Critical current of magnesium diboride/stainless steel composite tapes under tensile or compressive strains

We investigate the influence of mechanical strain on the critical current ( I c ) for magnesium diboride/stainless steel (SUS316) superconducting tapes. The tensile axial strain along the tape length is successfully induced in the sample by using a U-shaped holder made of stainless steel (SUS304). Two samples are examined at 4.2 K and 5 T (B is applied perpendicular to the tape surface). The I c –strain relation can be divided into two regions. Rapid and large degradation occurs at a strain exceeding ∼0.5%. On the other hand, I c change is reversible against strain change between −0.4% (compressive strain) and 0.4%. I c increases and decreases with increasing and decreasing external strain in this region, respectively. The critical temperature ( T c ) also changes with the change in the external strain; T c increases with increasing external strain. The reversible change in I c originates in the change of T c .