sensitive structures such as aircraft fuselages, submarine hulls and space launch vehicles, are essentially subjected to membrane stresses and are efficient due to the high strength to weight ratio and stiffness to weight ratio. 1 However, they are vulnerable to instabilities (buckling) when subjected to static or dynamic compressive stresses. 2 The introduction of faster supersonic aircrafts, ballistic missiles and launch and re-entry vehicles has necessitated investigations of dynamic buckling. The growing demand for safety of transport vehicles has also had a strong impact on the increasing interest in dynamic buckling. 3 A cylindrical shell under compression in the meridional direction can fail by overall buckling (global/Euler), local buckling or the material strength being reached. Various failure mechanisms of composite cylindrical shells, as affected by initial geometric imperfections, boundary conditions, lamina stacking sequence, anisotropic coupling effects and load eccentricity, were identified by Weaver, 2 in terms of laminate configurations and shell proportions. The buckling response of the shells is very sensitive to changes in boundary conditions. A significant discrepancy between theory and experiment is possible in the case of cylindrical shells unless the boundary and loading conditions are accurately modeled and the initial geometric imperfections are precisely taken into consideration in any theoretical model. Unlike shells made of
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isotropic materials, composite cylindrical shells could experience failure due to a stronger coupling between membranes and bending strains. Degradation of the buckling strength
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