TRANSPORT CRITICAL CURRENTS OF BI(2223) TAPES AT 77K UNDER MECHANICAL-STRESS

The transport critical current, j(c), depends on the mechanical stress al,plied during or before the j(c)-determination. Two experiments wit h different aim were performed : a) bending of the tape tests the resi stance against winding (coils, power cables) b) axial strain tests giv e information on the effect of forces acting on the conductor during o peration. Bending of Bi(2223)/Ag tapes from a radius r = infinity to r = 1 cm as well as an axial strain of about 0.2% decreases j(c) by som e 80%. For bended as well as for elongated tapes we find an almost una ffected field dependence of j(c), which is only on a lower j(c) level due to crack formation, i.e, a reduction of the percolation path. The strong j(c) reduction can be avoided by a reinforcement of the sheath material by dispersion hardening with 2% Mg. The j(c) decrease after b ending in these improved tapes is only some 20%, the maximum axial str ain tolerance about 0.8%. The yield of the reinforced tapes is 300-350 MPa, which is more than 5 times the value for Ag sheathed tapes.