Effects of Welding-Induced Imperfections on Behavior of Space Shuttle Superlightweight Tank

Results of linear-bifurcation buckling and nonlinear analyses of the Space Shuttle superlightweight external liquid-oxygen tank are presented for an important prelaunch loading condition. These results show the effects of actual, measured welding-induced initial geometric imperfections on an important response mode for thin-walled shells that are subjected to combined mechanical and thermal loads. This type of initial geometric imperfection may be encountered in the design of other liquid-fuel launch vehicles. Results are presented that show that the liquid-oxygen tank will buckle in the barrel section, but at load levels nearly four times the magnitude of the operational load level, and will exhibit stable postbuckling behavior. The actual measured imperfections are located in this section of the tank. Results of imperfection sensitivity analyses are presented that show that the largest degradation in the apparent membrane stiffnesses of the liquid-oxygen tank barrel section is caused by an imperfection shape that is in the form of the linear-bifurcation buckling mode with a relatively small amplitude. These results also show that the effect of the relatively large-amplitude measured imperfection is benign.