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shape. In these applications, the lack of distortion with FSW is an enabling charac- teristic for these concepts. ere is also a variant of FSW, called fric- tion stir processing (FSP), that can be used in marine applications. FSP is also a patented process that can be used to locally modify material properties. While the eects of FSP vary between applications, FSP has been demonstrated to increase ductility, improve fatigue properties, eliminate porosity (in castings), and improve hardness. In most alu- minum alloys, FSP has been demonstrated that it can be used to locally significantly improve the ductility of the material. This enables aluminum to be used in applications where forming would be desirable over arc welding multiple components together and can signicantly reduce part count. One such application is for fabrication of C-channels, angles, or zee shapes that are of a size or shape that otherwise cannot be extruded. If we consider the fabrication of an angle in this application of FSP, a strip of aluminum is rst cut from a large plate. The strip is then friction stir processed (in the at) along the future bend line. e fric- tion stir processed strip is then put in a press brake and bent along the line of FSP to form an angle. An example of an angle fabricated with this process is shown in Figure 9. e traditional method to fabricate such a shape would include arc welding of various strips together. e traditional method is expen- sive and fraught with signicant distortion. Friction stir welding is a new joining process with wide application for the fab- rication of aluminum based ship structure. While FSW is enabling shipyards to real- ize significant benefits and cost savings, most traditional superstructure design is not readily suited to take advantage of FSW. To take the greatest advantage of FSW and its benets, consideration for its use should begin at the design stage. þÿ M TMTChristopher B. Smith is co-founder and vice president of engineering at Friction Stir Link, Inc., and holds a master of science degree in mechanical engineering. Figure 7: Two FSW C-Channels Figure 8: Fabricated I-Beam via FSW Figure 9: Friction stir process stieners in Marine Superstructure January 2012 www.sname.org/sname/mt With FSW, multiple smaller extrusions can be welded together to form a custom or more complex extrusion, to enable more ecient designs. 01_25_FDept_SNAME_Jan12_P4.indd 2312/22/11 3:36 PM