Statement of Proposed Research Characterization of Tool Wear in Friction Stir Welding of Metal Matrix Composites I. the Wear Problem/preliminary Studies

In his seminal text Friction and Wear of Materials, Ernest Rabinowicz defines wear as “the removal of material from solid surfaces as a result of mechanical action” [1]. The wear problem is incredibly important from an economic perspective; in the manufacturing industry, cost is in direct proportion to the frequency with which a particular component must be replaced. In many applications, worn machine elements can result in catastrophic failure of a part or entire system. Wear as a phenomenon is undertheorized, a deficiency Rabinowicz attributes to the pervading idea among researchers that wear is a chaotic process, so complex that it cannot be robustly characterized or predicted. The undercharacterization of wear is especially true for Friction Stir Welding (FSW), a solid state welding process developed by The Welding Institute and currently used by NASA for structural welds on the Space Shuttle external tank, Ares I upper stage, and Orion Crew Exploration Vehicle. Traditionally fabricated from tool steels, FSW tools have a nearly infinite life when used to join Aluminum alloys. Tool wear in FSW is a phenomenon unique to high strength alloys, having been documented in the literature only for FSW of steels and metal composites [2].