On the development of shell buckling knockdown factors for imperfection sensitive conical shells under pure bending

Thin-walled conical shells are used as adapters between cylindrical shells of different diameters in launch-vehicle systems or as tailbooms in helicopters. A major loading scenario for conical shells is pure bending. The buckling moment of these shells is very sensitive to imperfections (geometry, loading conditions) which results in a critical disagreement between theoretical and experimental results for conical shells under pure bending. The design of these stability critical shells is based on classical buckling loads obtained by a linear analysis which are corrected by a single knockdown factor (0.41 - NASA SP-8019) for all cone geometries. This practice is well established among designers and hasn't changed for the past 50 years because the buckling behavior is till today not very well understood. Within this paper a reduced stiffness analysis for conical shells under pure bending is performed. Data of previous experimental testing campaigns are used to validate the new design criteria for different conical shell geometry configurations. The results show that the application of the new design recommendation for conical shell structures results in increased knockdown factors for the buckling moment which in turn may lead to a significant weight reduction potential. All ABAQUS-Python scripts and the results generated for this article are deposited in the Elsevier repository.