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 (similar to1 mum thick) on Inconel substrates (100 mum thick) with IBAD buffer layers had critical-current densities J(c) exceeding 1 MA/cm(2) 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.