On the structural design of imperfection sensitive laminated composite shell structures subjected to axial compression

Shell structures are used as primary structures of space launch vehicles. These structures are thin-walled and are thus prone to buckling when loaded in compression. Because of the imperfection sensitivity of these structures, small deviations of the real shell from the theoretically perfect shell may result in a tremendous decrease in load carrying capacity. For this reason, geometrical imperfections need to be taken into account. When designing unstiffened composite shells, the laminate stacking sequence influences both, the buckling load of the geometrically perfect shell and the imperfection sensitivity of the shell. Consequently, to derive laminate stacking sequences that maximize the buckling load of real shell structures, geometrical imperfections need to be taken into account already in an early design phase. In this paper, two laminate stacking sequences that were derived to maximize the buckling load of the geometrically perfect and imperfect shell structure are studied using stochastic methods. To this end, combination of non-rotational symmetric imperfections derived from measured data and variations of the ply orientation are studied in a stochastic analysis on basis of Monte Carlo simulations. The results of this study will be used to evaluate the influence of the stacking sequence as one of the essential properties dominating the structural response of geometrically imperfect laminate composite shell structures.