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This Defense Intelligence Reference Document from the Defense Intelligence Agency, dated 12 January 2010, is one of a series of advanced technology reports produced in FY 2009 under the Advanced Aerospace Weapon System Applications (AAWSA) program. It reviews materials for launch vehicles, space vehicles and reusable rocket engines, including aluminum alloys, polymer and metal matrix composites, titanium and nickel alloys, ceramics and titanium aluminides. It concludes that newer materials and design methods offer many ways to improve structural efficiency and cost compared with the space shuttle.
“The Times”14 pages
UNCLASSIFIED,5;UiQR tlitliliillAI: 1!191! 8Hllf The newer Al alloys also can be specially processed to render them superplastically formable. This capability opens a realm of possibilities to replace structures that, in the absence of this capability, are machined from thick plate. Very large structures are produced in sections that must be joined. Conventional fusion welding techniques do not work for high-strength Al alloys such as 7075, 7050, 2024, or 2050 because either the welds lead to cracks or the welds made under conditions that avoid cracking have greatly reduced tensile properties. Because these alloys are not amenable to welding, heavier, fatigue-prone mechanically fastened joints must be used. Recently, scientists developed a joining process that permits joining of Al alloys such as 7050. This process, called friction stir welding (FSW), allows joint designs in a variety of configurations that were not considered possible when fusion welding was the only alter.native. In FSW, a rotating steel tool is inserted into the seam between the two Al alloy pieces to be joined. As the rotating tool is driven forward, the friction between the tool and the work piece generates enough heat to soften the Al alloy without melting it. A schematic of this process is shown in Figure 1. • retreating side Tool Figure 1, Schematic Diagram of Friction Stir Welding The combined action of the rotation and the traversing of the tool essentially kneads the two pieces together, leaving a mechanically sound joint. Although the weld properties may be somewhat inferior to those of the base metal, they are good enough that a relatively small increase in thickness at the joint position can compensate. Although substantial development of the FSW process is ongoing, FSW already has been put into practice. For example, the current external propellant tank on the space shuttle is made from an Al-Li alloy fabricated through FSW. The weight advantage of using welded as opposed to bolted joints i.n a large structure such as a launch vehicle is considerable. With earlier high-strength alloys such as 7075, concerns about fracture toughness in conjunction with monolithic structures would have caused a welded 2 UNCLASSIFIED},OiOR: err1&1,1k .... 8Nbf/
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Report, from the dia collection. The PDF is mirrored here; the original link is under it. 27 pages are in the text index: search them above, or from the library's search.