Bending and axial strain dependence of the critical current in superconducting BSCCO tapes

A comparison is made between the critical current ( I c ) versus bending strain and axial strain of superconducting multi-filamentary Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) AgMg sheathed tapes. For the bending strain measurement the tape is sandwiched between a curved base and cover plate. Six sets of bending plates introduce bending strains ranging from 0% to 1.0%. The measurements show a slight decrease in I c after the first bending step after which the degradation becomes more pronounced. The I c in a bent conductor is calculated assuming a linear axial strain profile inside the conductor. For this calculation the I c degradation determined in an axial compression and elongation experiment is used. The model predicts an immediate decrease of I c , caused by the compressive strain dependence. There is a good agreement (within 5%) between the measured data and the calculated values. Based on this good agreement it can be concluded that a possible shift in the neutral line or the formation of additional cracks due to bending has no significant influence on the I c degradation. It is concluded that the influence of thermal contraction is crucial for a good calculation.