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타이틀	Space Transportation System (STS)-133/External Tank (ET)-137 Intertank (IT) Stringer Cracking Issue and Repair Assessment: Proximate Cause Determination and Material Characterization Study
저자	Piascik, Robert S.
Keyword	ALUMINUM-LITHIUM ALLOYS;; CHARACTERIZATION;; CRACKS;; DISCOVERY (ORBITER); EXTERNAL TANKS;; FABRICATION;; FAILURE ANALYSIS;; MECHANICAL PROPERTIES;; SPACE TRANSPORTATION SYSTEM;; STRINGERS;; TENSILE TESTS;; THERMAL PROTECTION;; TOUGHNESS;; TRANSMISSION ELECTRON MICROSCOPY
URL	http://hdl.handle.net/2060/20110023677
보고서번호	NASA/TM-2011-217318
발행년도	2011
출처	NTRS (NASA Technical Report Server)
ABSTRACT	Several cracks were detected in stringers located beneath the foam on the External Tank (ET) following the launch scrub of Space Transportation System (STS)-133 on November 5, 2010. The stringer material was aluminum-lithium (AL-Li) 2090-T83 fabricated from sheets that were nominally 0.064 inches thick. The mechanical properties of the stringer material were known to vary between different material lots, with the stringers from ET-137 (predominately lots 620853 and 620854) having the highest yield and ultimate stresses. Subsequent testing determined that these same lots also had the lowest fracture toughness properties. The NASA Engineering and Safety Center (NESC) supported the Space Shuttle Program (SSP)-led investigation. The objective of this investigation was to develop a database of test results to provide validation for structural analysis models, independently confirm test results obtained from other investigators, and determine the proximate cause of the anomalous low fracture toughness observed in stringer lots 620853 and 620854. This document contains the outcome of the investigation.