Fatigue Properties of Cu–Nb Conductor Used for Pulsed Magnets at the WHMFC

The Cu-Nb micro-composite wires are used as the conductors for the pulsed magnet above 80 T at the Wuhan National High Magnetic Field Center (WHMFC). The fatigue properties of the Cu-Nb wires carried out with uniaxial tensile test, uniaxial high-cycle fatigue test and four-point bend test at room temperature are studied. The tensile test indicates that a higher loading rate can enhance the hardening rate of the Cu-Nb wire especially at the initial stage of the plastic deformation, leading to a 4% increment of the tensile strength from the lowest strain rate level to the highest one. The four-point bend test reveals that the ratcheting strain occurs in every cycle after plastic deformation commences, which is believed to be one of the most important factors for fatigue life. Moreover, the ratcheting strain stabilizes after about ten cycles with the stable strain increases as the cyclic load levels up. The result of the uniaxial high-cycle fatigue test is found to be a circumstantial evidence for the effect of the ratcheting strain by illustrating that a higher stress amplitude undermines the fatigue life of Cu-Nb wire at the same maximum stress level.