3142. Transitioin From Aluminum 2219 External Tank to 2195 Al-Li Super-Lite Weight External Tank Design for the Space Shuttle La
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Paper
Abstract
2195 Al-Li alloy was developed to form the basis of the next generations of Super Light Weight External Tank (SLWET) design for space shuttle launch system. The first generation of external tanks was fabricated from 2219 aluminum alloy. The motivation for the replacement lies in weight savings of approximately 23% (7500 Lbs.) due to the lower density and higher stiffness to weight ratio of 2195 Al-Li alloy as compared to its predecessor.
Variable polarity plasma arc welding is the primary means of fabrication of SLWET. During the development work on SLWET, at MSFC, NASA, a peculiar nature of cracking tendency in the 2195 Al-Li welds was observed. A lighthearted historical account of the experimental research, conducted to understand the mechanism and nature of2195 Al-Li welds cracking problem is described. It was observed that some of the cracks in 2195 Al-Li alloy, were quite different in morphology from what generally was known about the weld cracks in aluminum alloys. The segment of work described in this paper has been picked from a large volume of research work, the ultimate objective of which was to characterize 2195 Al-Li welds for the fabrication of SLWET. The space limitation do not permit covering more than one aspect of the problem, which is described here to highlight the work that went into the grand goal of achieving weight savings.
The initial part describes the role of the external tank and some of its interesting features, which is necessary to put things in perspective. Certain initial phases of the research are highlighted, those that are included are the results from destructive and non-destructive analysis, and analysis tools like TGA, DTA, and SEM work with some relevant results are explored. It should be kept in mind at all times that these cracking problems had to solved, only then transition to the new lightweight alloy could be accomplished, and weight saving materialized.
