OPTIMIZATION OF STIFFENED LAMINATED COMPOSITE CYLINDRICAL PANELS IN THE BUCKLING AND POSTBUCKLING ANALYSIS.

Stiffened plates and curved panels are widely used as primary structural elements in aerospace, marine and civil engineering. Their stable postbuckling behavior and their capability to sustain loads far in excess of their initial buckling loads may lead to considerable weight savings, if their postbuckling strength is fully utilized and possible fatigue problems are eliminated. In the presence of large deflections, bifurcations, load and displacement limit points, the analysis of arbitrary anisotropic shells requires the adoption of incremental and iterative procedures capable of tracing the complete load- displacement path. Although the true response is dynamic in nature, a fully static solution is followed in most cases. Stiffened panels loaded in axial compression were extensively studied and employed in aeronautical structures in the thirties, forties and beyond, yielding the effective width. In the last decades, the trend to optimize the design shear panels, and the employment of composites and higher strength metals, has led to similar required relative stiffnesses in both civil and aeronautical engineering. The civil engineers employ stiffer flanges in order to improve the postbuckling strength of the web and the aeronautical engineers decrease the relative flange cross-sectional area in order to save weight. The nonlinear analysis of shells requires the efficient blend of finite element technology and path-following techniques. Due to the increased computational effort of the incremental and iterative solution process, it is imperative to obtain the structural response by simple, inexpensive and accurate finite elements. In this paper the postbuckling performance of composite shells using computer code LS-DYNA is analysed.