Composite Cylindrical Shell Buckling

Abstract

Guidelines dating back 50 years, NASA SP-8007, are employed today in the design of thin-walled launch vehicle structures. Due to advances in materials, structural designs, and manufacturing techniques since the publication of SP-8007, the development of new knockdown factors for contemporary launch vehicle structures is an ongoing subject of research. The work presented herein was performed in collaboration with the NASA Engineering and Safety Center on the Shell Buckling Knockdown Factor Project. A laboratory-scale composite cylindrical shell test article, which had previously been designed according to a novel scaling methodology, was the subject of simulation and testing. Its inner, outer, and boundary surface imperfection signatures were measured and implemented in finite element models for buckling test simulations. These were then used to provide prediction data for an experiment conducted at NASA Langley Research Center. Buckling loads from the two pre-test analyses were within 0.08% and 3.7% of the experimental buckling load. The concurrence of axial shell stiffness, localized strains, and buckling shape evolution was also established between the experiment and simulations. A slight loading imperfection was found during the test; however, it was demonstrated through post-test analyses that this did not affect the buckling load substantially. The test article's 0.91 normalized buckling load was much higher than the 0.59 knockdown factor specified by SP-8007. The correlation between the experimental and simulation results, as well as their contrast with SP-8007's prescription, suggests that directly measured imperfections are capable of playing a role in the development of modern and potentially less conservative knockdown factors for future launch vehicle structures.