Description
Ultra-fine A15 composite wires with a diameter of 0.03–0.05 mm are being developed by National Institute for Materials Science (NIMS). Since the bending strain is approximately proportional to the wire diameter, a cable composed of fine wires can be bent to a smaller bending diameter without a degradation of critical current (Ic). Thus, react-and-wind A15 cables are expected to be realized. In this study, the mechanical properties of bronze-processed Nb3Sn wires with a diameter of 0.05 mm were evaluated by using a technique of single fiber tensile test. Basic mechanical parameters such as 0.2% proof strength and fracture strength were successfully evaluated from stress–strain curves. Young’s modulus of such a fine wire was determined from unloading and reloading slopes of a load–stroke curve for the specimens with different gauge lengths. Fracture strain was estimated without using extensometers and strain gauges by correcting for machine deformation. A tensile test was conducted for a twisted cable composed of nineteen 0.05 mm-thick wires at room temperature. The stress tolerance of the single wire and twisted cable was assessed by measuring Ic at 4.2 K after applying various uniaxial tensile loads at room temperature. Through these experiments, we found that the tensile stress limit of Ic of the twisted cable can be predicted from that of the single wire.