Materials Selection Exercise for Electromagnetic Launcher Rails

Electromagnetic launchers (EML) are currently limited due to rail durability. The rail operating environment consists of large electrical currents, high local temperatures, large electromagnetic loads, and high sliding velocities. The desire to maximize magnetic energy for performance and durability for economic viability are the main objectives in selecting a rail material. A systematic process, often referred to as the Ashby method is used. The three steps include translating the design requirements into objectives and constraints, screening out materials that do not meet basic performance criteria, and ranking material candidates to maximize the objectives. Gouges, grooves, and fracture were identified as the three most life limiting forms of rail damage responsible for durability. Material property tradeoff plots show that magnetic energy and durability are conflicting objectives. A hybrid rail material in the form of a monolayer structure with an electrically conductive substrate and a damage resistant surface layer is the ideal configuration for maximizing the objectives. The results suggest that a conductive substrate, such as copper, is best for maintaining performance by means of magnetic energy and a damage resistant surface material consisting of tungsten, chromium, nickel, or tantalum has the best potential for increasing rail durability.