Reversible stress and strain limits of the. critical current of practical REBCO and BSCCO wires

Practical REBCO and BSCCO-2223 tape-shaped wires are now manufactured on an. industrial scale. They are a. typical composite material consisting of superconducting layer/filaments together with functional components. These functional components affect directly the stress and strain dependences of the critical current. When applying an external stress R, the critical current I-c was measured. Then the external stress was reduced to R - 0 and. the recovered critical current I-cr was again. measured. The tensile stress and strain dependences of both normalized critical currents divided by the original value, I-c/I-c0 and I-cr/I-c0 were investigated. In general. I-cr/I-c0 recovered close to unity when the applied stress was low, but its recovering level decreased gradually with increasing applied stress. The definition of. the reversible stress and strain limits was investigated and its validity was proved using. the cyclic loading test. The original definition of reversible stress and strain limits of critical current relates to: (1) when releasing the applied stress and strain, the I-c shall recover to the original value, and (2) when applying the cyclic stresses, the I-c shall keep the original value. Here, as a practical definition for the reversible stress and strain limits, the tensile stress and strain at 99% recovery of I-c have been proposed. On the other hand, it was made clear that the stress and strain at I-c 95% retention are not valid for use commonly as a criterion of reversible stress and strain limits for both practical REBCO and BSCCO-2223 wires.