On the Development of Shell Buckling Knockdown Factors for Stiffened Metallic Launch Vehicle Cylinders

Petersen

Khakimova³

et al. 2019

Composite Structures

Thin-walled shells like cylinders are primary structures in launch-vehicle systems. When subjected to axial loading these 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 imperfections and although imperfections exhibit comparatively low amplitudes, they can significantly reduce the critical load. Considering the influence of geometric imperfections adequately into the design process of thin-walled shells poses major challenges for structural design. An alternative to robust design of thin-walled shell by accurate consideration of geometric imperfections is the development of a robust or imperfection-insensitive shell architecture. In this article a special hybrid cylinder is presented and analyzed. The composite shell design is based on an interstage structure of the Ariane 6 by MT Aerospace and has special CFRP belts which are intended to reduce the imperfection sensitivity of the shell. The shell was tested at the German Aerospace Center in Braunschweig and the corresponding results are presented and described. The hybrid cylinder was analyzed with the Southwell-method and geometrically nonlinear finite element analyzes. The results show that the Southwell-method delivers conservative buckling load estimations and that the CFRP belts reduce the imperfection sensitivity significantly.

Section: Introductionmentioning

confidence: 99%

Buckling analysis of an imperfection-insensitive hybrid composite cylinder under axial compression – numerical simulation, destructive and non-destructive experimental testing

Petersen

Khakimova³

et al. 2019

Composite Structures

“…The most commonly used approach is based on the application of KDFs like the NASA SP guideline and Eurocode guidelines [18], [19]. Then there are concepts which are based on measured geometric imperfections as proposed by for example Hilburger et al [20], [21] or equivalent geometric imperfections as proposed by Khakimova et al [22] and Castro et al [23]. Advanced probabilistic methods which treat geometric imperfections as a random variable in order to design thin-walled shells were proposed by Arbocz et al [24], [25] Elishakoff [26], [27], [28] and Kriegesman et al [29], [30], [31].…”

Section: Introductionmentioning

confidence: 99%

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

Hühne

Khakimova³

2019

Thin-Walled Structures

Thin-walled cylindrical 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 cylindrical shells is 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 axially loaded cylindrical shells. 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 cylindrical shells under pure bending is performed. Data of previous experimental testing campaigns are used to validate the new design criteria for different cylindrical shell geometry configurations. The results show that the application of the new design recommendation for cylindrical 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.

“…It was demonstrated that they could approximate the corresponding stochastic distribution of the buckling load very well. The influence of real measured geometric imperfections (MGI) on the buckling load of cylindrical shells can be assessed very well nowadays as shown for example in studies by Hilburger et al [51] or Wang at al. [12], [52].…”

Section: Introductionmentioning

confidence: 99%

Probabilistic and deterministic lower-bound design benchmarks for cylindrical shells under axial compression

Hühne

Elishakoff

2020

Thin-Walled Structures

This article contains examples to demonstrate the use of different design concepts for cylindrical shells under axial compression. The examples are based on shells which were manufactured according to electroplating, machining, welding (isotropic cylinders) and prepreg hand layup on a mandrel (composite cylinders). Three of the four shell series are characterized by pure elastic buckling and one shell series buckled in the elastic-plastic region. All relevant data for the numerical analysis are described in the article and summarized in the Elsevier repository of this article (geometry, material, measured imperfection data and Python-ABAQUS scripts). The design concepts are based on the geometric imperfection signatures, probabilistic and deterministic lower-bound methods. The design concepts are representative for the development of design approaches for imperfection sensitive shells from the early 1980 to the late 2010 and are validated with experimental data. Recently developed design lower-bound curves for axially loaded cylinders are presented and compared with currently used design criteria like the Eurocode EN 1993-1-6 and the NASA SP-8007. The results of this article show that the design of imperfection sensitive cylinders has been significantly improved in the last 30 years.