Application of DIC to Extract Full Field Thermo-Mechanical Data From an HTS Coil

A digital imaging correlation (DIC) test setup was developed to accurately record the contraction of a Bi-2223 superconducting racetrack coil conduction cooled to 154 K. The coil was gripped at both ends to simultaneously measure the load and displacement induced by its own contraction. Postprocessing of the DIC data derived the displacement and strain fields from two areas of interest. The global deformation of the coil structure was influenced by how it was restrained, but the stress-strain curve in the
y
-direction of the HTS coil was established, and its stiffness when under thermally induced strain was found to closely match that of the epoxy resin. The coefficient of thermal expansion determined from the strain-temperature curve was in the same order of magnitude as dilatometer measurements performed upon a sample removed from a similar coil and the difference attributed to small variability in the temperatures across the coil and the mechanical restraint placed on the coil.