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A ring-stiffened shallow conical shell designed by NASA for entry into the Martian atmosphere

From Walter L. Heard, Jr., Melvin S. Anderson and Wendell B. Stephens, "The effect of ring distortions on buckling of blunt conical shells", NASA TN D-7853, February 1975

A rigorous analytical study of the buckling strengths of large, blunt, conical shells stiffened by many thin-gage, open-section rings is presented. The results are compared with data previously obtained from uniform pressure tests of the Viking mission flight aeroshell (initial configuration) and of the Viking structural prototype aeroshells. The study shows that conventional analytical techniques in which the small, thin-gage rings are modeled as discrete rigid cross sections, lead to large unconservative predictions of aeroshell buckling strengths. A more sophisticated technique of modeling the rings as portions of the shell structure (shell branches) leads to much more realistic predictions of buckling strengths and more accurately predicts the failure modes. It is also shown that if a small initial imperfection proportional to the shape of the buckling mode is assumed, the critical buckling modes from analysis and test are in agreement. However, the reduction in buckling strength from perfect-shell predictions is small.

This shell was tested at NASA Langley Research Center by Anderson and his colleagues and analyzed by G. A. Cohen with his shell-of-revolution computer program called FASOR. (Cohen, G.A., "User Document for Computer Programs for Ring-Stiffened Shells of Revolution," NASA CR-2086, 1973; "Computer Analysis of Ring-Stiffened Shells of Revolution," NASA CR-2085, 1973; "Computer Program for Analysis of Imperfection Sensitivity of Ring-Stiffened Shells of Revolution," NASA CR-1801, 1971.)

(Photographs by Leonard, Anderson, and Heard, NASA Langley Research Center, 1974)

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