Nonlinear behavior of Space Shuttle superlightweight tank under end-of-flight loads

Results of elastic, linear-bifurcation buckling and nonlinear analyses of t he new Space Shuttle superlightweight external liquid-oxygen tank are prese nted for an important end of-flight loading condition. These results illust rate an important type of response mode for thin-walled shells subjected to combined mechanical and thermal loads that may be encountered in the desig n of other liquid-fuel launch vehicles. Linear-bifurcation buckling analyse s are presented that predict several nearly equal eigenvalues that correspo nd to local buckling modes in the aft dome of the liquid-oxygen tank. In co ntrast, the nonlinear response phenomenon is shown to consist of a short-wa velength bending deformation in the aft elliptical dome of the liquid-oxyge n tank that grows in amplitude in a stable manner with increasing load. Imp erfection sensitivity analyses are presented that show that the presence of several nearly equal eigenvalues does not lead to a premature general inst ability mode for the aft dome. For the linear-bifurcation and nonlinear ana lyses, the results show that accurate predictions of the response of the sh ell generally require a large-scale, high-fidelity, finite element model, a nd that a design based on a linear bifurcation buckling analysis and a buck ling-load knockdown factor is overly conservative, Results are also present ed that show that the superlightweight liquid-oxygen tank can support loads in excess of approximately 1.9 times the values of the operational loads c onsidered.