Global and local buckling load for an unstiffened isotropic shell (left) -stable dimple in a cylinder from [70] (right)

Global and local buckling load for an unstiffened isotropic shell (left) -stable dimple in a cylinder from [70] (right)

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Thin-walled shells like cylinders, cones and spheres are primary structures in launch-vehicle systems. When subjected to axial loading or external pressure, these thin-walled shells are prone to buckling. The corresponding critical load heavily depends on deviations from the ideal shell shape. In general these deviations are defined as geometric im...

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... Data from the CMM were used to inform on the manufacturing quality and also used as inputs to the nonlinear finite element analyses with the as-manufactured imperfection signature. Following best practice in the experimental literature [18][19][20], to post-process these data, a cylinder of best fit is first fitted to the 20,000-point data cloud by minimizing the root mean square of the imperfection data cloud against the best fit cylinder. The best fit QI cylinder has an outer radius of 302.20 mm, 1.15 mm larger than the designed outer radius. ...
... The imperfection measurements were carried out between G = 40 mm and G = 1060 mm 93% of the unpotted length of the cylinder (0 to 24 mm and 1074 mm to 1098 mm is the end-potted region). Following best practice in the literature [18][19][20], the imperfection data cloud was deconstructed into Fourier coe cients and magnitudes based on a full four-term Fourier series decomposition. Once achieved, the Fourier series can be used to extrapolate the imperfections from G = 50 mm to G = 24 mm (the start of the bottom end-potting) and from G = 1060 mm to G = 1074 mm (the start of the top end-potting). ...
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... (27) and Eq. (28) of Ref. [37]. ...
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... Load-displacement curve for snap-through buckling (left) membrane stress state of a cylinder (right) from Ref.[75]. ...
... The elastic imperfection factor α current is based on studies by Rotter et al. and is currently used in the RRD. A new improved version of the elastic imperfection factor α new was developed by Wagner in Ref.[75]. The difference between the new and current version of the elastic imperfection factor is shown inFig. ...
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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.