Improvement of Ic by loading and unloading bending strain for high strength Nb3Sn wires

We investigated the influence of the repeated bending strain on the critical current properties. The bending strain was applied to the Ti-added high strength CuNb/Nb₃Sn wires at room temperature and released. We define this loading and unloading bending strain at room temperature as a "pre-bending" treatment. We found that the critical current I_c is much enhanced by applying the pre-bending treatment. The maximum enhancement of I_c due to the pre-bending treatment is about twice at 17 T, for instance. The stress dependence of I_c shows that I_c is improved in low stress states by pre-bending treatment. This phenomenon can be described well by the uniaxial strain analysis on the basis of the strain distribution. In addition, the increase of the maximum critical current of the strain dependent I_c is also observed. This may be related to the reduction of the radial/tangential prestrain.