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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
SUMMARY:
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 and the next four slides demonstrate interaction between local and general buckling of stiffened structures. There are two types of interaction:
1. The general buckling mode contains local components.(The general buckling mode is shown in the lower frame in this slide and two slides hence).
2. Local buckling of the skin of a stiffened structure causes reduction of the average effective stiffness of that skin as it acts in a general buckling mode (shown three and four slides hence).
This example and the next two slides demonstrate the first type of modal interaction.
The top photograph in this slide shows a shallow conical internally ring-stiffened shell - a NASA "aeroshell" to be used during entry into a planet’s atmosphere (Mars in this case). The small internal closely-spaced rings have a Z-shaped cross section. The loading is uniform external pressure.
The shell was tested by Anderson and colleagues at NASA and analyzed with the use of a shell-of-revolution computer program called "FASOR", written by Gerald Cohen in the 1970's.
The bottom photograph shows the buckled shell after the test.
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