Axial compression fatigue testing of epoxy impregnated BSCCO coils

In rotating superconducting machinery, the rotor coils experience compressive stresses due to clamping and centripetal forces, as well as high compressive thermomechanical stresses during cool down. For a customary racetrack coil configuration, these stresses correspond to transverse compression across the width of the embedded tape. We have characterized epoxy-impregnated flat pancake coils of 3-ply reinforced BSCCO tapes, under axial compression. Mechanical proportional limit and ultimate strength were determined at 77 K. Critical current as a function of both peak stress and fatigue cycle count was measured. These coils were found to exhibit excellent critical current retention and mechanical stability to at least 100 MPa peak stress, for at least 100,000 fatigue cycles.