Mechanical properties and strain effects in superconductors: Metallurgy, fabrication, and applications

This paper studies the mechanical properties and material strain effects for magnet design in superconductors. The material strain limit for typical magnet systems such as multifilamentary Nb3Sn, Nb3Sn dipoles plus small bore, pulsed NbTi:Cu, epoxy impregnated, and large SS reinforced are given, along with the limiting property, and the material limit. For each magnet type, a different mechanical property and material play the limiting role: In multifilamentary Nb3Sn magnets, uniaxial-strain degradation of I /SUB c/ is the limiting factor. If, in addition, the Nb3Sn magnet is a dipole or small bore magnet, the tight bend radius required of the conductor sets bending strain limits on the conductor thickness. In pulsed NbTi:copper magnets that will be cycled many times without anneal, fatigue degradation of the stabilizing copper matrix is the primary factor placing limits on the peak-to-peak strain amplitude. In high-current density, epoxy-impregnated magnets, excessive training caused by the low strain tolerance of epoxies at cryogenic temperatures generally plays the primary role. Finally, in large reinforced magnets, the yield properties of the structural reinforcement material set the mechanical design limits