Mechanical properties of Nb3Sn stranded superconducting potted cable windings

The electromagnetic stresses in projected designs of high-field magnet coils sometimes exceed the yield points or creep strengths of the presently used coil winding materials. This is especially true of react-after-winding Nb3Sn coils, plastic insulating materials, and the crossed strands of twisted cable. This report presents compression stress-strain curves of stranded and twisted flat cable coil winding specimens for reacted and epoxy-impregnated Nb3Sn coils, at 300 K and 80 K. The lateral and longitudinal strains of one specimen were measured along with the direct compressive stress-strain, at 300 K. A similar specimen was compressed to 40 MPa (6 kpsi) at room temperature and then to 145 MPa (20 kpsi) at 80 K. Plastic flow occurred up the maximum stress. Stress cycles subsequent to maximum stress were elastic. Some specimens were mounted in a rigid enclosure to simulate hydrostatic containment of the magnet coil. Pure annealed Cu was tested at 300 K, and pure epoxy was tested at 300 and 80 K. In addition the thermal contractions from 300 to 80 K were measured.