A statistical technique for the investigation of weak points and degradation of high-temperature superconductor tapes

Recent technological developments in manufacturing high-temperature superconductor (HTSC) tapes have improved their mechanical and electrical performances considerably. Now, a near future when HTSC cables will become a reality can finally be forecast. This brings about the need for work in the field of quality control and diagnostics of HTSC tapes. A new methodology for the analysis of the behaviour of tapes aged under different kinds of mechanical stresses is presented in this paper. The methodology is based on a probabilistic approach, where the two-parameter Weibull function is used to fit the cumulative and density probability distributions obtained from experimental V-I characteristics by numerical-analytical differentiation. Experimental results relevant to both long-term (aging) and short-term tests performed on 2223-BSCCO tapes are presented and discussed. It is shown that the time behaviour of Weibull function parameters provides useful information on the level of aging and on the kind of damage occurring to the tapes. In particular, the comparison between the results obtained from long-term and short-term tests, as well as from different types of mechanical stresses, points out that the shape of probability distributions constitutes a valuable diagnostic tool to distinguish between local or overall degradation and helps in identifying damage location.