Nonlinear behavior of Space Shuttle superlightweight liquid-oxygen tank under prelaunch loads

The new Space Shuttle superlightweight external fuel tank flew for the first time on 2 June 1998 (Space Trans portation System-mission 91). We present results of elastic linear-bifurcation buckling and nonlinear analyses of one of its major components; that is, the liquid-oxygen tank. The contents include an overview of the structure and a brief description of the finite element code that was used to conduct the analyses, Results are presented that illustrate three distinctly different types of nonlinear response phenomena for thin-walled shells that are subjected to combined mechanical and thermal loads that launch-vehicle shell designers may encounter. A procedure is demonstrated that can be used by structural analysts and designers to obtain reasonable, conservative estimates of linear-bifurcation, buckling-load knockdown factors for shells that are subjected to complex loading conditions or to characterize the effects of initial geometric imperfections on nonlinear shell response phenomena. Results an: also presented that show that the superlightweight liquid-oxygen tank can carry loads in excess of twice the values of the operational prelaunch loads considered and that a fluid-filled launch-vehicle shell can be highly sensitive to initial geometric imperfections.