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From the website:
http://www.nasa.gov/offices/nesc/home/Feature_ShellBuckling.html
Article produced by the NASA Engineering & Safety Center (NESC) in 2009(?). The title of the article is: "Launch Vehicle Shell Buckling Knockdown Factors Testing Underway". The anonymous author writes:
Problem:
The NESC Shell Buckling Knockdown Factor (SBKF) Project was established in March 2007 to develop and validate new analysis-based shell buckling design factors (i.e. knockdown factors) for Ares I and V metallic and composite launch vehicle structures. Refined knockdown factors will enable significant weight savings in these vehicles and will help mitigate launch vehicle development and performance risks.
NESC Contribution:
The NESC has supported a significant portion of the SBKF Project, including funding for the design and fabrication of a large-scale test facility, the first series of large-scale buckling test articles, programmatic and technical support, peer reviews, and advocacy.
Results:
In FY09, the SBKF Project made significant progress in several key work areas including sub-component and component testing and analysis, Ares V structures trade studies and associated mass savings estimates, and testing of an alternate aluminum-lithium (Al-Li) alloy for Ares V core stage. Some of the highlights for this year include successful testing of two 8-foot-diameter Al-Li orthogrid barrel test articles one of which was representative of a 45 percent-scale Ares I upper stage liquid hydrogen tank barrel section. The high-fidelity analysis predictions of these large-scale tests continue to correlate well with the test result and, once fully validated, will become the basis of new analysis-based design factors. The subcomponent analysis and test activity within the SBKF Project completed its first set of path-finding stiffened panel crippling tests at LaRC. These tests were used to integrate a typical local stiffener failure mode that is not well understood and is not accounted for explicitly in current Agency design practice. Analysis tools and nonlinear orthotropic material models are being developed to aid in the design of these important detail features. The Advance Aluminum Alloy Development activity and the Structures Trade Study activity worked together to identify the benefits of other Al-Li alloy materials on the design of several Ares V vehicle concepts. The results of the study indicated thicker Al-Li material would enable more structurally efficient orthogrid barrel components by increasing the height of the machined stiffeners. To this end, Al-Li 2050 was identified as a candidate replacement material for Al-Li 2195 in the Ares V core stage because it is available in thick plate material, has similar material properties to 2195, and is currently being used in commercial aircraft. The NESC supported the purchase of a large plate of 4-inch-thick 2050 material for preliminary material property and subcomponent screening tests to assess the performance of the material in typical launch-vehicle specific environments. The SBKF Project was peer reviewed in March 2009, and has published 13 technical reports summarizing trade studies, testing, analysis, and design activities and results.
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