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Recent increases in the critical current density of Bi2Sr2CaCu2O8-x (Bi-2212) composite wires have driven interest in superconducting magnet applications for this material. However, the round-wire composite material is comprised of brittle filaments in a soft silver matrix, leaving the wire susceptible to filament damage during operation.In this study, Bi-2212 wires were tested on a Walter spring and then imaged to reveal filament damage. Damage events were specified as a function of geometry (flat, concave, and convex wire surfaces), heat treatment condition (1 bar to 100 bar over-pressure processing) and mechanical test condition (tensile or compressive applied strain). After undergoing an external chemical etch process, scanning electron microscopy (SEM) was utilized to analyze the filament damage in each sample. In general, convex surfaces (generated from the Walter spring test) had large amounts and various types of damage compared to the concave surfaces (also from the Walter spring test). Other processing and test conditions are also compared. This new understanding of how damage evolves within Bi-2212 wires allows for better modeling of the wire’s mechanical performance, and influences coil design choices.
Acknowledgments: This work was financially supported by the U.S. Department of Energy (DoE), Office and High Energy Physics (OHEP), award DE-FG02-13ER42036, and benefited from the support of the Materials Science & Engineering Center at UW-Eau Claire. The authors thank Najib Cheggour at the University of Colorado – Boulder for providing electro-mechanical test results.