Results from a numerical and experimental study of the response of compression-loaded quasi-isotropic curved panels with a centrally located circular cutout are presented. The numerical results were obtained by using a geometrically nonlinear finite element analysis code. The effects of cutout size, panel curvature and initial geometric imperfections on the overall response of compression-loaded panels are described. In addition, results are presented from a numerical parametric study that indicate the effects of elastic circumferential edge restraints on the prebuckling and buckling response of a selected panel and these numerical results are compared to experimentally measured results. These restraints are used to identify the effects of circumferential edge restraints that are introduced by the test fixture that was used in the present study. It is shown that circumferential edge restraints can introduce substantial nonlinear prebuckling deformations into shallow compression-loaded curved panels that can results in a significant increase in buckling load.

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Results of linear bifurcation and nonlinear analyses of the Space Shuttle superlightweight external liquid-oxygen ( LO 2 ) 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 LO 2 tank will buckle in the barrel section 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 LO 2 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.