Bending strain analysis considering a shift of the neutral axis for YBCO coated conductors with and without a Cu stabilizing layer

Bending tolerance is one of the most fundamental mechanical properties of YBCO coated conductors for application to a superconducting coil. In order to reveal the origin of the difference in critical current (Ic) with bending radius among various conductors, it is essential to estimate the bending strain at a superconducting layer. In this study, the bending strain was evaluated both experimentally and analytically for YBCO coated conductors with and without a Cu stabilizing layer. The internal tensile and bending strain of YBCO film in a composite conductor was directly evaluated from the shift of the Bragg peaks of a YBCO film using synchrotron radiation. We also present an analytical method to calculate the neutral axis position by considering its shift due to the progress of plastic deformation of the components such as Cu, Ag and Hastelloy. The validity of our strain analysis was confirmed by agreement of the measured and calculated internal bending strains. The calculation result shows that yielding of the Cu stabilizing layer has a strong influence on the position of the neutral axis and results in a weaker dependence of Ic. A comparison with tensile strain measurements shows that the effect of bending can be predicted from the tensile strain dependence.