Thermal peeling stress analysis of thin-film high-Tc superconductors

Thermal peeling stress between a thin film and the substrate is caused by the mismatch of thermal expansion coefficients while the film and substrate undergo a temperature change. The thermal peeling stress resulting from the temperature decrease from ambient to operating conditions (cryogenic temperatures) between a thin-film high-temperature superconductor and its substrate is calculated using finite element analysis (FEA). The superconductor thin film is idealized as a long bridge on a large substrate. A two-dimensional FEA model is applied to calculate the tensile (peeling) stress at the thin film/substrate interface. Results are obtained for different geometries and temperature conditions, and these results are compared with analytical predictions. A stress singularity is found at the very edge of the thin film which is not predicted by the analytical prediction. The peeling stress can be very,high due to this stress singularity, even if the temperature change is not large. The stress singularity area depends on the local geometry of the edge, suggesting that refining the geometry of the thin-film HTS device is important. (C) 1998 Elsevier Science Ltd. All rights reserved.