Transverse stress and fatigue effects in Y-Ba-Cu-O coated IBAD tapes

Measurements of the effects of static and cyclic (fatigue) transverse stress on the critical current of Ya-Ba-Cu-O coated tapes made by ion-beam-assisted deposition (IBAD) are reported at 76 K in self magnetic field. Ya-Ba-Cu-O films (~1 μm thick) on Inconel substrates (100 μm thick) with IBAD buffer layers had critical-current densities J_c exceeding 1 MA/cm² and n values of about 50 (where n is an index of the sharpness of the superconductor-to-normal transition). Under static loads of 100 MPa, the degradation in J_c was less than 5% (7% at 120 MPa). When subjected to cyclic loading, there was less than 2% additional degradation in J_c after 2000 fatigue cycles. Microscopic examination of the samples indicates that this limited J_c degradation may have arisen from longitudinal cracks forming near the edges of the sample after being subjected to these high transverse pressures. This fracture mode would indicate that longitudinal side support from high-yield substrates or epoxy impregnation of magnet structures may provide additional tolerance against degradation in J_c from transverse stress