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Influence of Imperfections on Axial Buckling Load of Composite Cylindrical Shells

Keple, Jendi and Prusty, G. and Pearce, G. and Kelly, Don and Thomson, Rodney and Degenhardt, Richard (2013) Influence of Imperfections on Axial Buckling Load of Composite Cylindrical Shells. 19th International Conference on Composite Materials, 28. July-3.Aug. 2013, Montreal, Canada.

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There is a strong requirement for more robust, lighter and cheaper launch vehicle structures. Unstiffened composite cylindrical shells, which are essential to the fabrication of launch vehicle airframes, are prone to buckling and are highly sensitive to imperfections which arise during the manufacturing process. The buckling load is an important characteristic in design, and may vary drastically from the buckling load of the perfect structure when realistic imperfections are present. [1] The current design guidelines for imperfection sensitive shells are based on the NASA-SP 8007 [2] which dates from 1965. Typically, the theoretical buckling load of a given cylinder design is predicted by performing a linear bifurcation analysis using closed-form equations of the geometrically perfect structure. This theoretical buckling load is then reduced by applying an empirical knockdown factor to account for the differences between theory and test. From recent literature [3-5], the NASA-SP 8007 knockdown factors used in the design of aerospace-quality shell structures were found to be overly conservative and inappropriate for shells constructed from modern manufacturing processes and materials such as composites. Such a conservative approach means that structures are therefore heavier and more costly than need be. Dependable and verified design criteria for thin-walled cylindrical shells are required, particularly for shells constructed from advanced materials and manufacturing techniques. A new design criterion using a new robust optimization methodology in conjunction with the Single Perturbation Load Approach (SPLA) and the stochastic approach is being developed by the collaborative European 7th Framework Program project: New Robust Design Guideline for Imperfection Sensitive Composite Launcher Structures (DESICOS) [6]. The design criterion will account for real behavior of composite materials including imperfections to provide less conservative and more accurate knockdown factors. This paper provides a measure of the Sensitivity and Influence of initial imperfections on the axial buckling load of 50 nominally identical composite cylinders which were numerically generated from actual shell measurements [5], as a contribution to the overall DESICOS project. The effect of initial geometric, loading, thickness and material imperfections on the axial buckling load of unstiffened composite cylindrical shells was investigated and compared using probabilistic finite element (FE) analysis in conjunction with the stochastic approach and metamodels. The magnitudes of the imperfections were plotted against the axial buckling load and the effect of each imperfection type on the overall axial buckling load determined. The results displayed may be used for the robust optimization of shells which may improve the reliability of their knock-down factors.

Item URL in elib:https://elib.dlr.de/83846/
Document Type:Conference or Workshop Item (Speech)
Title:Influence of Imperfections on Axial Buckling Load of Composite Cylindrical Shells
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Keple, JendiUNSW, Sydney, AustraliaUNSPECIFIED
Prusty, G.UNSW, Sydney, AustraliaUNSPECIFIED
Pearce, G.UNSW, Sydney, AustraliaUNSPECIFIED
Kelly, DonUNSW, Sydney, AustraliaUNSPECIFIED
Thomson, RodneyCRC-ACS, AustraliaUNSPECIFIED
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:buckling, monocoque cylinder, robust optimization, spectral representation
Event Title:19th International Conference on Composite Materials
Event Location:Montreal, Canada
Event Type:international Conference
Event Dates:28. July-3.Aug. 2013
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Transportation
DLR - Research area:Raumfahrt
DLR - Program:R RP - Space Transportation
DLR - Research theme (Project):R - Raumfahrzeugsysteme - Numerische Verfahren und Simulation (old)
Location: Braunschweig
Institutes and Institutions:Institute of Composite Structures and Adaptive Systems > Structural Mechanics
Deposited By: Degenhardt, Richard
Deposited On:10 Dec 2013 18:54
Last Modified:31 Jul 2019 19:41

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