Dependence of the critical current of YBa2Cu3O7−δ coated conductors on in-plane bending

A new method to measure the effect of in-plane bending on the critical current of YBa2Cu3O7−δ coated conductors is presented. Such a bending mode can be important in transmission cables, saddleback magnets, and double-pancake windings. A linear strain distribution over the width of the conductor develops in this bending mode, where one half of the conductor is under axial compressive strain and the other half is under axial tensile strain. A reversible reduction in critical current of up to 5% is measured in 4 mm wide conductors at a critical bending radius of 0.25–0.28 m. The critical current degrades irreversibly for bending radii less than this because the strain at the edge of the conductor that is under tension irreversibly damages the conductor. The results are described by use of a model that calculates the critical current as a function of in-plane bending radius by taking into account the strain gradient over the width of the sample and the measured dependence of the critical current on axial strain. A similar approach can be used to calculate the degradation of the critical current n of other deformation modes, such as torsion, or other more complex geometries.