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The results of a study of the response and failure to these impact-energy levels follow a similar trend.Residual strength results for plates with barely visible impact damage suggest that the compression-afterimpact residual strength is also a function of plate radius.The residual strength of impact-damaged fla_ plates appears to be lower than the residual strength of the corresponding cylindrically curved plates.

Results of a geometrically nonlinear finite element parametric study to determine curvature correction factors or "bulging factors" that account for increased crack-tip stresses due to curvature for longitudinal and circumferential cracks in unstiffened cylindrical shells subjected to combined loads are presented. Nondimensional parameters varied in the study include the shell curvature parameter, λ , which is a function of the shell radius, the shell wall thickness, and the crack length; a pressure loading parameter, η , which is a function of the shell geometry, material properties and the applied internal pressure; and a biaxial loading parameter, χ , which is the ratio of the farfield axial stress to the farfield circumferential stress. The major results are presented in the form of contour plots of the bulging factor as a function of these three nondimensional parameters. These plots identify the ranges of the shell curvature and loading parameters for which the effects of geometric nonlinearity are significant, and show the effect of the biaxial loads on the value of the bulging factor. Simple empirical expressions for the bulging factor are then derived from the numerical results and are shown to predict accurately the nonlinear response of shells with longitudinal and circumferential cracks.

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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.