Uniaxial Tensile Stress Tolerance of Ultra-Thin Nb3Sn Composite Wires and Twisted Cables

Ultra-thin A15 composite wires with a diameter of 0.03-0.05 mm are being developed by National Institute for Materials Science (NIMS) to realize flexible Rutherford cables for high field superconducting accelerator magnets. Since the bending strain is approximately proportional to the wire diameter, a cable composed of thin wires can be bent to a smaller bending diameter without the degradation of critical current ( I-c ). Thus, react-and-wind cables with ultra-thin Nb-3 Sn wires are expected to be realized. In our previous study, the basic mechanical properties including fracture strength and Young's modulus of 0.05-mm-thick bronze-processed Nb-3 Sn wires were evaluated by a single- fiber tensile test. As a next step, in this study, a tensile test was conducted for a twisted cable with 19 0.05-mm-thick wires at room temperature to confirm whether the mechanical strength of the twisted cable can be predicted from that of the single wire. The stress tolerance of the single wire and twisted cable was assessed by measuring I-c at 4.2 K after applying various uniaxial tensile loads at room temperature. The tensile stress limit of I-c was compared between the single wire and twisted cable.