The Influence of Strain Rate on the Tensile Properties of a Nb–Ti/Cu Superconducting Composite Wire Under Variable Cryogenic Temperature

The tensile properties of superconducting wires usually play an essential role in practical applications. The effect of strain rate on the tension responses of commercial superconducting composite wires consisting of niobium-47wt.% Ti filaments in a copper matrix (Nb-Ti/Cu) with a Cu:superconductor ratio of ~4.3, under variable cryogenic temperature, is experimentally investigated in this paper. A variable temperature cryostat system is employed, which provides the cooling environment from room temperature to liquid nitrogen temperature, and a compact-scale cryogenic-type extensometer is utilized to measure the tensile strains on the superconducting wires. Under a range of cryogenic temperatures, the corresponding stress and strains are recorded during the elongation of the wire with a broad range of strain rates (10
^-1
to 10
^-4
s
^-1
). The cryogenic mechanical behaviors of the Nb-Ti/Cu composite wires, including the tensile strength and elongation at fracture, as well as the yield stress, are captured experimentally. It is shown that the ultimate tensile strength and the yield strength of the Nb-Ti/Cu superconducting wires increased linearly with cryogenic temperature for the lower strain rates, while notable nonlinear features appear at a higher strain rate. The elongations always increased nonlinearly with decreasing temperature for each tested strain rate, but the elongations decreased with higher strain rate. The Young's modulus approximately increases linearly with decreasing temperature for each strain rate. Additionally, the effect of strain hardening rate derived from the stress and strain relations for the superconducting wires at different cryogenic temperatures and strain rates is discussed.